Inspection of a Vessel Containing Corrosive Material
A major chemical company in Virginia needed an on-stream inspection of a vessel to determine its reliability. The product in the vessel is highly corrosive to the material of the vessel, so it is lined with a Teflon coating. Due to a faulty pump leaking product onto the vessel numerous times, the surface was heavily pitted on the outside surface. It was determined an API 510 inspection would give the needed information as far as the extent of the corrosion damage by evaluating the pit depths, along with any other ramifications from the damage. There was also concern whether the Teflon lining on the inside was still adequate.
TesTex put together a team to scan the tank with the LFET system, in order to determine the condition of the vessel lining. Due to the product inside the vessel being highly corrosive, a break in the lining would create an area of major wall loss very rapidly. This would give an indication of wall loss with the LFET system. TesTex also provided an in house API 510 inspector to visually inspect the unit and determine the condition of the vessel in general and evaluate the corrosion (pitting) damage.
Above are two waveforms of the pitted area.
Above is a waveform of the non-pitted area.
Sample of a calibration scan with four pits
TesTex first performed an API 510 inspection on the vessel and determined the pitting damage was extensive enough that the vessel did not meet API 510 code per the ASME Section VIII. The calculated minimum wall was 0.151”. Some of the pitting measured 7/32” deep which gave a wall remaining of 0.094”. Also during the API 510 inspection, a 5” crack was found at a nozzle to shell weld along with pitting in HAZ of some welds.
TesTex also performed a Low Frequency Electromagnetic Technique inspection on the Stainless Steel shell in order to confirm the remainder of the shell was in good shape. This inspection confirmed there were no indications other than the pits on the outside of the vessel in the damaged area.
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