Common use of Plastic liners Clause in Contracts

Plastic liners. The tensile yield strength and ultimate elongation shall be determined in accordance with paragraph A.22. (Appendix A to this annex). Tests shall demonstrate the ductile properties of the plastic liner material at temperatures of -50 °C or lower by meeting the values specified by the manufacturer; the polymeric material shall be compatible with the service conditions specified in paragraph 4. of this annex. In accordance with the method described in paragraph A.23. (Appendix A to this annex), the softening temperature shall be at least 100 °C." 6.4. Test pressure The minimum test pressure used in manufacture shall be 30 MPa; 6.5. Burst pressures and fibre stress ratios For all types of cylinder the minimum actual burst pressure shall not be less than the values given in Table 6.3 of this annex. For type CNG-2, CNG-3 and CNG-4 designs the composite over-wrap shall be designed for high reliability under sustained loading and cyclic loading. This reliability shall be achieved by meeting or exceeding the composite reinforcement stress ratio values given in Table 6.3 of this annex. Stress ratio is defined as the stress in the fibre at the specified minimum burst pressure divided by the stress in the fibre at working pressure. The burst ratio is defined as the actual burst pressure of the cylinder divided by the working pressure. For type CNG-4 designs, the stress ratio is equal to the burst ratio. For type CNG-2 and CNG-3 designs (metal-lined, composite over-wrapped) stress ratio calculations shall include: (a) An analysis method with capability for non-linear materials (special purpose computer program or finite element analysis program); (b) Elastic-plastic stress-strain curve for liner material shall be known and correctly modelled; (c) Mechanical properties of composite materials shall be correctly modelled; (d) Calculations shall be made at: auto-frettage, zero after auto-frettage, working and minimum burst pressures; (e) Pre-stresses from winding tension shall be accounted for in the analysis; (f) Minimum burst pressure shall be chosen such that the calculated stress at minimum burst pressure divided by the calculated stress at working pressure meets the stress ratio requirements for the fibre used; (g) When analysing cylinders with hybrid reinforcement (two or more different fibre types), the load share between the different fibres shall be considered based on the different elastic moduli of the fibres. The stress ratio requirements for each individual fibre type shall be in accordance with the values given in Table 6.3. of this annex. Verification of the stress ratios may also be performed using strain gauges. An acceptable method is outlined in the informative Appendix E to this annex. 6.6. Stress analysis A stress analysis shall be performed to justify the minimum design wall thicknesses. It shall include the determination of the stresses in liners and fibres of composite designs. 6.7. Leak-before-break (LBB) assessment Types CNG-1, CNG-2 and CNG-3 cylinders shall demonstrate Leak-Before-Break (LBB) performance. The LBB performance test shall be carried out in accordance with paragraph A.6. (Appendix A to this annex). Demonstration of LBB performance is not required for cylinder designs that provide a fatigue life exceeding 45,000 pressure cycles when tested in accordance with paragraph A.13. (Appendix A to this annex). Two methods of LBB assessment are included for information in Appendix F to this annex. 6.8. Inspection and testing The manufacturing inspection shall specify programmes and procedures for: (a) Manufacturing inspection, tests and acceptance criteria; and (b) Periodic in service inspection, tests and acceptance criteria. The interval of visual reinspection of the external cylinder surfaces shall be in accordance with paragraph 4.1.4. of this annex unless varied by the Type Approval Authority. The manufacturer shall establish the visual reinspection rejection criteria based on the results of pressure cycling tests performed on cylinders containing flaws. A guide for manufacturer's instructions for handling, use and inspection is provided in Appendix G to this annex.

Plastic liners. The tensile yield strength and ultimate elongation shall be determined in accordance with paragraph A.22. (Appendix A to this annexA). Tests shall demonstrate the ductile properties of the plastic liner material at temperatures of -50 °C or lower by meeting the values specified by the manufacturer; the polymeric material shall be compatible with the service conditions specified in paragraph 4. of this annex. In accordance with the method described in paragraph A.23. (Appendix A to this annexA), the softening temperature shall be at least 90 °C, and the melting temperature at least 100 °C." 6.4. Test pressure The minimum test pressure used in manufacture shall be 30 MPa; 6.5. Burst pressures and fibre stress ratios For all types of cylinder the minimum actual burst pressure shall not be less than the values given in Table 6.3 of this annex. For type CNG-2, CNG-3 and CNG-4 designs the composite over-wrap shall be designed for high reliability under sustained loading and cyclic loading. This reliability shall be achieved by meeting or exceeding the composite reinforcement stress ratio values given in Table 6.3 of this annex. Stress ratio is defined as the stress in the fibre at the specified minimum burst pressure divided by the stress in the fibre at working pressure. The burst ratio is defined as the actual burst pressure of the cylinder divided by the working pressure. ; For type CNG-4 designs, the stress ratio is equal to the burst ratio. ; For type CNG-2 and CNG-3 designs (metal-lined, composite over-wrapped) stress ratio calculations shall include: (a) An analysis method with capability for non-linear materials (special purpose computer program or finite element analysis program); (b) Elastic-plastic stress-strain curve for liner material shall be known and correctly modelled; (c) Mechanical properties of composite materials shall be correctly modelled; (d) Calculations shall be made at: auto-frettage, zero after auto-frettage, working and minimum burst pressures; (e) Pre-stresses Prestresses from winding tension shall be accounted for in the analysis; (f) Minimum burst pressure shall be chosen such that the calculated stress at minimum burst pressure divided by the calculated stress at working pressure meets the stress ratio requirements for the fibre used; (g) When analysing analyzing cylinders with hybrid reinforcement (two or more different fibre types), the load share between the different fibres shall be considered based on the different elastic moduli of the fibres. The stress ratio requirements for each individual fibre type shall be in accordance with the values given in Table 6.3. 6.3 of this annex. Verification of the stress ratios may also be performed using strain gauges. An acceptable method is outlined in the informative Appendix E to this annex. 6.6. Stress analysis A stress analysis shall be performed to justify the minimum design wall thicknesses. It shall include the determination of the stresses in liners and fibres of composite designs. 6.7. Leak-before-break (LBB) assessment Types CNG-1, CNG-2 and CNG-3 cylinders shall demonstrate Leak-Before-Before- Break (LBB) performance. The LBB performance test shall be carried out in accordance with paragraph A.6. (Appendix A to this annexA). Demonstration of LBB performance is not required for cylinder designs that provide a fatigue life exceeding 45,000 pressure cycles when tested in accordance with paragraph A.13. (Appendix A to this annexA). Two methods of LBB assessment are included for information in Appendix F to this annex. 6.8. Inspection and testing The manufacturing inspection shall specify programmes and procedures for: (a) Manufacturing inspection, tests and acceptance criteria; and (b) Periodic in service inspection, tests and acceptance criteria. The interval of visual reinspection of the external cylinder surfaces shall be in accordance with paragraph 4.1.4. of this annex unless varied by the Type Approval Authority. The manufacturer shall establish the visual reinspection rejection criteria based on the results of pressure cycling tests performed on cylinders containing flaws. A guide for manufacturer's instructions for handling, use and inspection is provided in Appendix G to this annex.