What does postweld heat treatment do?
by Admin
Posted on 12-09-2023 05:14 PM
Postweld
heat treatment
is mandatory under the following conditions
welded joints over 11/2 in. (38 mm) nominal thickness
for welded joints over 11/4 in. (32 mm) nominal thickness through 11/2 in.
(38 mm) nominal thickness unless preheat is applied at a minimum temperature of 200°f (95°c) during welding. This preheat need not be applied to sa 841 grades a and b, provided that the carbon content and carbon equivalent (ce) for the plate material, by heat analysis, do not exceed 0. 14% and 0. 40% respectively, where
a. For groove welds not over 1/2 in. (13 mm) size and fillet welds with a throat not over 1/2 in.
What are pre and postweld heat treatments?
When welding base materials, preheating and/or post-weld heat treatment may be necessary. These thermal treatments are generally required to ensure suitable weld integrity. They will typically prevent or remove undesirable characteristics in the completed weld. However, heat treatment is costly since it demands extra equipment, time, and handling.
Heat treatment should only be undertaken after carefully considering its advantages. Heat treatment will be mandatory in some instances, as with heavy sections of low alloy steel. It will be a justifiable precaution against early failure in service in other cases. There are several reasons for incorporating these thermal treatments within the welding procedure.
With the demand for inconel® 718 and other superalloys increasing over a broader range of application uses, the heat treater must first understand the desired performance characteristics of the application and then be prepared to devise recipes and heat-treatment strategies to maximize the alloy’s response to these treatments.
Stress-relieving is a form of post-weld heat treatment. During the thermal stress relieving process, a material is heated to a specific temperature for a specific amount of time to reduce or eliminate residual stress.
pwht for stainless steel is usually not required. However, to increase the corrosion resistance or reduce stress corrosion cracking susceptibility, stainless steel pwht may be used depending on the service conditions encountered. The requirements for pwht for piping are dependent on the p-numbers and group numbers of the pipe material. Clause 331. 1. 1 along with table 331. 1. 1 and table 331. 1. 2 of asme b31. 3 provides the requirements for pwht depending on pipe materials. However, if the proper pre-heat temperature is applied during the welding of pipes of specified thicknesses, the mandatory post-weld heat treatment can be exempted.
Webmail what is the post weld heat treatment (pwht)? post weld heat treatment (pwht) is a controlled process in which a material that has been welded is reheated to a temperature below its lower critical transformation temperature, and then it is held at that temperature for a specified amount of time. It is often referred to as being any heat treatment performed after welding; however, within the oil, gas, petrochemical and nuclear industries, it has a specific meaning. Industry codes, such as the asme pressure vessel and piping codes, often require mandatory performance of pwht on certain materials to ensure a safe design with optimal mechanical and metallurgical properties.
The primary role of post-weld heat treatment is to improve the weldment’s mechanical characteristics and make it outlast for particular service conditions. Pwht helps to reduce the residual stress level and hardness, achieving the required level of ductility in the weldments. This improves strength and resistance to brittle fracture and increases the material’s lifespan.