Welding Quality Control: Everything You Need to Know

Welding quality has always been the focus of attention of welders. Today I will collect some relevant information for your reference.

Summary

With the rapid development of modern welding technology, the continuous improvement of welding production level and the increasing expansion of international trade in welding products.

In order to ensure the quality of welding products, effectively use resources, and protect the interests of users.

The quality management of welding products has gradually embarked on the road of standardization and standardization.

In March 1987, the International Organization for Standardization (ISO) officially released the ISO9000-9004 standard series on quality management and quality assurance.

In 1994 and 2000, the International Organization for Standardization revised the ISO9000 family of standards twice to make them more simplified, more focused, more scientific and universal, and to raise the quality assurance system to the level of the quality management system.

In 2000, China issued GB/T19000:2000 Quality Management System, which is equivalent to this international standard series.

Modern quality management believes that in order to make products reach the required quality indicators, we should start from each process of production and ensure it by controlling and adjusting the factors that affect the process quality.

The process quality shall be realized through work quality and various management methods.

Therefore, in quality management work, work quality should be used to ensure process quality, and process quality should be used to ensure product quality.

It can be seen that in order to achieve the quality objectives, an effective and easy-to-operate quality management system must be established in the management system.

And this system is applied to the whole manufacturing process of products.

Knowledge point 1: influencing factors and countermeasures of welding procedure quality

Process quality refers to the degree to which the processing process guarantees the product quality in the production process.

In other words, product quality is based on process quality, and only with excellent process processing quality can we produce excellent products.

The quality of the product not only meets the requirements after the completion of all processing and assembly work, but also exists at the beginning of the processing process and runs through the entire production process through the full-time inspection personnel to measure a number of technical parameters and obtain the user’s approval.

Whether the final product is qualified or not depends on the cumulative result of all process errors.

Therefore, the process is the basic link of the production process, and also the basic link of the inspection.

The production of welded structures includes many processes, such as decontamination and rust removal of metal materials, straightening, scribing, blanking, groove edge processing, forming, assembly, welding, heat treatment, etc. of welded structures.

Each process has certain quality requirements, and there are factors that affect its quality.

Since the quality of the process will ultimately determine the quality of the product, it is necessary to analyze various factors affecting the quality of the process and take effective control measures to ensure the quality of the welding product.

The factors that affect the process quality can be summarized as follows: personnel, equipment, materials, process methods and production environment, which are referred to as “human, machine, material, method and environment”.

The influence of each factor on the quality of different processes is very different, which should be analyzed according to the specific situation.

Welding is an important process in the production of welded structures, and the factors affecting its quality are also the above five aspects.

1. Factors of welding operators

Different welding methods have different dependencies on operators.

For manual arc welding, the welder’s operating skills and cautious working attitude are crucial to ensure the welding quality.

For automatic submerged arc welding, the adjustment of welding process parameters and welding can not be separated from human operation.

For various semi-automatic welding, the movement of the arc along the welded joint is also controlled by the welder.

The quality of direct welding will be affected if the welder has poor quality awareness, careless operation, does not comply with the welding procedure specification, or has low operating skills and unskilled technology.

The control measures for welding personnel are as follows:

(1) Strengthen the quality awareness education of “quality first, user first, and the next process is user” for welders, improve their sense of responsibility and meticulous work style, and establish a quality responsibility system.

(2) The welders shall be trained regularly to master the process procedures in theory and improve their operation skills in practice.

(3) During production, welders are required to strictly implement the welding procedure specification, strengthen the self inspection of welding procedures and the inspection of full-time inspectors.

(4) Carefully implement the welder examination system, adhere to the principle that welders should work with certificates, and establish welder technical files.

For important or major welding structure production, more detailed consideration shall be given to welders.

For example, the length of welder training, production experience, current technical status, age, length of service, physical strength, vision, attention, etc. should all be included in the scope of assessment.

2. Factors of welding machines and equipment

The performance, stability and reliability of various welding equipment directly affect the welding quality.

The more complex the equipment structure, the higher the degree of mechanization and automation, and the higher the dependence of welding quality on it.

Therefore, such equipment is required to have better performance and stability.

The welding equipment must be inspected and tried out before use, and the regular inspection system shall be implemented for various in-service welding equipment.

In the welding quality assurance system, in order to ensure the quality of welding procedures, the following points should be done for welding machines and equipment:

(1) Welding equipment shall be maintained, serviced and overhauled regularly, and important welding structures shall be tried before production.

(2) Regularly check the ammeter, voltmeter, gas flowmeter and other instruments on the welding equipment to ensure accurate measurement during production.

(3) Establish technical archives of welding equipment status to provide ideas for analyzing and solving problems.

(4) Establish the responsibility system of welding equipment users to ensure the timeliness and continuity of equipment maintenance.

In addition, the use conditions of welding equipment, such as the requirements for water, electricity and environment, the adjustability of welding equipment, the space required for operation, and the error adjustment should also be paid full attention to, so as to ensure the normal use of welding equipment.

3. Factors of welding raw materials

Raw materials used in welding production include base metal, welding materials (welding rod, welding wire, welding flux, shielding gas), etc.

The quality of these materials is the basis and premise for ensuring the quality of welding products.

In order to ensure the welding quality, the quality inspection of raw materials is very important.

In the initial stage of production, that is, before feeding, it is necessary to control the materials to stabilize production and the quality of welding products.

In the welding quality management system, the quality control of welding raw materials mainly includes the following measures:

(1) Strengthen the incoming acceptance and inspection of welding raw materials, and re inspect their physical and chemical indicators and mechanical properties when necessary.

(2) Establish a strict management system for welding raw materials to prevent contamination of welding raw materials during storage.

(3) Implement the marking operation system of welding raw materials in production to realize the tracking control of the quality of welding raw materials.

(4) Select welding raw material suppliers and cooperative plants with high reputation and good product quality for ordering and processing, so as to fundamentally prevent welding quality accidents.

In a word, the inspection of welding raw materials should be based on the welding specifications and national standards, and their quality should be tracked and controlled in a timely manner, instead of just entering the factory for acceptance and ignoring the marking and inspection in the production process.

4. Factors of welding process and method

The welding quality is highly dependent on the process method, and plays a very prominent role in various factors affecting the quality of welding procedures.

The influence of process method on welding quality mainly comes from two aspects, one is the rationality of process formulation;

On the other hand, the strictness of the implementation process.

First, the welding process of a product or a material shall be assessed, and then the welding procedure specification shall be prepared according to the process assessment report and the technical requirements of the drawings.

The welding procedure specification or welding procedure card shall be prepared.

These various process parameters expressed in written form refer to the basis for conducting welding.

It is compiled according to the tests conducted under simulated similar production conditions, long-term accumulated experience and specific technical requirements of products.

It is an important basis for ensuring welding quality. It has the characteristics of regularity, seriousness, prudence and continuity.

It is usually prepared by experienced welding technicians to ensure its correctness and rationality.

On this basis, it is necessary to ensure the strictness of the implementation of the process method.

