OS-C501

Recommendations

Info

Offshore Standard DNV-OS-C501, November 2013 Sec.12 Operation, maintenance, reassessment, repair – Page 174 SECTION 12 OPERATION, MAINTENANCE, REASSESSMENT, REPAIR 1 General 1.1 Objective 1.1.1 The objective of this section is to provide requirements for operation and in-service inspections. This section also provides general guidance on structural integrity assessment of composite components to demonstrate fitness for purpose in case deviations from design appear during operation. 2 Inspection 2.1 General 2.1.1 An inspection philosophy for the component should be established. The philosophy shall at least contain: — the items to be inspected, arranged according to their order of importance — the parameters to look for and or measure, e.g. cracks, delaminations, impact damages, overheating (or damages from local burning), visible overloading (bending, unintended use), discoloration — methods of inspection to be applied for each item — inspection frequency — acceptance criteria — reporting routines. 2.1.2 In case of findings at the inspections, a plan should be worked out listing suggested actions to be taken, depending on the type of findings. The plan may be included in the inspection philosophy. 2.1.3 Inspection procedures shall be defined for: — manufacturing control — detection of damage due to accidental loads or overloads in all phases — detection of damage due to unexpected high degradation of long term properties in all phases. 2.1.4 Inspection shall be linked to possible failure modes and mechanisms identified in the design. 2.2 Inspection methods 2.2.1 Available inspection methods can often not detect all critical failure mechanisms. However, the methods may detect preceding failure mechanisms. A link between detectable failure mechanisms and critical failure mechanisms shall be established. 2.2.2 The reliability and functionality of all inspection methods should be documented. 2.2.3 In many cases a complete inspection programme cannot be developed due to the limited capabilities of available NDE equipment. In that case the following alternatives in [2.2.4] to [2.2.8] may be used. 2.2.4 Inspection of components during or right after manufacturing may be replaced by well documented production control. 2.2.5 Inspection to detect damage due to accidental loads or overloads may be compensated for by monitoring the loads and comparing them to the design loads. 2.2.6 Effect of higher degradation than expected can be compensated for by using the failure type brittle in the long term analysis. If this method is used the component must be replaced or re-evaluated after all overloads or other events exceeding the design requirements. This approach shall be agreed upon with the customer. 2.2.7 If the failure mechanisms are not fully understood, or competing failure mechanism are present and one is uncertain about their sequence, inspection is required. 2.2.8 Inspection frequencies and acceptance criteria should be determined for each project. 3 Reassessment 3.1 General 3.1.1 Reassessment of composite components shall be based on the same criteria as designing and building a new component. 3.1.2 Old calculations and test data may be used as far as applicable. DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.12 Operation, maintenance, reassessment, repair – Page 175 4 Repair 4.1 Repair procedure 4.1.1 A repair procedure shall be given for each component. 4.1.2 A repair shall restore the same level of safety and functionality as the original structure, unless changes are accepted by all parties in the project. 4.1.3 An acceptable repair solution is to replace the entire component if it is damaged. This approach requires that the component can be taken out of the system. 4.1.4 It may also be acceptable to keep a component in service with a certain amount of damage without repairing it. The size and kind of acceptable damage shall be defined and it must be possible to inspect the damage. The possible damage shall be considered in the design of the structure. 4.1.5 If local damage may happen to the structure detailed procedures to repair such anticipated damage shall be given. 4.1.6 If the damage is due to an unknown loading condition or accident, an analysis of the damage situation shall be carried out. The analysis shall identify whether the damage was due to a design mistake or an unexpected load condition. If the unexpected load may reoccur a design change may be required. 4.2 Requirements for a repair 4.2.1 A repair should restore the stiffness and strength of the original part. If the stiffness and or strength cannot be restored, the performance of the component and the total system under the new conditions shall be evaluated. 4.2.2 It shall be documented that local reduction in strength may not be critical for the total performance of the structure. 4.3 Qualification of a repair 4.3.1 A repair is basically a joint introduced into the structure. The repair shall be qualified in the same way as a joint (see Sec.7). 4.3.2 The repair procedure used to qualify the joint shall also be applicable for each particular repair situation. 4.3.3 Suitable conditions for repair work shall be arranged and maintained during the repair. This is mandatory, irrespective of whether the repair is carried out on site or elsewhere. If suitable conditions cannot be arranged and maintained on site, the component should be moved to a more suitable site. 5 Maintenance 5.1 General 5.1.1 A maintenance procedure shall be given for each component. All aspects related to maintenance should be covered. Guidance note: Most composites are fairly maintenance free. Cleaning agents and solvents that can be used and others that should not be used should be described in the manual. If the component is painted methods to remove the paint and to apply new paint should be described 6 Retirement 6.1 General ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 6.1.1 A method for retirement of all components shall be documented. DET NORSKE VERITAS AS
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OS-C501

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