ASME Pressure Vessel Welding Process Evaluation Requirements

We are based on the U.S. ASME Boiler and Pressure Vessel Code, Volume IX, ‘Welding and brazing evaluation’ of the relevant provisions, as well as for ordinary steel structures of the U.S. AWD1.1 ‘Steel Welding Code’ of the relevant chapters of the provisions of the brief description of the ASME code The relevant requirements of the ASME Code on pressure vessel welding process evaluation.
Boiler and pressure vessel welding process evaluation principles
Boiler and pressure vessel welding process assessment of the necessity of the project, in principle, according to the welding process to determine the important parameters. Any kind of important parameters are different from the original welding process regulations, or its changes over the scope of the regulations allowed by the corresponding welding process assessment test must be made. Welding process assessment project to joint form classification, and the following three basic joint form as the assessment of the test piece joint form, including the product structure may appear in a variety of joint forms.
1) Open bevel full weld-through butt joints, can be used to evaluate all open bevel full weld-through butt joints and corner joints, including open bevel full weld-through T-joints.
2) Open bevel partially welded through butt joints, can be used to evaluate all open bevel partially welded through butt joints and corner joints, including open bevel partially welded through T-joints.
3) Angle joints without bevelling, can be used to assess all angle joints without bevelling, including the angle welds between the receiver and the barrel.
Which welds need welding process evaluation?
In the manufacture of boilers and pressure vessels, the manufacturing regulations do not require welding process evaluation for all welds on the product structure, but only the following welds must be tested for welding process evaluation.
1) Various forms of joints on welded pressurised parts. 2) Various forms of joints on non-pressurised load-bearing welded parts, such as all permanent or temporary lugs and reinforcing plate connections to pressurised parts. 3) Non-pressurised and basically non-pressurised load-bearing parts (e.g. attachments to increase the heat transfer surface - mackerel sheets, insulation supports, pins, etc.) and pressurised parts. 4) Welded joints between the welded parts and the pressurised parts. 5) Welded joints between the welded parts and the pressurised parts. Pins, etc.) and the pressurised parts of the weld is determined in accordance with the following principles: such as manual, or mechanised welding methods, should be made to assess the welding process of fillet weld test. If the fully automatic welding method, it is not necessary to make welding process assessment.
According to the welding process to determine the important parameters of the welding process assessment rules
1. Welding method
From a welding method to another welding method, should be made welding process assessment test. Applicable to the boiler and pressure vessel welding methods are: gas welding, electrode arc welding, submerged arc welding, fusion electrode gas shielded welding, tungsten electrode gas shielded welding, plasma arc welding, electroslag welding, laser welding, electron beam welding, flash butt welding, inductive heating pressure welding, resistance welding, aluminium hot press welding, pneumatic welding, inertia and continuous drive base metal welding, stud arc welding and stud resistance welding.
In the actual weldment of the same weld, such as the use of two or more different welding methods, or different important process parameters when welding, it can be welded according to each welding method of welding the base material, metal thickness of the test piece of welding process evaluation. Can also be used in the actual weld seam weld the combination of welding methods or welding process welding the same payment process evaluation test pieces. But each welding method, or welding process welded weld metal thickness should be able to meet the requirements to take out the required tensile and flexural specimens. For electrode arc welding, tungsten electrode gas shielded welding, fusion electrode gas shielded welding, plasma arc welding and submerged arc welding, or a combination of these methods, if the completed welding process evaluation using a thickness of more than 13 mm specimens, the welding process evaluation report can be used with another welding method of the process evaluation report for the same actual weld, including the root weld channel.
2. Types of base metals
There are many types of base metals used in boilers and pressure vessels. If the base metal is assessed by the steel number or the grade of the material, the assessment workload is very large and unnecessary. In order to reduce the repetition of this meaningless assessment, the U.S. ASME Code of practice is to provide for the recognition of standard materials, according to their chemical composition, mechanical properties and weldability to be classified, that is, the alloy composition is similar to the strength level and weldability of the material close to the rules into a class, and marked with P classification number. In the same class of parent metal, but also according to the strength and impact toughness of the level of grouping, and the grouping number marked in the classification of the number of the back, for example, SA106-A carbon steel belongs to the first class, group 1, the classification of the group number of the method of expression for the P1-1. The latest version of the ASME code has been used in the boiler and pressure vessels in the nearly The latest edition of the ASME Code has classified nearly 1,000 types of steel used in boilers and pressure vessels into 23 classes and 52 groups. This classification of base metals is based on a large number of material weldability tests and welding process test data as well as years of actual production experience. Therefore, listed in the same category of various base metals, such as the proposed welding procedure, the other important parameters of the welding process is the same or within the tolerance range, the use of a certain base metal welding process evaluation report can be common with each other. For example, SA106-B and SA-36 carbon structural steel belongs to the same P-1 category, such as the use of the same welding method, welding materials and similar welding process parameters for welding, and the thickness of the weldments in the process of evaluating the standard within the scope of the allowable, then SA -36 steel welding procedure can be based on the completed SA106-B steel welding process evaluation report to prepare, without having to SA-36 steel and then make a welding process evaluation test. Table 3-7 lists examples of the classification groupings of typical steel grades in the American ASME Code, Volume IX, Standard for Welding Process Evaluation. Table 3-8 specifies the various types of base metal mutual group welding, process evaluation test pieces used in the base material and the evaluation of the base material category between the general principles.
