Common welding defects

Many different types of weld defects in the internal and external common weld defects can be summarized as follows:

First, the weld size requirements of sub-solder wave thick, rough shape, weld height is too low or too high to enhance, varying the width of weld and fillet weld wave unilateral or excessive settlement, etc. are substandard weld size requirements, because:

Bevel angle weldment assembly space improper or uneven.
Welding current is too large or too small, improper selection of welding specifications.
Win a speed differential, the electrode (or welded to) the angle properly.
Second, the crack

Shape of the crack tip sharp, severe stress concentration, and impact on the bear alternating load, a greater impact of static tension is the most dangerous of the weld defects. According to the causes can be divided from the cold cracking, hot cracking and reheat cracking and so on.

(Cold crack) means a crack generated below 200 ℃, which is closely related with the hydrogen, and its main causes are:

Thick piece of large selection of pre-heating temperature and slow cooling after welding measures inappropriate.
Inappropriate selection of welding consumable  .
Welded joints rigid, process unreasonable.
Produced near the weld and its rigid organization.
Inappropriate choice of welding specifications.
(Thermal cracking) refers to cracks generated more than 300 ℃ (mainly solidification cracking), and its main causes are:

Composition. Welding of pure austenitic steel, high nickel alloy steel and some non-ferrous metals prone.
Weld contains more sulfur and other harmful impurities.
Welding conditions and the inappropriate choice of joint shape.
(Reheat crack) is annealed to eliminate stress cracks. Refers to the welding zone of high intensity, due to post weld heat treatment or high temperature use, resulting in the heat affected zone of intergranular cracks, and its main causes are:

Annealing heat treatment to eliminate undue stress.
Alloy composition. Such as chromium molybdenum vanadium boron and other elements have a tendency to increase the reheat cracking.
Welding consumables, welding specification poor choice.
Structural design of large stress concentration caused by the irrational.
Third, the stomatal

In the welding process, due to the gas too late to escape in time or in the weld metal surface inside the hole formed, the causes are:

Welding electrodes  , flux drying is not enough.
Welding process is not stable enough, the high arc voltage, arc too long, too fast welding speed and current is too small.
Filler metal and base metal surface oil, rust, etc. is not removed.
Back technique is not used arc melting point.
Preheat temperature too low.
Arc and not to stagger the position of extinction.
Protect the poor welding area, pool area is too large.
AC prone to porosity, DC reverse the tendency of the smallest pores.
Fourth, welding tumor

In the welding process, the molten weld metal to flow outside the base metal without melting the metal formed on the tumor, it changes the cross-sectional area of ??the weld on the dynamic load disadvantage. The causes are:

Arc too long, the bottom welding current is too large.
Li welding current is too large, improper operation of Article swing.
Weld assembly gap is too large.
V. Crater

Ending at the seam in the obvious lack of meat and depression. The causes are:

When arc welding operations received improper extinction time is too short.
Aluminium welding wire and cut off the power at the same time, without first stopping and then power wire.
VI undercut

The edge of the weld arc melting the base metal, the weld metal has not been added and left gaps. Undercut the force weakens the joint section, the joint strength decrease, resulting in stress concentration, so that may lead to a breach in the biting edges. The causes are:

Current is too large, the arc is too long, inappropriate speed operation section, the arc heat is too high.
SAW low voltage, welding speed is too high.
Rod, wire tilt angle is not correct.
VII slag

In the weld metal fusion line positions exist within or inclusions. Influence on the mechanical properties of slag, the effect and the number and shape of the inclusions. The causes are:

Multi-layer welding, each welding slag is not removed.
Rust on the left thick weldments.
The physical properties of electrode coating inappropriate.
Bad solder layer shape, bevel angle poorly designed.
Weld pool width and penetration depth ratio is too small, too deep undercut.
Current is too small, too fast welding speed, the slag floats too late.
VIII, no penetration

Between the base metal or base metal and deposited metal between the local lack of fusion phenomenon. It generally exists in one side welding of weld toe, is very sensitive to the stress concentration, fatigue and other properties on the strength of greater impact. The causes are:

Poor design of the groove, the angle is small, blunt edge of a large, small gap.
Welding rod, wire angle is not correct.
Current is too small, low voltage, welding speed too fast, the arc is too long, there are magnetic blow and so on.
Weldments on thick rust is not removed.
When submerged arc welding side.
 

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Comparative analysis of the JB4708, GB50236, "steam boiler technology to monitor the safety regulations", SHJ509, SY/T0452, JGJ81 six welding standards differences between their characteristics and a comprehensive analysis of the content that JB4708-2000 more detailed scientific assessment of the rules. JGJ81 standard steel products involved, the use of standard welding JGJ81 comment.

