Corrosion protection for Sulfuric Acid tankers 1

[erdyne]

Dear fellows,

I am working in a chemical handling company. We are mainly transporting H2SO4 and HCl by chemical tanker trucks. Recently, we measure the thickness of the tankers, we notified that there is quite noticeable thinning after using the tankers for 6 years. (The material used for tanker steel is 304) Is there anything you can recommend overcoming this problem? Type of rubber lining or any other solutions?

Sincerely thank you

 

[EdStainless]

H2SO4 will have almost no effect on 304 if it is highly concentrated.
Diluted H2SO4 and any HCl will be highly aggressive.
There are lots of different coatings used in acid handling.
Most of them are either based on rubbers or phenolics.
Such coatings are very susceptible to damage, but they are a lot less expensive than an entire tanker.
There are specialist manuals on handling these acids which will give details on acceptable coatings.


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P.E. Metallurgy, consulting work welcomed

 

[ER_Azza]

H2SO4 with air space will chew up 304SS. Especially where the acid level is. The interface between liquid and air space (assuming with humidity) will dilute that portion.
Teflon coating in an option

 

[erdyne]

Dear Gents,
Thanks for your replies. As an update,
- We are advised to install vacuum valve onto the tankers to stop the effect stems from humidity.

Regarding teflon coating, do you think it is flexible enough when subject to vibration due to movements of the trucks?

 

[ER_Azza]

Teflon (and PVDF) is flexible. But the concern if it will adhere to the metal tank.
Previously, not fantastic. Have not been in the H2SO4 game for awhile.
You might want to check if presence technology have improve since.

My suggestion, do regular UT on the tank(s) where the acid level sits during transportation.
That would give you a good indication if the vacuum system is doing its job.

 

[MJCronin]

My thoughts..

1) Tanker trucks transport and deliver concentrated sulfuric acid. The customer then stores and MAY dilute the acid on hi site. Dilute sulfuric acid is typically not transported. The truck design is controlled by the weight of the acid. DOT MC-310, MC-311 and MC-312 stainless steel tank trailers all are used to transport sulfuric acid over roads and highways with a capacity up to 20 to 23 tons (weight limited to 2600 to 3000 gallons)

https://www.ausimm.com/globalassets...g-toolbox/norfalco_sulfuric_acid_handbook.pdf

2) Tanker trucks are not designed for long term storage of concentrated (~96%) H2SO4 ... Using these tanker trucks for long term storage invites dilution and corrosion (Interestingly, the OP ignores this point)

3) Hydrochloric acid tanker trucks are completely different than the H2SO4 tanker trucks. Linear Low-Density Polyethylene (LLDPE) or High-Density Polyethylene (HDPE) are commonly used as a liner as well as rubber linings

https://www.oxy.com/globalassets/do...s/chlor-alkali/hydrochloric_acid_handbook.pdf

MJCronin
Sr. Process Engineer

 

[shvet]

@erdyne
Note that any steel is not immune to >95% H2SO4 and only a thin layer of sulfates on metal surface prevents from immediate leaking. The only issue is how to last this layer longer by preventing:
- flushing by limiting of velocity
- dissolving by ensuring high concentration of H2SO4
- scrubbing by avoiding H2 grooving
- overheating by ensuring low temperature
I strongly recommend to bear in mind this sulfate layer when considering a vessel service life. Not steel grade or thickness.
Note than even air humidity may become a problem in some conditions causing a local corrosion in H2SO4 surface. I have met a H2SO4 vessel that had dehumidifiers installed on inbreathing nozzle. Note that even short-term sporadic fails in preventing means above lead to immediate corrosion (several minutes).

H2SO4 is one of the oldest product in chemical industry but inspite of this fact H2SO4 system proper design and operation is some sort of engineering art as details are crucial (e.g. washing procedure). Note that most plastics/resins are not compatible with H2SO4 (e.g. see chap. 9.2 Plastic Piping handbook).

More info you will find in NACE RP0391, NACE SP0294, and doc attached. Note that retailers consider PP, PVC, or HDPE for HCl storage and handling, not steel of any grade, - see doc attached for example.

Note that as per para. 2.3.1 NACE RP0391 SS304 should not be used for <93% H2SO4 what means only 2% safety factor for process variations - quite narrow as for my point view. Be sure that you always transport >93% H2SO4. Note that in you particular case the tanks deterioration may be related to an inadequate technical culture (e.g. inadvertent transport of diluted H2SO4).

https://files.engineering.com/getfi...0-2bb9113bcaeb&file=VEOLIA_Sulphuric_Acid.pdf

https://files.engineering.com/getfi...le=NI_CEB-1_Ni-containing_Alloys_is_H2SO4.pdf

https://files.engineering.com/getfi...fa-4efd-8d00-7f8e9e8a631c&file=Solvay_HCl.pdf

 

[MJCronin]

Again, the OP, erdyne, now ignores his original question ...

These people demand an immediate responses, then ignore them ... same as it ever was ...

We will get his statement about "how busy he was" or "family emergency" ... in about a week

Stay tuned ... the clock is ticking

(shvet gives a complete and informative answer... thank you!!)

MJCronin
Sr. Process Engineer

 

[erdyne]

Dear Collegues,

We ended up applying partial rubber coating where the most of the thinning down of metal occurs. (We applied to 5 trucks and I will keep watching to see how it will be)

Thanks for your efforts and sincere support.

 

[EdStainless]

Did you actually cost the entire inferior of the tanks?
If not you are likely to see accelerated attack in the areas that were left exposed.

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P.E. Metallurgy, consulting work welcomed

 

[shvet]

Curious to know how rubber-to-metal junction is made. As for me seems this design is just an imitation of protection as rubber is going to flake rather soon as metal under the rubber at the edge of rubber remains exposed.

Note that after this modification it became challenging or even impossible to control metal loss under rubber so bottom line of pros and cons is not obvious.