Without sufficient basis, it is not allowed to change the process parameters at will. Even if it is really necessary to change, certain procedures and formalities must be performed.

Unreasonable welding process can not guarantee qualified weld, but with correct and reasonable process specification verified by evaluation, qualified weld can not be welded without strict implementation.

The two are complementary and interdependent, and can not neglect or neglect any aspect.

In the welding quality management system, the effective control of factors affecting the welding process and method is as follows:

(1) The welding procedure must be evaluated according to relevant regulations or national standards.

(2) Select experienced welding technicians to prepare the required process documents, which shall be complete and continuous.

(3) According to the provisions of the welding procedure specification, strengthen the on-site management and supervision during the welding process.

(4) Before production, test plates for welding products and test plates for welding process inspection shall be made according to the welding process specification to verify the correctness and rationality of the process method.

In addition, there is no detail in the preparation of welding procedure specification.

For important welding structures, there should be a remedial plan for quality accidents to minimize losses.

Refer to Table 1-1 for important factors and supplementary factors of various welding methods, and refer to Table 1-2 for secondary factors of various welding methods.

Table 1-1 The relationship between important factors of welding process method, supplementary factors and welding defects

Process conditionsSlag inclusionUnfusedIncomplete penetrationUndercutDeformationStomaCrackleReceiving personnel
Welding method
Welding material 
Welding position
Welded joint
Welded structure    
Tack welding 
Welder training

① Description:

◎ means it has a lot to do with

○ indicates a certain relationship

△ indicates general relationship

Table 1-2 Relationship between Secondary Factors of Welding Process Method and Welding Defects

Welding processSlag inclusionUnfusedIncomplete weldingUndercutDeformationStomaCold crackingHot cracking
Weld groove type 
Groove cleaning      
Middle weld bead shape      
Slag removal of welds       
Preheating before welding   
Welding current   
Welding arc length     
Electrode moving angle     
Welding electrode handling mode       
Weld deposit mode    
Welding position    
Natural environment wind      

① Note:

◎ indicates a great relationship; 

○ indicates a certain relationship; 

△ indicates a general relationship.

5. Environmental factors

In a specific environment, the welding quality is also highly dependent on the environment.

Welding operation is often carried out outdoors, which is inevitably affected by external natural conditions (such as temperature, humidity, wind, rain and snow).

If other factors are certain, welding quality problems may also be caused simply by environmental factors.

Therefore, some attention should also be paid.

In the welding quality management system, the control measures for environmental factors are relatively simple.

When the environmental conditions do not meet the specified requirements, such as strong wind force, wind speed greater than Grade IV, or rainy and snowy weather, relative humidity greater than 90%, welding can be temporarily stopped, or welding can be carried out after taking wind, rain and snow protection measures.

When welding at low temperature, the temperature of low-carbon steel shall not be lower than – 20 ℃, and that of ordinary alloy steel shall not be lower than – 10 ℃.

 If the temperature limit is exceeded, the workpiece can be properly preheated.

Through the above analysis of the five factors affecting the quality of welding process and their control measures and principles, it can be seen that the five factors are interrelated and cross each other, and the consideration should be systematic and continuous.

Knowledge point 2: welding production quality management system

1. Concept of welding production quality management

The core connotation of quality management is to make people believe that a certain product (or service) can meet the specified quality requirements, and to enable the demander to have sufficient evidence and confidence about whether the supplier can provide products that meet the requirements and whether it has provided products that meet the requirements.

At the same time, it also enables the enterprise to organize production with confidence that it can provide products (or services) that meet the quality requirements.

The essence of welding production quality management is to effectively control all links and factors in the fabrication and installation of welding structures based on a complete quality management system and the following six basic points of view:

(1) System engineering perspective;

(2) Full participation in quality management;

(3) The viewpoint of realizing the enterprise management objectives and quality policies;

(4) The viewpoint of implementing overall quality control over people, machines, materials, laws and environment;

(5) Quality evaluation and viewpoint based on witness data;

(6) Quality information feedback perspective.

2. Quality management system of welding production enterprises

In order to achieve quality management, the enterprise shall formulate quality policies and quality objectives, decompose the product (project) quality formation process, set up the necessary organization, define the responsibility system, equip the necessary equipment and personnel, and take appropriate control methods to control the five factors that affect the product (project) quality, so as to reduce, eliminate, especially prevent the occurrence of quality defects.

An organic whole of all these is the quality management system.

The establishment and operation of the system can provide the demander with various evidences that its quality system meets the contract requirements, including quality manual, quality records and quality plans.

In order to ensure the welding quality of products, the State Bureau of Technical Supervision officially issued GB/T12467-90, GB/T12468-90 and GB/T12469-90 National Recommended Standards for Welding Quality Assurance on September 8, 1990, which were implemented nationwide since January 1, 1991.

This is a set of professional standards with rigorous structure, clear definition, specific and practical provisions, which stipulates the general principles of quality assurance for steel welding products; Requirements for enterprises;

Quality requirements and defect classification of steel fusion welded joints.

Seriously study and study this set of standards, combine it with the GB/T19000:2000 standard series and the actual situation of the enterprise, and establish a relatively perfect welding structure quality management system, which is of great practical significance for improving the enterprise’s welding quality management level and quality assurance ability, and ensuring that the quality of welding products (projects) meets the specified requirements, and also conforms to the long-term development and interests of the enterprise.

Since the product quality management system is established by using the basic theory of system engineering, the whole process of product manufacturing can be divided into several relatively independent and organically linked control systems, links and control points according to their internal links, and organizational measures can be taken to follow certain systems, so that the work quality of these systems, links and control points can be effectively controlled and operated according to the specified procedures.

The so-called organizational measures are to have a complete quality management organization and provide qualified quality control personnel at each control, link and point.

1. Setting of quality control points

Quality control points are also called “quality management points”.

Any production and construction process or activity always has many quality characteristics requirements, and the importance of these quality characteristics has different impacts on the use of products (projects).

For example, the safety of pressure vessels is closely related to the quality of raw materials and welds, while uneven paint brushing on the surface of vessels only affects the appearance of vessels.

The consequences of the former are fatal and very serious;

The latter is the appearance problem. Under certain conditions, the customer can still accept it.

Therefore, in order to ensure that the process is under control, under certain time and conditions, the quality characteristics, key components or weak links that need to be emphatically controlled in the product manufacturing process are quality control points.

Where to set quality control points, it is necessary to comprehensively analyze the quality characteristics requirements of products (projects) and each process in the production and construction process to determine.

In general, the following principles should be considered when setting quality control points:

(1) Quality control points shall be set for key quality characteristics, key parts or important influencing factors that have a serious impact on the applicability (performance, accuracy, life, reliability, safety, etc.) of products (projects);

(2) Quality control points shall be set for key quality characteristics and parts that have strict requirements on process and have a serious impact on the work of the next process;

(3) For processes or projects with unstable quality and many nonconforming products, quality control points shall be established;

(4) Quality control points shall be established for important defective items fed back by users;

(5) Quality control points shall be established for critical items that are in short supply or may have a serious impact on production arrangements.

