Equipment material selection issue (low-temperature carbon steel + duplex steel)
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This post was last edited by guoshu258 on 2015-12-11 at 10:26. It is a pressure relief tank; the design pressure of the equipment is -0.1/0.34 MPa, and the design temperature is -59/85 °C. The medium involved is acidic natural gas (40% CH4, 20% CO2, 18% H2O, 10 PPM H2S, with Cl ions present). The diameter of the equipment is 3900 mm and its length is 12000 mm. Since it is an ASME-compliant device, SA537 CL.1 + SA240 S31803 composite steel plates were chosen for construction. Is this a suitable choice? How should the flange material be selected? If following national standards, how should materials be selected?
The low-temperature threshold of the base material is sufficient. However, composite plates (including surfacing layers) must not undergo any heat treatment.
It is possible to assess the corrosion of the medium in the case of duplex steel, but various conditions must be taken into account. If it is designed according to domestic standards, it is recommended that the person in question choose a different cladding material. S31803 duplex steel corresponds to China’s S22253 duplex steel; according to the standards, the minimum operating temperature for duplex steel is -20°C. The person in question should check whether the minimum operating temperature specified for S31803 under ASME standards meets the requirements of the specific application.
:Regarding the heat treatment of composite plates, ASME specifies that post-weld heat treatment should be carried out when the base material requires heat treatment. As for the sensitization issue of stainless steel, it is alleviated by increasing the rate of heating and cooling. Of course, whenever possible, post-weld heat treatment should be avoided.
:Can’t a handshake be used at temperatures below -20°C either, when it is used as a layered structure without being under pressure?
I think at 85 degrees, it’s completely possible to use low-temperature steel plus an epoxy coating. The coating can be reapplied every two years at a low cost
Composite panels definitely require heat treatment at 700–800 degrees; it’s difficult to ensure that the microstructure of the duplex steel remains unaltered. Therefore, the material choice made by the original poster is not reasonable in the first place
The embrittlement of duplex stainless steel at high temperatures (316°C), characterized by an increase in strength and a decrease in impact toughness, is a very serious issue. In the past, there was a severe accident in which a duplex stainless steel clad plate equipment exploded during commissioning – at the Kela gas field.