Removal of production deck - operations performed from TETRA’s Arapaho Derrick Barge

Removal of production deck - operations performed from TETRA’s Arapaho Derrick Barge

Wind energy, platform decommissioning and sub sea projects are all growth areas for offshore cranes. Euan Youdale looks at these applications and the cranes involved.

Liebherr has delivered the first of its giant 1,600 tonne capacity MTC 78000 heavy lift offshore slewing cranes.

The company's biggest crane to date was installed on the heavy load vessel OSA Goliath at Liebherr's maritime crane factory at Rostock in Germany. Two 208 tonne capacity Liebherr LHM 600 mobile harbour cranes were used in tandem for the assembly, carrying out lifts of up to 400 tonnes each.

OtetSA Goliath will be delivered to Mexican purchaser Oceanografia. Liebherr has received orders for three further units, it says.

One of the main applications for MTC 78000, says Liebherr's Wolfgang Pfister, will be the erection of offshore wind farms, a major growth sector.

The MTC 78000 offers its maximum lifting capacity of 1,600 tonnes at up to 35 m radius. This corresponds to a maximum dynamic load moment of 78,000 tonne-metres, with the crane still being able to slew 360°.

The boom length of the first unit is 87 m. At a maximum radius of 74 m for the main hoist, the crane achieves a lifting capacity of almost 530 tonnes. In addition to the main hoist, the MTC 78000 offers two auxiliary hoists with lifting capacities of up to 500 tonnes and 50 tonnes, respectively.

Despite its size, the MTC 78000 has been designed as a slewing crane and is supported by traditional large-diameter anti-friction bearings. With a weight of 70 tonnes, the slewing ring is about 9 m in diameter.

The manufacture of such large mechanical parts needs complicated custom processes, explained Liebherr. Conventional gear cutting machines are only available for large diameter anti-friction bearings up to 5 m diameter.

Liebherr, however, has acquired large enough machines and equipment for the mechanical machining of these flanges.

Decommissioning

The surge in offshore wind turbine erection is well documented but another, less widely discussed, growth area for offshore cranes is platform decommissioning work. Dick Ward is vice president of global sales and marketing at Tetra Offshore services.

Ward says a great deal of decommissioning is to be found in the Gulf of Mexico where there are three main drivers for the increase in work there.

Firstly, there are offshore facilities that are no longer producing which have to be removed based on US Department of the Interior's Minerals Management Service (MMS) regulations.

Secondly, hurricanes Katrina, Rita, Gustav and Ike have destroyed or damaged more than 120 offshore platforms since 2005. "Operators have found that the cost to decommission and remove a damaged or destroyed platform is 12 to 15 times greater than taking out the platform that has not been damaged."

This leads to the third reason, adds Ward, namely, that insurance underwriters are now imposing extremely high premiums and deductibles to provide hurricane protection coverage. "It turns out that idle facilities can be removed prior to hurricane damage much more economically than they can be repaired."

Productive life

Worldwide, decommissioning work is growing because of the large number of offshore platforms that were installed from the 1960s to the 1980s and have outlived their productive life, explains Ward.

"Regulatory authorities worldwide are following the example of the US MMS in requiring operators to decommission and remove these facilities. Examples are in the southern North Sea, Southeast Asia, India and the Middle East."

Oil & Gas UK is the authority for the Southern North Sea, while in Asia it is generally the national oil companies, including Petronas and Pertamina, with international operators.

The offshore services division of Tetra claims to be the only decommissioning contractor to provide the complete range of in-house single source services needed to decommission an offshore platform whether or not it has been damaged in a storm.

In the Gulf of Mexico the company has three anchored heavy lift barges supporting the decommissioning and removal projects. They include the 350 x 100 foot (107 x 30 m) DB Arapaho, with an 800 US ton (726 tonne) capacity revolving crane.

Another is the 615 US ton (558 tonne) lifting capacity DB 1 vessel, with the same dimensions, and the DB Southern Hercules, a 198 x 68 foot (60 x 21 m) vessel with a 100 US ton (91 tonne) crawler crane. A range of dive support vessels are used in conjunction with lifting vessels.

Flexible

"These derrick barges and dive support vessels are very useful in decommissioning and removal work because they provide a stable work platform to support the well plug and abandonment work, the mechanical cutting of the decks, jackets and piles and the actual lifting of the structures on to material barges for ultimate scrapping or other designated salvage solutions, as approved by the operator and the MMS.

"Removal work is much more flexible than installation of new facilities because it doesn't generally matter if the facilities are cut into smaller pieces for removal," explains Ward.

In 2009 the company has seen a reduction in new constructions, resulting from the economic crisis and the downward slide of crude oil and gas prices. "However, we are not seeing a reduction in demand for oil and gas in the USA or in the rest of the world.

"We feel that this trend of reduced construction will reverse and we will see new construction increase to previous levels. This downturn has not impacted the Gulf of Mexico decommissioning market which is quite strong this year."

Subsea

The company is also seeing a significant increase in deepwater developments in the Gulf of Mexico, West Africa, South America and Southeast Asia. As the market expands beyond the continental shelf, the technology to build and later decommission deepwater facilities is evolving rapidly. Ward says Tetra is active in the development of the technology, tools and procedures needed to meet the challenges of deepwater and subsea work.

"We have completed testing on a new subsea rig-less, riser-less package that can work in 2,000 feet (607 m) of water, and we have recently introduced a new subsea multi-string hot tap tool to enable us to work on plugging damaged wells safely.

"We are also in the final stages of developing a large diameter mechanical cutting tool which can be used on removal of caissons and subsea piles. In addition, we are studying the heavy lift capabilities that we will need for our future operations."

Charles Nicolson, general manager of Jumbo Offshore, active in the subsea sector, says there are every few vessels able to lower heavy objects to the sea bed. "A lot of them are complicated pipe-laying vessels but do not have significant craneage, or very large vessels which have good craneage but cannot really go subsea.

"There are a number of structures that need to be placed on the sea bed and, at the moment, they try to design them for less than three 300 tonnes, ideally less than 200 tonnes. We can pretty much lift 1,000 tonnes up and take it offshore and install it."

Lowering system

The company has two DP2 (deepwater capability) crane vessels: the Jumbo Fairplayer and Jumbo Javelin, both featuring dual cranes with a combined lifting capacity per vessel of 1,800 tonnes. Two Huisman deepwater winch systems have been ordered for the Fairplayer, which will be fitted in August and September 2009.

With these lowering systems the company says it will be able to install subsea structures and mooring systems in depths of more than 3,000 m. At 3,000 m the two winch systems, working together, can install 210 tonnes. They are capable of 660 tonnes at a depth of 1,500 m and more than 900 tonnes at 900 m, says the company.

Through changes in the installation method, structures weighing more than 500 tonnes can be installed at depths of 3,000 m. The modular winch system can also be transferred to the company's other DP2 vessel.

This, says Nicolson, will allow the company to win major subsea-related projects, which are rapidly increasing. "In terms of the installation of heavy structures, it is fair to say there are six or seven projects with structures over 400 tonnes which are on the market for tendering.

"I don't think that there have ever been so many projects with such large structures at any other time."

However, the deep sea winches do not spell the end for the offshore crane. "In all installation work you do you need to lift from deck. The winches that we have are at the base of the crane - we have just made that capacity significantly greater. But we are still reliant on cranes for the offshore operation."

Newsletter

Delivered directly to your inbox World Crane Week features the pick of the breaking news stories, product launches, show reports and more!

Sign up for free

Newsletter

Delivered directly to your inbox World Construction Week features the pick of the breaking news stories, product launches, show reports and more!

Go to newsletters