BJ PPS pre-commissions final segments of West African Gas Pipeline
  by: OilOnline
  Monday, March 17, 2008

BJ Process and Pipeline Services (BJ PPS) has completed pipeline pre-commissioning services for the final segments of the West African Gas Pipeline (WAGP) system on behalf of Willbros West Africa Inc., an Ascot Offshore Services Company.

One of the largest pipeline networks in the region, the WAGP system measures 678 km (421 miles) and will gather natural gas from fields in the Escravos region of the Niger Delta for delivery to customers in Ghana, Togo and Benin. The pipeline system comprises the existing Escravos-Lagos pipeline, a new onshore pipeline in Nigeria, and a new offshore pipeline together with a recently built compressor station.

Willbros West Africa Inc., an Ascot Offshore Services Company that is 100% Nigerian indigenous company, selected BJ PPS to prepare the new pipelines for commissioning and start-up. BJ PPS coordinated the delivery of all primary equipement, including some units weighing over 10 tonnes each, to commence operations in just two weeks, based on the project's narrow timeframe.

Displacing More Than 100,000 Tonnes of Seawater
The offshore pipeline, which measures 20 inches in diameter and stretches from the Lagos Beach Compressor Station (LBCS) near Badagry, Nigeria, to Takoradi, Ghana, extends 568 km (354 miles) through water depths to 71m. BJ PPS removed more than 100,000 tonnes of seawater that filled the pipeline before drying it in accordance with strict parameters. Final air in the pipeline had to be so dry that it would only form dew if cooled below -20°C. That required moisture content to be less than 100 kg for the entire length of the pipeline.

The BJ PPS project team designed a dewatering program using a train of six bi-directional pipeline pigs. Fresh water was used between the first and second pigs to treat the salt from the seawater. Then, dry air was injected between the remaining four pigs and used to drive the train from the LBCS to Takoradi. The discharged seawater was routed offshore for safe disposal.
The dewatering run was completed in less than 19 days and deemed successful when the pigs arrived conveying a clear change from water to air discharge. A good seal maintained by the pigs left no significant amount of water in the line.

At the end of the dewatering phase, the air pressure in the pipeline was 8.8 bar. To commence the air drying process, pressure was vented at Takoradi, in the same direction as the pigging run. The expanding air takes up water vapour and moves it along the line to the vent. When venting commenced, a small discharge of dust signalled the dewatering run had been effective. BJ PPS vented the offshore pipeline in just six days.

Special care was taken to ensure all pressure was vented from the long line and that it was safe to remove the pig receiver. All six pigs were examined and found to be in good condition. BJ PPS then restarted the equipment spread at the LBCS to continue air drying the offshore line. A final low-rate purge verified the line was dried to less than -20°C dew point following a 14-day dedicated operation.

The final phase of the operation was to fill the pipeline with nitrogen so that it would be inert in preparation for commissioning with natural gas.

Complete Pre-commissioning Service
The new onshore pipeline measures 30 inches in diameter and runs 56 km from the Alagbado Tee connection on the Escravos-Lagos line to the LBCS. BJ PPS provided a full range of pre-commissioning services, including pipeline flooding, cleaning, gauging, hydrostatic pressure testing, dewatering, drying, and filling with nitrogen to make inert. Again, the project team dried the line to less than -20°C dew point. BJ PPS overcame challenges associated with the project, including securing a supply of water to flood the pipeline (by pumping from the Atlantic Ocean) and moving equipment in difficult site conditions.

The scope of the WAGP system required BJ PPS to plan and manage several different phases, including operating the air equipment spread continuously for several weeks. Operations were carried out efficiently and completed ahead of schedule in less than 115 days.

"WAGP greatly appreciates the partnership with BJ PPS during the pipeline pre-commissioning phase of the project. In particular, BJ PPS are to be recognised for an exemplary drying programme during which the high levels of equipment uptime and dewpointing capability contributed to a reduced duration of critical path works. Well done to all concerned," said David Simons, engineering and construction manager for WAPCo, the owner and operator of the pipeline transmission system. WAPCo is a consortium consisting of partners Chevron, Shell, Nigerian National Petroleum Corporation (NNPC), Ghana's Volta River Authority (VRA). Societe Beninoise de Gaz (SoBeGaz), and Societe Togolaise de Gaz (SoToGaz).

"In addition to operations and management personnel, BJ PPS maintenance personnel were always onsite to ensure that the operation progressed smoothly. The overall success can be attributed to the combined expertise and commitment of everyone involved. We are extremely pleased with the results, and look forward to working for Willbros West Africa in the future," said Lindsay Link, general manager of BJ PPS.
BJ PPS managed the WAGP operation from its operations base in Port Harcourt, Nigeria, with support from its base in Aberdeen, Scotland. The project commenced in September and was completed in December 2007. To carry out this operation, BJ PPS used a full 5,400 scfm and 24 bar primary air compression package with dryers and a nitrogen membrane unit. In addition, a full 20 m3/min flooding and testing spread was used on the 30-inch onshore pipeline.
BJ PPS has worked on several projects in the past on behalf of Willbros West Africa Inc, an Ascot Offshore Services Company.

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