TPT May 2010

A rticle

Tested and analysed models In total, in experimental part, four experimental specimens were tested after manufacturing. All specimens had similar geometric properties such as 2.46m length, 10.2cm diameter and 0.25mm thickness. Rings had 10.2cm inner diameter, and 12.2cm outer diameter and 2mm thickness. The only difference between specimens was the number of attached rings on specimen. For identifying specimens they were labelled such A4. This label shows that the specimen has geometric properties such was mentioned elsewhere, with four ring stiffeners where two of them were end rings and two others were middle rings. In fact, in each specimen, rings had equal spacing. In FEM analysis, all experimental specimens were exactly modelled and analysed. Three other models were also analysed, which had no corresponding experimental specimen, because of the difficulty of manufacturing them experimentally. Two of them had four rings such as model A4 but with different thickness. They were labelled as A4 t20 that shows the model is a similar model A4 with four rings but with 20mm thickness. These models were analysed for comparing with model A4 to investigate the effect of the ring’s thickness on behaviour of pipeline. Another model had no rings but different thickness which labelled B0. This model had geometric imperfections such model A0, and weight equal to model A13. This model was analysed, for comparing two same weight models A13 and B0 with model A0 to investigate the economic benefits of using of ring stiffeners. Geometric properties of models and specimens and their labels are shown in table 1. As is shown in table 1, in total four specimens were experimented with, buckling behaviour of specimens are shown in figures 6, 7, 8, 9, 10 and 11. In these figures behaviour of specimens are about axial, circumferential-pressure strains and radial displacement- pressure. Figures 6 and 7 are about axial strain of specimens. Figure 6 shows axial strain-pressure curve of specimen A0 as basic specimen. Initial buckling of test occurred at 6.0 Kpa. Figure 7 shows comparisons between specimens A4, A7 and A13 with the buckling pressure 17.0 Kpa, 27.8 Kpa and 61.9 Kpa respectively. When comparing figures Experimental buckling and post buckling modes

Figure 6 : Axial strain-pressure curve of specimen A0

Figure 7 : Comparison of axial strain-pressure curves of specimens A4, A7 and A13

6 and 7, differences between initial buckling of specimens and their behaviour are identified (table 2). When comparing the curves it is clearly indicated that a specimen ’ s buckling pressure was increased when rings spacing decreased. At this point, firstly initial buckling was started in a small part of specimens in circumferential and longitudinal direction of specimens, then buckling propagation gradually started on post- buckling region. With test continuing, inner pressure of specimens reduced. In fact, increasing value of buckling pressure intensively related with 2L c /D .

Table 1 : Geometry of test models and specimens

Rings thickness (mm)

Length (m) L

Diameter (m) D

Thickness (mm) t

Rings spacing (m) L c

Study type

Rings inner radius (m)

Rings outer radius (m)

Rings number

Label

A0 A4 A7 A0 A4 A7

0 4 7 0 4 7 4 4 0

2.46 2.46 2.46 2.46 2.46 2.46 2.46 2.46 2.46 2.46 2.46

0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102

0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25

-

-

-

-

0.82 0.41

0.102 0.102 0.102 0.102 0.102 0.102 0.102 0.102 -

0.122 0.122 0.122 0.122 0.122 0.122 0.122 0.122 -

2 2 2 2 2 2 -

EXP

A13

13

0.205

-

0.82 0.41

A13

13

0.205

FEM

A4 t20

0.82 0.82

20

A4 t0.25

0.25

B0

0.3625

-

-

-

-

107

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M ay 2010

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