Material specs for high level of H2S. 2

[FC2008]

Hey,
I have to choose a material to be used in an environment with:

52000ppm H2S
Tmax = 95C (maximum temperature)
Pmax= 10 000psi (maximum pressure)

pH2S = 520psi (partial pressure)

I've read a bit in NACE MR0175 and found that I could use some cold-worked alloys of type 4e.

Could someone give me some pointers?

Thanks

 

[FC2008]

I've found Inconel 725 to be a possible choice, but since I'm making a tube with a pretty large diameter I don't think I will be able to make the whole thing in inconel.

I've heard something about adding a layer of inconel to other materials to increase the corrosion resistance, anyone have some good resources on this?

Thanks

 

[SJones]

Why do you feel that something like Inconel is necessary right from the start? Why can't a low alloy steel be used?

Steve Jones
Materials & Corrosion Engineer

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

 

[TVP]

What kind of strength level do you need? Ni-based alloys are deposited over other metals for locally improving certain properties (corrosion). Go to the Special Metals or Haynes websites for more information:

http://www.specialmetals.com

http://www.haynesintl.com/

 

[FC2008]

SJones: we usually use Duplex and it's corrosion resistance when h2s levels are as high as this isn't good enough.

TVP: Thank you for the links.

 

[SJones]

I'm still asking what drives you to select a corrosion resistant alloy. Carbon steel can handle the H2S; it can't handle corrosion generated by water and H2S. If you don't have water you may not need a CRA. If you do need a CRA, there are many complex factors to consider in a final selection. A process too complex for a valid answer on a forum such as this.

Steve Jones
Materials & Corrosion Engineer

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

 

[FC2008]

The flow is hydrocarbons, saltwater and gas. Duplex isn't good enough. Thank you for the links!

 

[FC2008]

By the way, we went for a weld overlay of inconel to save money and still get good results.

 

[strider6]

If you don't have any CO2 in the fluid then is not necessary to select a CRA. You can have water, formations or condensation water, but if you don't have CO2 nor oxygen in the fluid then your corrosion rate will be negligible and you can use Carbon or Low alloy steel ...

it seems a waste of time and money to select an inconel...

S.

Corrosion Prevention & Corrosion Control

 

[FC2008]

Could you please explain a bit more on the effect of CO2?

So if I have a high concentration of h2s in a flow without co2, there isn't any danger of h2s related corrosion?

Interesting!

Thank you

 

[SJones]

If you are discarding inhibition as a corrosion control measure for carbon steel, then yes, duplex is no good and your choice of Inconel may stand up, assuming that it is 625. In trolling through ISO 15156 you will have to know the chloride level to select a material and 10000 psi looks suspiciously as if the pressure rating rather than the design pressure is being used to calculate pH2S. Incidentally, if you went for inconel weld overlay, why are you asking what material to select on here?

Steve Jones
Materials & Corrosion Engineer

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

 

[FC2008]

Well, we havn't totally decided yet. But as we have used inconel overlay in similiar situations before, I'm thinking that's what we'll do.

I'm still interested in hearing a bit more about CO2, if someone has the time.

Thanks

 

[SJones]

NACE Corrosion 2005, Paper 05624

Materials Performance, August 2002, pp60-64

Corrosion, Vol 59, (8), pp659-683, 2003

Steve Jones
Materials & Corrosion Engineer

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

 

[FC2008]

Thank you, I will look into it.

 

[strider6]

FC2008

In Oil&Gas when selecting materials the first assessment is based on CO2 corrosion for Carbon Steel. There is a model based on DeWaard-Milliams model (1991) that allow you to calculate the corrosion rate for carbon steel.
The corrosion rate for carbon steel due to CO2 is a function of several factors.
- Partial pressure of CO2 in gas phase
- Temperature
-Pressure
-Water cut
-Water analysis (mainly bicarbonate content) and if ti's formation water or condensation water from a gas phase.
-Fluid velocity...
Using the model, now there are severeal model based on the original and also several software, you calculate the corrosion rate for carbon steel, then if this corrosion rate allow to specify a corrosion allowance of, usually the maximum is 6 mm, the you can select carbon steel, with corrosion inhibitor if applicable, otherwise you'0ve to go to a CRA (corrosion resistant alloy).
H2S has an effect on CO2 corrosion rate mainly increasing the likelihood of localized corrosion type.
this is a good paper that can explain how to calculate corrosion rate and tehre is also a free software from NORSOK. This model is limited to a partial pressure of 0.5 abr of H2S.

http://www.ivt.ntnu.no/ipm/und/fag/....06.2004 Corrosion in hydrocarbon systems.pdf

http://www.standard.no/imaker.exe?id=10405

here you can find a lot of useful paper on CO2 and H2S corrosion:

http://www.corrosioncenter.ohiou.edu/publications.asp

http://www.corrosionist.com/Corrosion_Control_Offshore_Oil_Gas.htm

this is a good paper on H2S corrosion and NACE/ISO 15156 use:
Use of International Standard NACE MR0175/ISO15156

http://www.capp.ca/raw.asp?x=1&dt=PDF&dn=109839

hope this help u:

S.

Corrosion Prevention & Corrosion Control

 

[FC2008]

Wow, great reply! Thank you very much!

As of using carbon steel, where I work we only use duplex S31803, super duplex or inconel. There's never talk of anything else..I'm very new and dare not ask too many questions