CRA Inconel 625 vs Incoloy 825

[Weko]

For sour gas plant, which material is preferable, Inconel 625 or Incoloy 825?

Some project specify Inconel, and other specify Incoloy

Anybody can advise what are their advantage and limitation? Which material to be used in what condition?

Also in terms of price and availability, which one is better?

thx

 

[brimmer]

625 will be much more expensive & less available. 625 generally much more resistant than 825. There is a lot of literature on service conditions for 625, 825, etc. Check NACE MR 0175 for service conditions & acceptable materials. If you have elemental sulfur forming, especially wet you will want 625. Your question is also very general, if you want to build a sour gas plant from these materials, go ahead, but we use very little of these materials in our sour gas plants.

 

[brimmer]

Here is a paper, but you should start searching on your own, there is a lot of info our there on this subject, CRA's for sour service in general. Also depends what else you have in your gas field, CO2, brine, etc...

 

[EdStainless]

Remember that 825 is a high alloy stainless steel, not a Ni based grade.
Very different high temperature strength and corrosion issues with the two alloys.
In my experience unless the high temp strength is an issue 625 is not your best option. There are similarly priced Ni alloys with better corrosion resistance, and there are high Cr SS grades that are not far below.

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Plymouth Tube

 

[Weko]

I was just wondering.. In my previous project.. the matrial selection based on "severeness" of sour gas / corrosion are
1. CS + 3mm CA
2. CS + 6mm CA
3. SS 316
4. Duplex
5. Super duplex
6. Inconel 625

Currently (another project)... the spec are only
1. CS + 3mm CA
2. SS 316
3. Incoloy 825

Which one will be more cost effective?

 

[Guest102023]

Which one will be more cost effective?
++++++++++++++++++++++++++++++++++++++
Impossible to answer with any degree of accuracy.

p.s., the word would be 'severity'

 

[EdStainless]

Not the 316, under any conditions.
It has low strength and mediocre corrosion resistance.
In many cases a higher alloy product (2205) will be much less expensive.

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Plymouth Tube

 

[SJones]

Brimmer - you shouldn't really be posting up NACE papers; they will stop our access for copyright violation!!

Weko,

You will select the material according to the gradation of 'severity' as defined by the documentation that listed the possible materials. Some end users are happy with ISO 15156, some end users relax ISO 15156 for some materials and tighten it for others.

For a start, you cannot compare the carbon steel plus corrosion allowance with the CRA materials since it will corrode thereby incurring operational expenditure for integrity status verification (it will also require painting)!! On the other hand, the CRAs could be prone to types of cracking that the carbon steel is not. This will negate the simplicity of a direct capital expendure comparison.

The optimum material will be the one offering the best lifecycle cost for an acceptable corrosion risk, unless (as is usually the case), lowest CAPEX has been stipulated as the evaluation criterion; in which case, good luck!

Steve Jones
Materials & Corrosion Engineer

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

 

[Weko]

Thx all for the advices

For Steve Jones.
Currently, I work in an EPC contractor. Most of the project tenders here, does only looks at the lowest EPC cost (starting cost). Thats why we mostly compare the "cost" of CS+CA to CRA material.

 

[brimmer]

Oooooops.

Weko, we use a lot of carbon steel with corrosion inhibition in our sour gas plants, no exotics.

 

[SJones]

It depends upon the customer's materials selection rules. Shell and Exxon have very detailed rules and the former has a decent model for predicting carbon steel corrosion rates in the corrosion risk assessment. Naturally, an EPC contractor will go straight for the cheapest option - carbon steel. I have the amusing experience of issuing a highly detailed materials selection specification (down to nuts and bolts level) with a vast amount of CRAs of various types selected. One tenderer flew in a consultant from the UK to the tender meeting and proceeded to explain how they were going to build it all from carbon steel!! All I could do was point out that the materials selection report was actually a specification and not up for negotiation. The consultant spent the next two days at the beach club! And that sums up the general EPC approach: the base case is always carbon steel unless instructed otherwise; simply because the corrosion risk is not the EPC's to bear.

Steve Jones
Materials & Corrosion Engineer

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