Welding Definitions and Terms

In order to understand codes and specification, it is important to spend a brief moment on definitions. Please note that some of definitions may slightly be different in wording, depending on the code or specification one is reading. However, the general message or meaning should be rather identical.

The listed terms and definitions are largely based on ISO 15607. Terms and definitions which cannot be found in ISO 15607 are identified accordingly. The list below is non-compulsory.

Welding procedure

Specified course of action to be followed in making a weld, including the welding process(es), reference to materials, welding consumables, preparation, preheating (if necessary), method and control of welding and postweld heat treatment (if relevant), and necessary equipment to be used.

Welding process

The process applied to produce a weld joint. Welding processes are differentiated by factors like level of mechanization (manual, partly mechanized, fully mechanized and automatic).

Preliminary welding procedure specification (pWPS)

A document containing the required variables of the welding procedure, which has to be qualified has to be qualified by using one of the methods acceptable by the applicable code or specification.

Note 1: A pWPS could also be described as the document applied to record administrative, essential, supplement, and non-essential welding parameter, when performing a test to quality a WPQR.

Note 2: AWS or ASME do not use the term preliminary welding procedure specification (pWPS).

Welding procedure specification (WPS)

A document that has been qualified by one of the accepted methods described in the applied code or specification. It provides the required variables of the welding procedure to ensure repeatability during production welding.

Prequalified welding procedure specification (Prequalified WPS) (in consideration of ASME/AWS)

Prequalification of WPSs shall be defined as exempt from the WPS qualification testing. All prequalified WPSs shall be written. In order for a WPS to be prequalified, conformance with all the applicable requirements of the applicable code or specification shall be complied with.

Work instruction

Simplified specification of the welding procedure, suitable for direct application in the workshop.

Welding procedure qualification record (WPQR)

Record comprising all necessary data needed for the qualification of a preliminary welding procedure specification

Note: It is important to consider the wording and definitions of the applicable welding code or specification. For instance, AWS refers to the qualification of WPS. This wording emphasizes the need that the qualification testing is done to provide proper instructions to the welding or welding operator, by issuing a “certified” WPS. However, the testing and approval for a “certified” WPS is based on the issuance of a WPQR. The range of approval of a “certified” WPS is based on the welding conditions and variables documented and validated in the WPQR.

Welding procedure test

Making and testing of a standardized test piece, as indicated in the pWPS, in order to qualify a welding procedure

Pre-production welding test

Welding test having the same function as a welding procedure test, but based on a non-standard test piece representative of the production conditions

Standard welding procedure specification

Welding procedure specification, which has been qualified by a welding procedure test not related to the manufacturer and qualified by an examiner or examining body

Note: A standard welding procedure may then be made available to any manufacturer.

Previous welding experience

When it can be shown by authenticated test data that the manufacturers established production welding procedures have been capable of consistently producing welds of acceptable quality over a period of time

Tested welding consumable

Welding consumable or consumable combination tested according to appropriate standards for testing of welding consumables

Welding consumable

Materials consumed in the making of a weld, including filler metals and auxiliary materials

Essential variable

Welding condition that requires qualification

Non-essential variable

Welding condition addressed in the WPS but not requiring qualification

Range of qualification

Extent of qualification for an essential welding variable

Parent material

Material(s) to be joined by welding

Test piece

Welded assembly which is used for testing purposes

Test specimen

Part or portion cut from the test piece in order to perform a specified destructive test

Homogeneous joint

Welded joint in which the weld metal and parent material have no significant differences in mechanical properties and/or chemical composition

Note: A welded joint made of similar parent materials without filler metal is considered homogeneous.

Heterogeneous joint

Welded joint in which the weld metal and parent material have significant differences in mechanical properties and/or chemical composition

Dissimilar material joint

Welded joint in which the parent materials have significant differences in mechanical properties and/or chemical composition


Discontinuity in the weld or a deviation from the intended geometry. For instance, imperfections are cracks, lack of penetration, porosity, and slag inclusions.

Note: For instance, EN ISO 6520-1 and EN ISO 6520-2 contain comprehensive lists of imperfections.

Manufacturer (acc. to ISO 15607)

Person or organization responsible for the welding production


Person who has been appointed to verify compliance with the applicable standard

Note: In certain cases, an external independent examiner can be required

Examining body

Organization that has been appointed to verify compliance with the applicable standard

Note: In certain cases, an external independent examining body can be required

Manufacturer of consumables

Party who manufactures the consumables totally or performs the final part of production, which determines the quality of the consumables

Welding co-ordination personnel

Personnel who have responsibilities in the manufacturing operation for welding and welding related activities whose competence and knowledge has been demonstrated by e.g. training, education and/or relevant manufacturing experience

Heat input

Energy introduced into the weld region during welding

Parent material thickness

Nominal thickness of the materials to be welded

Weld metal thickness

Thickness of the weld metal excluding any reinforcement