Crack control technology for the X80 large OD 1422 mm line pipes

Abstract High-grade (API 5L X80) and large-diameter (OD 1422 mm) line pipes are used in the Sino–Russian eastern route gas pipeline project for high pressure (12 MPa) transmission, and this can significantly increase the transmission capacity and meet China's energy strategic demand. With the increase of steel grade, transmission pressure, pipe diameter and design coefficient, however, ductile crack of line pipes becomes the dominant crack mode, so it is necessary to focus on crack arrest and control study. In this paper, therefore, an intensive study was performed on the Battelle Two-Curve (BTC) method which is the major solution to the calculation of arrest toughness, as well as the crack resistance curve and decompression curve. Based on the study, the principle and application range of the BTC method were confirmed. In addition, a series of analysis were conducted on the issues which occurred when the BTC method was applied to high-strength, high-toughness line pipe steel, and the commonly used modified approaches to BTC calculation results were also provided. After the crack control scheme of the X80 large OD 1422 mm line pipes for the Russian Bovanenkovo–Ukhta was reviewed, the BTC calculation results were corrected on the basis of the design parameters of the Sino–Russian eastern routine gas pipeline project, the Charpy V-notched (CVN) impact energy which meets the project requirement was finally worked out to be 245 J.