Scope
Pipeline pigging is essential for maintaining cleaning and inspection performance. When debris or liquids accumulate in the line, throughput can be reduced so maintaining pigging intervals is important. Foreign objects within the pipeline introduce new risks during pigging and can create operational challenges that must be resolved to maintain system integrity.
The client operates a gas export pipeline transporting gas from an offshore platform to an onshore terminal. After subsea tie‑in work, four high sealing bidirectional pigs were run for dewatering and drying. A fifth pig was later launched to separate gas export and nitrogen.
When this pig was received, damage was observed on the front sealing disc and the transmitter holder was broken with no transmitter recovered. Seven foam pigs were then run to try to locate or retrieve the transmitter but none were successful.
The client approached Jee for support to understand the cause of the damage, identify the potential hold up location of the transmitter and define a safe and effective forward pigging strategy.
Solution
Jee reviewed the available data and identified three likely hold up locations within the system. These were a check valve, a wye and a barred tee at receipt. The check valve was considered the highest risk area due to a lip shown on the valve drawing where the transmitter could become lodged perpendicular to the flow. A hold up in the wye would not affect current hard bodied pigging operations.
Jee assessed the risk of hard bodied pigging through the wye with the transmitter in place and identified that the operational pig nose, which was thicker and larger than a standard design due to system requirements, could increase the risk. Jee therefore proposed modifications to the pig design. Working with the client and pig vendor, this led to the development of two alternative, less aggressive pig designs.
As a spare duplicate check valve was available for a future tie in, Jee recommended onshore testing of the current and modified pig designs. Testing simulated the transmitter in the worst possible configuration to assess the force required to transit the valve.
Testing showed that both modified designs required significantly lower differential pressure to pass through the check valve. The tapered nose enabled them to ride over the transmitter. The original pig design could not ride over the obstruction and required additional differential pressure to break the transmitter, which may not have been achievable in the live system. This would have created a risk of a stalled pig.
Conclusion
Based on the successful onshore testing, the client gained confidence in reinstating hard bodied pigging using one of the modified pig designs proposed by Jee. This ensured continued management of liquid dropout and potential debris within the pipeline without increasing operational risk.
Jee’s client said: “The pig performed exceptionally well, surpassing even the foam pigs. Thank you once again for your invaluable guidance. We have gained significant knowledge from [Jee’s] expertise.”
For more information, visit www.jee.co.uk/pigging
To contact Sean Tucker, email sean.tucker@jee.co.uk, or call +44 (0)1732 371 371.