Robert A Walters reports on an innovative subsea pipeline rehabilitation system
Petronas Carigali (PCSB) is the owner and operator of an extensive network of sub-sea pipelines that are situated offshore from main land Malaysia, in the South China Seas. Many of these pipelines run from platform-to-platform and platform-to-onshore facilities over distances of between several hundred metres to several kilometres, in varying water depths. Internal corrosion, due in large part to sulfate reducing bacteria (SRB) can cause the pipelines to have a relatively short life cycle, which has historically resulted in the replacement of pipelines becoming necessary within a time period as short as four years.
Thus far, there has not been a viable methodology that could be utilised to install such a corrosion barrier to within a sub-sea pipeline, therefore a project for the design and development of Infield Liners (IFL) was instigated.
The project began in April 2011 and operating under the joint management of Petronas and Anticorrosion Protective Systems, which is a globally recognised pipeline rehabilitation specialist, it was possible for the project team to deliver a substantially market-ready product within a two year time-frame.
The IFL research and development project was aimed at realising the primary objective of developing the materials and technologies necessary to successfully implement the installation of plastic liners to existing and new sub-sea carbon steel pipelines being operated by PCSB and other Petronas companies, for the conveyance of corrosive hydrocarbon media, where SRB is one of the principal sources of corrosion activity. The IFL liner will protect the internal pipe bore from corrosion of any kind and will also offer a secondary containment capability in the event of a rupture or damage to the outer steel pipeline.
The project start point has been the testing and qualification of an existing nominal 8in Kevlar-reinforced plastic liner product, which is produced and manufactured for the utility market by a German company, Raedlinger. This material was selected as a good starting point for the project development work as it was recognised that although it was not previously used for the purpose of lining sub-sea pipelines, the general liner matrix does demonstrate many of the physical attributes that are perceived as being necessary to contribute toward the likely requirements for success. These attributes include: high tensile and good physical properties; moderate chemical resistance; a high degree of flexibility; and the ability to be manufactured and spooled in long lengths.
Liner qualification and development
The qualification of the liner has been generally undertaken in accordance with the API Recommended Practice 15S (First Edition March 2006) “Qualification of Spoolable Reinforced Plastic Line Pipe”, with further reference to the applicable ASTM test standards, API 17 series and Nace standards. The testing and qualification procedures have been undertaken in a number of locations including Germany, Norway and the UAE.
The final enhanced IFL Liner matrix comprises of a solvay Solexis PVDF inner liner, a tightly woven Aramid core, using Dupont Kevlar fabric, with an outer layer of abrasive resistant Thermoplastic Polyurethane from BASF. Other versions of the liner are also available for less aggressive service conditions, such as water reinjection and gas transmission.
All the principal objectives and milestones of the project have been fulfilled. A new enhanced version of the IFL liner has been developed. Performance testing has been undertaken that has been able to completely justify the utilisation of the liner in very aggressive, hot, sour hydrocarbon service conditions of up to 120 degrees centigrade, with the liner exhibiting a stand-alone burst capability of up to 120 Bar.
Motivation to use the new solution
The majority of sub-sea pipelines are constructed from carbon steel, laid by barge lay, during which single or double random joints of steel pipe are welded together on the deck of the barge and gravity laid onto the seabed. After completion of the welding process, crews on the barge can ‘make-up’ the external corrosion protection and ‘infill’ the missing concrete protection because this is easily accessible. It is not however possible to make-up any damage that may be caused to any internal coating by the welding process, or infill any cutback to the internal coating that would be necessitated so as to facilitate the steel weld. To compensate for this it is common for most sub-sea pipelines to be laid without an internal coating and an additional wall thickness of sacrificial steel to be added to the design so as to compensate for the calculated rate of corrosion throughout the design life of the pipeline.
Unfortunately however, corrosion is rarely a linear phenomenon and certain types of corrosion can cause damage to the pipe wall much more quickly than was allowed for at the design stage. Pitting, grooving, cracking or crevicing to the interior pipeline wall can occur in a remarkably short period of time, such that, for instance, a pipeline installed with a 20 year design life, may experience failure after as little as four years in service.
IFL offers the pipeline industry a viable, fast, economical option to new-lay pipeline replacement. IFL can be utilised for the rehabilitation of an existing sub-sea pipeline where it is desirable to extend the service life of the pipeline beyond the period of operation for which it was originally designed. It can be used when unforeseen operational parameters such as CO2 or SRB corrosion have caused the pipeline to reach the end of its useful life ahead of the originally intended schedule. The pipeline may or may not have at that point, already been shut down and abandoned for safety and/or environmental reasons. It can also be used when routine inspection of the pipeline has shown that greater than anticipated corrosion is taking place and that unless the corrosion is arrested, the pipeline will fail at some predictable point in the future, at a time which is less than the design life. Finally, the solution is also ideal in instances where pipelines have been decommissioned or abandoned due to integrity related issues.
Overall pipeline liner lengths that can be achieved are dependent upon the pipeline diameter, configuration and number of short radius bends, but trials would indicate that the rehabilitation of a typical 6 or 8in diameter hydrocarbon flow line could be feasible over distances of up to 10kms.
The replacement of a pipeline by the process of designing and laying of a new one and the abandonment and/or removal of the old one is normally representative of a major engineering, procurement and installation campaign and an equally major capital expense.
The insertion of an IFL liner into a defective pipeline is perceived as being a process of a far lesser magnitude in terms of planning, implementation and expense. It may well be possible (in terms of project turn-around) to achieve with IFL in weeks, what may otherwise take months or even years, with conventional pipe lay replacement, especially if the necessary pipe-lay barges for conventional barge lay are not located in the region.
The IFL development project has successfully achieved its primary goal, having delivered Petronas a viable alternative to the replacement of deteriorated offshore pipelines.
Following the successful conclusion of the IFL development work, APS has already installed several IFL Liners for the Petronas subsea pipeline network in Malaysia whereby re-commissioning of previously shut-down pipelines has been enabled. Petronas is favouring the option of pipeline rehabilitation over that of new-lay pipeline replacement and in so doing will be able to drastically reduce its offshore operational cost base.
The IFL system will become globally available in the first quarter of 2015 and several major oil companies have already expressed their sincere interest in this revolutionary subsea pipeline rehabilitation system, whereby major anticipated cost savings compared to new lay, are the main driving factor.
Robert A Walters is IFL’s global project director.