PSI - Issue 37

Jan Kec et al. / Procedia Structural Integrity 37 (2022) 598–605 Jan Kec / Structural Integrity Procedia 00 (2019) 000 – 000

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commercially known as Cold Lock (CL). The DN500 pipe is seamless made of 13 030 steel according to Č SN 42 0074, from the point of view of mechanical properties, comparable with X42 according to API 5L. Two corrosion defects of 75% and 63% of the wall thickness were found on the outer surface of the DN500 pipe during operation. The defects were repaired in 2000 with two CL sleeves. The pipe DN500 was operated with the CL sleeves until 2020, subsequently cut out and subjected to full-scale tests. Before the pressure tests had started, the pipe was shortened to a length of 5 m and both ends of the pipe were covered with cups. A drawing of the DN500 pipe is shown in Fig. 1.

Fig. 1. Pipeline DN500 with Cold Lock sleeves

The DN700 segment (720 x 10 mm) was 8 m long and had a CS sleeve. The DN700 pipe is also seamless made of 13 030 steel according to ČSN 42 0074, comparable with X42 according to API 5L. Internal corrosion defect of 79% wall thickness was found on the DN700 pipe during operation. The defect was repaired in 2000 with a 300 mm wide CS sleeve with 6 layers. A girth weld was located 250 mm from the edge of the CS sleeve. The pipe DN700 was operated with the sleeve until 2020, subsequently cut out and subjected to full-scale tests. Before the pressure tests had started, the pipe was shortened to a length of 5 m and both ends of the pipe were covered with cups. A drawing of the DN700 pipe is shown in Fig. 2.

Fig. 2. Pipeline DN700 with Clock Spring sleeve

Both pipes were tested in special equipment developed at SVÚM a.s. In Fig. 3, you can see a schematic illustration of the unique pipe testing system. Pipes are pressurized with water from a pressure pump, a servo valve is controlled by the PLC computer to maintain the pressure values within the set range. The full-scale test consisted of three parts, the first part was a static loading of the pipes with four dwells up to yield strength for stress-strain analysis on the bare pipe and sleeve. This was followed by a fatigue pressure test with parameters Δp = 2 -6,3 MPa, Nf = 10 000 cycles. The last part was the burst test, the results of which enabled to determine the limit state, burst pressure and position of the fracture.