PSI - Issue 17

V. Chmelko et al. / Procedia Structural Integrity 17 (2019) 520–525 Chmelko, V., Bíro, D./ Structural Integrity Procedia 00 (2019) 000 – 000

522

3

Fig. 2. Supplying of multiple defects with the single rectangular defect and irregular shape defect by the rectangular defect.

The burst pressure of pipe with defect defined by DNV RP F101 is: = 0.9 2 − ( 1 1 − − ) where

(3)

= √1 + 0.31 ( √ 1 ) 2

(4)

The burst pressures calculated by these criteria for pipes with outer diameter D = 151 mm and with wall thickness t = 4 mm are compared in Tab.1. Table 1. The burst pressures p depending on the depth of the defect in % of the wall thickness calculated by eq. (1) and (3). Depth of corrosion defect (%) 0 5 10 15 20 25 30 35 40 45 50

p ASME (MPa)

19.9

19.6

19.2

18.9

18.5

18.1

17.7

17.2

16.7

16.2

15.6

p DNV (MPa)

23.7

23.2

22.7

22.1

21.4

20.8

20.0

19.3

18.4

17.5

16.6

The presented criteria are used in real pipe operation. Regarding to the simplifying assumptions (e.g. integration of separate defects into one common by the DNV criterion) and the origin of the relationships, a conservatism can be assumed. However, it is difficult to obtain an exact burst pressure value for a pipe with weakened wall thickness, because the stress-strain state in corrosion defect is fundamentally different from remainder of the pipe material. Suitable solution is to create a numerical model of pipeline by FEM and verification by experimental by direct measurement of burst pressure in laboratory conditions. 3. Experiments and simulations Three experimental cylindrical pressure vessels were made for the experimental determination of burst pressure. The external diameter was 151 mm and wall thickness in working region of samples was 4 mm with simulated corrosion defect of wall thickness loss of 24%, 35% and 75% (Fig. 3). Samples were loaded with increasing internal pressure (used hydraulic oil) until fracture.