Within the framework of a Joint Industrial Project sponsored by several petroleum companies the behavior of several Precipitation Hardened (PH) Ni-based alloys with respect to Hydrogen Induced Stress Cracking (HISC) resistance was studied using the Slow Strain Rate Tensile (SSRT) test method conducted under hydrogen charging conditions (applying a constant cathodic current density throughout the test). Among the test materials several industrial heats of UNS N07718 UNS N09945/945X UNS N09925 UNS N07725 were evaluated.A detailed microstructural analysis was performed on each heat at different levels involving SEM-FEG examinations at high magnification on etched samples to reveal the phases present at grain boundaries. Methodologies were developed to quantify the grain boundary coverage (length of precipitates at grain boundary divided by the total grain boundary length) and to study the distribution in size (equivalent diameter surface shape factor) of the grain boundary precipitates and applied to the studied materials.Elemental chemical analysis of the precipitates was also conducted by Energy Dispersive Xray spectrometry. Systematic fracture surface examinations were performed after SSRT tests under hydrogen charging conditions and compared to those obtained after SSRT tests in an inert environment.The performance of the different alloys with respect to HISC resistance is discussed on the basis of the plastic elongation obtained in the SSRT tests under cathodic polarization the microstructural features the cracking mode and the microstructural criteria given in the API 6A CRA standard.

Within the framework of a Joint Industrial Project sponsored by several petroleum companies the behavior of several Precipitation Hardened (PH) Ni-based alloys with respect to Hydrogen Induced Stress Cracking (HISC) resistance was studied using the Slow Strain Rate Tensile (SSRT) test method under hydrogen charging conditions. Three laboratories were involved in this program 28 industrial heats of different PH Ni-based alloy grades and yield strengths were tested. The experimental method selected for assessing the HISC resistance was the SSRT technique per NACE TM0198 performed at a strain rate of 10-6 sec-1 in both an inert environment and under Cathodic Polarization (CP) in 0.1N sulfuric acid at 40°C (using applied current density of 5 mA/cm2). In the preliminary phase of this program a round robin was performed that highlighted the need to measure the effective strain rate of the specimen during the elastic part of the SSRT test. Indeed depending on the equipment and the cell configuration significant differences can be found which may impact the test results. Other parameters such as the current density the gas cap composition were also studied in the preliminary work allowing the selection of the final test conditions. Once the test conditions had been optimized the study of each industrial heat (round bar approximately 8 inches in diameter) was carried out on specimens sampled in three locations 120 degrees apart and at mid radius. It was found that sampling different areas could lead to changes in the test results resulting mainly from microstructural variances at different locations of the bar. The results generated in this program could then be studied by relating plastic elongation obtained under CP as well as cracking mode and microstructure compliance with the API 6A CRA standard.

Environmentally assisted cracking of high strength nickle based alloys was investigated in 3.5wt% NaCl under cathodic protection.