This report summarizes the derivation of fatigue curves for studless and studlink chain mooring lines for inclusion in API 2SK, Third Edition. The Second Edition of API 2SK has a single fatigue curve for mooring chain, this curve is a non-unique lower bound to all of the in-water and in-air studlink fatigue test data. API 2SK, Second Edition does not have separate fatigue curves for studlink and studless chain.

The studlink fatigue curve derived in this report is based on the salt water tension-tension fatigue tests performed by the National Engineering Laboratory, Glasgow, UK (NEL) and Exxon Production Research Company (EPR) on oil rig quality (ORQ) studlink chain with bar diameters of 2 in., 3 in., and 4 in. The studless fatigue curve is based on the saltwater tension-tension fatigue tests performed by NEL on R3 and R4 studless chain with a bar diameter of 3 in.