OS-C501

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Offshore Standard DNV-OS-C501, November 2013 Sec.10 Component testing – Page 160 2 Qualification based on tests on full scale components 2.1 General 2.1.1 The purpose of tests is to investigate the load effects. Usually displacements and the characteristic strength are determined. 2.1.2 The load cases in the tests shall be combined in a realistic manner. Test results are only valid for the load cases tested. 2.1.3 The environment defined in Sec.3 [10] shall be represented in a realistic manner. The environmental effect can be accounted for either by: — carrying out tests on components that have been subjected to a representative ageing (accelerated or not accelerated) — carrying out tests on components combined with ageing (accelerated or not accelerated). An example is the standard techniques used for qualification of pipes. Test results are only valid for the environments tested. 2.1.4 The failure mode(s), failure mechanism(s) and location(s) of failure shall be recorded and verified during/after the tests. The partial/safety factor(s) applied shall correspond to the actual failure mechanisms. 2.2 Short term properties 2.2.1 Short term failure shall be analysed based on the general failure criteria for single or multiple loads as described in Sec.6 [2.2] - [2.3]: — the partial resistance model factor g Rd can be set equal to 1.0, if the tests represent design and material properties in a satisfactory manner — the partial load model factor g Sd can be set equal to 1.0, if the tests represent actual applied loads in a satisfactory manner. If loads are representing effects of other phenomena, uncertainties in the conversion from the other phenomena to the loads shall be included in γ Sd , i.e. uncertainties in the transfer function as describe in Sec.9 [1.4] shall be included — the characteristic strength of the tested component shall be determined based on the test results as described in Sec.4 [2.4] for static data — the safety factors shall be chosen based on distribution and COV of the load and COV of the component test results (material’s COV) as in Sec.8. The distribution and COV of the load shall be based on the loads the structure will experience in the application, not on the loads of the test. 2.2.2 At least three specimens shall be tested. The relationship between number of tests and characteristic strength is given in Sec.4 [2.4]. 2.3 Long term properties 2.3.1 Long term failure shall be analysed based on the principles for obtaining time dependent properties described in Sec.6 [10] and [11]: — the partial resistance model factor γ Rd can be set equal to 1.0, if the tests represent design and material properties in a satisfactory manner — the partial load model factor γ Sd can be set equal to 1.0, if the tests represent actual applied loads in a satisfactory manner. If loads are representing effects of other phenomena, uncertainties in the conversion from the other phenomena to the loads shall be included in γ Sd , i.e. uncertainties in the transfer function as describe in Sec.9 [1.4] shall be included — The characteristic strength shall be determined based on the test results as described in Sec.4 [3.11] for time dependent data — the safety factors shall be chosen based on distribution and COV of the load and COV of the component test results (material’s COV) as in Sec.8. The distribution and COV of the load shall be based on the loads the structure will experience in the application, not on the loads of the test. 2.3.2 At least ten specimens shall be tested. The relationship between number of tests and characteristic strength is given in Sec.4 [3.11] for data that must be extrapolated to longer lifetimes and for data that can be used within the test period. 2.3.3 If data must be extrapolated to longer lifetimes than the measured time it shall be shown that no other failure modes may develop between the test time and the expected lifetime of the structure or component. It is usually not possible to show this by component testing only. Some analysis and calculations are necessary, see [4.3.5]. 2.3.4 The static strength of the structure after long term exposure shall be the same as the extrapolation of the long term test data of the fatigue or stress rupture tests. DET NORSKE VERITAS AS
Offshore Standard DNV-OS-C501, November 2013 Sec.10 Component testing – Page 161 2.3.5 Higher static strength values after long term exposure may be used if experimental evidence can be provided. A procedure to obtain strength data after long term exposure is suggested in Sec.4 [3.4] and [3.9]. 3 Verification of analysis by testing and updating 3.1 Verification of design assumptions 3.1.1 Tests under this category are carried out to verify that the assumptions on which the design is based are correct and that no important aspects of the design have been overlooked. Verification tests should be carried out to compensate for: — incorrect description of, or an unsatisfactory large uncertainty in the failure mechanisms — incorrect description of load combinations or corresponding large uncertainties — incomplete understanding of the effect of the environment — lack of experience of similar structures or components — uncertainty in the accuracy of modelling large stress gradients — assumptions that can be questioned or are difficult to document — unknown effect of large scale manufacturing procedures. 3.1.2 Tests under this category are carried out to verify that the analysis tools predict the response to the most critical load cases and environments in a correct or conservative manner. This type of testing shall be done if the particular analysis method has never been used for a similar structure and load situation before. 3.1.3 As it is not possible to test all load conditions that the structure will experience, the most critical load conditions should be selected. The selection shall be based not only on the most critical loads the structure is most likely to see. It shall also show that critical failure modes that can be caused by secondary loads are adequately modelled ([1.2]). 3.1.4 It may be necessary to test more than one aspect of an analysis. This may mean that two or more separate test programmes should be carried out, unless both aspects can be evaluated in one test. The remaining parts of this section explain the requirement for one test programme. Guidance note: The end fitting of a pipe has been analysed. There is uncertainty about fatigue performance and long term static strength. In this case both aspects should be tested separately. There is uncertainty about long term fatigue performance of new specimens and of specimens with impact damage. In this case the specimen can most likely be exposed to impact before the fatigue testing and only one test programme is needed. This test programme would cover both aspects in a conservative way. ---e-n-d---of---G-u-i-d-a-n-c-e---n-o-t-e--- 3.1.5 In general the environment defined in Sec.3 [10] should be represented in a realistic manner. The environmental effect can be accounted for either by: — carrying out tests on components that have been subjected to a representative ageing (accelerated or not accelerated) — carrying out tests on components combined with ageing (accelerated or not accelerated). An example is the standard techniques used for qualification of pipes. Since these tests are used to increase the confidence in calculation techniques other environments may be chosen if it can be demonstrated that the effects of the real environment can be predicted in a conservative way by a combination of analytical tools and the test results obtained from a special test environment. 3.1.6 The following steps shall be followed when defining and carrying out test under this category: 1) The load condition(s) and environments are defined as specified in Sec.3. 2) The failure mode, failure mechanism and location of failure etc. on which the design is based are specified. 3) The number of test specimens required per load condition is specified. The number of test specimens may have to be determined based on an engineering judgement. 4) Carry out testing. 5) Verify failure mode, failure mechanism and location of failure. If these are as predicted in 2. the assumptions for the design are considered corroborated. If one or more of these are not as predicted in 2. the reason for the discrepancy shall be investigated and the validity of design assumptions re-evaluated. 3.1.7 Instead of testing the full component it may be more relevant to test parts or details. Which test is the best should to be evaluated considering relevant failure modes and all possible interaction effects. 3.1.8 The failure mode(s), failure mechanism(s) and location(s) of failure shall be recorded and verified during/after the tests. DET NORSKE VERITAS AS
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OS-C501

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