Laboratory Testing of OCTG grades UNS N08028 and UNS N08029

摘要

The international standard NACE~((1)) MR0175/ISO~((2))15156-3 is essentially used for the material selection in H_2S-containing environments when choosing corrosion resistant alloys (CRAs). Temperature and H_2S partial pressure are mainly considered. Earlier experiences indicated that UNS N08028 and UNS N08029 could withstand more severe environmental testing conditions compared to the standard required for type 4c alloys. A recent laboratory testing program has been carried out on the OCTG tubing of UNS N08028 and UNS N08029 in 91000 mg/l chloride, 1000 psi CO_2, and 2200 psi H_2S at temperature from 150°C and up to 220°C, using constant load and slow strain rate testing (SSRT). The materials could in essence withstand the testing conditions. Pitting was observed on these materials when chloride concentration was increased to 250000 mg/l using constant load testing. Failures have been observed after SSRT when chloride was 254000 mg/l. Critical pitting temperature (CPT) determination in 3-12 wt% chloride solutions showed that UNS N08029 has significantly higher CPT compared to UNS N08028 because of its higher Mo content. However the environmental limits have not been defined for these materials in the tested conditions. The effects of chloride and other possible parameters on the pitting and failures are discussed.