Specifications for hardness values after post-weld heat treatment
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I would like to ask: is it necessary to specify the hardness value for post-weld heat treatment of containers? What is the purpose of indicating the hardness value? Under what circumstances is it necessary to set an upper limit for hardness values?
It’s not to increase hardness, but to reduce the hardness value.
During the manufacturing process of pressure vessels, frequent heating and cooling cycles subject the interior of the workpiece to continuous tension and compression, resulting in uneven stress distribution and stress concentration. Additionally, welding causes changes in the structure and properties of the weld area, leading to the formation of residual stresses in that region. In some pressure vessels, hydrogen enters the steel during the forging of the raw material. As hydrogen gradually dissolves into the metal, it significantly reduces the strength and ductility of the steel, leading to hydrogen embrittlement in the workpiece. To remove hydrogen from the workpiece, post-weld heat treatment is typically used.
For vessels subject to stress corrosion, hardness testing shall be conducted after post-weld heat treatment, with the upper limit of hardness specified by relevant standards. The main purpose is to control strength through heat treatment, reduce hardness, and improve plasticity and toughness.
Yeah, it’s to reduce the hardness, right? Eliminate stress and improve toughness.
Reduce hardness, minimize welding stress, and improve the overall performance of the material
Could you specify which standards require post-welding hardness? I happened to encounter a client who required that the hardness of the welds at the joints between carbon steel heat exchange tubes and tube sheets, after heat treatment, be ≤220 HB.
Tell me what standard you want to know about; give me the relevant standard……
Please refer to HG/T 20581, the specifications for the selection of materials for steel chemical storage vessels; detailed descriptions can be found in clause 7.8, \"Restrictions on the operating medium\".
1. For CS, the medium can be water, air, nitrogen, or general hydrocarbons; no specific requirement is imposed. The medium is hydrogen; it is required for wet hydrogen sulfide. Up to 200~225HB. 2. For 0.5MO, Mn-MO steel, all tests are required, with a maximum of 225HB. 3. All 1Cr-0.5Mo, 1.25Cr-0.5Mo, and 2.25Cr steels are required to meet this requirement, with a maximum value of 225HB. 4. 2.25Cr-1MO-V steel requires testing to be performed on the entire batch, with a maximum hardness of 235HB.
Which standard is being referenced? Evidence is urgently needed