Welding production is the most important content and link of welding structure quality control.

There are 164 quality control points in the whole process of pressure vessel manufacturing (including on-site assembly) formulated by the International Welding Society (IIW), including 122 quality control points related to welding, as shown in Table 1-3.

Table 1-3 Key points of pressure vessel manufacturing quality control of International Welding Society (IIW)

Control itemsCheck the number of points to be counted
Plan and calculation review;
Base metal acceptance and control;
Acceptance and control of consumable materials such as welding materials; 
Welding procedure qualification;
Control of preparation before welding; 
Welding process control;
Post-welding control;
Heat treatment control;
Pre delivery test (hydrostatic test, etc.).
6
20
30
23
4
15
20
20
6

2. Main control systems and links of welding production quality management system

The control systems in the welding production quality management system mainly include: material quality control system, process quality control system, welding quality control system, nondestructive testing quality control system and product quality inspection control system.

Each control system has its own control links, working procedures, check points and responsible personnel.

(1) The material quality control system is used to control the whole process from the preparation of material plan to ordering, procurement, arrival, acceptance, storage, distribution, marking transfer, etc., with the emphasis on the factory (site) acceptance, strict management and reliable distribution, and adhering to the marking transfer system.

(2) The process quality control system is a process to control a series of work such as analysis and determination of production process or construction scheme, preparation of process procedures and process cards, and estimation of production quota.

(3) The welding quality control system covers a wide range, mainly including five control lines: welder examination, welding procedure qualification, welding material management, welding equipment management and product welding.

(4) The NDT quality control system has different tasks and control procedures.

As long as ultrasonic inspection is required for raw materials, the NDT responsible engineer shall sign and issue the flaw detection record report and submit it to the material inspector as part of the raw material inspection data.

However, the control procedures for welder skill examination and procedure qualification test plate are the same.

After the flaw detection record report is issued, it shall be submitted to the welding laboratory for filing.

(5) The product quality control system actually reflects the control of the whole process of product manufacturing.

Due to different responsibilities, such as materials, welding and NDT are controlled by independent systems.

3. Quality management organization and working method

The setting and complexity of quality management organization mainly depends on the division of product quality management control system, links and points.

Generally, the more detailed these systems, links and points are divided, the more complex the quality management organization is, and the more responsible personnel are needed.

The quality management organization is composed of certain functional departments (such as the quality management office of the enterprise).

The main person in charge of product quality (generally the factory director or manager of the enterprise);

The main guarantor of product quality (generally the general technical director of the enterprise or the main guarantor of quality management, often referred to as the quality management engineer);

 The person in charge of each control system (often referred to as the system responsible engineer or the engineer in charge) and the person in charge of each control point post (mostly held by the production personnel of each key process post) are composed.

The person in charge of quality control at all levels shall not only be responsible for the work quality of his/her own post, link and system, but also guarantee the work to the person in charge of quality control at the next higher level, the general person in charge of quality management, and finally to the factory director (manager) of the enterprise, forming a complete quality control network.

4. Establish “three inspection system”

The three inspection system, including self inspection, mutual inspection and special inspection, is a concrete manifestation of the implementation of the full participation in quality management.

(1) Self check.

1) During the operation, the operator must carry out personal self inspection and fill in the self inspection items in the relevant inspection and evaluation form.

The production and construction of other parts can be continued only after the acceptance of the team leader.

2) The team leader must check the operation quality of the team members one by one during the production process according to the inspection contents listed in the corresponding quality inspection and evaluation table for the construction of the subdivisional works or the production of parts and components he is responsible for.

After the completion, the team shall carry out self inspection item by item together with the quality officer, and carefully fill in the self inspection record.

After the self inspection is up to the standard, the team leader or workshop director can organize the quality acceptance.

3) The foreman or workshop director shall not only urge the team to carefully conduct self inspection, fill in self inspection records, and create self inspection conditions for the team, but also conduct intermediate inspection on the team’s operation quality.

Organize the construction team or workshop to conduct self inspection on the basis that the self inspection of the team meets the standard.

After passing the self inspection, it can be submitted to the project manager or the unit quality director to organize full-time quality inspectors to conduct quality inspection.

4) The project manager or the unit quality director must carefully organize the special inspectors, relevant foremen (workshop directors) and team leaders to carry out the quality inspection of the production projects undertaken.

The special inspector shall consult the self inspection record of the team before checking.

If there is no self inspection record of the team, the quality inspection and assessment will not be carried out.

5) The project manager and foreman shall not arrange the next process for the sub divisional tasks that have not been verified by the special inspectors or have not reached the standard after verification.

Otherwise, the responsibility shall be investigated until a fine is imposed.

(2) Mutual inspection.

1) Handover inspection between types of work: after the completion of the previous process and before the insertion of the next process, the foremen and team leaders of both parties to the handover must be organized for handover inspection.

The foreman of the handover party shall fill in the “Type of Work Handover Checklist”.

After careful inspection and signature by both parties, the next process can be started.

The receiving party may refuse to insert the products that have not passed the handover inspection or have passed the handover inspection but fail to meet the requirements.

2) Handover inspection between the general contractor and the subcontractor: for the items that need to be inspected in the process as specified in the specifications, procedures, standards and construction drawings, the handover party shall carefully handle the handover inspection form of the general contractor and the subcontractor according to the requirements of the receiving party.

Hand over relevant data and carry out handover visa, otherwise the next process shall not be carried out.

3) Handover inspection of hidden items: after many operations are completed, their outputs will be covered or closed by the outputs of the next operation.

For example, the welds in the box girder are closed and hidden.

The unit responsible for the next process must fill in the “Handover Checklist for Concealed Items” before concealing, and go through the handover inspection procedures with the unit responsible for the previous process.

After the self inspection of the handover party (referring to the concealed parts in the installation project) or the joint inspection of the handover parties, the construction and production of the next process can be carried out after reaching the quality standard and being signed by both parties.

Otherwise, the unit or department making the last process shall bear all consequences.

4) Finished and semi-finished products protection handover inspection:

① Before the construction of the next process, the unit must protect the finished products and semi-finished products.

During production and construction, effective measures shall always be taken to prevent damage (or pollution) of finished products and semi-finished products.

② If the finished and semi-finished products from the previous process are not protected from the next process, the unit responsible for the previous process shall bear the consequences if the finished and semi-finished products are damaged, polluted or lost.

③ For the items that have been handed over for protection of finished products and semi-finished products, if the finished products are damaged, polluted, lost, etc., the unit making the next process shall bear the consequences.

(3) Special inspection.

1) All sub divisional tasks, “hidden inspection” and “pre inspection” items must be submitted to special inspection personnel for quality inspection and evaluation as a process according to procedures.

Items that have not been inspected and evaluated by special inspectors, or have not reached the quality standards after inspection and evaluation, shall not proceed to the next process.

The special inspectors have the right to impose fines on those responsible for violating this provision.

2) Before checking the quality of sub divisional tasks, the special inspector shall first check whether the self inspection records of the team meet the requirements.