0 Introduction
Steel structure with its light weight, low cost base for soft ground, easy to install, construction of fast, short period, the investment recovery faster, less environmental pollution and earthquake resistant construction and good performance, and its superior performance and good structure overall economic efficiency in the domestic housing, bridges, tower masts, pipes, tanks, pressure vessels and hydraulic and other aspects of a wide range of applications.
Welded steel products(Stainless Steel Electrode), processing technology has become an important one. At present, the materials used in welding engineering, welding has been mastered it, to ensure the quality of welding engineering, welding units should possess the necessary technical capabilities, and equipment and establish and improve the welding quality system.
Welding procedure qualification welding unit is used to assess the ability to meet the appropriate welding procedures, specifications and technical conditions required product of welding joint, the same time, through the welding procedure to verify the welding unit of instruction to develop the welding technology is appropriate.

1 of the installation of the current standard of welding procedure qualification
Evaluation of the management of the welding process, with the world's advanced countries, it also included a standardized management and integration with the international standardization of maturing. But our industry management in the national economy also account for a large proportion of all walks of life to the characteristics of each welding engineering, welding procedure established for the corresponding standards.
In this paper, welding operations involve the installation of the welding procedure qualification standards (later referred to as the "standard", commonly used criteria in Table 1) were compared, to talk about the welding procedure qualification (later referred to as "welding Review") management recommendations and welding procedure qualification report (hereafter referred to as the "Report").

2 The "standard" terms of
We are in a different installation, there will be corresponding procedures, norms, standards, from the national standardization requirements, industry standards will be uniform, different from Table 1, the "standard" content point of view, are from the general rule, assessment rules, testing and evaluation of three main aspects of the "welding Comment on" request.
2.1 General provisions
JB4708, GB50236, SHJ509, JGJ81 made four standard general provisions, "steamed rules" no obvious list, but the first 1 to 9 of the general content and consistent with the provisions of three criteria are provided in different ways: for " Welding Review, "the condition is confirmed by the welding material, a" welding Comment on "Time is the product prior to welding. On "Comments welding" process equipment, instrumentation, steel, welding materials and welding puts forward the basic requirements. GB50236 standard section 4.1.7 reads: "in the same quality system of the different construction units, when the NDT personnel to meet the state authorized by the professional examination for the Examination of qualified persons in accordance with items and passing the examination authority, engaged in welding inspection and audit work, for the same welding procedure can not be repeated. "It is a reference to the American Society of Mechanical Engineers standard ASME-â…¨ (9), combined with our construction and development group, that by the number of units the same quality management system, quality system within this unit, there is no need to repeat the same "Welding Review."
SY/T0452 Standard 2.0.8 reads: "The consent of the owners, the pressure pipeline construction between the various units of the same qualification can be assessed according to the standard use of each other qualified report. As the preparation of technical rules (instructions) basis, but advance license units should be assessed and approved by the division unit welding responsibility. "In the other there is no clear standard. Which can not meet: validation of welding procedure qualification welding unit developed the correctness of the welding process, welding units and assess the capacity.
JGJ81 Standard 5.1.2 provides that the steel produced by the installation companies to complete welding assessment also shows that the same quality system. Higher than that of other standards is: "... ... the provisions of this regulation by welding specimen, the sample was cut by the national quality and technology supervision department certification qualification testing unit testing."
In fact, JB4708, SHJ509, "steamed rules" three criteria in the "welding units, construction units" are implied in the scope of the same quality system.
The "standard" are provided for "welding assessment" procedures, welding units should be combined with the business situation, according to the "standard" to introduce the unit, "Welding Review" program.
JGJ81 standards this special requirements: Section 5.1.7 of "welding procedure qualification test is complete, evaluation units should be made based on the results of welding procedure qualification test reports, together with the welding procedure qualification instruction, assessment records, inspection and evaluation with the results of the sample reported acceptance of project quality supervision departments and relevant units review of the record. ... ... "
2.2 Evaluation Rules
Listed in Table 1, the six "standard", are welding process factors on the mechanical properties of welded joints extent, as does the need to re-assess the basis of welding process and welding procedure qualification provisions of the rules, alternative range.
Affecting the mechanical properties of welded under the same process factors, each qualified "welding assessment" can meet a range of (material, specifications, welding position, joint type) products, these products are applied before welding, can be based on coverage of the "report" to develop welding operation instruction, welding units there would be no need to repeat the work, you can reduce the "welding Comment on" workload.
(1) The important factor is the tensile strength of welded joints and bending properties of the welding process factors.
(2) additional factor is the impact toughness of welded joints of welding technology factors.
(3) refers to the requirements of the secondary factor is the determination of no significant effect on the mechanical properties of the welding process factors.

