A Welding Procedure Specification has several variables which should be carefully specified. The values selected for the variables discussed below have a significant impact on weld soundness and mechanical properties. It is critical that these values be appropriate for the specific requirements of applicable code and job specifications. The variables in a WPS are the following.
- Process – The ideal welding process is that which produces the minimum required mechanical properties at the lowest cost. Common arc welding processes are SMAW, GTAW, FCAW-S, FCAW-G, GMAW, SAW.
- Electrode Specification – This is the specification assigned by AWS to the electrode (i.e. E7018, ER70S-6, EM12K, etc.).
- Electrode Diameter – Specifies the size of the electrode (.030”, .035”, .040”, .045, .052”, 1/16”, 1/8”, etc.)
- Electrical Characteristics – Preferred or required polarity (DC+, DC-, AC)
- Base Material Specification – ASTM number or other designator for the base material that is being joined
- Minimum Preheat and Interpass Temperature – If required, the temperature that the base material needs to reach before welding can commence (preheat), and the temperature at which the material needs to be between welding passes.
- Welding Current or Wire Feed Speed – Amperage at which welding will be done. This can be expressed as current (amps) or inches per minute (wire feed speed). For current a WFS a range is usually specified instead of a specific value.
- Arc Voltage – Welding voltage, usually specified for a wire process, but can be dictated for a constant current process such as SMAW and GTAW. In a constant-current processes the voltage is determined by the arc length that the welder maintains, it is not a pre-settable variable.
- Travel Speed – How fast the welding is done. It can also be a range.
10. Position of Welding – Specifies whether welding is done in the flat, horizontal, vertical up, overhead or other positions (i.e. 1F = Flat Fillet, 2F = Horizontal Fillet, 3G = Vertical Up Groove, etc.).
11. Post Weld Heat Treatment – If required, instruction on the temperature that the welded assembly needs to maintain and for how long. Post weld heat treatment is done with the intent to preserve or improve mechanical properties.
12. Shielding Gas Type and Flow Rate – If using a process that requires shielding gas specify the gas or gas mixture as well as the flow rate. Gas mixtures should be exact (i.e. 75% Argon, 25% CO2) and flow rate can be a range (i.e. 40-45 cfh).
13. Joint Design Details – Provide a description of the joint. This can include material thickness, type of joint, gap (if any), land (if any), if it has backing, etc.
Source: “What Every Engineer Should Know about Welding Procedures” by D.K. Miller, Published in The National Steel Construction Conference Proceedings, Chicago, AISC, 1997
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