Stainless steel 1

[Pras]

Hello,

I need to offer products made in stainless steel grades F316L(ASTM A182), CF3M(ASTM A351)and CF8M(ASTM A351) for one of the off-shore projects. The fluid used is water having following contents :
Ion symbol concentration in mg/l

Sodium Na+ 30,390
calcium Ca2+ 9,383
Magnesium Mg2+ 1,021
Barium Ba2+ <0.5
Strontium Sr2+ 400
Chloride Cl- 66,930
Bicarbonate HCO3- 138
Sulphate So42- 954

Are above mentioned grades of stainless steel suitable for this application.

Thanks in advance.

Pras

 

[mcguire]

These materials are at the margin of resistance to this environment. Elevated temperatures ( above room temperature), stagnant conditions, or biofouling will result in pitting.
If any of these conditions exist, you must upgrade accordingly. To gauge how much you must upgrade consider that pitting resistance number=%chromium+3.3x%molybdenum+16x%nitrogen. Each unit increase in pitting resistance number buys you resistance for an additional 4C in temperature. Your 316 has an PRN of about 27. To be completely safe you will need about 35.

 

[Pras]

Mcguire,

Thanks for the reply. I need to have your comments on the following -

(1)The operating temperature in the above mentioned case is 60°C. Now based on your feedback, SS316 having PRN as 27 at room temperature (25°C, I presume) has corrosion resistance to the above mentioned fluid, which is just marginal. I could select grades like CE8MN (ASTM A351)having PRN 39.575 and CN3MN having PRN 45.97 for this application.
Frankly speaking, I do not know if other two factors mentioned by you i.e. 'stagnant condition'and 'biofouling' will be present on the site.
Would the alternate grades CE8MN / CN3MN be suitable for this fluid at 60°C.

(2) Could you please let me know if such information is also available in any standard or reference book.

(3) We also need to use Titanium ASTM B348 gr2 and a Inconel 718 ( Nickel plated) seal for the same application / conditions. Would they be suitable?

Thanks,

Pras

 

[mcguire]

PRAS
My information comes from conference proceedings which I do not think you will be able to find. Manufacturers of these grades of stainless should have accurate data, however. There may be reference books, but I am unaware of them. Try Avesta-Sheffield or Allegheny.
Since the temperature is 60C, I want you to stick with PRN of 45 or more. Stagnant conditions affect the amount of oxygen available which can agravate pitting. Secondly, biofouling can result in metal being covered with biomass, excluding oxygen and sometimes producing sulfurous compounds.
Both the Inconel 718 and the titanium 348 are acceptable.
I hesitate to recommend further without learning much more about the application. I hope this helps.
Mike McGuire

 

[Pras]

Mcguire,

Thanks a lot for your response.
I fully understand that selection of the material and its chemical compatibility with medium is an 'involved' and 'complex' task. I do appreciate your point of view that recommending materials without having first hand and complete iinformtaion on the application is dangerous.

I have already indicated to the customer that final acceptance / approval of the material for the given application is the responsibility of the user as he is in the 'best' position to judge the same. However we have no choice but to suggest him few alternate materials which might work on this application.

Now we have been aksed if Hatselloy-C would be suitable for this application. Would you please indicate if this material could work.

I'm extremely sorry for bothering you again. However at this point of time, only you could guide us in this matter. Please revert.

Pras

 

[mcguire]

Hastelloy C is very satisfactory, if a bit expensive.

 

[gunnarhole]

Gentlemen,

In the 1980's, when I first got involved in produced water treating systems the systems were moving away from low carbon steels to 316/316L. In the 90's we went to duplex stainless steels whenever the temperature went above 65 C. Once DSS became common I guess it was only a matter of time before people started asking for Inconel 600, Titanium, (and Hastelloy?)options. My opinion is that PRN's of 45 and over are pretty extreme for the service describd. By the way, what is the dissolved oxygen content? With the water analysis given, I would be more concerned about the radioactive scale that I was going to be facing.

Regards,

Gunnar

 

[Pras]

Gunnar,

Unfortunately the information on 'dissolved oxygen content' is not available from the customer. Could you please elaborate on ' radioactive scale' as mentioned by you. I also request you to explain your detailed views on the on the PRNs please.

Regards,

Pras

 

[mcguire]

One should assume,unless otherwise told, that the application of the material is sufficiently deep that dissolved oxygen is low, meaning that corrosive attack is stronger.
Gunnar is probably refering to the strontium, assuming it's a radioactive isotope. I hope that's not the case.
As far as high PRN's being extreme, I suppose that could be true, but having the assurance that corrosion will not compromise your project has a real economic value as does the exemption from the future costs of remedial actions against corrosion. How many of us have seen the carbon steel rebar going into the concrete of an expensive structure, like a bridge, knowing that the whole raodbed will be being replaced at a huge cost in the near future because a corrosion-resistant alloy wasn't used?

 

[mcguire]

I have written several FAQ's in the corrosion engineering section that summarize the pitting information.

 

[stanier]

A good reference is

http://www.nidi.org

website. Nidi also undertake consultancy services.

 

[mcguire]

Stanier
The quality of Nidi is clear. There are also people who have no particular product to sell. Be cautious and seek second opinions when it comes to expensive alloys as there are many good ones that don't have nickel. The resistance of ferrous alloys to corrosion resistance. It is due to chromium, molybdenum, and nitrogen; not nickel.
There are great alloys with or based on nickel, but its value is sometimes overstated by Nidi.