JB4708 standard, GB50236 standard and the "steam regulation" SY/T0452 standards will affect the mechanical properties of welding process factors into important factors, additional factors and secondary factors. Important factor in the standard listed above (welding, heat treatment, base metal thickness and the thickness of deposited metal, welding consumable  , gas shielded welding wire) In addition to differences in the base metal outside the group are classified the same, and make lists in different ways plus factors, the same content. JB4708 standard lists only a secondary factor.
SHJ509 an important factor in the standard list, in addition to the first four criteria listed in the content, an increase of welding position (except for flat welding position changes for the whole position; tubular specimen level to the level of fixed rotational position welding; tubular level of fixed specimens and vertical position for the assessment other than the all-position welding sheet metal), interpass temperature, heat input, clear the root to the root unclear, double-sided welding to weld the inclusion of important factors. These additional important factor in other criteria were included in the additional factors.
SHJ509 standard did not specify and lists of additional factors, secondary factors to change the assessment requirements.
JGJ81 standard evaluation rules from welding, steel, joint type, specimen thickness, heat treatment and welding parameters, has made provisions. No division of important factors, additional factors and secondary factors.
For the "standard" not listed in the additional factors and secondary factors, refer to table 1 JB4708 standard (or GB50236 standard table 4.2.6) implementation.
In order to reduce the number of welding procedure qualification, the "standard" according to the base metal chemical composition, mechanical properties and welding performance of classification groups, as the "standard" does not involve the same product range, each group included in the base metal classification are different.
<<Steam Regulation>> Standards Appendix 1, section 10, paragraph 2, the base metal steel, divided into 4 categories, no further grouping, only involving carbon steel, low alloy steel and heat-resistant steel, qualified assessment of the same type of steel range of (alternative) provides that no specific action is not convenient. But on the other "standard" in the body not related to the foreign steel, but also made specific provisions.
JB4708 standards and SHJ509 standards, the base metal steel, basically the same group classification, except that the class number corresponds to the order of steel, steel in JB4708 standard Cr5Mo included as a separate category, lists 14 groups of 52 class 8 steel grades; SHJ509 standards included in the heat-resistant alloy steel Cr5Mo a separate set of categories, a total of 58 species of Class 7 of 19 groups of steel grades. In addition, non-ferrous metals aluminum and aluminum alloy, copper and copper alloys as a separate sub-categories. But these differences, there was no alternative in the contradiction between the base metal.
GB50236 standard classification table 4.2.3 of the base metal group is more comprehensive and detailed breakdown of the 28 groups of 23 class of 64 kinds of grades of steel, with the exception of aluminum, magnesium, copper and its alloys, the addition of a nickel alloy and titanium, the heat steel and stainless steel and subdivided into classifications, it is mainly based on the standard American Society of Mechanical Engineers ASM-â…¨ classification group. In the alternative scope than the other "standard" relaxation, reflected in:
1) P3 + P3 (12CrMo +12 CrMo) can replace P3 + P2A (16Mn \ 16MnR \ 16MnRc \ 15MnV \ 15MnNR, etc.), P2B (16MnDR \ 09Mn2VD \ 09MnVDR) or P1 (Q235-A, B, C \ 20R \ 20G \ 20HP \ 10 \ 20 \ 25 \) composed of dissimilar steel welded joint; P4 + P4 (15CrMo +15 CrMo) alternative to P4 + P2A, P2B, or P1 consisting of dissimilar steel welded joint; P5A + P5A (12Cr2Mo +12 Cr2Mo) alternative P5A + P2A, P2B, or P1 consisting of dissimilar steel welded joints. However, the applicability of three conditions is not strong, because the P3, P4, P5A qualified assessment of their own kind of steel, each with low-alloy steel, carbon steel composition of dissimilar welding, welding the top three grades (or steel wire) to change, important factors are changes to be re-"weld evaluation." For not included in the "standard" in the steel, the "standard" are given the same requirements.
2) JB4708 standards, there is a unique content, that is, the assessment of the corrosion layer welding rules.
3) JGJ81 standard view of the welding parameters of the current implementation of standardized procedures and the implementation of strict product quality standards was inadequate, and some products are also the lack of significant long-term application of practical assessment projects; a lot of steel production, and installation enterprise established at the beginning, the lack of welding expertise and practice experience, inadequate quality assurance system operation. Review welding demanding rules than other standards. Alternative terms such as steel, JGJ81 standards. Section 5.2.2 ... .... â‘  different types of steel, welding procedure qualification results may not be with each other instead. â‘¡ â… , â…¡ similar type of steel in strength and impact toughness level when changes occur, the high-level assessment of the results of welding steel can replace low-level steel; â…¢, â…£ similar type of steel results in the welding procedure qualification shall not be replaced with each other. Combination of different types of steel, welding should be re-assessed, not with the same kind of steel instead of the assessment results. "JGJ81 standard classification of steel used in Table 5.1.6-2 (see Table 2).

