20# steel pipe with 16Mn flange
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It’s my first time working on a project; I have no experience. The contract for purchasing the control valve specifies that it comes with matching flanges. Later, upon making a request, they presumptuously specified matching flanges with the appropriate pressure rating based on the pipe material, which is 20# steel. Who knew that later the design institute found out and issued requirements for matching flanges. Many 20# steel pipes are equipped with flanges made of 16Mn material. Embarrassingly, the 20# steel flange has arrived! Can one of the corresponding pressure rating alternatives be used?
You can contact the designer to see if a replacement is possible
Flanges of the same material cost much more when purchased together with instruments and pipes
It is best to check the maximum allowable operating pressure for the flange’s pressure rating. The mechanical properties of 20 and 16MN differ significantly; based on the principle of equal strength design, the fitting corresponding to 20 will be thicker than that of 16MN. Considering the welding issues, internal notching of the weld area is required.
It is necessary to consider both standard compliance (whether there is a material group corresponding to this material in the flange standards, whether the temperature and pressure curves meet the requirements for operating temperature and pressure, and whether it matches the yield strength of the butt-welded pipe) and welding procedure qualification (whether there are WPS and PQR documents specific to this material and the pipe material).
It is necessary to communicate with the design agency, as only they have the authority to determine whether substitution is possible.
Under normal circumstances, no! Firstly, from our personal understanding, the maximum impact resistance of 20# flanges drops significantly above 300°C, whereas the maximum impact resistance of 16Mn flanges at this temperature is higher than that of 20# flanges ； Secondly, 16Mn is more expensive than 20#. In most cases, when 20# can be used, 16Mn will not be used instead; however, there are exceptions, so it’s better to contact the design team.
Generally, some stringent conditions are taken into account during design, and calculations are carried out; as for whether it will work in practice, one still needs to ask the designers. Only the designers have the authority to decide