13th International Conference on Fracture June 16–21, 2013, Beijing, China (PMCs), such as potential reinforcing materials. Accordingly, material databases contain data of steel pipe materials, mechanical properties, geometrical dimensions; polymer matrix composite materials, mechanical properties; physical properties of steels and PMCs [6]. The most frequently joining technology in the field of steel pipes is the welding, numerous girth welds can be found on the pipelines. The girth welds, as separated parts of the pipeline, have own integrity [9] and the girth weld integrity has influence on the pipeline integrity. The girth weld integrity depends on many factors – Y/T ratio, weld metal yield strength (YS) mismatch, continuous or discontinuous yielding, elastic or non-elastic design, inspection level (x-ray or ultrasonic), failure mode (brittle vs. ductile) – interacting with each other [6, 9, 10]. Based on the above mentioned facts, the direct purpose of the paper is to present the role of the external and internal reinforcing on the fatigue and burst behaviour of transporting steel pipelines, reviewing our full-scale examinations. External and internal reinforcement was developed using carbon fibre (CF) and glass fibre (GF) polymer matrix composites (PMC), respectively [6, 11]. Known external reinforcing technology (Clock Spring) was used, too [12]. Fatigue and burst tests were performed on full scale pipeline sections containing natural and artificial metal loss defects, and girth welds including weld defects. Both unreinforced and reinforced pipeline sections were examined. Safety factor, burst pressure divided by Maximum Allowable Operating Pressure (MAOP), was defined and their calculated values demonstrate both the reserves of steel pipes and the usefulness of the reinforcing materials and technologies. 2. Testing circumstances Full-scale, seamless (SMLS), seam welded (SW and SW/HFW) and spiral welded (SPW) steel pipeline sections were examined. Pipeline sections with and without girth welds were investigated, too, in order to study the influence of the girth weld quality and integrity on the pipeline integrity. Manual metal arc welding (111) and tungsten inert gas welding combined with manual metal arc welding (141/111) technologies were used for the making of the girth welds. The main characteristics of the investigated pipeline sections are summarized in Table 1, where DN is the diameter nominal of the steel pipe, dk is the external/outside diameter of the steel pipe (OD) and ta is the wall thickness of the steel pipe. Table 1. The main characteristics of the investigated pipeline sections Mark DN dk, mm ta, mm Pipe Material Pipe Type Girth Weld A_e 100 108,0 4,5 L360NB SMLS 111 B_a 200 219,1 5,0 L360MB SW/HFW no or 111 or 141/111 B_b 200 219,1 5,0 L360MB SW/HFW no or 111 or 141/111 C_d 300 323,9 7,1 L360MB SW/HFW no CS_a 400 410,4 7,2-8,0 A35K SMLS 111 CS_b 400 405-412 7,7-8,3 DX42 SPW 111 D_c 600 609,0 7,92 DX52 SW no E_o 200 219,1 5,0 L360MB SW/HFW no The investigated pipeline sections are divided into testing sections, as follows: burst test of base (unwelded) pipeline; fatigue test (105 cycles) + burst test of base (unwelded) pipeline; burst test of operated (fatigued and replaced) pipeline containing girth weld with „NOT PASSED” quality; fatigue test (2*104 cycles) + burst test of pipeline containing girth weld with „PASSED” quality; -2-
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