SMACNA - SHEET MTL WELD GUD
SHEET METAL WELDING GUIDE
|Publication Date:||1 January 2007|
The Sheet Metal and Air Conditioning Contractors' National Association, Inc. (SMACNA) has found that joining metal by welding is one of the most labor−intense operations in the sheet metal industry. Predicting and controlling the costs and quality of welding is absolutely essential if contractors are to manage work effectively. This Third Edition was undertaken to refine and clarify several areas and to upgrade this manual and to promote its use as an effective guide for contractors.
Codes, specifications, and classifications are voluntary consensus standards developed by committees whose membership is balanced among interested parties such as producers, consumers, general interest and others. Others, such as government, may have their own category if substantial interest is shown. No single group may dominate a standards committee. Well known examples of this type of organization are American Welding Society (AWS), American Society for Testing and Materials (ASTM) and American Society of Mechanical Engineers (ASME). For a standard such as AWS D1.1, Structural Welding Code - Steel the producer group would be made up of contractors, manufacturers, and distributors. Consumers would be developers, inspection agencies, and owners. General interest would represent the general public interest, and they may from academia, government, or the general public. Any individuals, whether committee members or not, have the right to comment on a proposed standard. The committee is required to consider all comments and to advise the individual of the disposition of the comment.
Contractors can expect the requirements of national codes and standards to be reasonable and equitable as they apply the same requirements to all practitioners, therefore contractors can fairly compete for such work. The additional requirements imposed by these national codes and standards are more record keeping such as mill test reports (MTRs), welding procedure specifications (WPSs), performance qualification test records (PQTRs), and inspection records.
Rules for development of the WPSs and PQTRs, are provided in the application codes such as AWS D1.1, Structural Welding Code - Steel, AWS D1.3, Structural Welding Code - Sheet Steel, and D9.1, Sheet Metal Welding Code. Alternatively qualification rules may be found in AWS B2.1, Specification for Welding Procedure and Performance Qualification. Most AWS codes and specifications accept welding qualifications that are performed under B2.1.
Welding is a special process because, except for hardness, we cannot evaluate the mechanical properties without destroying the weld. Therefore, we control the properties of the weldment by using written qualified procedures (WPSs). The soundness of the weld is maintained by using trained and qualified welders and welding operators.
Welding Procedure Specifications (WPSs) provide several benefits such as:
a. QUALITY AND REPEATABILITY − Welding performed in strict adherence to welding procedures can assure consistent quality and repeatability in welding production.
b. INCREASE IN PRODUCTIVITY − Consistent use of welding procedures can give the contractor much better control of the welding operations by providing written instructions for the welder to use, including the welding process, machine setting, type of electrodes, etc.
c. MEASURE PERFORMANCE − Welding procedures provide the basis for comparison of welder performance to previously established production methods.
d. MATERIAL REQUIREMENTS − Use of written welding procedures not only establishes the type and size of electrodes, shielding gases and materials that are required for the job, they can also be used in determining the quantities of electrodes and gases and the arc time needed for the size of weld to be made in accordance with the joint design.
e. TRAINING − Training programs can be established to train welders in particular welding processes using the procedure as the base line document.
There has been a mystique in the past about welding. Too often the sheet metal contractor's management has been totally reliant upon the welder for guidance in such matters as the correct welding procedure, achievable productivity, welding costs and, in many instances, the type of equipment to be purchased.
This publication is intended to provide the contractors' managers and supervisory employees sufficient information to predict welding costs, audit welding productivity and source information to recognize weld quality even though they may not have extensive experience in "laying down a weld."