The operational safety of oil and gas storage units is crucial, as any potential imperfections or cracks in a container wall could result in fracture. The key parameter in ensuring the integrity of oil and gas storage units is their fracture toughness. For its determination, compact tension (CT) and single-edge notched bend (SENB) specimens are commonly used. However, these specimens may lead to unnecessary conservatism in safety assessments. Single-edge notched tension (SENT) specimens, on the other hand, could be a more acceptable substitute, as they are shown to lead to less conservatism. The aim of this study was to determine the J-R curve for SENT specimens from pipe steel X65 using an experimentally determined J-R curve for CT specimens. This study was motivated by the fact that the use of the Gurson—Twergaard—Needleman (GTN) model for R-curve determination can significantly reduce the number of physical tests. Calculations were performed using the GTN constitutive model, calibrated on a CT specimen of width w = 50 mm, thickness B = 8.7 mm, and initial crack length a = 25.15 mm, used for the determination of the R-curve. The width and thickness of the SENT specimens considered in the calculations were similar to those for the CT specimens. Ideal clamping of the SENT specimens in the jaws was considered. A comparison of the SENT R-curve with the experimental CT R-curve showed that these curves were practically equidistant, with the former R-curve being superior to the latter one. The SENT R-curve has not been verified experimentally, because the physical specimens that match the models used for calculation do not meet the requirements of the related standards on specimen thickness. However, a comparison of this SENT R-curve with another SENT R-curve, published in the literature and obtained on the basis of the results of a two-parameter fracture mechanics approach, showed a very good agreement between the two R-curves.

The aim of this article is to quantify the loads exerted by heavy-duty vehicles when crossing over buried pipeline. This problem arises in connection to the question pertaining to the use of protective sleeves (casings) applied to gas pipelines in regions with increased demands on pipeline operation safety. An experiment was conducted on a test pipe section made from L360NE pipeline steel equipped with strain gauges along the pipe perimeter, measuring strains in the axial and circumferential directions. Strain measurements were taken after back-filling the pipe trench, then during vehicle crossings over the empty pipe, and again after pressurizing the test pipe with air. Strain-based hoop stresses at the surface of the empty test pipe were found to exceed 30 MPa after back-filling the trench and increased to more than 40 MPa during the vehicle crossings. Similarly, axial stresses reached extremes of around 17 MPa in compression and 12 MPa in tension. Applying internal air pressure to the test pipe resulted in a reduced net effect on both the hoop and axial stresses.

The purpose of this article is to compare two predictive methods of J integral assessments for center-cracked plates, single-edge cracked plates and double-edge cracked plates produced from X52 and X70 steels, and a longitudinally cracked pipe produced from X70 steel. The two methods examined are: the GSM method and the J_s procedure of the French RCC-MR construction code, designated here as the FC method. The accuracy of J integral predictions by these methods is visualized by comparing the results obtained with the “reference” values calculated by the EPRI method. The main results showed that both methods yielded similar J integral values, although in most cases, the GSM predictions were slightly more conservative than the FC predictions. In comparison with the “reference” values of the J integral, both methods provided conservative results for most crack configurations, although the estimates for cracks of a relative length smaller than 1/8 were not found to be so conservative. The prediction of burst pressures for external longitudinal semielliptical part-through cracks in X70 steel pipe showed that the magnitudes of predicted burst pressures came very close to each other, and were conservative compared to FEM (finite element method) calculations and experimentally determined burst pressures.

This work was motivated by the need for knowledge about the natural decrease in water pressure from room temperature creep, separate from the decrease in pressure caused by leakage in tightness tests of new and/or repaired pipelines. In this context, a case study was conducted regarding the decrease in water pressure in a test pipe with dimensions of 530 mm in outside diameter and 7.8 mm in wall thickness. The system was pressurized to a pressure of 8.985 MPa, after which the water supply was stopped. The test pipe, 4 m in length, was made from linepipe steel L360NB and was closed by torispherical heads at both ends. Special attention was given to the thermal insulation of the test pipe, ensuring an average temperature of 14.5°C, with variation within 0.1°C over a period of 24 h. A nonlinear ordinary differential equation was derived to describe the time gradient of the water pressure in the test pipe in relation to time, pressure, coefficient of compressibility of water, and cross-sectional dimensions of the test pipe. The necessary creep parameters and static tensile properties were obtained from specimens manufactured from a ring 30 cm in width taken from the same pipe. The orientation of the specimens was circumferential. The creep tests were performed over a period of 24 h at ambient temperature. The creep strains were measured by the strain gauge technique, and the effect of temperature variation during the test period (24 h) was compensated by the use of a compensating strain gauge. The calculated decrease in pressure with time compared quite well with experimental results when the beginning of the pressure decrease was considered 2 h after reaching the initial pressure of water ($p_0=8.985\mathrm{MPa}$ ) and the supply of water was ended. The time period of 2–24 h follows the recommendations of a pipeline operating pressure standard. A family of “pressure-time” curves were constructed for a pipe from steel pressurized by water to specific initial pressure levels taken as multiples of the pressure at the yield. These curves cover a time interval of 2–24 h, and they can be used to check the total decrease in water pressure after the tightness test has been completed.