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[Zauberberg]

From the first start-up of olefin alkylation plant, we are faced with very frequent plugging and bursting of fresh H2SO4 dozing lines, which causes severe process upsets. In such circumstances, fresh acid is routed to the contactor vessel through "fresh acid fill" piping (which normally serves only in the start-up phase of process, after turnarounds), untill regular H2SO4 dozing lines are isolated, emptied and replaced (safety and environmental hazard). All acid lines are made of carbon steel.

What are possible reasons for frequent H2SO4 piping (1.5") blockage and leaking/bursting? One of the senior operators is suspecting steam tracing that, in his opinion, causes sulfuric acid to overheat at some spots, making it extremely agressive (fresh acid storage tank temperature is 20C). Calculated velocity of acid through the piping is very small which eliminates erosion concerns. It is interesting that spent H2SO4 lines do not suffer from these kind of problems, or at much lesser extent, in spite of lower acid concentration and higher level of corrosiveness.

Any experience with this? Do you suggest special metallurgy upgrades, line re-sizing, or something else? I am very interested to hear your opinions.

Regards

[Qalander (Chem)]

Dear,Although it's very old post and you might be alredy out of this with solution to the problem. However I envisage localised problems of
1)Pipeline material realted or
2) Some comtaminants(foreign materials 'Paticulates ')in H2SO4
3)The other possibility is process related that the NRV at downstream side is not working properly and lets processs related materials to back-into injecting pipeline and this gets solidified affecting the available X-sectional are and then bursting of pipeline may result.
Hope this indicates some possibilites.