If there are no self inspection records or they do not meet the requirements, the special inspector shall not check them, so as to promote the quality management of the team.

For sub divisional tasks with self inspection records, the project manager shall organize the foreman and the team leader to carry out the evaluation together.

The quality grade checked and assessed by the special inspector shall prevail.

3) When checking and evaluating the quality grade of sub divisional tasks, special inspectors must carefully check and strictly control according to the quality standards and quality control design objectives;

During the construction, carefully check whether the quality of raw materials, finished products and semi-finished products meets the requirements, and actively assist the foreman and team leader in quality management and project quality.

We should pay attention to the weak links, the key parts, the prevention (treatment) of common quality problems, and the hidden and pre inspection work.

5. Establish and improve the quality information system

The establishment and improvement of quality information system should be mainly carried out by full-time quality management personnel and technicians.

However, production workers should also play an active role in it.

The quality defect prevention, quality maintenance, quality improvement and quality assessment in the production site are inseparable from timely and correct quality dynamic information, instruction information and quality feedback information.

It is one of the basic conditions to ensure the normal development of on-site quality management to collect, sort out, transfer and process various required data to form an efficient information closed-loop system.

Quality dynamic information refers to the quality inspection records, various quality reports, process control records, and quality dynamics of raw materials, semi-finished products, components and accessories at the production and construction site.

Instruction information refers to various instructions related to quality work issued by the superior management department.

These instructions are the criteria that must be followed in quality work and the standards for comparison in quality management activities.

Quality feedback information refers to the deviation information generated during the implementation of quality instructions, that is, the abnormal information after comparing with the specified objectives, requirements and standards.

Such abnormal information shall be fed back to relevant personnel and corresponding decision-making organization in time, so as to make new judgments quickly and form new regulatory instruction information.

In daily production activities, on-site production workers should provide necessary quality dynamic information and quality feedback information.

These information can also provide first-hand information for the formulation of instructions.

The following three points shall be paid attention to in site quality management:

(1) In the field quality management, corresponding responsibilities and mutual coordination relations should be clearly defined according to the quality functions of quality defect prevention, quality maintenance, improvement, evaluation, etc. during the construction process, and the due authority should be given to relevant departments and specific personnel, and inspection and assessment should be insisted on, linked with rewards and punishments.

(2) The above work and activities should also be standardized, institutionalized and programmed according to the quality objectives to be achieved during the on-site construction process, thus forming the on-site quality system.

(3) In order to promote workers to strictly observe the process discipline, it is necessary to establish a reward and punishment responsibility system to investigate the implementation of process discipline.

Knowledge point 3: welding quality control contents and items

1. Quality control before welding

The quality inspection before welding is the beginning of the welding quality control, which mainly includes the quality control of welding raw materials, the quality control of the processes before welding, and the welding process qualification. “A good start is half the battle”.

1. Raw material quality control

(1) Quality inspection of metal raw materials

There are many kinds of metal materials used for welding structures, even if the same kind of metal materials also have different models.

When using, it shall be identified according to the model of metal materials and the ex factory quality inspection certificate (certificate of conformity).

At the same time, external inspection and sampling recheck shall be conducted to detect external defects during transportation and prevent model confusion.

Those with serious external defects shall be picked out and discarded.

For materials without factory certificate or newly used materials, chemical composition analysis, mechanical property test and weldability test must be carried out before they can be put into use.

(2) Inspection of welding wire quality

The chemical composition, mechanical properties, welding performance, etc. of welding wires used for welding carbon steel and alloy steel shall comply with national standards.

Before use, each bundle of welding wire shall be checked for chemical composition, external inspection and diameter measurement if necessary.

The surface of welding wire shall be free of oxide skin, rust, oil stain, etc.

If the chemical pickling method is used to remove the oxide skin and rust on the welding wire, the pickling time shall be controlled.

If the pickling time is too long and the wire is used immediately, the welding quality will be affected, even cracks will appear.

(3) Inspection of welding rod quality

For the quality inspection of welding rods, the appearance quality shall be checked first, and then the chemical composition, mechanical properties, welding performance, etc. shall be checked to see if they meet the national standards or factory requirements.

When checking the chemical composition and mechanical properties of the electrode, first use this electrode to weld the weld, and then measure the chemical composition and mechanical properties of the weld.

The chemical composition and mechanical properties of the weld metal of the qualified electrode shall meet the requirements specified in the instructions.

The so-called electrode with good welding performance refers to the electrode that is easy to arc, stable in arc, less in spatter, uniform in coating melting, no influence of slag on continuous welding, good in fluidity, uniform in coverage and easy in deslagging when welding under the specifications recommended in the instructions;

In general, there shall be no process defects such as cracks, air holes and slag inclusions in the weld.

The coating of the welding rod shall be tight, free from air holes, cracks, swelling and uneven clusters.

At the same time, it shall be firmly attached to the welding core and have a certain strength.

The welding rod with a diameter of less than 4mm shall fall freely on the steel platform from 0.5m, and the coating shall not be damaged.

The coating shall be concentric on the core.

The electrode with eccentric coating will not only cause arc deflection, but also damage its welding performance.

When using welding rods, it is also necessary to pay attention to whether they are damaged and damped during transportation and storage.

The deteriorated and damaged welding rods cannot be used. Welding rods shall be dried before welding to remove moisture.

(4) Inspection of flux

The flux shall be inspected according to the national standard. Flux inspection is mainly to inspect its particle size, composition, welding performance and humidity.

The welding flux shall be used together with the welding wire to ensure that the chemical composition and mechanical properties of the weld metal meet the requirements.

For welding different types of steel, different types of welding flux shall be used together.

The flux with good performance has stable arc combustion, good weld metal formation, easy deslagging, and no defects such as pores and cracks in the weld.

The particle size of flux varies with the type of flux, for example, the particle size of low silicon medium fluorine type and medium silicon medium fluorine type is 0.4~3mm, and that of high silicon medium fluorine type or low silicon high fluorine type is 0.25~2mm.

The unit volume weight (false specific gravity) of the flux is the ratio of the weight to the volume of the OOcm3 dry flux.

For example, the glass flux should be 1.4 ~ 1.6g/cm3, and the pumice flux should be 0.7 ~ 0.9g/cm3.

The moisture content of 100g flux shall not exceed 1% after baking at 300-400 ℃ for 2 hours.

Before use, the welding flux must be dried according to the specified requirements, and those without specified requirements must be dried at 250 ℃ for 1-2 hours.

2. Quality control of each process before welding

(1) Production drawings and processes

Before welding, you must be familiar with the production process drawings and processes of welding structures, which is an important link to ensure the smooth production of welding products.

The main contents are as follows:

1) Structural form of products, types of materials used and technical requirements;

2) The size of the product welding position, the structural form of the welding joint and groove;

3) Welding method, welding current, welding voltage, welding speed, welding sequence, preheating and interpass temperature control during welding;

4) Post weld heat treatment process, weldment inspection method and quality requirements of welding products.

(2) Base metal pretreatment and blanking

1) Base metal pretreatment

The pretreatment of metal structural materials mainly refers to the correction and surface treatment of steel before use.

