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Mysterious Grooving in Carbon Steel Pipe in 99% H2SO4 Service
Q. Recently, our plant changed out a 4" SCH80 carbon steel pipe from 99% sulfuric acid service and noticed that there was internal grooving along the length of the pipeline.
These grooves resemble hydrogen grooving, but are found around the full 360 deg internal circumference, instead of just at the top. The acid temperature is about 90F and the flow rate is on the order of 2,000GPM.
It should be noted that the sulfuric acid is used by a refinery in their alkylation process and thus they ship 90% sulfuric acid with a 10% alkylate back through the pipe at 2,000GPM. Flow rates as high as 3,500GPM have been seen, but not often.
What could be the cause of the grooving?
Patrick Reillysulfuric acid regeneration - Bellingham, Washington, U.S.A.
2003
A. At the flow rates stated for the 4" Sch. 80 cs pipe, the velocity of the acid is exceeding the recommended 3 fps velocity for sulfuric acid carbon steel piping. The high velocity is removing the protective ferrous sulphate ferrous sulphate [affil links] film on interior of the pipe. There are also solids and sulfur dioxide gas present primarily in the spent acid stream that also accelerates the removal of the protective film. Fittings, valves, bends, reducers, and other piping components that cause turbulent flow can cause grooves in any position within the pipe.
Rich Phelps- Baton Rouge, Louisiana USA
2007
A. Hydrogen Grooving due to high velocity of the acid in piping.
Cedric Bolduc- Canada
September 6, 2013
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