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Tue 16 Oct 2007 04:11 PM

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Offshore services

A look at the mechanical, electrical and plumbing side of readying an offshore rig for work.

The offshore rigs in the Gulf remain a symbol of the region. Integral to the success of their operation are the mechanical, electrical and plumbing (MEP) services.

To maintain 24/7 operations safely and effectively, rig occupants must be assured of a continued supply of fresh air, water and power. And perhaps even more essential, the MEP services on a rig provide a means of ensuring the drilling equipment remains operational at all times, by maintaining critical conditions where necessary. But how do these installations differ from their onshore counterparts?

If the rig is to be used in a country that has signed the Kyoto Protocol the systems must meet these standards.

Safety, standards, redundancy and co-ordination are key aspects to an offshore MEP installation explain Jean Pierre Halin, senior projects manager with Thermo Offshore and Industrial Division. Standing aboard the Thule Power rig in Sharjah's Hamriyah free zone, the first thing that strikes home is the huge scale and volume of equipment involved and the compact area in which it is all installed. Valves measuring up to 900mm diameter join air conditioning pipe work and a reverse osmosis desalination plant producing 2 000 l of fresh water daily, is positioned alongside the drilling floor on the 53 m triangular rig.

Thermo won the contract for the installation of heating, ventilation and air conditioning (hvac) on the Thule Power project in competitive tender. A large percentage of the firm's installation services the rig's two accommodation blocks, however its scope of works also includes ventilation for the machinery floor, engine room, transformer room and the central switchgear room, as well as air conditioning for the driller control room.

Owned by Norwegian firm Thule Drilling, Thule Power is a rebuild of the salvaged AD19, a 25-year old, rig damaged by Hurricane Katrina. The central structure has been kept, but the overall rig has grown in size and sophistication from its original form.

The 6000 tonne rig, has a 1.2 tonne drilling derrick and tower that is attached to a cantilever section. This section slides clear of the main deck area during drilling for safety. It can be sited in water up to 235 ft deep and will be able to drill to depths of 30 000 ft.

Also essential for this section of the rig is guaranteed controlled temperatures, and fresh air supply in the drilling control room. To ensure that this is possible, two 35TR air handling units serve the room on a 100% standby basis. "This room must be kept in positive pressure incase of any gas leaks," explained Halin.

This is to protect the drill operator's safety, but also to ensure that no equipment is damaged.

Some essential equipment can only operate under certain temperature criteria and the control systems for these systems must be protected.

The reasoning behind this is the need for autonomy during operation; when at sea the amount of maintenance possible will be limited - and costly.

"Nothing can fail on the rig. You have to have redundancy, especially with the air conditioning for the main switchgear and areas like that," said Halin. "While the rig is drilling nothing can stop it, because if the drill is stopped, depending on the depth being drilling they can lose all of the drill and that costs millions, so that can be very harmful financially."

The rig is based on the Friede & Goldman Super M2 rig design, which features a layout with accommodation areas ‘wrapping around' the rig's forward leg to give more deck space and a more efficient facility. Divided into two three-storey blocks connected by two bridges, the accommodation for 105 personnel is sited on the opposite side of the rig to the main drill floor.

Nothing can fail on the rig. You have to have redundancy, especially with the air conditioning for the main switchgear and areas like that.

The products and installation techniques used for the HVAC services on the rig are similar to those on a ship. All products such as cabling and ductwork are to marine-grade specifications to counteract the environmental conditions to which they will be exposed. To ensure safety, certain products are also explosion and fireproof.

"Some zones are classed as hazardous areas because of the possible existence of hydrocarbon gases," explained Halin. A comprehensive sensor and alarm system for gas and smoke ensure safety throughout and a ‘cascade' system provides a safe supply of oxygen for workers to plug safety masks into should a leak be detected.

The distribution of services had also to be carefully considered. Marine industry rules and regulations are stringent in terms of installation. The rig is treated as a ship, so for example if the ventilation ductwork goes though compartments, each penetration must be watertight.

Within the accommodation block the main distribution route is above ceiling in a central corridor. Fresh air is fed into the rooms from above ceiling units then exhausted through a grill in the door and via a main exhaust in the corridor. This airflow pattern is again to ensure the health and safety of the onboard operatives.

"We have to keep a positive air pressure in the bedrooms; this is to avoid humid and warm air entering, but also to keep any potential leaking gas outside the rooms. There is a 24/7 operation on the rig so we must make sure the air is kept clear for the people sleeping," stressed Halin.

The division of services into several small hvac and electrical systems ensures continued use of the accommodation blocks. "There is a non-centralized system, so only a quarter of a floor would be affected if there was a problem with the air conditioning or power," said Halin.

There are three main standard organizations for rig building: The American Bureau of Shipping (ABS), Norwegian-based DNV and the UK's Lloyds Register of Shipping. Thule Power is being built to ABS standards and daily checks are made by an on-site ABS engineer to ensure conformity. In addition, all work carried out on the rig must meet several other sets of standards including those imposed by the client and the civil aviation authority.

Environmental regulations are also enforced. For the hvac system one if these is the use of refrigerants. "Our operatives are specially trained concerning the environmental protection in the use of refrigerant gases. We are equipped to recover the gases for disposal by official disposal," explained Halin.

Gases of particular concern are those refrigerants such as R22, the use of which is now banned or restricted in many countries. As well ensuring the environmental impacts are minimized, this is important when seeking work. "If the rig is to be used in a country that has signed the Kyoto Protocol the systems must meet these standards," said Halin. A firm found illegally venting such gases may find itself banned from future work on the oilfield projects.

Fitting the services

The need for upfront designs and co-ordination between members of the construction teams were vital on the project. The main structure had to be largely complete prior to installation of the MEP services beginning, which meant all distribution routes and location of plant and equipment had to be agreed early in the process.

"If you don't have proper coordination on a project like this it can't be done, because everything is way tighter than in an onshore building," said Halin. "You have false ceilings but they may only be 30cm deep and you have to pass everything in there, so if you don't have the proper coordination you will have clashes everywhere, which is a waste of money and a waste of time."

Co-ordination was carried out using AutoCAD; each subcontractor supplied their installation drawings to the main contractor and these were superimposed to ensure clashes were eradicated at design stage. Regular meetings were then held between the team members to discuss any necessary changes.

Once installation began, co-ordination was just as vital with tight working spaces. "Most of the time we ask for priority for the MEP services, especially in tight spaces; - a duct is not as flexible as a cable or pipe, so we dealt with space issues by designing the ductwork first then adding the pipes and finally the cables," explained Halin. "Co-ordination is quite a heavy cost initially, but if you do it well at the beginning it pays at the end," he adds.

Ductwork was prefabricated onshore in sections of up to 2m diameter and 1.5m long, with ductwork walls ranging from 3 to 12 mm thick depending on the area in which they were used. These were craned in sections from the pier.

Many of the products used were sourced from Europe and the USA, with lead times of six to eight weeks for the standard products and 12 to 14 weeks for the more specialized explosion-proof equipment.

At peak Thermo had around 100 staff working on the project. With around 80 permanent staff in the division this meant the firm had to recruit additional operatives from another source.

The solution was to engage staff from owner group Thermo's construction division in Dubai. "The extra staff are mainly used for helping the permanent operatives," explained Palin. "They are not specifically skilled for rig work so we mix them in groups with our full-time staff." All staff is given intensive health and safety training and this is continuously updated stresses Palin; additional training in specific areas of work such as refrigerant gases is also given where needed.

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