Caustic Lines

[NickVil]

Hello,
I want to know if somebody knows about installation criteria for piping carrying caustic. I mean, if there is any rule forbidding the layout of caustic lines on the piperack.
I believe that installing the piping at grade is dangerous not only because of the tripping hazard it creates but because it is exposed to being hit during movement of heavy equipment during maintenance.

 

[Montemayor]

NickVil:

While Caustic Soda (Sodium Hydroxide) doesn't burn or explode, I would consider it a hazardous substance - even within the confines of an oil refinery.

I have made it my policy to route caustic solution pipes totally away from areas of potential human traffic. This solution will cause severe and dangerous burns. It attacks the human cells with ferocity and causes total blindness if it hits your eyes. It will leave you with permanent scars -if you survive. Overhead piping particularly poses a very dangerous scenario due to leaks falling directly upon human traffic below. All piping carrying the stuff should have a "healthy" corrosion allowance - and be totally butt-welded throughout its routing.

I don't know of any rules except my own: Never run caustic solution piping in a piperack with a potential for personnel below. I would always route the piping away from traffic areas and color-code it for quick and easy identification.

 

[sshep]

What is the concentration and temperature?

I think a high integrity piping system is an important consideration. There are well documented corrosion rates and pwht requirements for carbon steel at given concentrations and temperatures, and nickle is recommended for severe service. Insulation (freeze or heat conservation) can sometimes lead to pipe problems, especially cases where steam tracing is used on caustic lines due to the potential for local hot spots. Applying good initial coating and insulation specification is a must. As age takes a toll on carbon steel piping, leaks are always real possibilities if the piping is not routinely inspected and maintained. As to routing pipe in rack or grade, I know of nothing except such as common sense dictates in regards to the hazard.

best wishes,
sshep

 

[NickVil]

Thanks Montemayor and sshep for your comments.
The fresh caustic is at 20°Baumé and 25°C. Part of the pipe is installed at the side of the traffic areas and part is over the traffic areas.
I know that units like Alkylation contain most of the piping carrying Sulfuric acid or Hydrofluoric acid in large quantities: there are several rules from API and EPA for the design of these plants but none mandates to run the pipes on the ground.

Regards

 

[sshep]

NickVil,
Your conditions are pretty mild service. Your freeze point (-17C), carbon steel corrosion rates (0.001 IPY), and embrittlement (PWHT may not be required) indicate a piping system which is uninsulated with proper priming and coating, and otherwise designed and installed per this service.

You seem to know your hazards so I would trust to your good judgement with respect to routing. My own experience with hydroflouric acid is that HF is a significantly greater hazard to which we apply standards of catagory M fluid per ASME 31.3, and also restrict access to areas where used (via color coded curbing and pipe markings, entry/exit through a decon building, specialized ppe, etc). Caustic we do not treat so rigorously but still have specific pipe standards and procedures given the hazards of the fluid.

best wishes,
sshep

 

[PAN]

sshep,
I understand that NFPA health rating of caustic solution is 3. My consultant used to advise that health rating 4 should be considered as category M fluid per ASME B31.3

NickVil,
In my experience, some parts of caustic line may be placed above grade near road access. However, the barricade is necessary.

 

[NickVil]

Thanks sshep!
I suppossed NFPA that you mean is the NFPA 704.

Regards

 

[mbeychok]

NickVil:

To follow up on the excellent comments by sshep, steam tracing of caustic-carrying lines (carbon steel lines, in particular) can be quite dangerous if the tracing lines touch the caustic lines. Hot caustic causes embrittlement of any weld joints in the caustic lines. Hot caustic can actually cause carbon steel piping to literally "fall apart". It is good practice to wedge pieces of insulation between the steam trace lines and the caustic lines so as to prevent the tracer lines from touching the caustic lines.



Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[Ashereng]

NickVil,

At an integrated pulp and paper mill that I worked at, the caustic was contained as a solid in totes (carrried by the fork lifts) and moved to just beside where it is needed. There, it was prepared and put into whatever vessel needed it.

I did not recall seeing very many caustic lines over head, but then again, it's been a while.

From the response above, it seems like there are not specific codes preventing caustic pipe routing, just good design and plant practices.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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[MJCronin]

Nick...et al..

I am a bit surprised that nobody has metioned double-walled piping systems......

While I agree that caustic piping is dangerous and should be carefully routed to avoid injury, I also know that there is sometimes no other choice than routing via a pipe rack.

Personally, I do not see a problem with a double walled piping system routed within a pipe rack. This can be combined with an interstitial leak protection system and "all welded" piping construction to provide a reliable system.

Comments ?...Objections ???

-MJC

 

[drjeckles]

Generally, my "personal rule of thumb" is to try and avoid having strong acids and bases overhead where they may drip on someone. If necessary, I would reccomend trying to avioid or minimized joints over areas where people an vehicles go. Also, one can have catch pans underneith such pipe racks that drain to one side. I personnally hate cringing every time a drop of liquid from the pipe rack hits me, grin. As far as regulations, I always like to ask one of our OSHA or Safety folks and have them chase down the appropriate codes.

About double containment pipes: While I find them an "interesting concept," because of fabrication and inspection issues, as well as the inability to properly inspect the inside pipe, I would investigate this thoroughly (with sources that are not selling them and do not have a vested interest in defending a very expensive expenditure) prior to considering this particular option.

I would rather use a higher grade of material along with an automatic tube or pipe welder, than spend this money on piping that will be more difficult to install and inspect.

 

[djack77494]

I know facilities where I've worked that used caustic did NOT run the caustic lines overhead. I never really inquired as to the reason, and can't state that it is or isn't required. It does seem to be good practice, however, especially if the lines are traced (very common).

Double walled pipe, while interesting, are way too expensive in my experience to be considered an option here. I've worked with much more challenging situations with specialty chemicals where jacketed piping was a strong contender for a solution, but only after its extremely high costs were justified.
Doug