The peculiarities of fatigue failure for pipe steels of different strength classes (pipes with welds)

Abstract

Variable loads, as compared with static loads, have a greater impact on the condition of pipelines. They lead to the degradation of metal and significantly reduce the service life of pipelines. This paper considers the mechanism of fatigue crack development in steels of different strength classes (K50, K60 and K62), which helps to specify the fracture mechanism and evaluate the residual life of a pipeline material.Fatigue tests were carried out until the complete failure of specimens at a maximum tensile load below the yield strength of the steels. The number of cycles to failure of specimens with no visible weld defects was reduced by more than 40%, as compared with seamless specimens. If there were allowable defects of up to 0.4 mm in size, then the number of cycles was reduced by 5-12 times. Photographs of the fractures are provided.The tests allowed the authors to establish the peculiarities of K60 steel failure and to calculate regression equations of the second order between the number of cycles to failure of the specimen, the maximum tensile stress and the stress range during fatigue tests. An essential effect of the stress range (in the range of 18-44 MPa) on the number of cycles to failure of the specimen has been established. After its reduction to 6-8% of the maximum tensile stress, the stress range ceases to affect the number of cycles. Since the appearance of the first visually perceptible cracks, the specimens endured from 4,000 to 10,000 cycles to failure. This makes it possible to detect the initiation of a failure and take steps to repair the defective part.Knowing the number of pressure fluctuations in the pipeline, which are registered in the control room, one can use the equations to predict the residual life of a particular section of the pipeline.

Advances in Machine Learning Techniques Used in Fatigue Life Prediction of Welded Structures

“…When examining the unique features of fatigue failure for steel pipes with various strength levels, it was discovered that the stress range no longer influences the number of cycles once maximum tensile stress is reduced to 6-8%, However, regression equations that can be used to forecast the remaining life of a specific pipeline section were created [25]. Similarly, the number of required analyses to obtain SIF and FL in pipes would become less by about 20%, if the technique by Shobeib was implemented [67].…”

“…Using fatigue testing, Kuskov et al [25] investigated the nature of fatigue in welded pipes with various strength classes and thereafter developed regression equations that can be used to forecast the remaining life of a specific pipeline section. Duraffourg et al [26] created a novel set of criteria for fatigue in spot welds and fatigue data editing techniques to calculate the fatigue lifecycle of full body-in-white via optimization with a non-linear multiple regression method.…”

“…Steel [21][22][23][24][25][28][29][30]38,45], metal composite [29], stainless steel [34,35], titanium [39].…”

“…Rail bending stress [21], NSIFs [22], strain [23], stress-related performance indicator [24], residual life, impact strength [25], SIF [31], impact energy [38].…”

“…Rail, motorcycle [21,22], bridges [23,24,32,35], pipelines [25], automotive [26], infrastructure [28,30], offshore [37].…”