Alloy 825 in H2S Service

Krishnnaa26 · Mar 28, 2023

thread338-310345

Dear All,

I have come across the following paper

"Environment-Assisted Cracking of Corrosion-Resistant Alloys in Oil and Gas Production Environments: A Review by P.R. Rhodes"

There are two figures in the above papers (attached) Figure 23 and Figure 24 indicating the effect of Alloy composition on SCC resistance.
Both Figure 23 and Figure 24 providing the info on SCC resistance (Ni+2%Mo+0.5%Cr) w.r.t temperature, however the testing conditions are different.

Considering the typical composition of Alloy 825 and the PREN

1) Can an Alloy 825 solid pipe be used at >120°C, w.r.t to Figure 23 and Figure 24, assuming the same set of test conditions?
2) If an increase in H2S and/or chlorides is considered, do the line in Figure 23 further drops resulting in lower than 150°C SCC limit?
3) If an increase in H2S and/or chlorides is considered, do the line in Figure 24 shifts to right resulting in non-acceptance (potential SCC) of Solid Alloy 825 pipe at >120°C.

Any technical papers/literature references greatly appreciated on this topic.

Thanks in advance

Krishna

EdStainless · Mar 28, 2023

I like the fig 23 test conditions better. Including S is usually a wise move for testing.
Though neither one talks about what stress was applied or how it was applied or the duration of the test.
In general for SCC and similar environmental cracking mechanisms the change of chemistry (H2S or Cl in this case) is usually minor.
It often takes a change of >50% to be highly noticeable.
However any change in temperature or pH is huge as these have a geometric impact.
You need to get copies of these two original papers and read all of the details about this testing.

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P.E. Metallurgy, consulting work welcomed

Krishnnaa26 · Mar 28, 2023

Dear Ed

Thank you for your quick response.

Fortunately, the referred paper in Figure 23 is available, but I could not understand the basis for the curve in Figure 23.
As per my understanding any increase in H2S content (partial pressure) would push the lower limit of Alloy 825 to less than 150°C.
The noticeable point is that Figure 23 is with S presence and Figure 24 is without S presence, but both figures are indicating roughly 150°C limit for Alloy 825.
I am confused a bit on the limits indicted in Table A.14 of ISO 15156-3 with reference to the Figures in the paper. Any idea on the references for Table A.14 of ISO 15156-3?.

It is understood that most operators have their own set of limits for Alloy 825 which are different from Table A.14 of ISO 15156-3.
Alloy 825 weld overlay is not acceptable for the limits in Table A.14 of ISO 15156-3 due to dilution issues, leaving roll bonding/explosive cladding and Solid Alloy 825 options.
And, due to lower PREN of Alloy 825, limited usage on offshore platforms due to external CISCC concerns.
NORSOK m-001 or ISO 21457 do not have temperature limits for Alloy 825 for uncoated condition. But based on PREN values would it be around 80°C-90°C?

Krishna

EdStainless · Mar 28, 2023

I haven't worked with 15156-3 for many years so I don't recall the limits there.
I have worked with a number of companies that use a bit more restrictive limit, more like 135C for 825.
And yes, external corrosion can also be an issue with this alloy.

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P.E. Metallurgy, consulting work welcomed

SJones · Mar 29, 2023

@Ed - ISO 15156-3 doesn't have any limits for solution annealed 825, only for solution annealed and cold worked; and then only for temperature and pH2S above 132 deg C.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones