Carbon Steel Corrosion/damage

[aasd25]

Hello experts,

I'd like to get your opinion on the type of failure of this carbon steel (SA516 gr70N). See attached pictures. The pieces that came out from the main part seem to have multi layers. I'm not sure if this is a type of corrosion or a material problem. This carbon steel part is in contact with a stainless steel (it shouldn't be in contact but due to some issue it was in direct contact in this case). The surface temperature is about 300°C. Could this be a galvanic corrosion? Or something else?


multi layered piece from the main part:

main part, missing piece can be seen:

Thank you!

 

[cap1a79]

If you share some detail information as below, you will get some advice to establish guideline to find out the root of the cause.

i) Temperature - 300 C
ii) Service unit / Detail location
iii) Type of the facility (ex., heat exchanger, pressure vessel)
iv) Any corrosive component (ex., H2S, CO2)
v) Service fluid
vi) Any other information?

Lee SiHyoung,

 

[SJones]

300 deg C - insulation? Corrosion under insulation (CUI)

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[aasd25]

Hi cap1a79,

i) Temperature - ~300 C
ii) Service unit / Detail location: hydrocracker unit
iii) Type of the facility: heat exchanger
iv) Any corrosive component: shouldn't be but Cl and S was detected on the CS piece

 

[aasd25]

Hi SJones,

I don't think it is CUI because it is not on the surface in contact with the insulation material. It is the inner side.
It is strange to see carbon steel material turned into layers like this, never seen that before.

 

[SJones]

Glad we established that it's on the inside.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[cap1a79]

Considering the service unit, temperature and the selected material, the failure is very similar to H2 / H2S corrosion or Sulfidation.
Check whether the original material selection and the corrosion allowance were proper or not based on Couper-Gorman curve (for H2 / H2S Corrosion) & McConomy curve (Sulfidation) and if yes, check if process conditions were properly operated with the given CS selection and the corrosion allowance.

Lee SiHyoung,

 

[Corroneer]

Looks like high temperature damage. Are you sure the temperature did not increase significantly from 300 oC.

 

[aasd25]

Thanks Lee!
I will check on it.

 

[aasd25]

Hi Corroneer,

In fact the highest temperature observed before the failure was 373°C. This is the fluid temperature, not the CS surface temperature, I guess it could be close to 373°C but still within the design temperature.
If it is high temperature damage, does it mean that the material is not suitable?
The design temperature is 400°C though.

 

[cap1a79]

It depends on H2S %, elemental sulfur wt% and corrosion allowance mm. Share the above information.










Lee SiHyoung,

 

[mrfailure]

I think it is difficult to understand what really happened without at least making a metallographic cross-section through-wall through the damage. Both metallography and microhardness should help in this instance.

 

[aasd25]

Hi mrfailure,

Yes we are going to do that soon. I just would like to have some insights if anyone here have seen a similar damage before.