Mating Inconel 625 to Duplex S31803

[JamieW]

Hi,

I was wondering if anyone has any experience with mating an Inconel 625 flange to a Duplex S31803 flange? It is a 16" class 300 compact flange connection. The service is production fluids; so a mixture of oil, water and gas. The condition outside the pipe is salt air as this is on an offshore facility. There is no insulation, no heat trace and no coating on the pipe or flanges. I am not concerned with galvanic corrosion with these materials but my concerns are with the differing thermal expansion coefficients of the materials and when the lines heat up during production (~80 Deg C) what affect will it have on the joint and in particular the seal ring. I found the coefficients of linear expansion for Inconel to be around 0.000012 and Duplex S31803 to be 0.000013 which gives a difference of 0.02mm radial expansion on the radius of the duplex over the Inconel. This does not seem like a big amount to me but i am unsure. Are there any special considerations that i need to take into account for the seal ring for this joint? Would it be best to go with a Duplex seal ring over an Inconel one?

any help would be appreciated.

thanks,
jamie

 

[XL83NL]

I dont see much of an issue, but thats from my experience. I have never dealt with 16" piping flanges, only equipment body flanges, which have always been the same material. The one time I did find an issue with different materials, was at very high temperature (range 600-900°C). The difference in bolt material (800H) vs flange material (617) caused a decrease in bolt load, thus leakage, due to different coefficients for thermal expansion. Have you checked if PCC-1 provides any guidelines for your question?

 

[JamieW]

Thanks for your input!! We are at very low temps in this case so not expecting much issues but wanted to get some other opinions. I have not checked PCC-1 but will, thanks again

 

[EdStainless]

The thermal expansion difference does not concern me.
We commonly see bigger mismatches.
The choice of filler and heat input are bigger issues.
You do what to make sure that your geometry is such to minimize stress concentrations and also make sure that the filler has a CTE that is in the range of these two alloys.

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P.E. Metallurgy, Plymouth Tube

 

[JamieW]

thanks, it's good to know that this has been done before! we're planning to qualify an appropriate weld procedure in the coming weeks.
jamie