TPT May 2010

A rticle

Experimental buckling pressure (Kpa), pressure ratio with basic specimen (A0)

FEM analysis buckling pressure (Kpa), Difference with basic specimen (%)

Differences between experimental and FEM study (%)

Specimen label

A0, Basic specimen

6, 1

7.1, 1

18%

A4 A7

17, 2.83

18.1, 2.54 32.4, 4.56 49.8, 7.01

6%

27.8, 4.63 61.9, 10.31

16.5%

A13

24%

Table 2 : Comparison between experimental and FEM studies results

buckling pressure with 43% and 3.8% differences to the basic model (table 3). As indicated, deceasing or increasing the ring thickness does not have a great effect on pipeline behaviour against the amount of steel that is used in rings. It is so economical that as thickness of rings decreased if it will be enforceable. These curves are shown in figure 14.

Buckling pressure (Kpa)

Difference between basic specimen (%)

Model label

A4, basic model

7.1

1

A13

49.8 20.5

7.01 2.88

B0

Table 4 : Comparison between models A13, B0

Circumferential buckling mode Another observation in experimental and FEM studies, was made to do with circumferential waves on wall of specimens and models which identified with n and strongly depend on geometric ratios of D/2 t and D/2L c . The higher ratios have higher number of n and therefore higher value of buckling pressure. There were some differences in this case between two studies, such as the made-up waves number on the specimen panels in experimental study were different but these values were constant in the FEM study (table 5). As shown, initial buckling of specimens was increased by increasing the number of circumferential modes of specimens. Figures 16, 17, 18 and 19 indicate the number of waves which were used on panels of specimens.

Figure 14 : Comparison of radial deformation-pressure between models A4 t0.25 and A4 t20

Buckling pressure (Kpa)

Difference between basic specimen (%)

Model label

A4, basic model

18.1 18.8

0%

A4 t0.25

3.8% 43%

A4 t20

26.05

Table 3 : Comparison between models A4, A4 t0.25 and A4 t20 In addition, another model was analysed without rings, but with more thickness and the same weight was used with the model. This model was for investigating the economical aims of the study. As indicated in figure 15 initial buckling of this model is 20.5 Kpa and the pressure ratio of the basic model (A0) was equal to 2.88 whereas this ratio for model A13, with the same weight model B0, was 7.01 (table 4). This shows the economical benefits of decreasing the amount of steel used.

Figure 16 : Three and two made-up wave mode on panels of specimen A4 in experimental study

Figure 15 : Radial deformation-pressure curve of model B0

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M ay 2010

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