Welding procedure specification (WPS)
Some of the EPC activities that are critical in the oil and gas industry are welding. Welding is carried out when the EPC enters the third phase, ie Construction, for example when manufacturing pressure vessels, storage tanks, process piping, and pipelines. Welding is also often done at the time after the EPC project is finished or Plant has started up, for example when there is an improvement or when Turn around. Welding that is done when the plant is operational has a much greater hazard than when the EPC project. When the plant is operational, there are two things that must be considered, namely Process safety and personal safety. while at EPC, focus more on personal safety. to ensure welding can be carried out safely and technically accepted, it is necessary to make welding procedures that meet the requirements. This procedure is often referred to as Welding procedure specification (WPS)
why we require a welding procedure specification?
The welding process that is not in accordance with the procedure can cause work accidents that even cause fatalities or cause equipment to break faster. there are some cases of work accidents due to the welding process. ASME Boiler and Pressure Vessel Code are one of the standards used in the oil and gas industry, consisting of 12 sections. In this article we discuss the qualifications of WPS that refer to the ASME Boiler and Pressure Vessel Code Section IX – Welding and Brazing Qualifications standards, namely:
- provide an explanation of the welding process that is commonly used in the oil and gas industry
- provide an explanation of the procedures for qualifying welding procedures or the Welding Procedure Specification (WPS)
ASME Section IX QW-490 describes the definition of welding as a localized connection of metal (metal) or non-metal produced by heating the material to welding temperature, with or without using pressure (pressure), or only pressure, with or without the use of filler metal (filler metal). Most of the oil and gas industries use an arc welding process, namely SMAW, GMAW, GTAW and SAW.
welding procedure specification – 3 variables
Welding Procedure Specification (WPS) or specification of welding procedures is a written procedure about welding that has been qualified to provide direction in making production welds in accordance with the requirements of the standard used. WPS can be used to provide direction to welders to ensure compliance with the requirements of the standard used. Variables involved during welding are grouped into 3, namely essential variables, nonessential variables, and supplementary essential variables (if needed).
Essential variables are all variables which, if changed, will affect the mechanical properties of the weld results require re-qualification of WPS (QW-251.2). nonessential variables are all variables which, if changed, can be made in WPS without requalification (QW-251.3). Whereas the Supplementary essential variable will be an essential variable if the welding process requires a notch-toughness test or an impact test. This impact test is often required by the Designer or Code for equipment used in low-temperature conditions that cause changes in material properties from ductile to brittle.
Each welding process has different variables. This variable data can be seen in full in ASME Section IX. For example, the SMAW welding process is regulated in QW-253. The test coupon used when qualifying WPS is considered an essential variable. If the test coupon uses a plate with T = 1.5mm thickness, then the WPS is only valid for use in welding production with a material thickness of 1.5 mm to 3.00 mm (according to QW-451.1). If production welding has a 4mm material thickness, it needs additional WPS.
testing requirement for welding procedure specification
WPS needs to be tested to ensure that the procedures made can produce good production welds. The test method is divided into two, namely the Destructive Test and Non-Destructive Test. Following are the types of tests used:
1) Mechanical Tests (QW-141) are used for WPS qualifications and welder qualifications consisting of:
- Tension tests. This test is a destructive test method to determine the ultimate strength of the groove type welding joints on the test coupon.
- Guided-bend tests or bending tests, to determine the degree of smoothness (soundness) and ductility of the groove type welding connection.
- Fillet-weld tests, to determine the size, contour, and degree of soundness of the fillet type welding joints.
- Notch-toughness tests, to determine the notches of welding. This method uses Charpy V-Notch and Drop Weight
2) Radiography Examination. This test can be used to replace the mechanical test in qualifying the performance of groove type welding to prove the ability of welders to make sound welds (QW-142).
3) Visual examination. this test to show complete joint penetration and complete fusion between weld metal and base metal