Category Archives for Fabrication
Welding Procedure Review
The degree of welding procedure review (if any) and who performs the review should be decided depending on the criticality of the pressure vessel. In general, it is typically not justified for a materials or welding engineer to review welding … Continue reading
Procedure Qualification Record (PQR)
A PQR is a document that proves by mechanical testing that a WPS is capable of producing acceptable weld quality, thereby “qualifying” the WPS. For a PQR, a welder completes a weld on a coupon of the material specified by … Continue reading
Welding Procedure Specification (WPS)
A WPS is a document that specifies the critical welding parameters (called “essential variables” by Section IX) which are required to produce the specific type of weld covered by the WPS. Changes to the essential variables will significantly affect the … Continue reading
Annealing, Normalizing, and Quenching
Other higher-temperature postweld heat treatments are also available, but are very uncommon for pressure vessels welds. They would typically only be used when the metallurgical structure of the weld must be changed to more closely match that of the base … Continue reading
Alternatives to “Stress Relief” Heat Treatment
Several alternatives to conventional stress relief heat treatment are available, although they are considered to be inferior, and are therefore only rarely used. These alternatives include: 1. Higher preheat temperatures for carbon and carbon-moly steels 2. Temper bead (also called … Continue reading
Stress Relief Heat Treatment
The most common form of PWHT is a “stress relief” or “tempering” heat treatment. This heat treatment involves heating the material to a temperature high enough to significantly relax residual stresses from welding, but low enough to avoid metallurgical phase … Continue reading
Welding Interpass Temperature Control
Interpass temperature control is a process of controlling the temperature of the deposited weld metal between specified limits during multipass welds. The lower limit is usually the same as the minimum preheat temperature, and accomplishes the same functions. However, an … Continue reading
Welding Preheating
Preheating is the process of raising the temperature of the base metal above ambient temperature immediately before welding and holding it during welding. Preheating is not recommended for austenitic stainless steels. However, for carbon and alloy steels it is extremely … Continue reading
Consumables – Backing Gas
Inert backing gas (such as Ar, CO2, or possibly N2 for stainless steel vessels) is required with GMAW and GTAW processes for root passes of one-sided welds on alloys with more than 3% Cr content. Inert backing gas is required … Continue reading
Consumables – Shielding Gas
Shielding gases for GTAW, GMAW and FCAW-G processes are used to shield the welding arc and molten weld metal from nitrogen and oxygen in the atmosphere. Inert shielding gases (argon and helium) are required for the GTAW process to avoid … Continue reading