If the relevant operating procedures are not strictly followed during the hoisting, transportation and storage of steel, various deformations will often occur.

For example, overall bending, local bending, wavy deformation, etc. cannot be directly used in production but must be corrected.

Multi roll shaft leveler is widely used for thin plate straightening, and leveler can also be used for uncoiling reel steel plate.

The thick plate shall be corrected on the platform with a large hydraulic press, and the bending deformation of the section steel can be corrected with a special section steel straightener.

Local bending of steel plate and section steel can be corrected by flame correction method.

Generally, the heating temperature shall not exceed the tempering temperature of steel.

After heating, it can be cooled in air or sprayed with water.

Oxide, rust and oil stain on the steel surface will have adverse effects on the quality of the weld, which must be removed before welding. Cleaning methods include mechanical method and chemical method.

Mechanical cleaning methods include sand blasting, shot blasting, grinding wheel grinding and steel wheel grinding.

The shot blasting effect is good, and the shot blasting process is mostly used in the continuous production line of steel plate pretreatment.

The chemical cleaning method usually adopts acid solution cleaning, that is, steel is immersed in 2%~4% sulfuric acid solution tank.

After a certain period of time, it is taken out and put into 1%~2% limestone solution tank for neutralization, and then taken out for drying.

The residual lime film on the steel surface can prevent the metal surface from being oxidized again, and it can be removed from the cut or groove surface before cutting or welding.

2) Blanking

Cutting and blanking of welding blanks is an important work to ensure the structural dimension accuracy, which should be strictly controlled.

When mechanical shearing, manual thermal cutting and mechanical thermal cutting are used for blanking, the metal blank to be blanking shall be marked according to the drawing and 1:1 ratio.

For the workpieces produced in batch, the template line made according to the drawing and actual size can be used.

Each piece shall be marked with product, drawing number, specification, graphic symbol and hole diameter, and can only be used after passing the inspection.

The dimension tolerance of manual scribing and template shall comply with the standard, and the shrinkage of welding and machining allowance shall be considered.

The steel can be cut by shearing machine or by thermal cutting.

Common thermal cutting methods include flame cutting, plasma arc cutting and laser cutting.

Laser cutting is mainly used for precision cutting of thin plates.

Plasma arc cutting is mainly used for cutting stainless steel and non-ferrous metals.

When cutting and blanking stainless steel plates, attention should be paid to the hardening near the notch.

Because the hardened band has adverse effect on the performance of the steel plate, it should be removed by mechanical processing.

When cutting high strength steel and heat-resistant steel thick plates with alloy element content more than 3%, the surface will be hardened, which will lead to cutting cracks in severe cases.

Therefore, before cutting low alloy high-strength steel and heat-resistant steel thick plates, the initial end of the notch shall be preheated by 100~150 ℃.

When the thickness of the steel plate exceeds 70mm, the steel plate shall be annealed before cutting.

3) Groove processing

In order to make the thickness of the weld reach the specified size without welding defects and obtain full penetration welding joints, the edges of the weld shall be processed into various forms of grooves according to the plate thickness and welding process requirements.

The commonly used welding joint groove forms are V, X, U and double U.

When designing and selecting groove welds, the groove angle, root gap, blunt edge and root radius shall be considered.

During arc welding with welding rod, in order to ensure that the welding rod can approach the root of the welding joint and the side fusion is good during multi-layer welding, a certain proportion relationship shall be maintained between the groove angle and the root gap.

When the groove angle decreases, the root gap must be increased appropriately.

Because the root gap is too small, it is difficult for the root to penetrate, so smaller welding rods must be used to reduce the welding speed;

On the contrary, if the root gap is too large, more filler metal is required, which increases the welding cost and welding deformation.

The narrow gap butt welding of I-shaped groove of thick plate (more than 200mm) can be realized by using thin welding wire and special conductive nozzle in MIG welding.

For the welded joint with groove, it is generally required to leave a blunt edge to ensure the weld quality.

The height of the blunt edge is preferred to ensure penetration without burning through.

The V-shaped or double-sided U-shaped groove of shielded metal arc welding is 0~3mm, and the double-sided V-shaped or double-sided U-shaped groove is 0~2mm.

The penetration of submerged arc welding is greater than that of shielded metal arc welding, so the blunt edge can be appropriately increased to reduce the filler metal.

For joints with blunt edges, the root gap mainly depends on the welding position and welding process parameters.

The gap shall be reduced as much as possible on the premise of ensuring penetration.

Groove can be machined or hot cut.

V-shaped groove and X-shaped groove can be processed by double or three cutting at the same time during mechanical gas cutting blanking.

The dimensional tolerance of groove processing has a great impact on the assembly and welding quality of weldments, which should be strictly checked and controlled.

The dimensional tolerance of groove shall not exceed ± 0.5mm generally.

4) Forming

Most welded structures, such as pressure vessels.

For ships, bridges and heavy machinery, many parts need to be formed before welding in order to meet the requirements of product design drawings.

The forming process includes stamping, rolling, bending and spinning.

Cylindrical and conical weldments, such as the cylinder and transition section of pressure vessels, boiler drums, large-diameter pipes, are rolled with steel plates of different thicknesses.

Coiling is usually carried out on=three roller or four roller plate rolling machine, and thick wall cylinder can also be formed by special die stamping on hydraulic press.

The rolling of the cylinder is essentially a bending process.

When bending at room temperature, that is, during the so-called cold bending, the bending radius of the workpiece shall not be less than the specific minimum value of this material.

For ordinary carbon structural steel, the bending radius shall not be less than 25δ (δ is the plate thickness), otherwise the mechanical properties of the material will be greatly reduced.

When the elongation of the outer fiber of the cold rolled cylinder exceeds 15%, it shall be tempered after cold rolling to eliminate the adverse consequences caused by cold work hardening.

Generally, the steel plate with a thickness of less than 50mm shall be formed by hot rolling or hot pressing.

The normal hot coil or hot stamping temperature shall be selected at the normalizing temperature of the material to ensure that the material still maintains the mechanical properties specified in the standard after hot forming.

When rolling some alloy steel plates which are sensitive to high temperature, the base metal test plate shall be prepared, heated in the furnace and discharged with the workpiece at the same time to check whether the mechanical properties of the base metal after forming meet the requirements of the standard.

Spherical heads, heads and spherical tanks such as pressure vessels, drums and storage tanks are usually made by cold stamping or hot stamping on special molds by hydraulic or hydraulic presses.

When the cold deformation degree of the stamping workpiece exceeds the allowable limit or the stamping temperature exceeds the normal normalizing temperature of the material, the stamping workpiece shall be subject to corresponding heat treatment.

To restore the mechanical properties of the material. Austenitic stainless steel cold stamping parts shall be subject to solution treatment after stamping.

Pipe fittings and profiles are widely used in many welding structures, which are also generally required to be bent and formed according to the design drawings.

Manual, electric, hydraulic and CNC hydraulic pipe benders can be used for pipe bending according to the pipe diameter, wall thickness and forming accuracy requirements.

