Study For Mooring Chain Grade R5 On Its Heat Treatment Parameters And Properties

Grade R5 is the highest grade of mooring chain products which could be produced in batch and used for mooring of offshore structures. Extremely high properties are required for R5 chain due to its extremely severe service condition, and one of the most important factor that will influent these properties is heat treatment. Various combination of heat treatment parameters are studied in this work to investigate there effects on final performance of the products.Three different quenching temperature, tempering temperature and soaking time are chosen for test using orthogonal method. An optimized heat treatment parameters are determined to obtain an optimized comprehensive properties through the test. Furthermore, effect of different quenching cycle on lower temperature toughness is studied, e.g. one time quenching and cycle quenching method. Meanwhile, resistance capability to crack growth of mooring chain is analyzed by crack-tip opening displacement(CTOD) test to verify the weld quality at such heat treatment condition. As the mooring chain is served in sea water in long term, the resistance capability to environment assisted cracking(EAC) should be taken into consideration during manufacture of chain cables. The author invests the resistance performance of R5 chain by comparing the reduction of area in testing environment with the reduction of area in air condition through slow strain rate testing(SSRT). The resistance capability to fatigue, another important property of mooring chain, is analyzed by simulation and actual testing according to API 2SK rule.