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316 Chloride Cracking - Short Duration Exposure

316 Chloride Cracking - Short Duration Exposure

(OP)
Does anyone have experience with the chloride cracking resistance of 316L for short exposures to environments normally associated with cracking? Specifically, high temperature solutions containing a moderate concentration of sodium chloride?

This is a thermal oil recovery application where steam is temporarily injected into producing wells. These wells usually have alloy screens at the bottom to keep sand out. Wells typically produce a mixture of oil, water, and gas over their 15-20 year service life. The producing conditions are approximately 100-115C, 20-50psi CO2 partial pressure, 100-1000ppm H2S, and water with 20g/L NaCL (no oxygen present). Occasionally (meaning 3-4 times over service life of well), steam is injected to lower the viscosity of the oil to increase production. During these short duration steam injection periods (7-10 days), the alloy screens are exposed to 50g/L NaCL at 200-220C (again, no oxygen present).

Based on the literature (see the example linked below from the Nickel Institute, figure 4), our normal producing conditions are no problem for 316L and no cracking is expected. On the other hand, short periods of steam injection conditions are a potential problem because they fall outside the recommended service envelope (shown in figure 4).

Nickel Institute - Corrosion Resistant Alloys in the Oil and Gas Industry

I have field experiences with 316L screens NOT showing signs cracking for short exposures (250 hours) to 50g/L NaCL at 200-220C. This is contrary to what the literature suggests is an environment where cracking failure would be expected. After exposure steam conditions, the 316L is then returned to production and exposed to oil/water/gas at 100-115C, 20-50psi CO2 partial pressure, 100-1000ppm H2S, and water with 20g/L NaCL.

My question: How long do you need to be in a cracking environment you expect to start seeing cracking problems? 1 hour? 10 hours? 100 hours? 300 hours? 500 hours? 1000 hours? Is there some sort of "incubation period" or "threshold exposure time" required to initiate cracking? Does re-exposure to normal producing conditions somehow re-passivate the 316L and prevent cracking?

I am trying to reconcile my practical experiences of 316L succeeding in a service environment that the literature suggests would almost certainly cause cracking failures. Any experience, opinions, or literature references you have that could provide background would be very helpful.

Thanks in advance for your input!

RE: 316 Chloride Cracking - Short Duration Exposure

Your missing one little bit of information - what is the pH??

RE: 316 Chloride Cracking - Short Duration Exposure

(OP)
Under production conditions, pH is ~5-5.2 (this is a calculated pH at bottom of well, based on partial pressure of CO2 and H2S as well as the alkalinity of the water).

Under steam injection conditions, the pH is much higher. There are no acid gases present. The steam quality is low (about 50% by mass steam) and the liquid fraction of the steam has 50g/L NaCl at a pH of 8-9 (or more).

RE: 316 Chloride Cracking - Short Duration Exposure

I think your best hope is that oil wets the metal surface and the acidic chloride water does not get to it. Although I had associates that tried to used incubation times , I was never a believer. Any way that you could expose test coupons ? Have the screens been annealed or do they have residual stress ?

RE: 316 Chloride Cracking - Short Duration Exposure

theleftcoast;
Your practical experience may be your best guide and don't necessarily be fooled into having corrosion test data in literature be your guide. I agree with blacksmith37 suggesting test coupons but it sounds like you have already established a baseline with 316L screens and no cracking.

RE: 316 Chloride Cracking - Short Duration Exposure

(OP)
My concern was primarily with "short" exposure of 316 to steam conditions (50% quality with liquid phase having 50g/L NaCl, 200-220C, at a pH of 8-9). During steam injection, oil wetting is really not something I count on. It is safe to assume there is little (or no) oil coating the 316.

In the mildly acidic producing conditions (low pH caused by acid gases), the 316 screens have a long service record without failure.

RE: 316 Chloride Cracking - Short Duration Exposure

(OP)
blacksmith37 - The screens are not annealed so they have some residual stress from being shaped.

My primary goal with this post is to gain understanding around why short term exposure success might not agree with literature data. How long does an exposure need to be? What mechanism might be offering protection? I really don't have the background to answer any of these so I wanted to ask the community.

I never thought about the steam pH impacting the chloride cracking performance. Not sure why that wasn't on my radar until now. Does a higher pH somehow help the 316 remain protected?

Just a thought, does anyone have experience with 316 in low pressure steam systems? That is probably a relatively analogous environment to bottom hole cyclic steam conditions.

