Welding-procedures specifications typically include the following information:Procedure number,Reference to the specific engineering drawing and to the detailed operation covered,Standard designation and condition of materials, thickness,Sketch describing form of joint with dimensions and tolerances,Need for preheating or post weld heat treatment,Welding jigs and fixtures, tooling, welding position, positioners or special holders,Special techniques to minimize distortion,Joint fit-up, backing if required,Number, position and size of tack welds, Welding process, specific welding equipment or type,Welding consumables type and size, baking if needed,Voltage, Current [AC, DC (polarity) or pulsed (time and curr. levels)],Electrode extension (stick-out), torch to workpiece distance, arc length,Weld speed,Cleaning procedures,Inspector approval of weld preparation if needed,Welding sequence, number of passes and their order,Welding technique details (weaving) if needed,Possible back gauging, inter-pass cleaning and grinding stages, Interpass temperature if control is to be used,Maximum heat input allowed.
Additional operations required like pre-heating, slow cooling if needed (by what means) or stress relieving after welding (the maximum time interval from end of welding may be prescribed) are detailed with complete description of means and parameters to be used.
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A coordinated activity originated by a common initiative of the Welding Research Council (WRC) and the American Welding Society (AWS) has resulted in the publication of a number of prequalified welding procedures, that can be adopted by industry:ANSI/AWS Standard Welding Procedure Specifications (SWPSs) are intended to meet the rules of the major codes. Single documents differ in processes, base metal and thickness range.
Welding Techniques involve details of a welding operation which are controlled by the welder or welding operator within the limitations imposed by Welding-procedures. Optionally Welding-procedures may include specific welding techniques.
Acceptable different welding techniques include the advancement direction of welding which may influence heat input and speed of welding: for simple joining operations the selection of the technique is left to the welder according to his/her preference and experience.
Also the best angles of torch or electrode from the work surfaces and the way of feeding filler metal are details included in the technique, which the welder learn during training and become part of his/her experience to control successfully the outcome of welding operations.
A number of Organizations, most notably AWS (American Welding Society), publish Recommended Practices which address practical aspects of welding processes and are most useful to learn how to improve welding results.
Tip!: The best welding procedure cannot help a sloppy or inadequate welder to produce successful work, so that there will always be a request and a need for competent and excellent welders.
However well informed and expert you may be, you could certainly benefit from a vast repository of online authoritative welding information.The following may be just what you need...
We would like to propose to you a FREE subscription to our Practical Welding Letter and also a FREE download, right to your computer, of our book on PRACTICAL HARDNESS TESTING MADE SIMPLE. Please just Subscribe.Hardness is important, it should always be known before welding a metallic item, because it can affect the Welding-procedures.To reach a Guide to the collection of the most important Articles from Past Issues of Practical Welding Letter, click on Welding Topics.
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For everyone involved in any phase of welding steel structures---engineers, detailers, fabricators, erectors, inspectors, etc. - the new D1.1 spells out the requirements for design, procedures, qualifications, fabrication, inspection and repair of steel structures made of tubes, plate and structural shapes that are subject to either static or cyclic loading.
The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) covers all aspects of design and manufacture of boilers and pressure vessels. All sections contain welding specifications, however most relevant information is contained in the following:
The American Petroleum Institute (API) oldest and most successful programs is in the development of API standards which started with its first standard in 1924. API maintains over 500 standards covering the oil and gas field.[2] The following is a partial list specific to welding:
International Organization for Standardization (ISO) has developed over 18500 standards and over 1100 new standards are published every year.[6] The following is a partial list of the standards specific to welding:
The European Committee for Standardization (CEN) had issued numerous standards covering welding processes, which unified and replaced former national standards. Of the former national standards, those issued by BSI and DIN were widely used outside their countries of origin. After the Vienna Agreement with ISO, CEN has replaced most of them with equivalent ISO standards (EN ISO series).[7]
Welding of 13CrMoV9-10 vanadium steel requires care due to an increased susceptibility to stress relief cracking during post weld heat treatment. Previous research into the crack formation in creep-resistant steels has focused on thermal and metallurgical factors; however, little knowledge has been gathered regarding the crack formation during post weld heat treatment considering real-life restraint conditions. This work is subdivided in two parts. Part I showed that an increasing heat input during submerged arc welding under restraint led to an increasing stress level in the joint prior to the post weld heat treatment. The magnitude of stress relief cracking observed in the heat-affected zone after the post weld heat treatment is affected by the heat input. In Part II of this work, the cracks and the associated microstructure which occurred under restraint were studied. The application of a special acoustic emission analysis indicated that the cracks formed in a temperature range between 300 and 500 C during the post weld heat treatment. The toughness in the heat-affected zone of the restrained welds was affected by the welding heat input. Microstructural analyses of all specimens revealed accelerated aging due to precipitation of carbides during post weld heat treatment under restraint.