Three roll or four roll profile bending machine can be used for profile bending.

5) Assembly

In order to ensure product quality, welding structures often need to be equipped with welding machinery.

There are many kinds of welding machines, including simple clamps and complex welding displacement machines.

See Table 1-4 for the characteristics and application occasions of assembly and welding mechanical equipment.

Table 1-4 Characteristics and application occasions of assembly and welding mechanical equipment

Mechanized equipmentFeatures and application occasions
FixtureSingle function, mainly for positioning and clamping; The structure is relatively simple, mostly composed of positioning elements, clamping elements and clamps, and generally there is no transmission mechanism with continuous action; Manual clamps can be carried and moved, and are suitable for on-site installation or assembly and welding of large metal structures
Weldment positionerThe weldment is clamped on a variable position table or frame, which is changed in space by a mechanical transmission mechanism to meet the needs of assembly and welding, and is suitable for assembly and welding of weldments with compact structure, short welds and irregular distribution
Welding machine positionerThe welding machine or welding head can realize translation, lifting and other movements through the machine, so that it can reach the welding position and complete welding. It is mainly used for welding of large metal structures with difficulty in weldment displacement, and can be used only with weldment positioner
Welder positionerThe lifting is realized by mechanical transmission mechanism, and the welder is sent to the welding position, which is applicable to the assembly, welding and inspection of tall welding products

6) Preheating before welding

Preheating before welding is one of the effective measures to prevent welding cracks in thick plate welded structures, low alloy and medium alloy steel joints.

Preheating before welding is conducive to improving the thermal cycle of the welding process, reducing the cooling rate of the welding joint area, preventing cracks in the weld and heat affected zone, reducing welding deformation, and improving the plasticity and impact toughness of the weld metal and heat affected zone.

The preheating temperature of the weldment shall be determined according to the carbon content and alloy content of the base metal, the structural form of the weldment and the restraint degree of the joint, the diffusible hydrogen content of the selected welding material, welding conditions and other factors.

The higher the carbon content and alloy content of the base metal, the greater the thickness, and the higher the preheating temperature required before welding.

Refer to Table 1-5 for the thickness of steel grades preheated above 100 ℃ before welding of steel pressure vessels.

Table 1-5 Thickness of steel type for preheating steel pressure vessels above 100 ℃

Steel gradeCarbon steel16MnR15MnVR
Thickness>38>34>32

For welded engineering structures, the method of carbon equivalent (CE) and cold crack index can be used to determine the preheating temperature.

The preheating temperature for carbon equivalent and low alloy steel welding shall be determined according to the carbon equivalent range, as shown in Table 1-6.

Table 1-6 Determination of preheating temperature for typical steel grades according to carbon equivalent range

Carbon equivalent CE/%Preheating temperature/℃
CE<0.45No preheating required
0.45≤CE<0.6100~200
CE≥0.6200~370

3. Welding procedure qualification

(1) Purpose of welding procedure qualification

Welding procedure qualification is a procedure to verify the correctness and rationality of welding procedure specification through mechanical property or other property tests of welded joints.

The manufacturer shall organize and complete the welding procedure qualification by itself according to the relevant national standards, supervision regulations or international general regulations.

The welding procedure qualification test is different from the test carried out for the purpose of scientific research and technological development, which has two main purposes:

First, to verify whether the proposed welding process is correct before welding product manufacturing;

The second is to assess whether the welding structure production unit can manufacture the welding joints that meet the requirements of the technical conditions when the proposed welding process is qualified.

Therefore, the purpose of welding procedure qualification is to inspect and assess whether the proposed welding procedure is correct, reasonable and can meet the requirements of product design and standards, and whether the manufacturer is able to weld qualified welding joints, so as to provide a reliable basis for the development of welding procedures.

(2) General procedure for welding procedure qualification

Due to different product quality management organizations, the process evaluation procedures of each production unit will be different.

The following is the general procedure for welding procedure qualification.

1) Approval of welding procedure qualification;

2) Issue welding procedure qualification assignment;

3) Prepare welding process instructions;

4) Prepare the execution plan of welding procedure qualification test;

5) Preparation and welding of test pieces;

6) Inspection of welding test pieces;

7) Prepare welding procedure qualification report.

For the unqualified items in the assessment, the causes shall be found out and the assessment shall be carried out correctly after correction.

Finally, all software, such as welding procedure qualification specification, welding procedure qualification report, welding records, various inspection and test reports, shall be archived for future use.

In a word, the quality control before welding is to check whether the shape, size, assembly clearance and unfitness of the welded joint groove of the product to be welded meet the requirements of the drawing, whether the paint and oxide skin around the groove are clear and clean according to the process requirements, whether the selected welding materials are dried according to the specified time and temperature, whether the oil rust on the surface of the welding wire is removed, whether the welding equipment is intact, and whether the current and voltage display devices are sensitive.

Whether the materials to be preheated are preheated as required, and whether the welder has the corresponding qualification certificate or technical level.

Welding can be carried out only when all the above links meet the process requirements.

2. Welding process quality control

The quality control in the welding production process is the most important link in the welding process.

Generally, the welding process parameters are selected according to the design requirements, and then the production and inspection are carried out at the same time.

Each process shall be inspected according to the welding process specification or national standard, mainly including the inspection of welding specification, weld size inspection, inspection and adjustment of welding fixture, inspection of welding structure assembly, etc.

1. Inspection of welding specifications

Welding specification refers to the process parameters in the welding process, such as welding current, welding voltage, welding speed, electrode (wire) diameter, number of welding passes, layers, welding sequence, type and polarity of power supply, etc.

The correctness of welding specifications and executive specifications plays a decisive role in the quality of welds and joints.

The correct specification is obtained by testing and summarizing before welding.

With correct specifications, it is necessary to strictly implement them in the welding process to ensure the excellent and stable joint quality.

For the inspection of welding specifications, different welding methods have different contents and requirements.

(1) Inspection of manual arc welding specifications

For manual arc welding, on the one hand, it is necessary to check whether the diameter of welding rod and welding current meet the requirements, and on the other hand, it is required that the welder strictly implement the welding sequence, number of welding passes, arc length, etc. specified in the welding process.

(2) Inspection of welding specifications for automatic submerged arc welding and semi-automatic welding

In addition to the inspection of welding current, arc voltage, wire diameter, wire feeding speed and welding speed (for automatic welding), automatic submerged arc welding and semi-automatic welding should also carefully check the brand of welding flux, particle size, wire extension length, etc.

(3) Inspection of resistance welding specifications

For resistance welding, the output power of the chuck, power on time, upset forging amount, extension length of the workpiece, contact condition of the welding surface of the workpiece, clamping force of the chuck and the conductivity between the workpiece and the chuck are mainly checked.

When carrying out resistance welding, the mutual coordination among welding current, heating time and upset force should also be paid attention to.

Lack of penetration will occur when the pressure is normal but the heating is insufficient, or when the heating is correct but the pressure is insufficient.

