For pressure vessels, the steel plate used should be Q245R; can 16Mn forgings be used for the flange material?
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Today, a new pressure vessel DN600 was designed, with an operating pressure of 1.0 MPa and a design pressure of 1.6 MPa； The working medium is natural gas, the operating temperature is 65°C, and the design temperature is 80°C. When selecting materials, I chose Q245R (GB/T713) for the plates, and 20 (GB/T9948) for the pipes. Since the customer specified a PN16 flange grade, I selected 16MnⅡ as the material for the flanges. During the review of the drawings, our manager said that this approach was not appropriate. The instructor who gave the training session specifically discussed the issue of material matching – sheet metal of type Q245R corresponds to forgings of type 20Ⅱ, while sheet metal of type Q345R corresponds to forgings of type 16MnⅡ ； When it comes to the matching of steel plates and pipes, 20# steel pipes can be matched with both Q245R and Q345R steel plates). Could some expert please explain why this is the case, and what are the specific sources? Thank you:handshake
Is it purified natural gas or sulfur-containing natural gas? For purifying natural gas, it is fine to use 16MnⅡ for the pipe flanges. However, in the case of sulfur-containing natural gas, since materials with better toughness are required, using 16MnⅡ for pipe flanges is not very suitable; yet there are no mandatory regulatory requirements against this.
I suggest you take a look at this post; the analysis is quite reasonable: https://bbs.hcbbs.com/thread-1037257-1-1.html
In terms of material compatibility, 20 forging is more suitable, and it also has better resistance to stress corrosion.
Thank you to all the experts for their helpful guidance: handshake
Once you’ve learned it, you need to choose based on the usage conditions!
I studied it; using this question, I reviewed some knowledge that I had overlooked.
If 20II is selected and a PN16 flange is used, these temperature and pressure levels do not meet the requirements for using that flange. The corrosion resistance of 16MnII is not suitable; it is recommended to discuss with the user the use of PN25 20II flanges or to reduce the design pressure appropriately.
The natural gas supplied to the city’s official website has already been desulfurized; otherwise, the pipelines wouldn’t be able to handle it So, with this container, you essentially don’t need to worry about sulfide stress corrosion. As for whether to use 16MnⅡ for the pipe flange, I personally think it has little to do with whether the shell is made of Q245R or Q345R; even when considering strength matching, it is related to the connection between the pipes. Moreover, high-neck butt-weld flanges are generally used for natural gas applications.
The operating pressure is 1.0 MPa, while the design pressure is set at 1.6 MPa – which is a somewhat high value. If the design pressure is reduced to 1.3 MPa, then PN16 20II flanges can be used.