Pump material class

[Sabergg1981]

Hi all. We have a flare knock-out drum centrifugal pump in an arrangement of 1+1, and hydrocarbon with 80000ppm h2s and 150000ppm chloride. Our design temprature is -100c . What class do you suggest?
Thanks

 

[Sabergg1981]

Seems its too hard or too easy for pump specialist here.

 

[LittleInch]

That's because it's really a materials question. I don't recognise the term "material class". Pressure class yes, but a pump doesn't really care what it's made from to do it's job so perhaps try on the corrosion or materials forum.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[LittleInch]

Looking at your duty it's probably something like super duplex or bronze.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[DubMac]

Listen to Little Inch.....Hitch up your pants and walk over to your metallurgist office and ask him what materials YOUR REFINERY specifies for those concentrations...most likely above x% of H2S, he will go to Super Duplex wetted parts, may get away with 316SS... I don't think you will find an API MAtl class that covers H2S "carte blanche"....

If you don't have a metallurgist or specs for same, then quit working at that refinery.

 

[Artisi]

" Seems its too hard or too easy for pump specialist here. " always a good way of ensuring free advice from the guys/ gals in the forum.

Following on from LittleInch and DubMac -- pick-up the telephone and call your local metallurgist or for that matter your local pump supplier, as it would appear that you are going to specify a pump unit at sometime.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Sabergg1981]

Thanks guys
we are wondering between carbon steel and duplex. So let's follow this discussion in material forum. I think it's a useful matter for all of us.

 

[Sabergg1981]

Dear Artisi

I want to make a technical talk about this topic. our material team insist on duplex but i want to know more and confirm their opinion .

 

[LittleInch]

You'll need to supply more details. Did you mean minus 100 c?

If so presumably no water... If 100 C then c stl would seem not to be correct, but you've only given us about 10° of the data to give you any informed advice. Give people the info and respond to their questions and they will help you. Avoid sarcasm or ironic statements.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[TenPenny]

"our material team insist on duplex but i want to know more and confirm their opinion "

I agree completely. When your in-house specialists have a preference, it's always a good idea to ask for advice over the internet.

 

[Artisi]

Well, if it's on the internet it must be true.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[mirghaffari]

Think about material class S6 with Nace certificate.

 

[nfinit]

I would suggest asking your material team for their basis and justification before trying to find reasons why they may or may not be incorrect. Seems communication may be important.

 

[curtis26]

I think I can help here and feel that some general discussion of pump selection outside mechanical design and fluid dynamics is perfectly welcome since it is involved in every pump selection.
Metallurgist require a fluid analysis of the process fluid (not just the H2S level and Chloride level) to calculate pitting indexes for proposed metallurgies. They also look at what the source of acidity or bases are (some materials will stand up to certain acids/based better than others so just the pH value alone may not be enough to determine the best metallurgy. They look at temperature since increases in heat increase the rate of corrosion, they look at oxygen leaves and the form of oxygen present since that too makes a difference in the rate of corrosion holding all other chemical in the process fluid the same. They also use imperial data on corrosion rates of different fluid on metals, and any field operating experience that is available. What they do is a lot more scientific that what is required for most pump sizing. With a few rules of thumb I can get the same recommendation as the metallurgist on 90% of the applications before they spend 2 hours running calculations. The truth is that I only go to a metallurgist for the 10% of the applications that I am not really sure on what would be the clear cut material of choice.

I start by finding out which metallurgy our vendors can offer for the application. Usually that only gives us 3-4 choices. It sounds like your choices are carbons steel and some grade of Duplex Stainless Steel (2205 Duplex Stainless Steel?)

The only material that I know that any research or standards groups have ever recommended for H2S is Super Duplex Ferilium 255 (this is listed in NACE recommendations). It comes exclusively from a foundry in the UK. I cost about 4 times more than other super Duplex Stainless Steels and has very long lead times. So I would never use that material. I would just follow what other are using for H2S and what my metallurgists recommend.

In general I would use Carbon Steel for fluid with less than 20,000 PPM chlorides. Likewise I would use a cast 2205 DSS for chlorides up to about 70,000 PPM. I know of applications where 2205 has been used for up to 150,000 PPM, but again that is a metallurgist question and so anything over 70,000 PPM that a vendor is proposing 2205 DSS is one of my 10% applications that I would send to the Metallurgist to verify. Typically I have been seeing our vendors offering 2507 Supper Duplex Stainless Steel for application over 70,000 PPM chlorides.

On the H2S side I would use carbon steel for fluids under 50 mg/L (aprox. 50,000 PPM) and have my metallurgist confirm any selection for H2S over that level.

 

[SJones]

Indeed, but what would your 'metallurgist' make of the -100 deg C minimum design temperature?

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.

 

[curtis26]

I must be reading this different than everyone else. When I specify a minimum design temperature it is a temperature about 25 deg C over what I think the maximum temperature of my application ever is going to hit in the worst case scenario. For example, if my application is likely to operate at 40-50 deg C. I could specify that the minimum design temperature must be 75 deg C then if they have a pump rated for 100 deg C that is fine, but a pump rated for 45 deg C would not be.

I would NOT submit corrosion data on a metallurgist based on a minimum "design" values that is factiously high, but rather the average temperature of the application so I don't end up with material recommendations that are way off base with what I actually need. So, I simply eliminated the "design" temperature. Since the process temperature was not given I threw it out of any consideration at all.

My attempt was to give some practical advise on selecting materials with high Chloride and high H2S, NOT to go off on a tangent for something that I thought had to have just been poorly typed. 100 Deg C is very common for a minimum design temperature so either CS or DSS would be fine it that were the actual requirements.

The only pumps designed for 100 deg C below freezing are Cryogenic Pump. Those would require special consideration for material selection. The Titanic had a hull built out of carbon steel and in the 40 degrees below freezing artic water we know that it was quite brittle. So why don't present day ship hulls built out of Carbon Steel have the same problems in artice water? It is because there are hundreds of grades are carbons steel all with different Charpy test values. there are some low temperature grades of Carbon steel. I personally don't know if any are rated down to -100 deg C. and think that Duplex Stainless steel would be a lot more brittle in cryogenic applications, but to answer your question, the metallurgist would have to look at how brittle the proposed grades of Carbon Steel and the proposed grade of Duplex Stainless Steel. I would think that at -100 C that the properties of the metal at the design temperature would be more important than the corrosion a resistance.

 

[SJones]

They would be equally important because they are addressing two (out of many) different degradation mechanisms. The -100 deg C, or whatever temperature without the 'guess factor' margin, will be achieved during a flaring scenario which is typically low pressure and typically infrequent. The originator could thus attempt a fitness for service approach and determine a minimum allowable temperature to see whether -100 is within the realms of possibility for the materials selected, but some people might say that's not inherently safe design to have start off on a fitness for service basis. DSS at -100 deg C will probably have the toughness of a carrot. So, until the originator gives the full process data required by ISO 15156 to ascertain SSC resistance, they are staring at an austenitic nickel alloy to have both the sulphide stress cracking resistance and the brittle fracture resistance.

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.