Prequalified Welding Procedure Specifications

The AWS D1.1 code provides for the use of prequalified WPSs. Prequalified WPSs are those that the AWS D1 Committee has determined to have a history of acceptable performance, and so they are not subject to the qualification testing imposed on all other welding procedures. The use of prequalified WPSs does not preclude their need to be in a written format. The use of prequalified WPSs still requires that the welders be appropriately qualified. All the workmanship provisions imposed in the fabrication section of the code apply to prequalified WPSs. The only code requirement exempted by prequalification is the nondestructive testing and mechanical testing required for qualification of welding procedures.

A host of restrictions and limitations imposed on prequalified welding procedures do not apply to welding procedures that are qualified by test. Prequalified welding procedures must conform with all the prequalified requirements in the code. Failure to comply with a single prequalified condition eliminates the opportunity for the welding procedure to be prequalified (D1.1-96, paragraph 3.1).

The use of a prequalified welding procedure does not exempt the engineer from exercising engineering judgment to determine the suitability of the particular procedure for the specific application (D1.1-96, paragraph 3.1).

In order for a WPS to be prequalified, the following conditions must be met:

• The welding process must be prequalified. Only SMAW, SAW, GMAW (except GMAW-s), and FCAW may be prequalified (D1.1-96, paragraph 3.2.1).
• The base metal/filler metal combination must be prequalified. Prequalified base metals, filler metals, and combinations are shown in D1.1-96, paragraph 3.3, Table 3.1.
• The minimum preheat and interpass temperatures prescribed in D1.1-96, paragraph 3.3, Table 3.2 must be employed (D1.1-96, paragraph 3.5).
• Specific requirements for the various weld types must be maintained. Fillet welds must be in accordance with D1.1-96, paragraph 3.9, plug and slot welds in accordance with D1.1-96, paragraph 3.10, and groove welds in accordance with D1.1-96, paragraphs 3.11, 3.12, and 3.13, as applicable. For the groove welds, whether partial joint penetration or complete joint penetration, the required groove preparation dimensions are shown in D1.1-96, Figures 3.3 and 3.4.

Even if prequalified joint details are employed, the welding procedure must be qualified by test if other prequalified conditions are not met. For example, if a prequalified detail is used on an unlisted steel, the welding procedures must be qualified by test.

Prequalified status requires conformance to a variety of procedural parameters. These are largely contained in D1.1-96, able 3.7, and include maximum electrode diameters, maximum welding current, maximum root pass thickness, maximum fill pass thicknesses, maximum single-pass fillet weld sizes, and maximum single pass weld layers (D1.1-96, Table 3.3).

In addition to all the preceding requirements, welding performed with a prequalified WPS must be in conformance with the other code provisions contained in the fabrication section of AWS D1.1-96 Structural Welding Code.

The code does not imply that a prequalified WPS will automatically achieve the quality conditions required by the code. It is the contractor’s responsibility to ensure that the particular parameters selected within the requirements of the prequalified WPS are suitable for the specific application. An extreme example will serve as an illustration. Consider a (hypothetical) proposed WPS for making a 1/4 in. fillet weld on 3/8 in. A36 steel in the flat position. The weld type and steel are prequalified. SAW, a prequalified process, is selected. The filler metal selected is F7A2-EM12K, meeting the requirements of D1.1-96, Table 3.1. No preheat is specified since it would not be required according to D1.1-96, Table 3.2. The electrode diameter selected is 3/32 in., less than the 1/4 in. maximum specified in D1.1- 96, Table 3.7. The maximum single pass fillet weld size in the flat position, according to D1.1-96, Table 3.7, is unlimited, so the 1/4 in. fillet size can be prequalified. The current level selected for making this particular fillet weld is 800 amps, less than the 1000 amp maximum specified in D1.1-96, Table 3.7.

However, the amperage level imposed on the electrode diameter for the thickness of steel on which the weld is being made is inappropriate. It would not meet the requirements of D1.1-96, paragraph 5.3.1.2, which requires that the size of electrode and amperage be suitable for the thickness of material being welded. This illustration demonstrates the fact that compliance with all prequalified conditions does not guarantee that the combination of selected variables will always generate an acceptable weld.

Most contractors will determine preliminary values for a prequalified WPS based upon their experience, recommendations from publications such as Lincoln Electric’s Procedure Handbook of Arc Welding, the AWS Welding Handbooks, AWS Welding Procedures Specifications (AWS B2.1), or other sources. It is the responsibility of the contractor to verify the suitability of the suggested parameters prior to applying the actual procedure on a project, although the verification test need not be subject to the full range of procedure qualification tests imposed by the code. Typical tests will be made to determine soundness of the weld deposit (e.g., fusion, tie-in of weld beads, freedom from slag inclusions, etc.). The plate could be nondestructively tested or, as is more commonly done, cut, polished, and etched. The latter operations allow for examination of penetration patterns, bead shapes, and tie-in. Welds that are made with prequalified WPSs meeting the physical dimensional requirements (fillet weld size, maximum reinforcement levels, and surface profile requirements), and that are sound (that is, adequate fusion, tie-in and freedom from excessive slag characterized by inclusions and porosity) should meet the strength and ductility requirements imposed by the code for welding procedures qualified by test. Weld soundness, however, cannot be automatically assumed just because the WPS is prequalified.

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