Failure analysis of refinery tubes of overhead condenser

Failure analysis of cupronickel condenser tubes of a crude distillation unit of a petrochemical refinery has been conducted. Condenser tubes carrying sea water were found to undergo premature failure which was preceded by extensive overall thinning, formation of shallow channels, pits, etc., and greyish-black internal deposits in one of the units. In the other unit, the failure of tubes was noticed without any significant overall thinning and in the presence of adherent, hard and black-brown deposits. The studies indicated that the increased velocity of sea water as well as the deficiency of iron in the alloy had resulted in failure in one case whereas relatively low velocity of water associated with deposition of sludge and bio-fouling were the causes of failure in the other case. The failure of tubes could be controlled by maintaining the water velocity within a specified range, flushing the tubes with clean water, use of anti fouling paints, selecting a more appropriate composition of the cupronickel alloy, through control of sea water sulphur level, etc.