Welding Specifications Issues

Q: I need to qualify a welding procedure specification per the ASME Boiler and Pressure Vessel Code.
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A: To the new user, Section IX of the ASME Boiler and Pressure Vessel Code is very complex, and the rules for qualifying welding procedures vary depending upon the welding process used and the materials welded. However, a few fundamental concepts are commonly misunderstood, and gaining a firm understanding of those concepts makes it easier for a new user of this code section to determine how it works.

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Section IX, Part QG contains general requirements for all material-joining processes (welding, brazing and plastic fusing). It defines key portions of the qualification process: a procedure specification (QG-101), a procedure qualification record (QG-102), a performance qualification and performance qualification record, variables (QG-105), organizational responsibilities (QG-106), ownership transfers (QG-107), qualifications made to previous Section IX editions (QG-108) and definitions (QG-109). Before starting the qualification of a welder, welding operator (both of which are outside the scope of this article), or a procedure, a good practice is to review Part QG. The definitions in QG-109 can be especially helpful because some terms used throughout the text have evolved over the years and are specific to the welding field.

Section IX Part QW (which covers welding) is divided into five articles (I, II, III, IV and V). Article I contains general requirements for welding. Article II contains requirements for qualifying welding procedures. Article III contains requirements for the qualification of welders and welding operators. Article IV contains welding data (variables, base material groupings, test specimen requirements, etc.). Article V contains information on standard welding procedure specifications (which is outside the scope of this article).

A good practice is to read Articles I and II before beginning. It is not necessary to read through all of Article IV to get started because most of this article is dedicated to describing variables. However, the text at the beginning of each major section should be reviewed, including QW-401 (description of variables), QW-420 (base material groupings), QW-424 (base metals for procedure qualification) and QW-430 (F-Numbers).

The end goal is a viable welding procedure specification (WPS). The WPS is a document that provides direction to the welder/welding operator, and states requirements regarding the materials that may be welded, which welding process must be used, the filler metals to be used, the minimum preheat temperature, welding parameters such as current, voltage, travel speed, interpass temperature, post-weld heat treatment requirements, etc.

The WPS is based upon the successful creation of a welded qualification test coupon. The procedure qualification record (PQR) is a document used to record the required data associated with the creation and testing of the qualification coupon.

The rules in Section IX govern how the parameters specified in the WPS are determined using the PQR data as a basis.

In Section IX terminology, a variable is a parameter or factor determined to have an effect upon the welding characteristics or the resulting weldment. Section IX includes many variables and categorizes them for various welding situations as “essential,” “nonessential” and “supplementary essential.”

For a given welding situation, an essential variable is one identified as critical to the success of the welding process or to the properties of the resulting weldment. A change in an essential variable requires the requalification of the welding procedure (meaning a new PQR must be created).

A nonessential variable is a variable that must be documented in the WPS but may be changed by revision without the requalification of the procedure.

A supplementary essential variable is a parameter or factor that becomes an essential variable when impact testing is required by a referencing code section (e.g. Section I, Section III, Section VIII, etc.) or customer specification.

Essential, supplementary essential and non-essential variables for various welding processes are listed in tables immediately following paragraph QW-250. For example, QW-253 covers shielded metal arc welding joining and lists the paragraphs in Article IV that describe the essential, supplementary essential and nonessential variables that apply. Two examples of variables listed in QW-253 and their impact are:

QW-406.1 “Decrease > 100°F (55°C)” is an essential variable. Paragraph QW-406.1 states:

“QW-406.1 A decrease of more than 100°F (55°C) in the preheat temperature qualified. The minimum temperature for welding shall be specified in the WPS.”

Therefore, assuming the PQR lists a preheat temperature of 150°F (65°C), the WPS can be written with a preheat temperature as low as 50°F (10°C). If desired for creating or revising a WPS to use a preheat temperature below 50°F (10°C), the procedure would need to be requalified.

QW-406.3 “Increase > 100°F (55°C) (IP)” is a supplementary essential variable. Paragraph QW-406.3 states:

“QW-406.3 An increase of more than 100°F (55°C) in the maximum interpass temperature recorded on the PQR. This variable does not apply when a WPS is qualified with a PWHT above the upper transformation temperature or when an austenitic or P-No. 10H material is solution annealed after welding.”

Since this is a supplementary essential variable, it only applies if impact testing is required. If such testing is required, this supplementary essential variable also only applies to certain materials in certain heat treatment conditions as described in QW-406.3. Assuming it applies and assuming the PQR lists a maximum interpass temperature of 500°F (260°C), the WPS can be written with a maximum interpass temperature of up to 600°F (315°C). If desired to create or revise a WPS to increase the maximum interpass temperature to higher than 600°F (315°C), the procedure would need to be requalified.

Note: Many QW-4XX paragraphs describe variables; however, the only ones that apply to the welding procedure are those referenced in the QW-25X tables for the welding processes used.

A valid WPS lists all essential and non-essential variables (and supplementary essential variables when required) and provides appropriate values for each.

New users of Section IX sometimes think they can just use the example forms in Section IX Nonmandatory Appendix B and fill them in based upon what seems obvious. This approach is highly unlikely to result in a proce-dure that properly addresses the variables. The best way to ensure a WPS is complete and correct is to use the QW-250 tables to ensure all appropriate variables are included and properly addressed, and to review the definitions in QG-109 to ensure all terminology is interpreted and used correctly.

CHERRA MELOY is senior materials engineer, Flow Control, Emerson Automation Solutions (www.emerson.com). Reach her at cherra.meloy@emerson.com.