Ship shape

Elaine Maslin

April 1, 2017

Polymer steel composite repairs are becoming a popular solution for worn out plates in the growing floating production vessel fleet. Elaine Maslin reports.

The FPF3 on station. Images from Intelligent Engineering.

The industry has been searching for solutions to repair the world’s aging 270 floating production units without having to take them off station to a shipyard. UK-based Intelligent Engineering (IE) has one: composite repairs.

Last year, IE carried out below the water line repairs over more than 120sq m of plate on two floating production vessels – ExxonMobil’s floating storage and offloading (FSO) vessel Komi Kribi 1, stationed off Cameroon, West Africa, and the floating production, storage and offloading (FPSO) vessel FPF-003, operated by Petrofac, off Thailand – both while the vessels remained in operation on station.

Furthermore, the firm’s composite repair technology has been extended to be used to create an emergency tunnel onboard the newbuild Glen Lyon FPSO, which is due to start production west of Shetland on the UK Continental Shelf this year. It’s also being used for strengthening helidecks – to handle heavier helicopters – and for upgrading vessels to ice-class – among a string of other applications for which IE’s sandwich plate system (SPS) technology has been used.

Polymer sandwich anyone?

SPS plates comprise two metal plates bonded to a solid polyurethane elastomer core. The technology was developed by IE with Germany’s BASF supplying the core material. In repair and strengthening applications, perimeter bars and a new steel plate are welded over the thinned metal to create a void into which the elastomer core is pumped. The plates are continuously supported by the core, which fills the cavity, including uneven geometries in the corroded plate. This repair method means existing material doesn’t need to be removed – so on a below the water line repair, cofferdams and divers (plus dive support vessel) are not required.

Top plate positioning on the Komi Kribi 1. 

IE first started using SPS in the ro-ro (roll-on, roll-off) ferry market, where decks were thinned beyond classification limits due to repeat wear, and where repairs would then also keep failing. “The unique thing is that it acts in a global manner, adding strength to the whole deck,” says Ian Nash, business manager, IE. “From that, we discovered SPS had a lot of advantages over conventional steel. It has high shock absorption, acts as an external barrier, it’s a barrier for noise, it’s blast and ballistics resistant and fire retardant. We realized SPS could take a good battering and remain flat.”

It can also be applied to suit its use. For example, on a ro-ro or FPSO, the plate will be about 8mm-thick. On a bulk carrier, however, where it needs to withstand 10-15-tonne repeat loads, every day, 10mm plate will be used. The core is usually 20mm-thick, but sometimes it is higher, such as when it’s being used as a thermal barrier, when it could be 40mm.

The firm has been working in the offshore sector for about 10 years, with work including reinforcing pipe rack decks on semisubmersibles, without disturbing other decks or equipment.

Aging FPSOs

In the FPSO market, there are some older vessels which are starting to need some tender loving care. “It could be that a vessel’s steel wasn’t as thick as originally thought or that the maintenance wasn’t as good as it could have been,” Nash says. For a conventional below the water line repair on an FPSO, a cofferdam would first need to be installed and then divers deployed, Nash says. The time it takes them to do the work could vary. The alternative is to take it off station and tow it to a yard, which operators want to avoid. Instead, Nash says that IE can deploy a 4-5-man squad to do the job, while the vessel remains in production, without the need for divers.

FSO Komi Kribi 1

The FPF3 team. 

The firm’s first below water line repair was in 2013. Last year, the firm did six such repairs. One was on the FSO Komi Kribi 1, converted in 1977 from a very large crude carrier and operated by ExxonMobil for Cameroon Oil Transportation Co. 11km offshore.

The vessel had its sea chest, bottom shell and bulkhead reinstated using SPS, with a squad comprising two IE staff (a project manager and an elastomer injection engineer) and six local welders and platers from Cameroon Shipyard and Industrial Engineering. The SPS repairs, comprising a 10mm top plate and 25mm elastomer core, covering 25sq m, and approved by Bureau Veritas, took just under a month, from 30 August to 29 September.

After the Komi Kribi 1, some 96sq m of steel across five different areas was reinstated on the FPF-003, in Southeast Asia on station at Mubadala’s Jasmine oil field in the Gulf of Thailand.

FPF-003

The FPF-003 is an ABS-classed vessel, built in 1976 and converted in 2005. The repair work, carried out with EM&I and steelworkers Altamar, covered the engine room bilge, engine room side shell, pump room bottom shell, forward cofferdam bottom shell and bulk head and main deck. The work started on 2 October and completed on 3 November, 15 days ahead of schedule, with no disruption to the vessel’s day to day operations, despite the multiple complex and space constrained areas to be repaired, resulting in four machine and equipment moves, and atmospheric working temperatures of 35°C.

The process involves cleaning the corroded steel, with grit or sandblasting, then welding perimeter bars around the area needing reinstating, creating a picture frame. A top plate is added to the bars, creating a cavity. This is leak tested before the polyurethane elastomer, which is brought to the site in its component forms and then mixed at high pressure, is injected. Vent ports in the plate enable it to fill the cavity fully, before setting in a 10-minute exothermic reaction, bonding the plates together.

Everything is measured and tested – humidity, hardness of the polyurethane, and sample tested after 24 hours, Nash says. The cavity is then sealed by welding in the ventilation ports and the repair is complete.

“To do this work conventionally, we would’ve had to take some serious measures,” Nash says. Because the thinned plate is left in place, removal works are avoided. Also, all hot work is done away from the shell of the vessel. Classification rules mean you cannot weld directly to steel that has water on the other side of it, because the weld would cool too quickly and cracks could form, Nash says. Instead, IE uses the hull’s strengthening members to weld to, where the plate needs to be added to areas of the hull.

Further ideas

IE has more ideas for where this technique can be used. The work with BP on Glen Lyon gave IE an idea for enabling vessels to carry marine gas oil (MGO), in order to meet the 1.1% sulfur emissions regulations. “SPS enables vessels to hold both heavy fuel oil, which is kept at 80-90°C to achieve the required viscosity, and (the more environmentally friendly) MGO, which needs to be kept below 40°C,” Nash says. “SPS provides a thermal barrier between the two tanks. This has been successfully installed on a number of vessels for a leading UK oil major. Not only does SPS provides an efficient thermal barrier, it also maximizes available storage space as there is no need for void spaces between the tanks which would require through-life inspection.”

It has also been using SPS for side shell protection, instead of fenders, and is offering the solution for ice-class strengthening.

Despite composites not always getting a ready reception, IE appears to be making in-roads. “There was resistance in the early days, because it is a new technology and you have to push through the traditional barriers,” Nash says. “Using steel is generally what they wanted in the early days. But, [now] we are an established company with a huge portfolio of projects around the world.”