Cause analysis and Countermeasures of welding proc

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Cause analysis and Countermeasures of welding procedure qualification errors of pressure equipment

welding procedure qualification is an important link of welding quality control. The relevant departments of the state attach great importance to this. The standard specifications for the manufacture and installation of pressure equipment specify the content of welding process evaluation and clearly stipulate the practice of welding process evaluation. The welding process evaluation standard for pressure equipment is not applicable to boilers, pressure vessels (including gas cylinders), but also applicable to pressure pipelines including long-distance pipelines in the mining industry

welding procedure qualification is to prepare welding specimens according to the proposed welding procedure and standards, process and inspect the specimens, and determine whether the welded joints have the required service performance. Qualified welding procedure qualification can effectively guide welding production, but often due to poor understanding of standards, insufficient capacity of equipment and tools, and lax control of the evaluation process, the completed welding procedure qualification is not only a large number, but also can not guide actual production, and even has a negative effect. Each toothbrush is allowed to leave a bunch of Maowen to explain the causes of misfire in the welding process of pressure equipment, and propose solutions

reasons for errors in welding procedure evaluation of pressure equipment

1 poor understanding of the standard

the understanding of the content of the welding procedure planning standard is related to the comprehensive ability of welding technicians. Because welding technicians at different levels have different understanding of the standard content, or their understanding is not deep, transparent or even wrong, there are many cases that lead to the wrong calculation results. The common ones are:

(1) the applicable parts and common parts of material selection (including thickness, base metal material, welding material type or brand) are not considered. Regardless of the exchange factors of some materials in the standard, the instrument assigns the welding procedure qualification task according to the product material to be manufactured

(2) the electrode tensile testing machine is mainly suitable for testing the tensile strength and yield strength of the electrode under the rated experimental force, dead load and tensile force. The instrument cannot make full use of the condition that the thickness of the test piece is applicable to the effective range of the welding base metal, so as to use the minimum number of welding process evaluation test pieces to cover all the base metal thickness ranges of the same material, but determine the thickness of the welding process evaluation test piece according to the thickness of the base metal of the welding piece, This increases the number of process evaluations

(3) for butt weld weldments with unequal thickness, when the base metal thickness of thin edge and thick edge cannot be covered by the same assessment, only one assessment is often made, and the thickness range of thin edge or thick edge is ignored

(4) the V-notch is not used for the specimen of impact toughness test, and the original notch is still used for evaluation

(5) when the process qualification sample fails to pass the inspection, it is not to re formulate the welding process instruction and re evaluate, but to double the re inspection with the spare sample according to the welder examination or the inspection standard of the welding product test plate

(6) when dissimilar steel is welded and has impact toughness requirements, the impact toughness test of heat affected zone on both sides is not carried out

(7) welding procedure qualification is not required for imported steel plates. The instrument applies the category and group of domestic steel according to the chemical composition and mechanical properties in the quality certificate provided by foreign suppliers, and replaces the welding procedure qualification of imported steel with the welding procedure qualification of domestic steel grades

(8) after we can stand your test and complete the product welding, we can't do the welding procedure qualification at all, and we can't guarantee that the service performance of the product's welded joints can meet the design and standard requirements

2 insufficient capacity of equipment and tools

during the production process, due to the neglect of the management of welding experimental equipment and other processing equipment, the equipment is not in good condition or can not be used, which buried the hidden danger of unqualified welding process evaluation. Common ones are:

(1) the measurement of special weld inspection tools is inaccurate or not. The test pieces are assembled before welding, the relevant dimensions of the groove are not measured accurately, the appearance inspection after welding is not standardized, and there are not many quality inspection tools after sample processing

(2) the welding equipment is aging, with poor service performance, and its ammeters and voltmeters are not regularly calibrated or incomplete, resulting in inaccurate process parameters on the welding test record sheet

(3) aging of machining equipment leads to the accuracy of processed samples not meeting the standard requirements

(4) the processed impact specimen has no equipment to check the accuracy of V-notch size

(5) the mechanical performance test equipment is poorly maintained and has not been calibrated regularly

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