Stress corrosion cracking of carbon steel in ethanol

Abstract

Stress corrosion cracking (SCC) of carbon steels ST35 gr. B and SA106 (ASTM A106) was studied by slow strain rate tests in ethanol denatured with ETBE (ethyl tert-butyl ether). During the experiments ethanol was aerated by nitrogen/oxygen gas. Some of the tests were done with samples that had clean surfaces and some were made with samples that had pre-oxidised surfaces. In pre-oxidised slow strain rate test (SSRT) samples stress corrosion cracking was transgranular, while in industrial cases stress corrosion cracks were mainly intergranular. In the industry SCC of carbon steel welds in ethanol occurs as a result of residual stresses of the welds. A real stress corrosion failure case from an oil refinery (transmission line from the harbour to the storage tank) was also studied, and intergranular cracking close to a weld and corrosion products on the fracture surfaces were observed. In addition, selective dissolution of ferrite from the pearlite phase and dissolution of MnS inclusions in ethanol were observed both in the field failure case and the SSRT samples.