metal loss and internal pipeline corrosion . At the same time , IPs may be able to provide geometrical information or pick-up physical defects , allowing owners to obtained preliminary information for assessment together with the distance recording log . Based on the IP result , the owner can determine Fit-for-Service ( FFS ) of the said pipeline .
Repair Approach
In general , offshore pipelines for the oil and gas industry can be split into Sweet Service and Sour Service whereby the medium inside the pipeline is without hydrogen sulfide or H 2
S ( or relatively low ) and with H 2
S content respectively . Most of our subsea pipelines in Malaysia are considered Sweet Service . With this kind of characteristic , the mode of our pipeline leaking scenario will theoretically be due to severe corrosion or mechanical damage . Although the Kolva River Spill ( 1994 ) was a result of severe corrosion , pipeline leak from this factor can be minimised provided sufficient maintenance and inspection are conducted by the pipeline owner , including timely action taken when abnormalities are detected .
Remarks :
● The presence of Sour Service ( H 2
S ) in the process fluid may lead to Sulfide Stress Cracking ( SSC ) on Carbon Steel material . Thus , appropriate material selection and testing is required to prevent this situation .
● Rule of thumb , Engineers can determine whether the exiting pipeline is still compatible by comparing the maximum operating pressure ( P max
) which shall be greater than the calculated Safe Operating Pressure ( P S
).
Below shows the formula for P S per ASME
B31G ( 2012 ), Sec 1.5 :
● P s
= [ 2 x Material Yield Strength x Wall thickness ] / [ Outer Diameter x Design Safety Factor ]
Hence , the focus on this section will be on offshore pipeline leak caused by Mechanical Damage . One may wonder how a pipeline in the middle of the sea experience Mechanical Damage . While the probability may be low , it could happen with dropped objects during lifting activities or even hit by shipping anchor . Depending on the degree of damage , the pipeline may leak immediately , or it may give way at a later stage , or even be still fit-for-use . Regardless of the outcome , it is crucial for pipeline owners in Malaysia to immediately notify the Department of Safety and Health ( DOSH ) once they are aware of any dangerous occurrence related to their pipeline per regulation illustrated in Table 3 .
Petroleum ( Safety Measures ) ( Transportation of Petroleum by Pipelines ) Regulation 1985
Regulation 13 Dangerous Occurrence
1 . The owner , operator or contractor of a pipeline or his authorised representative shall immediately notify the Approving Authority .
2 . An owner or operator of a pipeline shall , as soon as he becomes aware of any defect in the pipeline or any circumstance which would affect the safety of the pipeline : a . rectify the defect or circumstance so as to ensure the safety of the pipeline . b . cease to operate the pipeline if the defect or circumstance cannot be made good or removed and inform the Approving Authority .
Table 3 : National Law Regarding Dangerous Occurrence on Pipeline
So , what is the strategic approach in handling a Mechanically Damaged Subsea Pipeline ? If leaking is observed , the response will be to depressurise the pipeline and activate the oil spill response before executing any repair . For damage that does not result in leakage , we can refer to common First Aid response analogy on a fractured bone or dislocated joint , whereby the initial step is to demobilise the injured area . Similarly for pipeline , if the damaged section is static , we can just leave it . However , if there is potential movement it is best to install “ Concrete Mattress ” on both the upstream and downstream locations . This is to prevent further motion as the Stress Concentration point in cyclic motion is a root cause for material failure ( break ).
Once the damaged section is secured , we need to continue with cleaning and examination to determine the degree of damage . In the medical discipline , doctors will use X-ray . For an offshore pipeline , cleaning can be done using high pressure water jets and grit blasting ( include seabed excavation ). Furthermore , engineers can technically inspect the pipeline using standard
53