OS-C501

Recommendations

Info

Offshore Standard DNV-OS-C501, November 2013 Sec.14 Calculation example: two pressure vessels – Page 186 2.6.3 A complete analysis should include all parts of the component and all phases. 2.7 Failure modes (ref. Sec.3 [7]) 2.7.1 The minimum list of failure modes is evaluated in Table 14-6 for the laminate of the main body. Table 14-6 Minimum list of failure modes for the laminate Minimum list of failure Evaluation modes Fracture (local or global) Relevant Buckling (local or global) Not relevant, since we have no compressive loads. (The liner may see compressive loads after yielding. Such loads can potentially cause buckling) Burst Here same as fracture, since no high rate loads are applied Leakage Relevant Impact Relevant, if tools can be dropped on the vessel etc. Excessive deformation, Ovalisation, Excessive displacement Wear No other failure modes than the ones given in the table have been identified. 2.7.2 The evaluation above should be carried out for all parts of the vessel, but this is not covered in the example. 2.7.3 The relevant failure modes shall be linked to the functional requirements of each part of the component. In the present example this link is only considered for the main body of the vessel, as shown in Table 14-7. 2.7.4 Discussions regarding the link between failure mode and limit state should take place between the designer and the client. All failures related to modes that lead to pressure loss or leakage are considered to be Ultimate Limit States (ULS) in this example, i.e. all failure modes are linked to an ULS condition. 2.8 Loads (ref. Sec.3 [9]) Relevant for vessel with liner, because the liner may have a failure strain that should not be exceeded. This strain may put a limit on the strain of the body of the vessel. Otherwise not relevant, since the vessel has no restrictions on deformation. Large deformations may be linked to some other failure modes, will be covered by analysing the other failure modes. Not relevant, since nothing slides over the vessel. Table 14-7 Link of failure modes and functional requirements Functional Failure mode Comments requirement Pressure containment Fracture, local fracture Shall always be checked. Impact Damage from impact may effect capacity to contain pressure. Excessive deformation Relevant if deformation is large enough to cause the liner to fail. Leakage Related to fracture, but often just a gradual release of fluid from a pressure vessel. Fracture will cause leakage, but other minor failure mechanisms may also cause leakage. Failure consequence is often less critical and related to normal safety class, but it depends on the fluid. Tightness/ Fluid containment Same as pressure containment 2.8.1 For each load a characteristic value shall be established. A checklist of common loads is given in App.A in the standard. Only pressure load is considered in this example as shown in Table 14-8 and Table 14-9. Table 14-8 Characteristic pressure load for gas tank with liner Load Char. value COV Sustained value Fatigue value Pressure loads: Maximum peak pressure*, here also identical to assumed operating pressure 46 bar 0 46 bar 0 – 46 bar (1300 times) Table 14-9 Characteristic pressure load for water tank without liner Load Char. value COV Sustained value Fatigue value Pressure loads: Maximum peak pressure*, here also identical to assumed operating pressure 14.8 bar 0 14.8 bar 0 – 14.8 bar (1300 times) The peak pressure is the maximum pressure the system can reach. DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.14 Calculation example: two pressure vessels – Page 187 2.8.2 The pressure vessel will be released once a week for less than 1 hour. In 25 years, this will add up to 1300 cycles between 0 bar and 46 bar for the gas tank and between 0 bar and 14.8 bar for the water tank. 2.8.3 The vessel will be pressure tested to peak pressure for certification after installation. 2.9 Environment (ref. Sec.3 [10]) 2.9.1 App.A [A.4] contains a checklist of common environmental parameters. Only relevant environmental parameters for this example are included in Table 14-10. Table 14-10 Long-term development of environmental parameters Environment: Char. value COV Sustained value Fatigue value Natural: Temperature external (surrounding air): 20 °C ±50% * 20 °C Not relevant here Functional: Temperature internal (water /air): 20 °C ±50% * 20 °C Not relevant here Exposure to water (for water vessel only) - permanent * Temperature changes of that magnitude do not modify the properties of the materials considerably. Therefore, the COV is not critical in this example. 3 Failure mechanisms 3.1 Identification of failure mechanisms (ref. Sec.6 [1]) 3.1.1 All failure mechanisms on the material level shall be identified. A minimum list is given in Sec.6 [1.1.2]. In this example the relevant failure mechanisms for a laminate are identified in Table 14-11. Table 14-11 Failure mechanisms relevant for laminates Fibre failure Matrix cracking Matrix crack growth Delamination Elastic buckling Unacceptably large displacements Stress rupture Fatigue Wear Fire* Explosive decompression* Impact* Chemical decomposition * these items are load conditions, but are treated here as failure mechanisms to simplify the approach in the standard. 3.1.2 Once the relevant failure mechanisms for the material are identified they shall be evaluated with respect to the critical failure modes of the component. Failure mechanisms that are linked to critical failure modes shall be analysed, other failure mechanisms can be ignored. Linking failure modes and mechanisms is shown in Sec.6 [1.5]. The results for this example are given in Table 14-12. DET NORSKE VERITAS AS
Page 1 and 2:
OFFSHORE STANDARD DNV-OS-C501 Compo
Page 3 and 4:
Offshore Standard DNV-OS-C501, Nove
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136: Offshore Standard DNV-OS-C501, Nove
Page 185: Offshore Standard DNV-OS-C501, Nove
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
show all

OS-C501

Create successful ePaper yourself

Delete template?

Save as template?