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Corrosion in rubber lined carbon steel by effect of H2SO4

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Q. Hi,

Actually, I'm using sulfuric acid in 98% concentration. Most of the system is fabricated from rubber-lined carbon steel and I face serious corrosion in two pipe segments:
1- corrosion between two valves.
2- corrosion in the open drain.
But the whole system is Okay!

For the time being, we removed the rubber lining and replaced with 316ss stainless steel as a temporary solution. Could you explain the reasons? And from your experience, what is the best material I can use for this purpose?

Sami ZOBEIR
- Yanbu, western region, K.Saudi Arabia


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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% sulphuric.

Re your problem, here are some ideas or thoughts.

Whereas mild steel is, I think, OK for 96% sulphuric, it ...along with stainless ... sure doesn't like being in diluted sulphuric, 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 sulphuric 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% sulphuric 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 !

freeman newton portrait Freeman Newton
- White Rock, British Columbia, Canada

freeman newton died

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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 Temperatures 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      Sulfuric acid (60%ěsat. 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 Sulfuric acid (>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.

Ken Vlach
- Goleta, California  

Ken received a special
"Contributor of the Year" award
from finishing.com for his numerous
helpful and well researched responses

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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% sulphuric.

For 96% sulphuric, 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% sulphuric. 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.

Freeman Newton
- White Rock, British Columbia, Canada
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