Corrosion in rubber/plastic lined pipe by H2SO4 (Sulfuric Acid)

A. Hola Carlos !

You say sulfuric but don't give any concentrations ...

For commercial 96% sulfuric then PVC is the choice. It will last till the cows come home. Use Sch. 80 pipe. Very carefully cement on any moulded fittings and then, min. 24 hours later, BACKWELD !

PVC (the normal type l, grade one uPVC, not sewer pipe!) .... unlike fibreglass or stainless ... should accept all concentrations of sulfuric to 96% but the German Trovidur is said to be OK to 98%.

There is another option IF, IF, IF you are ONLY using 96% or stronger sulfuric ... and that's to use mild steel. However, this is based on the pipeline being completely full all the time ...if you have any 'high spots' where air can accumulate, then the steel will fail (Case history Globelite Batteries in Toronto where the outlet pipe failed and inundated the roof with acid ... and when the fire brigade wetted it down or used an alkali, the resulting exothermic heat ruined the roof.

A. Hi Osvaldo,

Short-n-sweet ... please go and have a look at letter 15290, "sulfuric Acid corrosion to stainless steel".

At least you gave me a concentration factor. Thanks. This is often NOT given.

I assume and hope that this line is buried? If not, as with all plastics, allowances have to be made for thermal expansion! From a structural viewpoint, one could armour PVC with fibreglass if at all necessary.

A. Hi Sami !

First off I know nothing about rubbers' corrosion resistant properties, in fact I'm amazed that that rubber could stand up to 98% sulfuric.

Re your problem, here are some ideas or thoughts.

Whereas mild steel is, I think, OK for 96% sulfuric, it ...along with stainless ... sure doesn't like being in diluted sulfuric, i.e., concentrations in the 30% to 80% range perhaps. Hence your drain is allowing 'air' which contains moisture to 'contaminate', i.e.. dilute your 98% as the sulfuric concentration gets reduced. Maybe this thinking applies to rubber, I don't know. Anyhow,use PVC.

If you checked out PVDF, I think you'd find that it is OK for 98% sulfuric albeit with temperature limitations ... certainly the even more expensive weldable fluorocarbons should excel.

Re your line between the two valves ... no idea. Are you using the same type of rubber and the SAME thickness of rubber? Is air being included? If so, see above.

Hence, if the piping between the valves is subject to flow variations, scouring, turbulence... then maybe the passive barrier is disturbed.

Long, long ago, the UK firm of I.C.I. proved that whereas Polyethylene is attacked by chlorine, if the wall thickness is heavy enough, then a passive barrier forms. In other words a super heavy 'wall' is chorine resistant. Lastly, I'm a great disbeliever. Having been 'bitten' by chemical engineers with the wrong info, I say to myself, ah, 98%? Really? Is that true? Perhaps it's only 96% ... in which case uPVC @ r.t. will be OK ... but the German Trovidur PVC people claim that their 'red' PVC is OK at 98% ... Germany after all invented PVC.

I hope that this is of some help. Cheers !

A. According to Resistoflex's chemical resistance search, PVDF (Kynar) and PTFE (Teflon) may be suitable pipe liners. Polypropylene is not recommended > 85% sulfuric at 80 °C. As you didn't give the temperature, I give the search results:

Maximum Temp. for Liner  PP      PVDF     PTFE     
Corrosive Stream   °F °C  °F °C  °F °C         
Sulfuric acid (10%)   225 110  250 120  450 230      
Sulfuric acid (16%)   200  95  250 120  450 230  
Sulfuric acid (30%)   200  95  250 120  450 230  
Sulfuric acid (60%)   200  95  250 120  450 230  
(60% -- sat. w/Cl2)    75  25  200  95  450 230  
Sulfuric acid (85%)   175  80  200  95  450 230  
Sulfuric acid (93%)    NR  NR  200  95  450 230  
Sulfuric acid (96%)    NR  NR  175  80  450 230  
Sulfuric acid (98%)    NR  NR  150  65  450 230 
(>98% fuming)       NR  NR   NR  NR  450 230    

Another source rates PVC (Type I) as B for 85-100% sulfuric at 72 °F, whereas Kynar, Teflon, Noryl, & Viton rated A's.

A. Sami,

Ken Vlach hit it on the head ... you (and MOST other inquirers) don't give all the facts, in this case the temperature! So he went to a lot of trouble giving you PVDF data (I didn't because I'm too damned lazy).

One point, however ... always double check corrosion resistance charts. Ken mentioned a 'B' rating for type l PVC (which I call uPVC) for 80% to l00% sulfuric.

For 96% sulfuric, using uPVC, you can use it till the cows come home! But welding must be good and cemented pipe joints must be welded (24 hours min. later) after being cemented. .... and Trovidur's book does show one of their PVC's being OK @ r.t. @ 98% sulfuric. Personally I have encountered 98% but 96% frequently and made up piping and holding tanks which I'd assume would last for decades.

By uPVC I mean regular PVC schedule piping NOT, NEVER, EVER drainage sewer pipe which might have better impact properties but not top chemical resistance.

A. Hi,

Go for PTFE or PVC lined valves / pipes. Rubber and SS not suitable for 98% H2SO4. For storage tanks mild steel is Okay for 98% H2SO4 provided you have control on moisture -- generally the vapor is very aggressive mixed with moisture.
So always the storage tank roofs and top shell plate get corroded.