open to atmospere caustic / HCl vessels

[apiguy]

Hello once again,

I have another question for solving. My designers are designing vessels for 14.9 psi to keep from using an ASME code stamp. The problem is this:

These vessels will be located in the hot tropics in direct sunlight. There is to be a 2" open vent on each vessel as over pressure protection.

Question: Will condensation form on the inside of the vessel wall due to normal heating and cooling from the sun therefore diluting the HCl and Caustic which would increase the corrosion rate?

Evaporation and dewpoint calculations are totally unfamiliar to me.

Please advise.... Richard Schram
Mechanical Integrity Specialist
Pharmacia Global Supply Arecibo-P. Rico
rschram@pharmacia.com

 

[MJCronin]

apiguy,

Answer: probably...... Most tanks in the tropics are painted a light color to mitigate this effect.

As an apiguy, I am sure that you are aware of the design standard API-2000 that sizes vents based on several criteria...... This guideline can be used to evaluate the 2" vent line size.

Some companies make dessicant driers for tank vents

Try

http://www.drytechinc.com

as a start.....

MJC

 

[twjag]

The primary problem with breathing through an open vent is the accelerated corrosion of the vessel vapor spaces due to the combination of the moisture & product vapor to create weak acids & caustics. Solutions are: add additional corrosion allowance (in design) to extend tank life; provide properly engineered nitrogen blanketing system with conservation vents; use of properly sized dissicant breathers with conservation vents; or a combination or nitrogen blanketing & dessicant breathers. Emergency venting (pressure & vacuum) must be provided for the later two options. Among the disadvantages of dessicant breathers can be: high maintenance, replacement dessicant costs, & dessicant fouling if reverse (in & out) breathing allows product vapors to flow through dessicant. We have designed a number of successful systems with combinations of nitrogen blanketing & dessicant breathers. The dessicant breathers are installed upstream (atmospheric side) of the normal vacuum vents, which isolates them from the product, & reduces frequency of dessicant replacement. There are a number of vendors that suppy direct & pilot operated gas blanket valves, most for use on large tanks, but few with valves with small flow capacities for smaller volume tanks. For smaller tanks try Protecto Seal (USA) for a nice line of gas blanket valves. Imperative is to retain a knowledgeable engineer to properly size blanket & vent valves.

 

[apiguy]

MJCronin-

Unfortunately, our vessels are painted pretty much like they are everywhere else....Dark Blue Caustic, Dark Red HCL.

twjag-

Your information is exactly the concern I have, although I cannot convince the designers that a corrosion problem may exist.

Thanks for all the information guys, I am forwarding it on.... Richard Schram
Mechanical Integrity Specialist
Pharmacia Global Supply Arecibo-P. Rico
rschram@pharmacia.com

 

[ghopkins]

apiguy,

Why don't you build the tanks out of fiberglass/vinyl ester and be done with it? You can have tanks built to standards - Section X or RTP-1 - and not "stamp." This type of construction, if properly fabricated, can be resistant to almost any concentration of NaOH or HCl to 150F. If higher temps are needed or there are dissolved organics, fiberglass can be mechanically bonded to a thermoplastic (polyolefin or flouropolymer) liner to give even better corrosion resistance.

Let me know if you want more information about this. I know someone who builds these type of tanks.

Greg Hopkins