Designing casing for ultra-high pressure, high temperature (HPHT), hydrogen sulfide bearing wells creates a need to characterize the sour performance uncertainty (scatter) of higher strength, low alloy carbon steels casing such as grade C110. Casing properties generally vary by: source mill, degree of hot working, product type (seamless pipe vs. electric resistance welded pipe), steel chemistry, size and wall thickness, particular heat lot, particular joint of pipe, and location on the joint of pipe. Measured properties also can vary according to the number of and choice of laboratories doing the testing. All of these factors can contribute to the perceived scatter in the sour material properties associated with the product. In order to determine the mean and scatter of sour properties which characterize grade C110 casing and create a benchmark for the minimum possible scatter that can be achieved in a production order at a level practical for well design, Shell International E&P and Grant Prideco-TCA jointly generated a population of sour property test data across a single, commercially produced, heat lot of casing and using the services of a single NACE testing laboratory, OMNI Metals Laboratory. Grade C110 is a high strength sour service material, which is currently being considered for standardization by the American Petroleum Institute (API).
This paper details the results of sixty-six NACE Method D (DCB) tests and seven NACE Method A (tensile) tests conducted across one single, commercial production heat lot of Grant Prideco-TCA grade C110 low alloy carbon steel. All tests were conducted at OMNI Metals Laboratory. The data conceptually represent the tightest possible practical spread of sour material properties since all the data were obtained from a single heat lot of pipe sampled every 10th pipe-end and along a joint of pipe within the single lot. Hardness was found to be remarkably uniform. Results of the data are correlated in terms of model uncertainty for KISSC vs. hardness. The paper also presents a correlation between hardness measured on pipe-ends and hardness measured on the corresponding NACE specimens. Tests were performed in standard NACE A Solution and at milder conditions. For this grade material, the mean DCB results were significantly higher than the industry trend and the scatter was unusually low indicating high product consistency across the heat. Results quantify the impact of reducing the H2S concentration to a fit-for-purpose environment based on NACE Method D test data.