2.3 Testing and Evaluation
JB4708 standards, SHJ509 standards, "steam regulation" for "welding Comment on" Preparation of specimens, testing (visual inspection, radiographic testing), sample processing requirements, test methods, conformity index is consistent with the principles, except that the standard multi-resistant JB4708 corrosion layer welding test specimen and test and evaluation; SHJ509 added to the standard aluminum and aluminum alloy, copper and its alloys bending test compliance indicators.
GB50236 standard than the three "standard" combination of the lack of fillet weld and weld specimens, samples and testing, assessment content; bend specimen of thickness are not very consistent, but not contradictory. It provides for bending specimen (plane bending, back bending) thickness: when the specimen thickness T <10mm, the sample thickness t = T (and other "standard" the same.) When the specimen thickness T ≥ 10mm, the sample thickness t = 10mm (other "standard" as: 10mm ≤ T ≤ 20mm, the sample thickness t = T; T> 20mm, the sample thickness t = 20mm); different bending test specimen materials used in the curved shaft diameter and the other "standard" requires not the same. At the same time, GB50236 standards are bending angle 180 °, passing targets, and other "standard" the same.
JGJ81 standard "Welding Review" Specimen preparation and testing of samples, specimens and samples to the testing and inspection requirements, due to the special nature of the standards related to products and increase the inspection categories: T-shaped and cruciform joints bend , macro-etching and hardness.
3 standard implementation of the discussion
3.1 The "standard" compatibility, advanced
Article 2 of the control from the shows: Table 1, listed in the "standard" great compatibility between, there is no contradiction in principle, meaning that the "standard" further perfect. Possible future development to the industry to use the same "standard." Now, we are faced with several "standard" case, should not be the "standard" provisions of the use of constraints can be satisfied under the conditions of interoperability of assessment rules. Such as: welding units have been accumulated in line with JB4708 standard "report" some "reports" to press the "steam regulation" requires that the unit will cover the boiler to the welding joint, the unit would be no need to press the "Steam Regulation" request a new "welding assessment", it may already be covered by the "report" to develop welding operation instruction. Similarly, according to GB50236 standard to complete the "welding assessment" factors in all respects to meet the conditions, the qualified welding procedure can be used as JB4708 standards, SHJ509 standards, "steamed rules" applicable to welding operations guidance range of products developed based on the book, unnecessary re "weld evaluation."
JB4708 standard, GB50236 standards and content from the production's more SHJ509 standards and the "steam regulation" is quite advanced in the implementation of the latter two "standards" should learn from the former terms. Such as: classification of base metal group, additional factors, the division of secondary factors.
China's current standard "steel construction and acceptance" (GB50205) provide for the boiler and pressure vessel welding procedure qualification procedures. A variety of high-level (high-rise) building steel structure, steel structure high-capacity boilers, industrial furnaces, kilns and process equipment steel shell, all kinds of venues large span building pipe - pipe, tube - ball space truss, truss, etc. the thickness of steel used in steel, high strength, connection type complex, welding methods varied, technical difficulties, so boiler and pressure vessel welding procedure qualification procedures and test methods the content of these structures can not meet the type of welding procedure qualification requirements, JGJ81 implementation of standards in a timely manner to solve this problem. However, a variety of industries involved in the enterprise in terms of welding engineering, welding procedure qualification management more difficult.
3.2 "welding Comment on" Management
Welding units, "Welding Comment on" management development program file, refer to Appendix A JB4708 standard to regulate the welding of the unit instructions and "report" on the assessment issued after passing the "report" into the document management, new reports regularly directory to release the premises to facilitate welding site inquiries, on request. Enterprises have the ability in the circumstances, the recommendations into the computer network management, to improve efficiency.
Welding products before the product is not in welded joints of welding units have been assessed scope of accreditation of qualified welding process, the welding unit of product requirements shall be the "standard" re-"weld evaluation."
4 Conclusion
And GB50236, SHJ509, "steam regulation", SY/T0452 comparison, JB4708-2000 content more than the detailed rules of assessment more scientific and reasonable. If added to the material not covered by other standards, the practical side will be more extensive. Recommended to make use of JB4708 for welding procedure qualification, reduce duplication of work. JGJ81 standard steel products involved, the use of standard welding JGJ81 comment.

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