Does wet H2S damage occur in high temperature/pressure lines?

[abourandas]

API 571 says that wet H2S damage occurs from ambient to 300F. My example is an HOC reactor effluent line at 1655 PSI and 424F going to a High Pressure Hot Seperator. Will wet H2S be a concern at this high of a temperature since the pressure will keep the water in the liquid phase?

 

[SJones]

You are not quite reading API 571 correctly. Bullet item 1 under temperature on page 5-42 states - for blistering, HIC and SOHIC - "between ambient and 300 deg F OR HIGHER".

You will also need to take note of the parameters under the second bullet point of pH regarding aqueous phases.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

 

[abourandas]

Thank you for your reply, but I am still trying to understand what is going on.

In the process flow diagrams in API 571 Section 5.2, Figure 5-48 shows that sulfidation is a damage mechanism after the reactor (dry H2S damage in my mind), and after a water wash, that wet H2S is a damage mechanism.
I believe that 571 is a composite of different corrosion at different locations, but if the reactor operates at a high enough pressure to keep water below the boiling point, why is wet H2S not in that diagram prior to a water wash?

 

[JasonLouie]

You need liquid water to have wet H2S corrosion. The reactor outlets do not contain saturated water which could condense and form droplets of water. If the humidity of the line is less than 100% (or a lower number depending on your safety margin) there shouldn't be liquid water and hence no wet H2S corrosion.

Downstream of water washes obviously have tons of liquid water so that's why wet H2S corrosion starts there.

 

[TomEun]

As Steve and Jason mentioned, the free/condensate water is a necessary requirement for wet H2S corrosion. The water condensate temperature depends on the operating pressure (up to 300F or higher). Normally HHPS and CHPS in hydro-treating/cracking units are exposed to wet H2S corrosion due to the free/condensate water.

Meanwhile the reactor effluent flow sides of fresh feed/reactor effluent exchangers (series) will be exposed to sulfidation due to high temperature (> 650F).

Thomas Eun
Corrosion and Materials Selection/Design Specialist

 

[abourandas]

Thank you all very much for your insight.