Environmental Cracking Performance of Super Martensitic Stainless Steels 13Cr in High Chloride Reservoir Fluids Containing H2S/CO2

Within the Oil & Gas industry there is an increasing interest in the use of high strength tubing alloys in deep water, high temperature/high pressure (HPHT) and ultra high pressure wells.

ISO13680, category 13-5-2, group 1 steels have been developed and typically used in HPHT fields containing CO2 and small amount of H2S. The alloy application limits have not been fully defined with respect to parameters such as chloride concentration, pH, temperature and H2S partial pressure. These parameters influence both localized corrosion resistance and Stress Corrosion Cracking (SCC) susceptibility. 

The present work has been aimed at evaluating the SCC resistance of Alloy 13-5-2 grade 110ksi and in particular it is the follow up of experimental work presented in NACE paper 10314. The following topics are addressed:

o   Influence of load applied;

o   Definition of working window in terms of temperature;

o   Test duration (1 month versus long term three months tests): evolution of crack initiation sites of a few microns observed after 1 month of exposure.

This has been performed by means of the Four Point Bent (FBP) testing method according to EFC publication n°17. 

Furthermore, tubing steel performances have been compared with forged bar 13-5-2 grade 110ksi, for selected cases.