Material of pressure vessel bolts

Check what the design documents specify. Different operating conditions require different standards; it’s not accurate to simply say that stainless steel is always better than carbon steel, or that a higher grade is always superior to a lower one. The steel marking on the part is one factor to consider, but it’s also important to look at the documentation provided with the part, such as a \"material certificate.\" If such a certificate is not available, but the design documents specify certain material requirements, then a material analysis can be conducted. This is just my personal opinion, for reference only :)

In the flange connections of pressure vessels, it is important to choose the right materials for the bolts and nuts used; they must be able to withstand the stresses generated during the operation of the pressure vessel and meet the relevant safety standards. 35# steel belongs to carbon structural steel; it is a commonly used steel for mechanical structures, possessing certain strength as well as good plasticity and weldability. Steel grade 25# is an old naming convention; according to the new national standards, it is now referred to as Q235 steel, which is a type of low-carbon steel. These two materials can generally be used together in terms of structure, but whether they are suitable for use as flange bolts and nuts in heat exchangers requires consideration of the following factors: 1. **Operating environment and conditions**: It is necessary to know the operating temperature, pressure, and the corrosiveness of the medium; selecting an appropriate material that can withstand these conditions is essential. 2. **Bolt grade**: The performance grade of the bolt (such as 8.8) indicates its tensile strength and yield ratio. A grade of 8.8 indicates that the nominal tensile strength of this bolt is 800 MPa, and its yield strength is 640 MPa (which is 0.8 times the tensile strength). This needs to be compared with your design calculations and regulatory requirements to see if it meets the specifications. 3. **** and industry standards**: It is necessary to refer to relevant pressure vessel standards (such as GB150 in China) or international standards (such as ASME) to determine whether the materials and grades used meet the standard requirements. 4. **Supplier certification and quality assurance**: You mentioned that the bolts have a stamp indicating grade 8.8, but there is no stamp indicating the material. When purchasing, it is necessary to ensure that the supplier can provide qualified material certificates and quality assurance documents to verify the materials. 5. **Acceptance testing**: Upon delivery, it is possible to verify that the supplied products meet the requirements through material inspections (such as chemical composition analysis) and performance tests (such as tensile tests, hardness tests, etc.). The final recommendation is to work together with the design engineers and the quality control department to determine whether these bolts can meet the safety and performance requirements of your heat exchangers. If there are any doubts, it is best to consult the design agency for pressure vessels or a professional institution for evaluation. Bolts that do not meet safety requirements must not be used on pressure vessels; safety always comes first. .

Haha, it’s still great though. It’s very nice, really good

To view the fastener material and manufacturing standards of the design drawings. Moreover, the supplier should also provide a material certificate or quality certificate. See if these two match. Including materials and manufacturing standards. GB3098.1 specifies that for commercial-grade grade 8.8 materials, low-carbon steel is required, and mechanical properties are specified for metal elements. Steel 35# should be able to meet the requirements for bolts of grade 8.8. Section 7.7.1 of HG 20581 outlines detailed requirements for the material and manufacturing processes of commercial-grade bolts; it is quite thorough.

Thank you for letting me know~~~~ Both the drawings and design documents specify the use of 35# studs in accordance with the NB47027-2012 standard. However, the actual supplier is unable to provide such studs; they only have studs of grade 8.8 (although made of 35# material). Moreover, per the requirements of 47027, the steel mark on the studs should be “T”, but what’s actually marked is 8.8. Moreover, grade 8.8 is a commercial-grade level, while 47027 requires a professional-grade level. I wonder if the level 8.8 one can be used

Thank you for letting me know~~~~ Both the drawings and design documents specify the use of 35# studs in accordance with the NB47027-2012 standard. However, the actual supplier is unable to provide such studs; they only have studs of grade 8.8 (although made of 35# material). Moreover, per the requirements of 47027, the steel mark on the studs should be “T”, but what’s actually marked is 8.8. Moreover, grade 8.8 is a commercial-grade level, while 47027 requires a professional-grade level. I wonder if the level 8.8 one can be used

It seems that NB 47027 does not mention the issue of professional-grade bolts, and HG20581 also does not address this issue. It seems GB 20801 doesn’t exist either. Only in HG 20612 are there commercial-grade and professional-grade bolts.

Your supplier isn’t professional – 35 is just 35, and 8.8 is just 8.8