Because of our material series and the United States material series there is a big difference, and has not yet been implemented regulations material recognition system, so it is difficult to refer directly to the United States ASME Code, Volume IX listed in the material classification table. If the design drawings provide for the use of ASME code materials, it can be completely in accordance with the general principles of material classification listed in Table 3-8, to determine the necessity of welding process evaluation of the project.
When the use of domestic standards, can be used according to the above principles and against the ASME code similar to the chemical composition of steel and strength level, the domestic standard materials for classification and grouping. The above-listed welding process assessment standards in China have made an exploration and attempt to classify domestic steel, but some are not comprehensive enough, some do not meet the classification principle. Because from the welding process evaluation point of view on the classification of materials is a very complex and detailed work, and the need to accumulate a large number of basic information in order to achieve complete and correct. At this stage, for has mastered a large number of test data and accumulated many years of experience in the production of commonly used steel grades, can achieve a more correct classification and grouping. For the relevant data is not yet sufficient, the production of inexperienced steel and materials, it is required to complete the necessary weldability test before the welding process assessment. In possession of more adequate experimental information, it will be gradually categorised.
3. Thickness of base metal and thickness of weld metal
The thickness of the base metal and weld metal determines to some extent the properties of the joint. This is because, on the one hand, the strength properties of the base metal itself change as the thickness increases; on the other hand, the cooling rate in the weld zone is determined by the wall thickness of the joint; the greater the wall thickness, the faster the cooling rate and the higher the strength properties of the joint. Therefore, for a specific welding process parameters, base metal or weld metal thickness has a certain range of application. The size of the applicable range is related to the welding method used. For commonly used welding methods, such as electrode arc welding, tungsten arc welding, fusion electrode gas shielded welding and submerged arc welding, etc., the results of the open bevel butt joints test plate evaluation can be applied to the product joints where the thickness of the base metal is two times the thickness of the test plate. The evaluation test results for fillet welds can be applied to all base material thicknesses and all fillet weld sizes.
In the following cases, the welding process evaluation of the base material thickness is reduced to 1.1 times the thickness of the test plate. 1) single-pass or multi-pass welds, each layer of the thickness of the weld path is greater than 13mm. 2) The use of short-circuited transition fusion electrode gas shielded welding, and the evaluation of the thickness of the test plate is less than 13mm. 3) Specimen post-welding heat treatment temperature exceeds the critical transition temperature. For electrode arc welding, submerged arc welding, tungsten electrode gas shielded welding and fusion electrode gas shielded welding multi-pass weld, when the thickness of the joint is greater than 20mm, the welding process assessment applies to the base material thickness range of 1.33 times the thickness of the test piece.
For unequal thickness butt joints, the applicable range of base material thickness for welding process evaluation shall be handled in accordance with the following provisions: 1) The thickness of the thinner component of the butt joint shall be in accordance with the above range of application. 2) The thickness of the thicker component of the butt joint shall be unrestricted in terms of maximum thickness for the material that does not require notched impact toughness. For materials requiring notched impact toughness, the thickness of the thicker component shall be within the above range. If the thickness of the test specimen for the evaluation of the welding process is greater than 38 mm, the maximum thickness shall also be unrestricted.
4. Weld filler metal
According to the provisions of volume IX of the U.S. ASME Code, welding filler metal and base metal similar to the material can be classified according to the type of material, alloy adequacy, strength level and variety. Welding filler metal according to the variety and standard number of welding rod flux type, wire - flux combination, carbon steel and alloy steel welding filler metal can be divided into 6 categories, aluminium and aluminium alloy welding consumables into 4 categories, copper and copper alloy welding consumables into 1 category, and marked with F-No classification number, see Table 3-9. for a variety of steel welding filler metal can be divided into 12 categories shown in Table 3-10, according to the chemical composition of the weld metal. 3-10 shown in 12 categories, and labelled with A-No classification number, the classification of filler metals and base metal classification is similar to its purpose is to reduce the workload of welding process assessment. That is, belonging to the same class of welding filler metal can be common with each other. The use of a certain F-No or A-No welding filler metal completed welding process assessment report applies to the same F-No or A-No class belonging to any one welding filler metal.