Sour Service and Turbulent Flow Corrosion Issues

[GillP4]

We are considering using a ‘fingers’ type slugcatcher designed to take dry gas into a first stage separator for multi phase well fluids. The product has around 12% H2s with about 4% CO2. The inlet geometry is very complex with different headers of various diameters from 10” to 28”. The slugcatcher is carbon steel
I am particularly worried about pitting corrosion especially in the turbulent flow areas where inhibitors may not be very effective, has anyone experience of this type of flow and any suggestions regarding protection and or monitoring.
This is a temporary situation that may last 18 months, normal wall thicness is generally 15mm

 

[SJones]

In the first instance, you have to run a corrosion risk assessment. With 12% H2S, multiple fatalities are possible, so already the risk is probably not going to be ALARP. It is then a case of looking at the likelihood and measures to reduce it. Corrosion rate prediction with that amount of H2S is a bit hit and miss but generally errs on the conservative side (at least the Hydrocor model does that this case is probably using). Elemental sulphur will be an issue to assess irrespective of turbulent flow. One plus point appears to be absence of chloride with only condensed water and other factors such as expected slug arrival frequency and volume can also be used in the assessment. Having determined a notional degradation rate, corrosion control measures and their reliability have to be assessed. Retrospectively applying cladding or coating in situ will not achieve maximum reliability and probably will annoy the accountants for 'temporary' service. If you pick your inhibitor carefully, and your downstream processes can cope with the possible effects of having to put substantial quantities in, the high shear locations can be managed. Naturally, you will have to monitor and inspect fairly frequently, if not online. A possibility could be a UT mat system such as Rightrax supported by an inspection programme. Qatargas experience is attached for your perusal.

Steve Jones
Materials & Corrosion Engineer

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

 

[GillP4]

Thanks for the response, I agree with your thinking, I myself believe that the coating option that is being pushed here will cause more problems in the long run than anything we gain in the short term.