RE: 316 Chloride Cracking - Short Duration Exposure

(OP)
Also, the test coupon we used was an as-manufactured piece of product. We lowered it to the bottom of the well, exposed it to steam conditions, pulled it out, and inspected it. It is pretty hard to do extensive testing because it is very expensive. This is a great data point for us to have, but it is ONE data point without any similar conditions to compare against in the literature (as far as I have found).

RE: 316 Chloride Cracking - Short Duration Exposure

In reality pH, temp, O2, and stress are all that matter, once the Cl level is above 20ppm more doesn't really change things.
A well is the only place where I would believe is truly oxygen free.
If there is no active corrosion there will not be any CSCC.
But if the low pH and temp result in pitting initiation then I would bet on cracking as well.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: 316 Chloride Cracking - Short Duration Exposure



316L is limited to a few parts ppm (grams per liter) for useful lifetime, low pH, just a few hours even with stress levels below a 1000 psi,Hast. C works

RE: 316 Chloride Cracking - Short Duration Exposure

1 ppm = 1 milligram/liter.

RE: 316 Chloride Cracking - Short Duration Exposure

Quote (theleftcoast)

our normal producing conditions are no problem for 316L

The Nickel Institute application domain for 316L is based on the complete absence of H2S, so you may wish to rethink that statement. One element of the rethink could be an examination of the stresses experienced by the screens. Generally, they are not highly stressed items and it could be that the cold work in their forming is not overly severe either. It would be expected that cracking initiates from sites of pitting, so pitting might be the critical parameter.

Literature and real life can be two different worlds. Does your "field experience" include an assessment of the pitting behaviour?

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

RE: 316 Chloride Cracking - Short Duration Exposure

(OP)
EdStainless and SJones - After exposure of our test samples to steam conditions (~250 hours, 50g/L NaCL, 200-220C, pH 8-9), examination revealed no pitting or cracking. Based on what you both have said, cracking may follow after pitting is initiated. That is new information to me and very helpful.

SJones - The combination of H2S and chlorides under producing conditions hasn't resulted in problems for us (oil/water/gas at 100-115C, 20-50psi CO2 partial pressure, 100-1000ppm H2S, and water with 20g/L NaCL). There is data in the literature under even more severe producing circumstances (5% NaCl, 200-300F, 1.5psi H2S partial pressure) that have not resulted in cracking problems with 316. The paper is NACE 06156 -"Operation limits for austenitic stainless steels in H2S containing environments".

Thank you all for the discussion. I am learning a lot from your comments.

RE: 316 Chloride Cracking - Short Duration Exposure

I have found that H2S is not an issue with austenitic stainless until you get to very high concentrations.
H2S actually helps since it will assure that there is no oxygen.
pH and temp are critical, and it needs to be actual downhole pH, with CO2 you will get down to ~4 if pressures are high.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: 316 Chloride Cracking - Short Duration Exposure

water with 20g/L NaCL is too much. The possibility to have SCC is great within few hours.

RE: 316 Chloride Cracking - Short Duration Exposure

@theleftcoast my comment was related to your premise that producing conditions are within the application envelope of 316L shown in Nickel Development publication 10 073. Since this envelope is based on the absence of H2S, then the argument is open to discussion. You might also like to refer to ISO 15156-3, Table A.4 where it can be seen that it would support your observation of no failure, albeit showing 316 and not 316L. This table has been grandfathered in from NACE MR0175, of some past vintage prior to 2003, meaning that it is probably empirically based. Conversely, the environment limits shown in the other ISO 15156-3 table applicable to the screen, Table A.2, are not tablets of stone if documented service experience demonstrates satisfactory performance. Since these limits are generated from testing at stresses approximating yield, the supposition that the lower stresses experienced by the screen being beneficial still remains.

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

RE: 316 Chloride Cracking - Short Duration Exposure

(OP)
@SJones - I pulled up ISO 15156-3 and read through the sections related to austenitic stainless steels. Thanks for the reference. If applied stress is related to chloride cracking thresholds, has anyone attempted to scale cracking thresholds measured at high stress levels (say 1.0 x yield or 0.9 x yield) to much lower stress levels (say 0.1 x yield)? Just curious.

RE: 316 Chloride Cracking - Short Duration Exposure

tlc, I did a bunch at testing at various stress levels on highly cold worked 6%Mo SASS.
If saw what looked like a threshold value for CSCC.
Working from memory I recall that nothing below 30% yield cracked.
But remember, this was high strength material.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: 316 Chloride Cracking - Short Duration Exposure

@theleftcoast From a crack propagation point of view, try a Google search on the terms "316L" + "KISCC"

Steve Jones
Corrosion Management Consultant

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

All answers are personal opinions only and are in no way connected with any employer.

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