Suitable Material for 50% Sodium Hydroxide 2

[zwsa06]

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.

 

[hacksaw]

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.

 

[quark]

ZWSA06!

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?

 

[hacksaw]

We used bubblers on hot caustic, with taps in the side of the tank instead of the usual bubble pipe arrangement. The air purge protects the transmitter. Same idea was used to monitor the caustic density.

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.

 

[TrevorP]

Check out

http://www.hghouston.com/naoh.html,

it has some useful info. on suitable metals for Caustic at higher concentrations and temperatures.

 

[AEF]

Contact the tech. services department at Haynes International. I've used them in the past to solve problems on a caustic eductor that was made of B2 alloy and was failing every 6 months (changed it to C2000; no failures in last 4 years). They offer this service for free and respond quite quickly. Good luck!

 

[causticsoda]

I need some assistance re: design of a caustic soda membrane cell technology plant with 150,000 mtons annual capacity. Plant will be bult in Africa.Any suggstions.
Thanks.
iidris

 

[bewdley]

Hi causticsoda.... R U sure of the capacity? 150,000 MTPY is a hell of a big plant, more than 400 MTPD.

 

[causticsoda]

Thanks bewdley.
You are right the capacity is 50,000 mtpy.

 

[MJCronin]

ZWSA, Hack...

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://www.corrosionsource.com/technicallibrary/nidi/literature/pdf/10019.pdf

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

 

[all2win]

Hi Bewdley and CausticSoda,
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

 

[25362]

A question to quark: shouldn't the BP of a 50% NaOH solution be higher than 100[sup]o[/sup]C rather than the ~80[sup]o[/sup]C you have assumed ?

 

[TrevorP]

MJC,
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

Alloy 600 (NO660O) exhibits resistance similar to nickel up to and including the anhydrous product. It is favored for heating coils, because of higher strength at temperature then the pure nickel alloys. It...should be used in the stress relieved condition.

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.

 

[causticsoda]

Hi Bewedley & all2win,
Please advise a company/companies which could be interested in designing a 50,000 MTPY plant.
Thanks.

 

[natsamura]

Can titanium alloys be used for hot caustic soda handling? I need to evaporate 20% NaOH (from a membrane cell) to 50% for transport.

 

[bewdley]

Materials : As an evaporator designer, I have always used Nickel 200 over (simplifying) 40 % NaOH and 80 °C; Nickel 201 (low carbon) for the typical first effect, 50 % and 120 - 140 °C. 316 L for vapour pipes.
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.

 

[EdStainless]

Or use E-Brite. This 26-1 Cr-Mo ferritic stainless has long been favored for caustic service. It won't stress crack and can handle high Cl levels too.
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