Innovative Deepwater Pipeline Flooding / Pigging System

A Subsea Remote Pipeline Flooding and Pigging System developed by Norson Services Ltd. of Aberdeen has been used off Egypt to flood and pig several deepwater pipelines.

Known as the Remote Flooding Module (RFM), the system was used to flood and pig pipelines in the Simian, Sapphire and Sienna fields located in Egypt's West Delta Deepwater Marine concession in the Mediterranean that supply gas to the Egyptian LNG export market.

Norson Services performed part of the pre-commissioning scope of work in an alliance with Weatherford International Limited. Norson's scope of work included development of the RFM to flood, pig, clean and allow pressure testing of the pipelines which ranged from 4-26 inches in diameter, were more than 62 miles in length and located in more than 3,200 feet of water.

Les Graves, Director of Norson's Pipeline, Process and Umbilical Division, says: "Newly installed pipelines are laid on the seabed at atmospheric pressure. Our remote flooding module uses the available seawater pressure outside the pipe as a source of power and water to flood and pig the lines while still meeting the desired filtration and chemical protection specifications."

Citing other benefits of the RFM, Graves said it is ROV-friendly and removes the need for connection to a surface vessel, thus saving substantial time and costs. The basic premise of the RFM design is to use the sea's hydrostatic pressure difference to pig/ flood newly constructed pipelines, while meeting all specified filtration, chemical injection and flow rate parameters without the need for a surface vessel to be in full-time attendance or even a connection by a down line.

By using the available outside water pressure in a controlled manner, the RFM is able to accomplish what normally requires a large surface vessel-mounted pumping spread.

Modular in design, the system is easy to deploy and recover from the seabed. It can be used aboard any small vessel capable of operating an ROV Filtration and chemical treatment specifications are fully met by onboard facilities. Chemicals are also stored onboard in flexible tanks.

An onboard or ROV-mounted hydraulically driven centrifugal pump unit is used to complete operations where pigging is required. Usually driven by the ROV, which is in any case used to recover the unit to the surface, this pump is designed to overcome the differential pressure across the pig(s) and drive them into the receiver.

Although used in just over 3,200 feet of water off Egypt, the RFM can be used in any water depth. Where no pigging is required 100% flooding can be achieved, depending on the operation being undertaken; in deep water over 99% pigging can be achieved without a completion boost pump being required.

The following are benefits of the RFM over conventional surface and other subsea equipment:

• Removal of downline failure risk;
• Reduced vessel size, space, crew and project costs;
• Schedule flexibility;
• Allows vessel to do other work during flooding operations;
• Large chemical holding capacity, allowing less recovery and deployment cycles and use on longer and larger lines;
• Use of rigid loading arm technology to reduce subsea connection times and damage to HP flexible jumper hoses; and
• Reduced thermal stabilization for hydrotest due to subsea water used in flooding.

Sumber : "Innovative Deepwater Pipeline Flooding / Pigging System". 26 Januari 2014. http://search.proquest.com/docview/197491802?accountid=31562