ISO15156 NACE MR0175 - Carbon Steel

[Corroneer]

Hi Everyone,

We are designing a new gas vessel (it will separate liquids from the gas).

The partial pressure of H2S is > 100 KPa.
We do not have proper pH values, but the optimum working pH for the vessel is between 6 and 7. The operator confirmed that the pH can go lower than this (again no clear pH values given).
The temperature is between 200 to 300 F.

The current vessel had suffered severe cracking, but minor corrosion pitting.

We have selected a cladded CS for this because of the very high probability of SSC cracking and HIC (both were experienced in the old vessel), but the owner argues that if the equipment is manufactured from HIC resistant CS that is qualified for NACE MR0175, no cracking (neither SSC nor HIC) is expected.

Unfortunately, NACE MR0175 is unclear about the limits and the applicability/inapplicability of CS.

I am still not convinced that CS will withstand this as the equipment will be exposed to severe environment (high H2S, water content, temperature) during operation (dehydration units upstream are inefficient and gas with significant water content can reach this vessel during operation).

Any help is welcome!

Regards,
Corroneer

 

[Chumpes]

Hello
Conditions for HIC to occur are not simple because it dépends on numerous parameters such as the corrosion rate.
Having HIC resistant plates with HIC qualification as per NACE MR 0175 is better than nothing, but HIC plates are not immune to HIC damage. We already experienced HIC cracking of HIC resistant plates due to severe corrosion. With reference to NACE Pub 8X194, some users prefer SS clad in severe sour service.
If the client wants something special it may be difficult changing his mind.
regards

 

[SJones]

The owner feels lucky; you don't feel lucky, and that's without throwing welds into the equation. The outcome is dependent upon who is paying, but you could run through an API RP 581 assessment to try and shore up your side of the argument.

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.

 

[Corroneer]

@Chumpes and @SJones,
Thanks for the replies.

 

[MJCronin]

Call in a corrosion consultant .... pay him the going rate ...

MJCronin
Sr. Process Engineer

 

Concur x3

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."