Many pressure vessels and pipes require PWHT welding processes due to stringent codes governing chemical composition and thickness requirements of materials being welded together. PWHT is used to reduce residual stresses in materials and prevent brittle fractures, and requires extensive documentation in order to meet industry standards. Strength PWHT serves primarily to minimize and redistribute residual stresses left after welding, which could otherwise combine with load stresses to exceed material design limitations and lead to brittle fracture. PWHT effectively decreases these stresses to levels that are compatible with their final use application. PWHT also tempers base and weld metal microstructures, increasing their ductility and toughness beyond those found in as-welded …

続きを読む “The Purpose of PWHT”

Heat Rate PWHT processes typically reach temperatures above 450 degrees Celsius for one hour per inch of thickness, making it essential that heating and cooling rates match those required by material type, component size/configuration and desired soaking temperatures. Excessively fast heating or cooling rates could result in unacceptable distortions and thermally-induced stresses if they exceed appropriate levels. For large and unwieldy fabrications, using trestles or supports may be necessary during local plasma wand heat treating (PWHT). When designing such supports, take into account differential expansion/contraction capabilities of components as well as construction of these trestles from materials which won’t be damaged by high PWHT temperatures. Auxiliary heating widths play an …

続きを読む “PWHT Formula”

PWHT (Post Weld Heat Treatment) refers to a series of processes used to ensure welds and joints will function effectively under their intended service conditions. This may involve stress relieving, preheating, postweld and interpass. There is an array of PWHT equipment available, and this article will outline some of the more frequently utilized types. 1. Heat Treating Machines Induction heat treating machines offer multiple services, including hardening (case/surface and through), softening, tempering, stress relieving and normalizing. PWHT equipment is widely utilized across applications like automotive manufacturing, rail cars, nuclear power plants and mining; with precise localized heating limiting heat loss and distortion in order to increase production rates. Byington Steel …

続きを読む “PWHT Equipment List”

Local PWHT can be an effective means of mitigating welding residual stresses in ultra-large pressure vessels when furnace-based PWHT is impractical, but finding a universal calculation criterion for its auxiliary heat band width in current local PWHT standards can be challenging. After local PWHT treatment is applied to an ultra-large atmospheric tower, residual stresses on its axial and circumferential structures before and after PWHT are compared and the effects of an additional HB width simulation simulated. Cost Local post weld heat treatment (PWHT) is an effective means of mitigating welding-induced residual stresses in large and ultra-large pressure vessels. It may be employed when furnace-based PWHT becomes impractical for large components …

続きを読む “Local Post Weld Heat Treatment (PWHT)”

Power and process industries face issues related to variations between codes in terms of PWHT requirements for boilers. While some of these differences can be justified, others seem less important from a technical viewpoint. Current fabrication codes typically exempt certain structures from PWHT due to their Charpy fracture toughness at their minimum service temperature; however, these criteria are often subjective and vaguely defined. What is PWHT? Post Weld Heat Treatment (PWHT) of steel components is an essential step in the welding process, involving heating them at high temperatures for an extended period to correct thermal distortion, weakening strength and toughness of metal, which may render pressure vessel equipment more prone …

続きを読む “ASME PWHT Requirements”

Post weld heat treatment (PWHT) is an integral part of welding and fabrication industry. PWHT helps temper metal by relieving residual stresses and thus reduce brittle fracture, corrosion, and stress cracking risks. PWHT is often required by fabrication codes and standards for carbon steel components, although local supercritical PWHT above its critical transformation temperature would lead to undesirable temperature gradients across through thickness temperatures. Temperature Range PWHT (Post Weld Heat Treatment) is a process where metal is heated and soaked for a certain time to ease internal stresses induced by welding, which could otherwise cause cracking, fatigue or stress corrosion failure of material. PWHT is often required in construction codes …

続きを読む “Post Weld Heat Treatment Machine Specification”

Post Weld Heat Treatment is a standard and mandatory process in the oil, gas and petrochemical industries to reduce residual stresses arising from welding steel components together. Industry codes may require testing depending on the chemical makeup and thickness of material being tested, while testing also ensures optimal mechanical and metallurgical properties. Definition Post Weld Heat Treatment (PWHT) is a process which dissipates residual stresses in welded structures by reducing or redistributing them, hardness levels, improving ductility, and mitigating brittle fracture. PWHT is an integral component of welding procedures and required steps in many pressure vessel and piping codes; its necessity depends on various factors including the material’s chemical makeup …

続きを読む “What Is Post Weld Heat Treatment?”