Inconel overlay for tubesheet in hydrogen service

[AspenMech]

Hi,

Our heat exchanger specialist specified inconel overlay for tubesheets on the tube side which is hydrogen service. Is this necessary? The tubesheet and tubes are 1 1/4Cr.

Thanks,

 

[EdStainless]

Yes.
Steels will absorb Hydrogen under some conditions.

 

[NovaStark]

It will depend on your material of construction, the hydrogen partial pressure and temperature.

In most cases those overlays are to provide a barrier between the hydrogen and the steel to preven high temperature hydrogen attack. You can reference the Nelson curves in API 941.

 

[Christine74]

That's unusual. I don't think I've ever seen an alloy-clad tubesheet specified where the tube material didn't match the cladding material. Whether the cladding was added to protect against HTHA or some other corrosion mechanism the tubes would be left vulnerable.

Were Strength Welded tube-to-tubesheet joints specified?


-Christine

 

[GD2]

OP,
You need to spell out the operating/design conditions including hydrogen partial pressure. Design for hydrogen service is relatively a new area. By the way what is that 1 1/4 Cr? It's not the full material spec. can you provide the full spec?

 

[ShabsRBI]

As mentioned by GD2, operating/design conditions including Hydrogen Partial Pressure is required to fully analyse the HTHA issue. Other factors that API-941 highlights are the Primary Stresses ( Heat Treatment), Secondary Stresses (Thermal Stresses /Cold working) and Residual Stresses (PWHT).
Considering the Tube Sheet Inconel weld overlay over 1 1/4 Cr - 1Mo material indicates that Design Temperature and H2 partial pressure are on higher side. Under that condition leaving the tubes with 1 1/4Cr - 1Mo is not a good engineering practice and subjected for high corrosion.
Is it possible to provide the Design conditions and material specs?

 

[weldstan]

The selection may be due to the tube to tubesheet weld using a Ni based alloy filler to mitigate hydrogen cacking of the weld.