Design of Chemical Lines 1

[jph90]

Hi there,

Am in the process of developing a design for new bulk caustic (50% NaOH) and sulphuric acid (98%) storage and handling systems.Both will be stored and distributed at ambient temperatures

I am looking for a reference document that is useful to guide in the designs of these systems, or perhaps just input from you guys on the most critical things to consider. I know things to consider are 1) local legislation for handling of hazardous substances and 2) ASME B31.3, however i find the latter an un-easy read.

Things I am looking for help on:
-Material selection (looking at SS 316L Schedule 10 for both. Recommend PVC by a supplier for sulphuric but am skeptical over long runs and UV exposure. Do not plan to use carbon steel)
- Guidelines for design velocities (best practice for corrosion protection etc)
- Guidelines around general pipe run design e.g. fall to storage tank or fall to end users, secondary containment requirements (if any) that may apply to pipework
- Qualifications welders should have e.g. WPS, do they need to be certified to ASME IX welding?

Appreciate the help and let me know if i need to elaborate on anything

 

[EmmanuelTop]

On H2SO4 topic, Dupont FAQ is a good read: H2SO4 FAQ
Caustic, see: OXY Handbook and the image below.

On top of that, browse Eng-Tips forum (use Search method). There is plenty of threads on the subjects.

If you have impurities, things get more complicated.

Dejan IVANOVIC
Process Engineer, MSChE

 

[shvet2008]

I worked in a chemical plant with 10% NaOH and 94% H2SO4 for years. Some of my own advices (designers often forget about this):
1. Caustic can freeze at ambient temperature. Heat tracing (usually with steam) should be provided.
2. Caustic deposits always appear inside pipes in spite of 10% NaOH was stored. This deposits could be removed only by steaming. Utility connections should be provided. Long pipes are hard for steaming - the more fittings the better (see below).
3. There were leaks everywhere in caustic pipes. All fittings and insulation were coated with NaOH salt. The less fittings the better.
4. H2SO4 can freeze at ambient temperature (below +10°C). Be sure that H2O impurities are technically eliminated. If you can't avoid H2O potential impurity and have enough money - heat tracing would be desirable (usually electric cable).
5. Think better how to clean H2SO4 storage vessel for maintenance. H2SO4 storage vessel dead space was a problem. If you can't avoid this - caustic neutralization should be provided. H2O washing leads to guaranteed leaks.
6. NaOH and H2SO4 leaks are usual and they are very dangerous for personnel. Pipes should be traced low to ground - below people's eyes. If it is impossible there shouldn't be fittings.
7. In spite of H2SO4 are not volatile (ha, academic view) there are H2SO4 vapor inside the production facilities. Very good ventilation is desirable. I lost ~4 teeth during ~5 years. A tooth a year. The same for sense of smell and taste (partially).

 

[EmmanuelTop]

Thank you shvet2008, some good advice there. A word of caution on heat tracing, though - we have had numerous problems in H[sub]2[/sub]SO[sub]4[/sub] Alkylation Unit piping, caused by local overheating of the Sulfuric Acid which then caused frequent piping failure. Steam is probably not the best way to heat trace chemicals that become very aggressive at elevated temperatures. Self-regulating cables worked much, much better.

OP, remember to have a specialist looking at location and quantity of safety showers/eyewash facilities. They are typically according to ANSI/ISEA Z358.1.

Dejan IVANOVIC
Process Engineer, MSChE

 

[mk3223]

Check the local Code requirement, the secondary containment may be required for the Chemical storages of NaOH and H2SO4, including the tank/vessel and pumps. The proper coating is to protect the concrete from chemical corrosion.

 

[EdStainless]

There is also the MTI MS-1 on Material Selection for Sulfuric Acid.
It is very complete.

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P.E. Metallurgy, Plymouth Tube

 

[MJCronin]

Consider a tank sized for immediate dilution when caustic is delivered.... if suitable for the process.

Dilute to 22-26%

This makes many of the storage/heating/handling problems go away.

MJCronin
Sr. Process Engineer