Sample Industrial Code on Removal of Pipeline Defect via Grinding
ASME B31.8 ( 2019 ) Clause 851.4.2 Permanent Field Repairs of Injurious Dents and Mechanical Damage
( 3 ) External mechanical damage , including cracks , may be repaired by grinding out the damage , provided any associated indentation of the pipe does not exceed a depth of 4 % of the nominal pipe diameter . Grinding is permitted to a depth of 10 % of the nominal pipe wall with no limit on length . Grinding shall produce a smooth contour in the pipe wall . The remaining wall thickness shall be verified using ultrasonic testing . After grinding , the surface shall be inspected for cracks using a non-destructive surface examination method capable of detecting cracks , and the surface shall be inspected with a suitable etchant .
( a ) For pipelines operating at or above 30 % SMYS , grinding is permitted to a depth greater than 10 % up to a maximum of 40 % of the pipe wall , with metal removal confined to a length given by the following equation :
Whereby “ a ” = measured maximum depth of ground area , in . ( mm ); “ D ” = nominal outside diameter of the pipe , in . ( mm ); “ L ” = maximum allowable longitudinal extent of the ground area , in . ( mm ); “ t ” = nominal wall thickness of pipe , in . ( mm )
Table 5 : Sample Clause in Industrial Standard that mentioned Grinding on Pipeline .
Conceptual Flow of Offshore Pipeline Damage Detection and Repair
Identify Damaged Pipeline ( 1 ) |
Notify DOSH ( 2 ) |
Secure Damaged Pipeline ( 3 ) |
Evaluate the Damaged Section ( 4 ) |
Engineering Mitigation / Solution ( 5 ) |
Remarks : 1 . During normal pipeline maintenance or inspection , symptom of potential damage should be identified .
Pipeline owner needs to put effort to verify if any pipeline damaged exist . 2 . Important to notify DOSH as per the Malaysian Law on any dangerous occurrence . 3 . If pipeline is static always even with the presence of underwater current , no additional securing mechanism required , or else use may install concrete mattress to prevent further movement .
4 . Pipeline Damaged evaluation can comprise External and Internal segment via appropriate Non- Destructive Examination ( NDE ). During this stage , owner needs to ensure that Equipment has valid calibration , correct execution process via approved procedure , and competent NDE Personnel on the job . Extra NDE mock-up test may be performed for verification purpose .
5 . With all data in-hand , engineers will be able to advise the pipeline owner on the best way forward , including the cost factor . Wise to conduct FEA before and after mitigation for comparison , and to ensure high stress points of dent from Mechanical Damaged are removed , including improving fatigue life .
Table 6 : Example of Flow Chart on Subsea Pipeline Damage Response
justifications , sufficient emergency safeguards in place , and approval from the pipeline owner . Though this approach is rarely practised locally , the industrial code does include this option . For example , ASME B31.8 clause 851.4.2 do highlight the allowable wall thickness removal by grinding , including calculation as illustrated in Table 5 . During material removal activity , it is vital to regularly verify the pipeline metal thickness to ensure the required wall thickness exists . This can be done by using underwater Ultrasonic Testing devices via zero angle probe . Also , a diver can verify defect removal via MPI .
“ Fatigue ”, which is a failure mechanism that occurs on material below the tensile strength that is subjected to dynamic and fluctuating stresses
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