The creep resistant steel 13CrMoV9-10, a modified conventional low-alloyed 2.25Cr-1Mo steel with 0.25% vanadium is highly sensitive to stress relief cracking (SRC) during post weld heat treatment (PWHT). PWHT is applied after welding und necessary to adjust the mechanical properties in the weld metal and the heat-affected zone (HAZ) as well as to reduce welding-related structural and residual stresses. Although the basic mechanisms of SRC are generally known and widely documented in the literature, the influence and control factors as well as the detailed mechanisms of crack formation continue to be controversially discussed. In general, SRC occurs when stresses during heat treatment exceed the local deformation capacity of the material. In principle, the following mechanisms are necessary:
As a result of several occurrences of failure during welding of large reactors made of Cr-Mo-V steels, Chauvy and Pillot investigated different wire/flux combinations regarding its SRC susceptibility. They presented a new criterion for evaluating the cracking sensitivity of the weld metal [6, 19, 20]. The K-factor is a function of the elements Pb, Bi, and Sb (cf., Eq. 3) and is based on investigations on 25 different wire/flux combinations already used in vessel production. Relationship of Chauvy and Pillot (contents in ppm):
Second, there are test methods in which the specimens contain just parts of the weld seam. This can be done by simply over-welding the test area or by taking samples from completely welded seams. The advantages of these test methods are, on the one hand, the rapid and cost-effective realization of the tests and, on the other hand, better reproducibility. In addition, the test load can be varied in case of externally loaded tests and therefore critical loads be determined. Prominent examples are the (modified) implant test [24] or the C-ring test [23]. The result is often a ranking of the tested materials, but transferability to practice is not always possible.
Third is the testing of samples containing a thermally simulated HAZ. This is obtained before or during the test by means of an artificial welding temperature cycle. The welding simulation enables a good reproducibility as well as the targeted adjustability of the microstructure to be tested (also multilayer welding cycles). Furthermore, it is possible to introduce notches and thus concentrate the test area on a specific microstructure. A disadvantage, however, is the neglect of welding residual stresses combined with limited transferability to real welded components.
Temperature control during the simulated manufacturing process in the 2-MN test facility, (I): tacking + preheating, (II): welding, (III): DHT, (IV): cooling to ambient temperature, (V): PWHT (heating (a), holding (b), cooling (c), (preheating/interpass temperature 220 C and heat input per unit length 35 kJ/cm)
During preheating, welding, and dehydrogenation heat treatment (DHT), the system simulated the joining of two ring segments of a pressure vessel by restrained expansion and shrinkage of the specimen. In real component welds, the ring segments impede the expansion of the locally heated weld area. After the DHT, the specimen cools down to ambient temperature with shrinkage restraint. The stress-relief heat treatment usually takes place after welding of the entire component. The pressure vessel is heat-treated in a large furnace. Due to the almost homogeneous and slow heating, the vessel can expand freely, whereby the load resulting from the welding process remains until the necessary hot yield strength is reached. To simulate this behavior, the testing facility maintained the load level resulting from the welding process up to the prescribed annealing temperature of 705 C and compensated for the temperature-induced expansion of the weld area. After reaching the target temperature, the system enabled the relaxation of the welded joint during cooling to room temperature. 2ff7e9595c
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