Piping for Sulfuric Acid 1

[fastphantom]

I need to dose low flow rate 100L/h 98% Sulfuric acid through 60m of tube/pipe.

Would appreciate help in pipe material selection and for this low flow a pipe size that won't be effected too much by expansion and contraction in and out of the sun.

Any thoughts

Thanks

 

[waterexpert]

PTFE strongly recommended. Pretty much all other materials will go on the bends.

 

[hacksaw]

what is your acid purity level, temperature and pressure?

and what is the basis for solar heating. In some parts of the world, the metal temperatures can be up to 45-50 Deg C.

 

[BRT549]

You are justified in being careful with heating of plastic piping - it can really expand and contract in the pipe rack. Also, 98% sulfuric has a fairly high freezing point (30 F), so if it is outdoors you may want to switch to 93% sulfuric in the winter (freezes at -31 F).

You can run 98% H2SO4 in carbon steel with no problem. Sulfuric acid will only get really aggressive to carbon steel at 88% and below. Make it an all-welded system and use teflon gaskets like Garlock Gylon. Use Schedule 80 heavy wall pipe, and if it is seamed pipe put the seams on top. Keep the velocity below 5 feet per second.

If you want to run plastic pipe, Kynar (PVDF) is less expensive than PTFE (tefon) and has more structural strength, so you don't have to support the piping as often. Still, the industry standard is carbon steel for 98% sulfuric acid, and it will give years of service.

 

[Metalguy]

BRT549,

You have to be careful using CS with sulfuric. While 98% shouldn't be a problem at low velocity, anything less than ~ 92% can be bad unless the temp. is no higher than ~70 deg. F. 5 ft/sec. may also be a bit fast at lower conc. and higher temps. You frequently find a lot of whitish iron-sulfide in piping, and it can cause local higher velocities.

CS does much better for storage tanks than piping, but in THIS case he has low vel. and purer acid.

 

[fastphantom]

Thanks for the comments.

Hacksaw, the acid purity is 98%. Basis for solar heating? My concerns are at this low flow rate 100L/h, if a 20mm line was used the velocity will be very, very low (0.085m/s). So when a black poly pipe expands and contracts in a pipe rate, it will significantly effect the flow rate out the end.

Cheers

 

[ccfowler]

BRT549,

I don't think it is a good idea to put pipe seams at either the top or the bottom in any line, and I would particularly avoid these positions in a line where corrosives are being handled. When the flow rate is very slow or stopped, these are the most likely positions where localized "odd" concentrations (or dilutions) may form and produce severe corrosive attacks. The seam only makes these potential problems more likely to be troublesome. Having experienced such "entertaining" problems, I would always be very insistent about avoiding these seam orientations.

waterexpert,

I believe you are correct in recommending "Teflon" tubing for this service despite the cost and strength issues. The potential for high temperatures is reason enough for this selection. (Failures and their consequent costs assuredly would make the initial savings of other options appear unattractive.)

I would want to consider running the tubing inside sections of smooth interior steel pipe for support and mechanical protection. (Be certain that the ends of the support tube segments are well rounded to avoid scraping damage to the "Teflon" tube exterior.)

 

[kenvlach]

See the page 'Handling Sulfuric Acid' at

http://www.resistoflex.com/sulfuric.htm

These people seem to be the experts for plastic (PP, PVDF, PTFE)-lined pipe. Also, excellent source of info on sulfuric acid solutions: physical & thermodynamic properties.

The Chemical Resistance Ratings table (from menu on LHS of page) gives the temperature limits for the various plastic-lined pipes & fitting for various chemicals.

 

[waterexpert]

I recommended PTFE based on extensive experience of trying other materials on dosing lines in water treatment plants with 98% sulphuric. Corrosoin resistance tables may show other materials to be suitable, but we tried a number of them, only to have problems at bends and fittings. Seamless PTFE lines were eventually used, and are still doing good service 10 years later. I have to say though that temperature problems were the other way, as the plant was in Scotland!

 

[hacksaw]

The question of acid purity does not refer to its concentration but its level of contamination.

That said, you should used lined pipe, simply for the mechanical support.

Routing a 20 mm black poly pipe filled with strong acid in any facility is unsafe.

 

[BRT549]

Guys,

I can't believe you are all recommending lined pipe or PTFE for this application. Sure, it will last a long time, but its installation cost is many times higher. If you are going to be profitable in industry these days you need to be mindful of gold-plating your plant. If the piping was running overhead through my office I might consider lined pipe.

I've worked in 3 chemical plants, all heavy users of concentrated sulfuric acid, and in all cases carbon steel is the material of choice. The plant I'm at now is a manufacturer of sulfuric acid (we have a Lurgi and a Monsanto Enviro-chem unit). Put safety shields around the flanges as per OSHA. Keep your velocity down to prevent washing off the protective layer at elbows and reducers. But don't spend an arm and a leg on an outdoor sulfuric pipe run.

 

[Metalguy]

Hacksaw,

When the "contaminant" in sulf. acid is water (even demin. water), the corr. rate of CS just skyrockets. Take a look at a graph that shows corr. rates vs % conc. and temp. with CS. Notice what happens below 90%. At 60% you can almost watch it dissolve!

 

[waterexpert]

If I were building a plant using large quantities of sulphuric acid, I'd be with you, BRT, but 60m of 5mm NB pipe isn't going to cost too much whatever it's made of.

PTFE works.

 

[waterexpert]

Actually, 10mm would be more like it, headloss and line velocity a bit high at 5mm...

 

[hacksaw]

Water is hardly considered a contaminant of sulfuric acid.
strong acid refers to all concentration, above 96% w/w.
Acid purity refers to its color, Fe content etc.

moale97 has indicate use of 20 mm black PE tubing(!).
I don't like the idea of plastic tubing for strong acid.
You have to support it, and protect it, identify it, etc.

At least lined pipe gets him away from plastic tubing(!).

While C.S. can be and is used, it is hardly a standard for strong acid.

It all depends on your corrosion allowance, temperature, impurities, concentration, flow velocity and how often you want to replace it.

 

[Metalguy]

Hacksaw,

Actually CS IS the standard material for sulfuric acid IF 9and only if) the concentration is over ~94% and under ~90 deg. F., with very low velocity for piping.

 

[hacksaw]

Metalguy,

I don't disagree, but when have you seen a "standard" acid plant...