Specification Differences Between ASTM A320 B8M and ASTM A320 B8 for Low Temperature Bolting Liverpool

In refineries, LNG terminals, and offshore skids where low-temperature bolting is a must, stainless steel bolts are subject to stringent mechanical and impact property requirements. ASTM A320 B8M among the various grades specified is the one that is most often chosen for cryogenic application and this is mainly due to its austenitic 316 composition with the addition of molybdenum. It can be delivered either as Class 1 strain hardened or Class 2 solution annealed and the tensile strength will normally be in the range of 515 MPa to 690 MPa, depending on the diameter and the type of processing.

Generally, stud bolts and heavy hex bolts are available from 1/2 inch up to 4 inch, or M12 through M100, which will cover most of the assemblies of ASME B16.5 and B16.47 flanges.

In fact, during a real project execution in Dammam, Riyadh, and Jeddah, the purchasing department goes through the impact test report at minus 196-degree Celsius, checks the hardness level and also confirms the conformance to ASME B31.3 and other relevant pressure piping codes before issuing the approval. Depending on the class of flange and the load, the thread forms like UNC and 8UN are picked. On pipingmaterial.sa, purchasers have an opportunity to locate a certified wholesaler that will provide heat numbers that can be traced, MTCs, and large quantities that are in line with the EPC requirements. Where exposure to chloride is at a moderate level and there are tighter budgetary concerns, ASTM A320 B8 is still generally regarded as an acceptable solution.

This grade, which is based on the chemistry of 304 stainless steel, is typically delivered in Class 1 strain hardened condition, and features a yield strength that has been preset as well as carbide precipitation that has been controlled to make it suitable for use at low temperatures. The variation in the content of molybdenum and the resistance to corrosion between B8 and B8M impact how the two materials perform in environments that are sour or marine thus it is necessary to carry out a technical evaluation before the final selection of the material is made.

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