Excessive current or power on time will overheat the connector and reduce its mechanical performance.

For spot welding, check whether the welding current, power on time, initial pressure, pressure after heating, electrode surface and the surface of the workpiece to be welded meet the requirements of the process specification.

Carefully check whether the welding current, power on time and heating pressure are properly matched, otherwise defects will occur.

If the pressure after heating is too large, the workpiece surface will be significantly depressed and part of the metal will be extruded.

If the pressure is insufficient, it will cause incomplete penetration.

If the current is too large or the power on time is too long, it will cause metal spatter and solder joint shrinkage.

(4) Inspection of gas welding specifications

Gas welding mainly checks the brand and diameter of welding wire and the number of welding nozzle.

Check the purity of combustible gas and the nature of flame.

If too large welding nozzle is selected, the weldment will be burnt, and if too small, it will form incomplete penetration.

The use of excessive reducing flame will cause carburization of the metal, while the oxidation flame will cause severe oxidation of the metal, which will reduce the mechanical properties of the weld metal.

2. Inspection of weld size

The weld size shall be checked according to the accuracy requirements specified in the process card or national standards.

Generally, special gauges and templates are used for measurement.

The most common measuring tool for measuring welds is the template, which is manufactured according to the standard weld sizes of different plate thicknesses.

The serial number of the template corresponds to the thickness of the steel plate.

For example, if the butt weld of 12mm thick plate is measured, a piece of 12mm is selected for measurement.

In addition, it can also be measured with a universal gauge, which can be used to measure the protrusion and depression of the weld leg of the T-joint weld, the weld reinforcement of the butt joint, and the groove clearance of the butt joint.

3. Inspection of fixture working state

Fixture is the technological equipment used to fix and clamp the workpiece in the process of structural assembly.

It usually bears a large load, but also is subject to the effect of additional stress caused by heat.

Therefore, the fixture shall have sufficient rigidity, strength and accuracy.

It shall be regularly overhauled and checked during use.

Check whether it interferes with the welding of the workpiece, and whether the deformation of the workpiece due to heat after welding will interfere with the removal of the fixture.

When the fixture is inevitably placed near the welding place, whether there are protective measures to prevent the movable part of the fixture from being damaged due to the spatter during welding, which makes it difficult to remove the fixture.

It shall also be checked whether the position of the fixture is correct, and whether the workpiece size deviation and the workpiece deflection and deformation caused by the weight of the fixture itself will be caused due to improper placement.

In addition, check whether the clamping is reliable.

The fixture shall not become loose and lose its clamping capacity due to thermal expansion, cold contraction or external vibration of parts.

4. Inspection of structural assembly quality

Assembly quality inspection before welding is an important measure to ensure that the structure meets the drawing requirements after welding.

The following inspections shall be conducted for the welded assembly structure:

(1) Check whether the dimensions, datum lines and relative positions of each part are correct according to the drawings, and whether there is welding shrinkage allowance, machining allowance, etc.

(2) Check whether the groove type and size of welded joint are correct.

(3) Check whether the weld arrangement of tack welding is appropriate, whether it can play a fixed role, and whether it will bring excessive internal stress after welding.

At the same time, the defects of the tack welding seam shall be inspected at the same time, and any defects shall be handled in time.

(4) Check whether the welding joint is clean and free of defects (such as cracks, dents, interlayer, etc.).

3. Quality control of finished products after welding

1. Quality inspection of finished products after welding

Although the welding products have been inspected before and during welding, new defects may be caused by the overall requirements of the demander for the products, as well as the changes and fluctuations of the conditions during use.

Therefore, in order to ensure the quality of the products, the finished products must also be inspected.

There are many inspection methods for finished products, which should be selected according to the use requirements of products and the technical conditions of drawings.

The finished products of welded structures are mainly inspected for appearance and NDT.

At the same time, the inspection of welding products in use is also a part of finished product inspection.

Of course, because the inspection conditions of the welding products in use have changed, the inspection process and methods have also changed.

(1) Visual inspection and measurement

Visual inspection of welded joints is a simple and widely used inspection method, which is an important part of finished product inspection.

This method is also sometimes used in the welding process.

For example, when thick wall weldments are multi-layer welded, this method is used to inspect each weld bead to prevent the defects of the previous weld layer from being brought to the next weld bead.

Visual inspection is mainly used to find defects and dimensional deviations on the weld surface.

This kind of inspection is generally carried out by visual observation with the help of standard sample plate, gauge, magnifying glass and other tools.

Therefore, it is also called naked eye observation method or visual method.

(2) Compactness test

For welded vessels storing liquid or gas, the non compact defects of the weld, such as penetrating cracks, pores, slag inclusions, incomplete penetration and loose structures, can be found by densification test.

Tightness inspection methods include kerosene test, submerged water test, air blowing test, water flushing test, ammonia test and helium test.

(3) Strength inspection of welded joints of pressure vessels

Due to the particularity and integrity of pressure vessel products, the joint strength inspection of such products can only determine whether the welded joints meet the design strength requirements of products by inspecting the strength of their complete products.

This inspection method is commonly used for inspection of pressure vessels storing liquid or gas. Generally, strength test is required in addition to sealing test.

(4) Verification of physical methods

The physical inspection method is to use some physical phenomena to measure or inspect the relevant technical parameters of the inspected materials or weldments, such as temperature, pressure, viscosity, resistance, etc., to judge the internal problems.

Such as internal stress distribution, internal defects, etc.

The physical inspection method for the determination of material technical parameters belongs to material testing technology.

The nondestructive testing method is generally used to inspect whether there are internal defects of materials or weldments.

The current nondestructive testing methods include ultrasonic testing, radiographic testing, magnetic testing, penetrant testing, etc.

(5) Design qualification of welding structure

In order to carry out the welding inspection smoothly, the welding structure design must be evaluated.

The welded structure to be inspected shall be capable of inspection, that is, flaw detection.

A welding product can be inspected, which shall meet the following conditions:

1) There is an appropriate flaw detection space.

2) There is a detection surface convenient for flaw detection.

3) The bottom surface of the detection part with suitable flaw detection.

Because there are many and different flaw detection methods.

Therefore, the flaw detection space, detection surface and bottom surface of detection part required by various methods are also different.

See Table 1-7 for details.

Table 1-7 Requirements of various flaw detection methods for product flaw detection

Flaw detection methodRequirements for flaw detection space positionRequirements for detection surfaceRequirements for the bottom surface of the detection part
Radiographic inspectionLarge space position is required to meet the position requirements of the ray head and adjust the focusThe surface does not need to be machined, only the things that affect the display of defects need to be removed, and there are positions for placing type codes, lead arrows and penetrametersCan place magazine
Ultrasonic flaw detectionSmaller space is required, only the space for placing probe and probe movementSurface processing shall be carried out as far as possible to facilitate acoustic coupling. Surface range with probe movementFor the reflection method, a good reflective surface is required for the back
Magnetic flaw detectionThe magnetic particle shall be removed from the magnetic flaw detection part and the space position of the defect shall be observedRemove the oxide scale and other dirt that affect the magnetic particle accumulation, and have the working position of the probe 
Penetrant testingThere shall be space for coating flaw detection agent and observing defectsIt is required to remove dirt on the surfaceIn case of kerosene flaw detection, there shall be a space for kerosene coating on the back, and dirt preventing kerosene penetration shall be removed

After the welding products are made, if the flaw detection conditions cannot be met, the flaw detection shall be carried out step by step during the assembly and welding of the products, but the final assembly and welding welds shall be those with flaw detection conditions.

