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WPQR & WPS Approval Options and Relationships

TIG Welding Aluminum

TIG Welding Aluminum

This information is intended for those of you who would like to get familiar with process and performance of approvals. Its does relate to the following codes and specification, but is not limited to them: ISO 15614, ISO 15613, ASME Sect. IX, AWS D1.1, AWS D1.2, AWS D1.3, AWS D1.6, AWS D15.1, and others.

First we consider the approval flow and concepts of ISO 15607 (Specification and qualification of welding procedures for metallic materials – General rules / Note: ISO 15607 is applicable to manual, mechanized and automatic welding.) for the qualification of WPS, a good understanding of the relationship between different documents and their purpose can be outlined.

Welding is considered a special process in the terminology of standards for quality systems. Standards for quality systems usually require that special processes be carried out in accordance with written procedure specifications.

Welding procedure specifications are needed in order to provide a well-defined basis for planning of the welding operations and for quality control during welding. The preparation of a welding procedure specification (WPS) provides the necessary basis for fulfilling the applicable requirements, but it does not in itself ensure that the welds fulfil the requirements. Some deviations, notably imperfections and distortions, can be evaluated by nondestructive methods on the finished product, however, at time the applied NDE methods will not provide the essential testing results to document that a weld meets all acceptance criterion and hence engineering requirements.

Metallurgical deviations constitute a special problem, however, because non-destructive evaluation of the mechanical properties is impossible at the present level of non-destructive technology, this has resulted in the establishment of a set of rules for qualification of the welding procedure prior to the release of the specification to actual production.

According to ISO 15607, the manufacturer shall prepare a preliminary WPS (pWPS) and shall ensure that it is applicable for the actual production, using experience from previous productions and the general fund of knowledge of welding technology.

Each pWPS shall be used as a basis for the establishment of WPQR, qualified according to an acceptable method of the code or specification that is / which are applicable.

If the qualification involves welding of test pieces, then the test pieces shall be welded in accordance with the pWPS.

Per ISO 15607, the WPQR shall include all variables (essential, supplement and non-essential), as well as the specified ranges of qualification given in the appropriate standard. On basis of the WPQR, the WPS for production welding is developed under the responsibility of the manufacturer and its experts unless otherwise required.

Information Flowchart related to ISO 15607

iso-15607-flowchart-201611

 

ASME or AWS codes/specification maintain a slightly different definition of the approval of a WPS. The range of approval, or the scope of a given WPS, is outlined in the WPS only. The WPQR does not include a range of qualification, Since it is a testing record “only”. The WPQR is the foundation for the scope or range of approval a WPS can receive.

The question why ISO includes range of approval requirements for a WPQR is an ongoing discussion amongst experts. The ISO System (or EN for that matter) considers a WPS to be issued to support a specific welding application. The actual WPS range of approval might therewith be limited. With that said, the WPQR would provide possibilities, whereas the WPS is limits / restricts those essential, supplement and non-essential variables that apply to a given production need.

Information Flowchart related to ASME / AWS

asme-aws-flowchart-201611

 

At this point it is important to touch on one very important subject, which also creates discussions most often! Who defines the “true” range of approval for a given WPS? The quick answer is that the applicable code or specification outline the requirements for the range settings and information applicable to a WPS. As much this statement is true, as much it is not! If a manufacturer would indeed test the entire possible range of a WPS, it is likely that at times a sound weld cannot be placed or the welding conditions would indeed fall outside of the applicable code or specification. For instance, what often can be found is that a WPS is issued with a range in welding parameter that would result in a change of a transition mode. At times, multiple transition modes were not considered during the approval of the WPQR / WPS.

An additional consideration is the range of approval for welding positions. Even though many codes support the qualification range to be rather large, however, at times it is not possible to weld “out of position” with the given range in welding parameter. With that said, who truly is the one to determine the range of approval of a WPS?

Most, if not all, codes and specification require the approval by the responsible engineer, welding engineer, expert, supervisor or welding coordinator (definition depending on the applicable code / specification). The assigned expert shall have the knowledge to determine, if a possible range of approval is truly the range that leads to the desired / required acceptable weld.

Depending on the knowledge about and level of engagement in the science of welding, the approval of the maximum possible range or scope of a WPS might be applied; or it is limited to a specific case.

On a Personal Note: Even though a code or specification promotes a certain range of WPS qualification, it may not be suitable for the intended welding application.

We hope that the information in this WWW page provides some value and maybe discussion point. Feel free to send us an email to this rather interesting conversation! (info@eceglobal.com).

Important: Some of the wording is rather similar or identical to what is referenced in codes and standards. This outline does not claim total compliance or a flawless identity with welding codes or specification.

We have worked with over 400 companies in Asia, Europe and North America, to achieve either compliance with national of international certifications / approvals, or to implement sound welding systems or processes.

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