Materials selection for Pump (32% Caustic)

[jiang1976]

I have fresh caustic feed pump (metering pump). It has 32% caustic. Can I use Carbon steel for it.

The design temperature 65C. If carbon steel selected, it should be PWHT. right?

Thanks.

 

[Unotec]

By caustic I infer you mean sodium hydroxide, right? If so, I would strongly suggest against it.
My preference is to use this page:

http://www.coleparmer.com/techinfo/chemcomp.asp

or

http://flw.com/datatools/compatibility/

Sometimes they tend to give slightly different results but I find them to be a good guideline

 

[Artisi]

Do you have an existing pump or is this a new pump selection. If the former ask the manufacturer of the pump if the latter give the detail to the manufacturer and ask for their recommendation.

 

[jiang1976]

unotec, Artisi .

Thanks.

unfortunately, this is a new selection. I can not find the materials in API 610.

 

[Unotec]

We have several carbon steel pumps doing very high pH's. The internals or rotary assemblies were replaced for 361SS, however these would probably be big for your aplication (Gormann Rupp T4's). For a metering pump you might want to try ceramics, plastics, polypropilene.... Talk to your pump suppliers, there are lots of options

 

[pumpking]

An Engineered plastic pump is more than sufficient. We have a number of applications of Polypropylene on such diuties, however, at a temperature of 65'C would suggest you go to ETFE, PTFE or something like that. We use 60'C as the max temp for PP as it is heading toward its top end of temperature, and with the mechanical stresses that a pump generate, it is well worth upgrading materials to avoid potential long term problems.

What flow/head are you looking for ?

Ash Fenn

http://www.cdrpumps.co.uk

 

[jiang1976]

Thanks.

I will talk with our client.

 

[itdepends]

Are you heating the caustic up or is it supplied at 65degC max? If your heating it up your major risk areas are around your heating system (the system itself and the outlet nozzles).

Otherwise- if you've got a relatively stable temp carbon steel should be fine at that temperature- PWHT is recommended by the NACE chart- particularly if you expect to run that hot all the time

 

[hbw]

Carbon steel will have 20-50 mils per year of corrosion for 32% Sodium Hydroxide at 65 C.

Austentic stainless steels (304 SS, 316 SS, Alloy 20) should not be used above 140 F(60 C)due to onset of stress corrosion cracking. Nickel 200 is used above 140 F.

At 65 C you could use a teflon diaphragm metering pump with teflon ball checks.

Brands are American Lewa, Prominent, Bran+Luebbe, Milton-Roy, Pulsafeeder