Regarding post-weld heat treatment of pipelines (with H2S in the medium)
Thread Content
I recently encountered such a problem: 1. The basic details are as follows: The medium to be treated is natural gas containing H2S, condensate, and oily wastewater; the H2S content is below 5%, classifying it as an acidic environment in Zone 0. Pipe material: 20G (GB5310) and Grade 20 steel pipes (GB6479). Pipe diameter: 20–200 mm. Pipe wall thickness: 5–12 mm. 2. Issue: Clause 6.3.10 of the “Design Code for Natural Gas Purification Plants” (SY/T0011-2007) stipulates that “carbon steel pipes and equipment used in acidic environments shall undergo post-weld heat treatment”; therefore, the pipes in this project need to be heat-treated. The \"Code for Acceptance of Construction Quality in Oil and Gas Engineering – Natural Gas Purification Plant Projects\" (SY4209) specifies that hardness testing should be conducted on welds with a carbon content greater than 5% after heat treatment. The case of <5% is not specified, and the requirements for heat treatment processes are not defined. Do I not need to handle it? The \"Code for Construction and Acceptance of Welding Works for Field Equipment and Industrial Piping\" (GB50236) specifies temperature requirements only for pipes with a wall thickness greater than 30 mm; there are no such requirements or guidelines for thin-walled pipes. I urgently need the advice of an expert on how to handle this And what are the corresponding heat treatment methods and requirements? Thank you! ! ! I have searched for this issue on various forums, but found no similar questions or answers. I hope everyone will participate in the discussion to help me solve this problem. Thank you! Note: This question was also asked on other forums, and to date there is no answer. Please be lenient, moderator – I’m not spamming.
Is there no one who can answer this question? A master, please appear quickly!
Reply to 2# mangci5200: These standards are not contradictory. In accordance with GB50236, Section 6.4 on pre-welding heating and post-welding heat treatment, 6.4.1 states that pre-welding heating and post-welding heat treatment should be determined based on a comprehensive consideration of factors such as the hardenability of the steel, the thickness of the welded component, the structural stiffness, the welding method, and the operating conditions. 6.4.4 Welds subject to stress corrosion shall undergo post-weld heat treatment.
But according to what should the relevant technical requirements be implemented?
Stress-relief heat treatment should be applied to welds that are corroded. I haven’t read a few of the specifications, but they shouldn’t conflict. Only 5 percent of it is the hardness test after heat treatment, 5 percent. The stress-relief heat treatment temperature for carbon steel is between 600 and 650. The hardness after treatment should be less than 165. I use petrochemical standards here; I’m not very familiar with oil standards
Stress-relief heat treatment should be applied to welds that are corroded. I haven’t read a few of the specifications, but they shouldn’t conflict. Only 5 percent of it is the hardness test after heat treatment, 5 percent. The stress-relief heat treatment temperature for carbon steel is between 600 and 650. The hardness after treatment should be less than 165. I use petrochemical standards here; I’m not very familiar with oil standards
Pipelines carrying H2S-containing natural gas should undergo post-weld heat treatment as required to prevent stress corrosion; the specific methods for preventing stress corrosion can be followed as specified in the design documents. If no such specifications are provided in the design documents, heat treatment can be carried out in accordance with Article 7.4 of the SH3501-2002 Standard for Construction and Acceptance of Pipelines for Toxic and Flammable Media in the Petrochemical Industry, with the Brinell hardness after heat treatment not exceeding 200HB.
For the design of pressure pipelines, it is first necessary to determine whether they are industrial pipelines or utility pipelines, as well as whether they are used for power transmission or long-distance transportation. After identifying the safety technical specifications that must be followed, the relevant standards can be selected. The first two standards mentioned by the original poster are those issued by CNPC; if you are working on projects for CNPC, then these two standards must be complied with. There are no contradictions between the design specifications and the acceptance criteria. Heat treatment may be required in such cases. Standard 50236 is the design standard for industrial pipelines. The newly issued regulations on safety supervision of pressure pipelines – specifically those related to industrial pipelines – no longer refer to this standard; instead, GBT20801 should be used as a reference. If higher standards are required, 50236 can also be utilized