A post-weld heat treatment method for large-diameter thick-walled pipes

Abstract

The invention provides a large-diameter thick walled pipe postweld heat treatment method. By adopting the large-diameter thick walled pipe postweld heat treatment method provided by the invention, insulating temperature is determined according to a hardness range of a base material in the postweld heat treatment process, simultaneous heating of an inner wall and an outer wall is adopted, a heatingwidth is determined according to a formula, a power of a heater is determined according to a formula, and thus the heat treatment quality of a weld crater is effectively ensured, a temperature difference between the inner wall and the outer wall of the weld crater in postweld heat treatment is lowered to meet the standard requirement or a higher standard to avoid the phenomenon of base material overburning or difference between the weld crater properties of the inner wall and the outer wall caused by a temperature deviation, weld crater heat treatment can be ensured to mold at a time at the same time to avoid the phenomenon of heat treatment again, the heat treatment effect is improved, and the economic benefit is very considerable.

Description

technical field [0001] The invention relates to the technical field of welding heat treatment, in particular to a post-weld heat treatment method for large-diameter thick-walled pipes. Background technique [0002] P91 / P92 steel is basically used in ultra-high temperature and high pressure pipelines such as main steam pipelines and high temperature steam pipelines. Due to the high content of alloying elements, the tendency of welding hardening is large, and the degree of restraint is large. After welding, heat treatment must be carried out to eliminate internal stress and obtain tempered martensite structure. [0003] As the pipe wall thickness and pipe diameter increase, the greater the temperature difference between the inner and outer walls during the heat treatment constant temperature stage, the greater the impact on the material properties. [0004] At present, according to the technical regulations, the traditional heat treatment technology method, that is, the use o...

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Problems solved by technology

[0004] At present, according to the technical regulations, the traditional heat treatment technology method is adopted, that is, the use of armored thermocouples and ceramic crawler heaters cannot reduce the temperature difference between the inner and outer walls of post-weld heat treatment to the minimum or to the range required by the standard.

[0005] At present, there are not many guiding materials for controlling the temperature difference between the inner and outer walls of large-diameter and high-alloy welds. Among them, the welding technical regulations of thermal power plants point out the arrangement of thermocouples and heaters. Alloy welding joints (pipe diameter greater than 800, wall thickness greater than 70) have poor guidance and cannot effectively reduce the temperature difference between the inner and outer walls. The measured temperature cannot reach the process design temperature, especially for special-shaped pipe fittings. If only through repeated Arrange heaters to promote the closeness of the actual measured temperature of the welding joint to the process temperature. This method is not only time-consuming and labor-intensive, but also the effect of post-weld heat treatment is poor, and it cannot meet the on-site construction of on-site pipe fitting specifications and complex and changeable forms.