Suitable Material for 50% Sodium Hydroxide
Suitable Material for 50% Sodium Hydroxide
(OP)
I require some assistance in determining a suitable material for hot sodium hydroxide processes. The material we are currently using as the diaphragm wetted parts for our Fisher Rosemount level transmitter is Hastelloy C276. The level transmitter is used in a hot caustic service (150oC, 56% sodium hydroxide, -34 kPag), and recently we found the diaphragm had been chewed out. Looking at chemical compatibility charts, we found half the literature indicating Hastelloy C as a good to excellent material for 50% caustic. However, there isn’t much information for caustic services above 80oC. Could we use Inconel 600 or Monel 400, instead of Nickel 200? Thanks.





RE: Suitable Material for 50% Sodium Hydroxide
Put as much distance between the transmitter diapragm and the pipe, just to reduce heating and to take advantage of non-flowing conditions.
I don't think Hast.C is a good candidate for hot caustic solution. Nickle sounds like a better choice. Hot caustic is notorious for hydrogen embrittlement etc.
The ASM handbooks are a good source.
RE: Suitable Material for 50% Sodium Hydroxide
Caustic causes stress corrosion cracking and this is a grave problem under cyclic loads.We have used Monel metal in anhydrous caustic and 300 deg.C conditions but the thickness was 2mm (2mm monel on SS 304 in a process reactor) and never had problems.But the loads are noncyclic.At 50% concentration the boiling point is around 80deg.C. That is why the data is not generally given.
Just a thught - Why can't you use non contact type level sensors?
RE: Suitable Material for 50% Sodium Hydroxide
Non-contact might work too, but you are going to get a lot of solids carry-over (crystal build-up) with the liquid so near boiling.
RE: Suitable Material for 50% Sodium Hydroxide
RE: Suitable Material for 50% Sodium Hydroxide
RE: Suitable Material for 50% Sodium Hydroxide
Thanks.
iidris
RE: Suitable Material for 50% Sodium Hydroxide
RE: Suitable Material for 50% Sodium Hydroxide
You are right the capacity is 50,000 mtpy.
RE: Suitable Material for 50% Sodium Hydroxide
When the temperatures get high in hot caustic service, the only suitable material is pure nickel....Alloy 200....it is very expensive
There is much information, including published research papers and reports, available on the internet regarding caustic soda (NaOH) systems.
Based on the conditions you describe, neither alloy 400 or 600 is acceptable.....according to the document noted below
http://
Based on Table #2 of the NIDI Report, Alloy 600 and alloy 400 should provide acceptable setvice for 50% solutions only up to 125C
Hope that this helps.....
My opinion only
MJC
RE: Suitable Material for 50% Sodium Hydroxide
Dont get shocked. i am operationg a caustic soda plant which has 465 TPD caustic which means more than 180000Tons.we are using membrane cell tchnology.
bye
RE: Suitable Material for 50% Sodium Hydroxide
RE: Suitable Material for 50% Sodium Hydroxide
Good link. However, if you read further down the article, it contradicts your conclusions. Indeed, Alloy 600 and 625 can be used at much higher temperatures, with concentrated caustic. The article states on p.7 that Page 8 suggests Incoloy 625 can be used up to at least 320°C.
From p.5, it appears that Alloy 400 is indeed limited to less than around 200°C (Stress corrosion cracking occurs with 300-400 psi steam), so may not be suitable at 150°C.
Figure 4 shows lower corrosion rates for Alloy 600 than Alloy 200 with 50% caustic at 150°C.
RE: Suitable Material for 50% Sodium Hydroxide
Please advise a company/companies which could be interested in designing a 50,000 MTPY plant.
Thanks.
RE: Suitable Material for 50% Sodium Hydroxide
RE: Suitable Material for 50% Sodium Hydroxide
In anhydrous caustic, 98 % and over 200+ °C, Nickel 201 for tubes and plates, silver for critical points (seat and trim of CV on concentrate at 300 °C). Silver is the best choice for extreme critical conditions, but not really cheap, I dare say.
As far as I remember, Ti is less suitable than Nickel, and has similar price - so it is not used.
Bubbling in hot caustic is dangerous as NaOH carbonates promptly to Na2CO3, and air carries CO2. To bubble, use only anhydrous nitrogen - but I suggest to use other systems.
NaOH plants : the big names are DeNora, Asahi, Eltech, Uhde - sorry if I forget some.
RE: Suitable Material for 50% Sodium Hydroxide
If you can find the old A-L Blue Sheet it has some good caustic data.
= = = = = = = = = = = = = = = = = = = =
Corrosion never sleeps, but it can be managed.
http://www.trenttube.com/Trent/tech_form.htm