Chlorides under acidic conditions: what is the most cost effective piping material? 2

[guerky]

I have highly agressive streams that causes frequent pitting corrosion problems in the piping. I would like to change it in order to extend the lines lifespan, as well as improve the process safety and reliability.

The streams ranges from basic pH (12) to highly acidic (5% HCl). An aqueous phase has high chlorides concentration (>10%), and an organic phase has some key components that are believed to enhance the corrosion.

All the equipmente uses SS316L (for some reason, the reactors seems to be least affected), and holes in the piping are very common.

The problem is:
Glass could not be employed due to NaOH use around the process.
PTFE lined carbon steel pipes would be ideal, but cant be used due to operations under vacuum conditions.

There are some "cheap" stailess steel alternatives better than the 316L for hydrochloridric acid/chlorides?
All the "recomended" options reserached so far fell into special alloys range. Those are not very cost effective options.

Thank you all in advance.

 

[MJCronin]

I suggest a cost comparison ....

Take an example system, price it as both a flanged PTFE system (such as Resistoflex) and as a Sced 10 C276 system make sure that you include the cost of valves.

IMHO, due to the shell instabilities at larger diameters and at elevated temperatures, Sched 5S piping should never be used.

MJCronin
Sr. Process Engineer

 

[moltenmetal]

Durco and Xomox fully lined plug valves are a very economical pairing with lined pipe- definitely cheaper than any alloy C offering..

If you need to pull high vacuum for process reasons, lined pipe will be a poor choice because there are too many joints to leak and too much area through which gases may permeate. But of course, pipe which is corroded is tough to pull a vacuum on too...

 

[ehbadger]

Is normal ops under vacuum or is vacuum just on occasion? As others have stated PTFE pipe is available full vac rated through 12" sizes. If you run constantly under a deep vacuum you might run into some troubles but otherwise PTFE is fairly capable.

Also as moltenmetal mentioned, fully lined plug valves are available through that size range as well as lined ball valves. Flowserve (Durco) and Xomox generally make a solid product.

As far as the trace heating issue, I don't think that should cause much "spot heating" issue if you properly insulate the PTFE pipe (which you should do anyway to prevent permeation corrosion).

 

[guerky]

It's a multipurpose plant. Vacuum is used on some transfers with one product and distillations with the other, so the vacuum isnt intensively used. Also, the maximum vacuum barely reach 100 mbar, we're not talking about high vacuum. My main concern was about operational errors allowing the maximum level be reached inside the pipes (pretty possible due to the low level of automation).
I've done some research about lined tubes myself. Thanks to the posts too, I've became convinced that with Sched10S on 2" or even 3" pipes i dont have to worry too much about liner colapse, even in the worst case scenario (3 inches pipe with 100 mbar of vacuum).

I landed on the end of this project and almost all the material is already bought. I can request only a pipe section of a few meters for the worse region. But it will serve as a probe to the vacuum usage and the effect of the trace heating.
When done, I'll post the specifications and the outcomes.

Thanks for all the responses.