CASE STUDY: 1)

Before a scheduled maintenance work in the Port Harcourt refining company (PHRC), a leakage was detected in the splitter reboiler of a crude distillation unit (CDU). During maintenance, the exchanger bundle was hydrotested and tube leak was confirmed. A Heavy Gas Oil (HGO) is used as heating medium in the tube side which was first installed 25 years ago and had undergone series of inspection since installation. Corrosion rate was moderate as at 2005. The exchanger bundle indicated flow direction and severely corroded area on the surface of the heat exchanger. Corrosion occurred at the same areas in 2007 and 2008 according to inspection files. The tubes were twisted by irregular thermal expansion. The tubes had a diameter of 2 mm and original length of 1.5 m which expands to 1.75 m by a force of 315 N. Several tubes were sampled and were cut open and examined.

1.

(a) What are the types of corrosion in the exchanger bundle?

(b) Discuss the possible cause(s) of the leak in the exchanger bundle

(c) Describe the different methods for prevention of the leak as a result of corrosion in the CDU from: (i) Design rules (ii) Corrosion inhibitors

(d) (i) If the tubes are made of steel, write the corrosion half and full reactions. (ii) If the corrosion rate was moderate, at what range should it be?