When creating flaw detection conditions, economy, reliability and the highest flaw detection sensitivity shall be considered.

2. Service quality inspection of welding products

(1) Inspection after delivery of welding products

1) Welding product inspection procedures and inspection items

① Check whether the inspection data are complete.

② Check the quality certificates of welding products.

③ Check whether the actual welding product is consistent with the quality certificate.

④ The quality inspection of welding products shall be carried out according to relevant installation procedures and technical documents.

⑤ Special attention shall be paid to important parts of welding products, parts prone to quality problems, and parts prone to damage and deformation during transportation, with emphasis on inspection.

2) Inspection methods and acceptance standards of welding products

The inspection methods and acceptance standards of welding products shall be the same as those used in the manufacturing process of welding products

3) On site treatment of welding quality problems

① In case of missing inspection, supplementary inspection shall be carried out and quality certificates shall be supplemented.

② For quality problems caused by different inspection methods, inspection items or acceptance standards, the same inspection methods and evaluation standards shall be used as far as possible to re evaluate whether the welding products are qualified.

③ Welding defects that can be repaired or not repaired are generally not returned for repair.

If the welding defects obviously exceed the standard, they should be returned for repair.

Large welding structures shall be repaired on site as much as possible, and those with small welding structures and complicated repair process shall also be returned to the factory for repair in time.

(2) Inspection of service quality of welding products

1) Quality monitoring of welding products during operation

During the operation of welding products, acoustic emission technology is usually used to monitor the operation.

2) Review of welding product maintenance quality

The welding products working under severe conditions (corrosive medium, alternating load, thermal stress) shall be rechecked regularly in a planned way.

3) On site treatment of quality problems of service welding products

For the repair of important welding products, the process qualification shall be conducted again, the welding process shall be verified, the repair process measures shall be formulated, and the quality control instructions and record cards shall be prepared.

(3) Field investigation and analysis of welded structure damage accidents

1) Field investigation and analysis

① Protect the welding structure damage site and collect all operation records.

② Find out whether the operation process is correct.

③ Find out the fracture position of welding structure.

④ Check the surface quality and fracture quality of the welded joint at the fracture.

⑤ Measure the actual thickness of the damaged structure, verify that its thickness meets the drawing requirements, and provide a basis for re design and verification.

2) Sampling and analysis of base metal and weld

① Re conduct metallographic inspection on the damaged structure;

② Re check the chemical composition of the damaged structure;

③ Re check the mechanical properties of the damaged structure.

3) Review the manufacturing process of welded structure

Re check the design parameters of the welded structure against the design specification, check whether they conform to the national standards, whether the manufacturing process of the welded structure conforms to the regulations, find out the responsibilities, and make necessary preparations for determining the repair process.

3. Establishment of welding inspection archives

Welding inspection archives are also an important part of the whole welding production quality assurance system.

It not only reflects the actual quality of welding products, but also provides information for welding quality control, provides basis for statistics and analysis of quality control of various welding products, and provides quality inspection basis and historical evidence for maintenance, transformation, accident analysis, etc. during the operation of welding products.

Therefore, relevant personnel should attach great importance to it.

(1) Welding inspection record

The welding inspection record shall at least include the following contents:

1) Number, name and drawing number of welding products;

2) The number of the welding process documents used on site, such as the number or name of the welding process detail card, welding process card or welding process qualification and other documents;

3) Brand, specification and incoming inspection number of base metal and welding materials;

4) Welding method, welder name, welder seal;

5) Actual preheating temperature, post heating temperature, hydrogen removal temperature and time before welding;

6) Welding inspection methods and results, including visual inspection, nondestructive testing, hydrostatic testing and welding sample inspection;

7) Welding inspection report No.

The inspection report refers to the written report issued by the physical and chemical laboratory, non-destructive testing room and other full-time inspection institutions to certify the weld quality after the inspection of the weld quality.

The inspection report shall make a positive or negative judgment on the weld quality, that is, make a conclusion of “qualified” or “unqualified”;

8) Weld repair method, repair position, repair times, etc;

9) Record date of welding inspection and signature of the recorder.

The welding inspection record is an important part of the product quality record.

The inspection procedure shall be prepared according to the manufacturing process, and the quality control form shall be printed to standardize the record.

The record shall be recorded according to the specified inspection procedure to ensure that the record is timely and complete.

(2) Welding inspection certificate

The inspection certificate of welding products is the quality certification document prepared by collecting the original records of inspection work when the products are completed and summarizing them.

The form and content of the welding inspection certificate issued to the user shall be determined according to the structure of the specific product.

For products with complex welding structure and manufacturing process and high quality requirements, the inspection data shall be bound into a volume and provided to the user in the form of quality certificate.

The technical data in the certificate shall be practical, accurate, complete and up to standard.

For welding products with simple structure and manufacturing process and low requirements for operating conditions, the inspection certificate can be provided to users in the form of card.

However, any welding inspection certificate shall at least include the following contents:

1) Name, number and drawing number of welding products;

2) Technical specifications or service conditions of welding products;

3) Specifications of raw materials, including base metal, welding wire, welding rod, etc;

4) Welding process data, including welding methods and main welding processes, welders and welder seals, etc;

5) Welding inspection data, including NDT, sample inspection, hydraulic test results, etc;

6) Weld repair records, including repair parts, repair methods, repair times, etc;

7) The responsibility seal includes the signature or seal of the person who prepares the inspection certificate, the inspection team leader or section chief, the factory director, the factory quality conformance seal, the date of issue, etc.

The inspection certificates of welding products are generally printed in a fixed or standard format.

For the preparation of the welding inspection certificate, the original records shall be collected and summarized, and filled in according to the format requirements of the certificate.

The inspection data must be complete, systematic and the technical data must be true and accurate.

(3) Welding inspection archives

When the welding products are damaged during operation, it is necessary to check and repair, consult the inspection files and check the original quality of the products, so as to take corresponding measures to ensure the maintenance quality.

In order to improve the operation parameters of welding products or the maintenance and management conditions of equipment, users must also modify the drawings according to the welding inspection files and the original design in order to complete the technical transformation project.

The inspection archives of welding products shall include the following materials:

1) Complete welding production drawings;

2) Original records of welding inspection, including material inspection records, process inspection records and weld quality inspection records;

3) Documents in welding production, including material substitution sheet, temporary change sheet, work contact sheet, unqualified weld treatment sheet, etc;

4) Welding inspection report, including mechanical property, NDT, heat treatment and other inspection reports;

5) Welding inspection certificate, including welding product quality certificate (volume) or certificate of conformity.

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