Case story: Tubes in Sanicro 28 unaffected after five years in sulphide-rich environment
Tubes in Sanicro 28 proved to be a safe choice to fight hydrogen induced cracking in the heat exchangers of a large Indian oil refinery. Five years after the installation, thorough inspection showed no signs of corrosion.
A large Indian oil company decided to expand one of its oil refineries. It involved a new coker unit, where residual oil is cracked into lower molecular weight hydrocarbons. The operating environment in the coker unit is rich in hydrogen sulphide, making it extremely corrosive. From time to time substantial amounts of ammonia and cyanide are also present. The challenge for plant designers was to choose a material grade for the heat exchanger tubes that would ensure safe operation over longer periods of time.
The Sandvik solution
Because of the high content of hydrogen sulphide and subsequent risk of hydrogen induced cracking, the engineering company involved in the plant design decided to specify Sanicro 28 grade tubes. This grade is a safe choice when the process flow is rich in acids, chlorides and hydrogen sulphide. Sanicro 28 tubing was installed in 10 heat exchangers in the fractionator overhead condenser and the interstage cooler, amongst others.
The new refinery unit was started in 2005. Five years later, in 2010, the heat exchangers were opened for inspection. The tubes in Sanicro 28 were inspected visually and by non-destructive, eddy current testing. There were no signs of corrosion.