OS-C501

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Offshore Standard DNV-OS-C501, November 2013 Sec.14 Calculation example: two pressure vessels – Page 190 3.3.4 All failure mechanisms shall be checked for all loads of the different phases. The failure mechanisms are the same for the testing and operational phase in this example. Short-term loads are the same in both phases and the operational phase has long-term loads in addition. Due to the simple situation of this example it is sufficient to analyse the component for the operational phase only. 4 Material properties 4.1 General (ref. Sec.4) 4.1.1 Properties must be measured or obtained from representative data as described in Sec.4 [8]. This example uses the representative data from App.F and assumes that proper data have been obtained. 4.1.2 Only a small number of material parameters is needed compared to the extensive list given in Sec.4 [1] simplified 2-D analysis is performed in this example. Only the four 2-D orthotropic elastic constants of the ply are needed. Since the component is loaded in tension (due to internal pressure) only the tensile and shear ply strengths are needed. 4.1.3 Ply properties are needed for the component at the first day and after 25 years, when it has been exposed to permanent loads and fatigue. How these properties are obtained is explained in the following sections. A summary of the properties is given below in [4.1.4]. 4.1.4 The characteristic properties are summarised in the Table 14-15 and Table 14-16 below for a laminate without matrix cracks and with matrix cracks. Table 14-15 Ply properties for laminate without matrix cracks (water vessel) Property New component after 1300 fatigue cycles after 1300 fatigue cyclesin water Time to fibre failure Time to matrix failure after 25 years of permanent pressure after 25 years of permanent pressurein water E 1 fibre 23.7 GPa 23.7 GPa 21.3 GPa 23.7 GPa 21.3 GPa E 2 matrix 7.6 GPa 7.6 GPa* 6.8 GPa* 7.6 GPa 6.8 GPa n 12 0.29 0.29* 0.29* 0.29 0.29 G 12 linear 3.2 GPa 3.2 GPa* 2.9 GPa* 3.2 GPa 2.9 GPa fibre 1.69% 1.69% 1.69% 0.87% 0.87% ε ∧ 1t fibre 401 MPa 401 MPa 361 MPa 205 MPa 185 MPa σ ∧ 1t matrix 0.2% 0.2% 0.2% 0.2% 0.2% ε ∧ 2t σ ∧ 2t ε ∧ 12 σ ∧ 12 matrix 26.3 MPa 26.3 MPa 23.7 MPa 26.3 MPa 23.7 MPa matrix 0.37% 0.37% 0.37% 0.37% 0.37% shear 17.0 MPa 17.0 MPa 15.3 MPa 17.0 MPa 15.3 MPa Not applicable see [4.6] Not applicable see [4.7] DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.14 Calculation example: two pressure vessels – Page 191 For low cycle fatigue at low stresses Table 14-16 Ply properties for laminate with matrix cracks (gas vessel) Property New component after 3000 fatigue cycles after 3000 fatigue cycles in water after 25 years of permanent pressure 4.2 Ply modulus in fibre direction E 1 4.2.1 The ply modulus in fibre direction is 26.7 GPa according to the representative data from App.F. Data are for stitch-bonded materials, while the vessel is made by filament winding. Data should be corrected according to Sec.4 [8.12]: 26.7 × 0.8 / 0.9 = 23.7 GPa. Guidance note: It is recommended to use data measured from a laminate made by filament winding to avoid using the corrections made above. Good filament wound laminates can have as good properties as flat panels (see also Sec.4 [8.12.6]). ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 4.2.2 A reduction of 10% of E 1 fibre is suggested after 10 6 cycles in Sec.4 [3.6.2]. This component is only cycled 1300 times at relatively low strains, where experiments have shown that the modulus does not change. According to Sec.4 [3.6.3] the modulus can be chosen to remain the same, provided the data can be documented. 4.2.3 Exposure to water typically gives a reduction of 10% according to App.F [F.5.2.1]. Therefore, 10% reduction for the exposure to water has been used for long-term fibre dominated properties. 4.2.4 The material may creep (obtain plastic deformation) to some extend under the permanent load, but the response to short-term loads is still the same as for the original elastic constants (Sec.4 [3.2.2]). 4.2.5 The fibre dominated ply modulus is not influenced by matrix cracks and the same values are used for the laminate with and without matrix cracks (Sec.9 [2.2]). 4.3 Matrix dominated elastic properties 4.3.1 The ply modulus transverse to the fibre direction and in in-plane shear are 8.4 GPa and 3.5 GPa, respectively, according to the representative data from App.F. Data are for stitch-bonded materials while the vessel is made by filament winding. Data should be corrected according to Sec.4 [8.12]: — 8.4 × 0.9 / 1.0 = 7.6 GPa — 3.5 × 0.9 / 1.0 = 3.2 GPa. after 25 years of permanent pressure in water E 1 fibre 23.7 GPa 23.7 GPa 21.3 GPa 23.7 GPa 21.3 GPa E 2 matrix 0.08 GPa 0.08 GPa 0.08 GPa 0.08 GPa 0.08 GPa ν 12 0.003 0.003 0.003 0.003 0.003 G 12 linear 0.03 GPa 0.03 GPa 0.03 GPa 0.03 GPa 0.03 GPa fibre 1.69% 1.69% 1.69% 0.87% 0.87% ε ∧ 1t σ ∧ 1t ε ∧ 2t σ ∧ 2t ε ∧ 12 12 σ ∧ Time to fibre failure Time to matrix failure fibre 401 MPa 401 MPa 361 MPa 205 MPa 185 MPa matrix NR NR NR NR NR matrix NR NR NR NR NR matrix NR NR NR NR NR shear NR NR NR NR NR NR see [4.6] NR NR NR: Not relevant, since the matrix has already cracked DET NORSKE VERITAS AS
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