9Cr1Mo corrosion resistance versus 13Cr/420 or 25Cr Duplex 1

[MetalGuy10]

A part was submitted to our lab that was fabricated from 9Cr1Mo that was in an acidizing well environment (HCL was present, exact concentration or buffer unknown, no info on possible H2S) with a temperature around 275 F. The part exhibits massive corrosion as expected.
The 9Cr1Mo is a quasi stainless, but how would the corrosion resistance (mm/year) of the 9Cr (yield =95 KSI) compare to 13Cr/420 (yield=95 KSI) and 25Cr Duplex (yield=95 KSI) in an environment of X% HCl ph=3.5, at 275 F?
I have a broad background in Carbon steels, but my background with stainless is limited as confirmed with my novice question. I understand the formation of Cr oxides which improve corrosion resistance, and the importance of the PREN number, but what other factors should I be studying to improve my general knowledge of stainless alloys applications pertaining to corrosive environments?

 

[arunmrao]

I am no expert on the subject to advise. but a humble beginning can be done by reading "Stainless steel for design engineers" by Michael Mcguire,also a very helpful and active eng tips member.

 

[stanweld]

9% Cr alloy steel does not a stainless steel make; not even a quasi-stainless! Corrosion resistance will vastly increase at 11% Cr and greater. From your description of the service environment, it is highly doubtfull that 12% or 13% Cr would prove effective. Quite possibly the duplex stainless would would prove effective.

 

[EdStainless]

The 13Cr would be better, but not enough to matter.
The 25Cr duplex will be much better in acids, even more so if any chlorides are present.

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Plymouth Tube

 

[mqas]

MetalGuy10,

I am a bit intrigued as to why you would be interested in the corrosion resistance of 9Cr1Mo. This material is principally used in the power generation industry because of its improved creep resistance over conventional austenitic and martensitic steels at specific temperatures relative to base cost.

certainly in the power industry, it is not being considered as a replacement to other materials based on corrosion resistance.

If you google AD700, you will see where I am coming from.

 

[EdStainless]

91 is often used in oil field work. It has very good resistance to CO2 in a high Cl environment, with no oxygen present.
The oxygen can be very important.

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Plymouth Tube

 

[metengr]

Reference is to Grade 9, not Grade 91.

 

[stanweld]

Grade 9 is commonly used in hydrogen and sulfur service in petrochem plants.

 

[SJones]

If it's been in an acidising well environment, it's likely to be either the tubing, L80 Type 9Cr, or an associated item covered under ISO 10423, ISO 14310 or similar

Steve Jones
Materials & Corrosion Engineer

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

 

[mcguire]

Here's a hypothetical question for downhole types. What would be the practical value of alloy steel OCTG with the same hydrogen resistance as C90 but, say 20k or 30k more yield strength? Obviously this can be done with special high nickel or cold worked alloys, but I'm thinking of close to conventional compositions, which current large suppliers could make.

Michael McGuire

http://stainlesssteelforengineers.blogspot.com/

 

[SJones]

They already exist, for certain H2S environments, such as C110 for example. They will never get the same 'blanket' resistance as C90 and T95 but can be qualified for specific limits. With well depths measured in kilometres, there's every incentive to get a high strength steel to perform in H2S

Steve Jones
Materials & Corrosion Engineer

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

 

[MetalGuy10]

EdStainless,

I always enjoy your comments on stainless. Your correct the application is for oil field work.

Guys,

Thanks for your input as well.

 

[Guest102023]

Just remember that the 'stainless' part of 'stainless steel' was dreamed up by the marketing department. And there are no 'quasi' grades of stainless steel.