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Technical Article
The Eastern Trough Area Project (ETAP) was innovative in many ways. It allowed at least 7 marginal oil and gas fields of differing ownership to be developed in one of the largest projects in the later years of the British sector of the North Sea. The wells were spread over a distance of 35 kilometres feeding back to one Central Processing Facility (CPF). The work followed the “Alliance Contract” principle but with seven oil companies (BP, Shell, Esso, Agip, Mitsubishi, Murphy and Total) working together. Alliancing was a first for most of them, although BP had used it on the Andrew project.
The field production was planned at 205 thousand barrels per day (annual average) of oil on plateau for 2-3 years. In
addition, gas produced from each field, after processing and planned injection is exported at around 350 million standard
cubic feet per day (annual average) with an anticipated plateau of 4-5 years. Natural gas liquid products from the export gas will provide over 1100 tonnes/day of propane, butane and condensate. With these production levels from 30 wells working to one CPF, the fields could be made to be viable. However, the potential cost of downtime from any problem was assessed as being vast, so careful planning of all aspects was vital with fire safety high on everyone’s mind.
The Project Path
As with all offshore projects, planning begins with the availability of
floating lifting capacity and the first discussions took place as the
architects and engineers at Brown and Root considered the potential
weight of modules. These “first pass weights” included consideration of
the passive fire protection; Firetex M90 was used as the benchmark in these calculations.
The next stage involved some more detailed considerations as the
“Safety Case” was put together. The plan was to split the CPF into two
platforms linked by two 60m bridges with a ‘processing, drilling and riser’
(PdR) platform containing all the working elements and a ‘quarters and
utilities’ (QU) platform where the accommodation for 85 workers was
sited. Both of these modules were located over the Marnock field. A
normally unmanned platform was to be installed over the Mungo field to
separate liquids and gas from this field with manning limited to two
helicopter visits per week with a 6 – 12 man crew. An emergency shelter
was provided for any occasion when this crew could not return to the
CPF.
The helipad was placed on the QU platform to make it remote from the risers and processing equipment. By having the two platforms in the CPF, some temporary refuges could be located upwind of the production facilities and an optimal layout of the PdR platform that allowed for good ventilation, explosion mitigation and escape, could be achieved. Some lifeboats were also located on the remote QU platform. Many of these decisions reflected experience from Piper Alpha and this included the consideration of passive fire protection. It is the “passive” fire protection that is the subject of this study.
Key Partners
In alliance contracting key partners are chosen early and in this case, the main yards that would build the elements and some sub contractors were selected well before detailed designs were finalised. The selection of the passive fire protection supplier was also made early on and this was done by requesting a presentation of the features and benefits being offered by individual suppliers. For Leighs Paints we decided that a detailed presentation should also include the anti-corrosion links as we can offer a total coatings package. This presentation was done to a panel representing the lead oil company BP, designers Brown and Root, the yards and coatings contractors.
With this hurdle successfully negotiated, we then established another innovative element (for 1996) in the project by
installing Cad-Cam equipment and a computer link between the design offices and Leighs Bolton headquarters. This link enabled the fast passage of drawings to our experts to allow fire protection and coatings detail to be added before they were passed to the yards and sub contractors. Technical service staff were then allocated to the yards so that the application could be overseen and details confirmed on site. From sanction in December 1995 to start up in July 1998 the project was an opportunity for team working.
Systems Applied
The main coating used for passive fire protection was Firetex M90 epoxy intumescent that was required to provide protection mainly for hydrocarbon fire to H60, but often with jet fire capability for anything from 15 minutes to the full 60 minutes. The period of 15 minutes widely used for jet fire was determined by the time taken to operate the Emergency Shutdown Valves plus a suitable margin of error. With this requirement adjustments to the thickness of the intumescent coating were required with insertion of support scrim if not otherwise included in the simple H rating requirement. Specialist specifications were required to fit in with the risk assessment and the progressive collapse analysis on which the safety case had been agreed. By the end of the project, some 18,000m² of surface had been treated with passive fire protection materials.
It was decided that easier and quicker working would be facilitated if all the steel areas on the project were given a universal all weather priming coat of epoxy zinc phosphate and therefore it was not necessary to identify the fire protection areas for a special primer to be applied during the “black box” construction phase. As most of the fabrication work was done in either the north of England or Scotland from early 1996 to the spring of 1998 much work in low temperatures and poor weather was planned, for which this primer was eminently suitable. The same primer was used on the jacket for the splash zone treatment and the intumescent was then applied to both the jacket and the risers, down to the start of the splash zone.
Vital Links
Helidecks are a vital link in any emergency 200 miles out into the North Sea and so fire protection to the aluminium landing pad and steel substructure on the QU module was also required. The standard specification for epoxy passive fire protection onto aluminium is to flash blast using a non-ferrous abrasive, treat with a specialist adhesion primer and then the thickness of intumescent required. Specialist testing of Firetex M90 was undertaken to demonstrate the performance onto aluminium alloys for just this purpose.
For pipework, tests on the impact resistance of Duraglass glass flake polyester material showed that it was capable of considerable handling without severe damage so that lengths of pipe could be treated with the full specification of anti corrosive material in the shop under controlled conditions and only required the weld lines to be treated on site,
thus reducing costs considerably. This procedure reduced the man-hours and indeed the whole alliancing principle of this unusual contract allowed many such innovative co-operative techniques to be applied.
Epigrip glass flake epoxy material offers a tough, abrasion resistant finish for splash zone areas which can be applied over the intumescent fire protection.
Dual Purpose Specification
The risers offered a different challenge with a need to maintain temperature whilst also offering fire protection. This was achieved by using Firetex M89 epoxy thermal barrier coating applied over the primer but underneath the Firetex M90 intumescent material. This dual purpose specification offers protection also for vessels where there is a requirement to
maintain a working temperature of up to 150°C and also provide fire protection in hydrocarbon and jet fire conditions. Where a good aesthetic finish was required, for example onto some process vessels, a decorative coat of polyurethane to the required colour was used. In accommodation areas, the fire resistance requirements were reduced because of the remote
nature of the QU module and so some areas were protected to A60 with surface spread of flame ratings where required.
Conclusions
The important key to this project was that with the team working together on a basis that allowed any savings developed by innovation in techniques and materials to be shared, engineered solutions could be developed. The close links between the designers, material suppliers and contractors that were established on this project allowed it to be brought in on time and under budget with estimated savings over standard construction techniques being put as high as 1 million man hours.
Alliance contracting was a new technique brought in towards the end of the North Sea development era to reduce costs and
allow such marginal fields as these to be developed at a time when the price of oil was somewhat lower than the $18 per
barrel price for Brent crude that was usually considered the break even level. This was done under what was called the
“CRINE” initiative (Cost Reduction in the New Era) and the work proved that simple price competition for such jobs is not the only way to bring them in and that if all concerned in critical areas can be encouraged to work together, then engineered solutions that make considerable savings can be produced. The UK construction industry has agonized for many years over first the Latham and then the Egan reports in the 1990s that looked for ways to reduce conflict and barriers to improve the construction product and reduce its costs. Many saw the alliance method as the way to do this.
Entrenched positions on claim and counter claim are destructive and expensive and in the end often only the lawyers win.
This contract was an example of engineered solutions and co-operative working bringing excellent results. Recent checks
with the maintenance contractors show that the systems used for passive fire protection and anti-corrosive coatings are working well under the extreme conditions found in this area and the fields are producing well.
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