Category: Fabrication

Welding Procedure Review

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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 procedures for thin-wall carbon steel pressure vessels. An engineer following the guidelines in this section […]

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Procedure Qualification Record (PQR)

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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 the WPS. All essential variables (type of filler metal, welding process, etc.) specified by the […]

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Welding Procedure Specification (WPS)

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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 characteristics of the weldment. A separate PQR is therefore required for each combination of essential […]

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Annealing, Normalizing, and Quenching

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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 metal. These uncommon heat treatments include: • Annealing • Normalizing • Quenching These higher-temperature heat […]

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Alternatives to “Stress Relief” Heat Treatment

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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 half-bead) welding for carbon, carbon-moly, and manganese-moly steels 3. Peening 4. Vibrational stress relief A […]

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Stress Relief Heat Treatment

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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 transformation. Heat treatment at this temperature accomplishes the following functions: • Reduces residual welding and […]

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Welding Interpass Temperature Control

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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 upper limit is also relevant (especially when utilizing high heat input processes) to prevent the […]

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Welding Preheating

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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 important. Preheating carbon and alloy steels accomplishes the following functions: • Reduces residual stresses, shrinkage, […]

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Consumables – Backing Gas

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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 to prevent high temperature oxidation of Cr (sometimes called “sugaring”) on the inner surface of […]

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Consumables – Shielding Gas

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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 contamination of the tungsten electrode. The most common shielding gases for the GMAW and FCAW-G […]

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