Abstract

Most of the heavy thickness boiler and pressure vessel components require heat treatment — in the form of post weld heat treatment (PWHT) and sometimes coupled with local PWHT. It is also a common practice to apply post heating/ intermediate stress relieving/ dehydrogenation heat treatment in case of alloy steels.

The heat treatment applied during the various manufacturing stages of boiler and pressure vessel have varying effects on the type of material that is used in fabrication. It is essential to understand the effect of time and temperature on the properties (like tensile and yield strength/ impact/ hardness, etc.) of the materials that are used for fabrication.

Considering the temperature gradients involved during the welding operation a thorough understanding of the time-temperature effect is essential. Heat treatments are generally done at varying time and temperatures depending on the governing thickness and the type of materials. The structural effects on the materials or the properties of the materials tends to vary based on the heat treatment. All boiler and pressure vessel Code require that the properties of the material should be intact and meet the minimum Code specification requirements after all the heat treatment operations are completed.

ASME Code(s) like Sec I, Section VIII Division 1 and Division 2 and API recommended practices like API 934 calls for simulation heat treatment of test specimen of the material used in fabrication to ascertain whether the intended material used in construction meets the required properties after all heat treatment operations are completed.

The work reported in this paper — “Heat treatment of fabricated components and the effect on properties of materials” is an attempt to review the heat treatment and the effect on the properties of materials that are commonly used in construction of boiler and pressure vessel. For this study, simulation heat treatment for PWHT of test specimen for CS/ LAS plate and forging material was carried out as specified in ASME Section VIII Div 1, Div 2 and API 934-C. The results of heat treatment on material properties are plotted and compared. In conclusion recommendations are made which purchaser/ manufacturer may consider for simulation heat treatment of test specimen.

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