Battling the elements

9 October 2018


Offshore oil and gas exploitation presents some of the hardest environments for lifting equipment. Hoists must be robust, explosionproof and able to function perfectly after long periods idle. Julian Champkin looks at problems, solutions, and new developments.

Oil prices are rising. One might therefore expect increasing investment activity in the places that produce oil and gas. Lag times, however, are long, especially in the complex and demanding offshore extraction industry, so prices have not yet translated into extra activity in such regions as the North Sea. “It is still too early to see increasing activities and investments coming,” says Thomas Kraus, support centre director for Stahl CraneSystems, who are active in the area.

“It seems that companies are still waiting with their investments due to the overall political and economical situation.”

Gus Caldera, global product management and marketing leader for Ingersoll Rand, says the same: “We go to market through specialised distribution and service centres in key oil and gas markets. Most recently, we have seen a strong comeback in aftermarket activity. In the North Sea, for example, where we have strong representation, we have seen strong aftermarket activity, including in service and parts.

“Our authorized service distributors have been very busy with service and repair work, bringing winches and hoists that have been cold- or warm-stacked back to like-new state. When it comes to new units, we have not experienced the same level of enthusiasm that we have seen in aftermarket.”

German company JD Neuhaus, who has been making cranes and hoists for over 270 years, echo the sentiment: “We have found the same experience. The increased prices will not affect investments in offshore equipment in the short term.”

Short term, though, is not forever. Preparations are on foot, awaiting the word. Arno van Zaanen, sales director of Netherlands-based EMCÉ winches, says: “Many rigs were commissioned from yards in China, and were then put on hold when the markets deteriorated.

“They are waiting there, near-completed, and will be finished and brought to their sites as soon as the right economic moment arrives.”

So, when the word is given, we may expect activity—and possibly at that stage rapid activity with rigs and platforms being brought into commission and production at speed. What are the challenges connected with hoists and lifting equipment in the offshore oil and gas industry?

Safety of course is paramount. In particular, environments are hazardous and vapour-filled. Explosion is an ever-present risk. The EC’s ATEX directives give a basis for uniform explosion protection in Europe, and hoists used offshore in the North Sea have to be compliant with ATEX directives. The last ATEX update took place in April 2016. “Updated regulations are expected in October 2019,” says Kraus. “Outside Europe, the IECEx system is of major importance.”

Introduced in 1996, the IECEx scheme supports the harmonisation of standards worldwide and the creation of uniform certificates of conformity so as to simply the free movement of goods globally. 26 countries have already joined IECEx and there are 34 accepted IECEx certification bodies and 36 accepted test laboratories worldwide. “It has the advantage over ATEX that in the countries that recognise it, appropriately certified devices can be put into use without additional testing,” says Kraus. “The European ATEX directives and IECEx regulations already largely concur. This means ATEX could one day be shed.” Until that day, however, ATEX product directive 2014/34/EU (ATEX 95) and ATEX user directive 1999/92/EC (ATEX 137) are the relevant ones here.

Directive 95 stipulates the quality requirements for operating equipment for safe use in explosive areas. Directive 137 stipulates the duties of operators and employers to protect employees in potentially explosive atmospheres. The user must, for example, estimate the risks and classify the potentially explosive areas into zones so that the operating equipment as required by Directive 95 can be used safely.

A major requirement in rendering hoists and similar equipment explosion-proof (and ATEX- and IECEx- compliant) is sparkproofing. Obvious sources of sparks are friction, where metal-on-metal movement takes place, or in electrical switching, where sparks can jump between contacts. If inflammable gases are present, an explosion can result.

Stahl CraneSystems has been developing explosion-proof hoisting technology since the end of the 1920s. Much has happened since then technically, says Kraus—but nothing has changed regarding the mode of action and importance of explosion protection:

“In the case of hoists, for example, it is possible for electrical contacts to generate a spark when energised. Should the spark react with gas and oxygen, an explosion will result. With standard machinery casings this explosion would pass into the environment and ignite the gas mixture there.

“Flameproof casings are designed such that the ignition would cool down or be extinguished via the threaded joint or flat joint of the cover. This means that the surrounding area is not at risk.

“The explosion-proof controllers from Stahl CraneSystems are mainly in the ‘flameproof enclosure’ and ‘increased safety’ ignition protection class. The difference between standard control boxes and boxes in flameproof design for Zone 1 lies in more stable and solid construction—heavy cast aluminium and steel enclosures have stood the test of time in this regard. The installation materials such as cables, screw connections and cable lead-ins also have to comply with the standards and directives, and must be tested and certified accordingly.

“In the case of most hoists, a second separate housing made of sheet steel or stainless sheet steel is usually fitted in addition to the safe cast aluminium enclosure of the connection box. Both housings are connected using explosionproof wire lead-throughs.

“Only trained and certified personal should do the maintenance on explosion proof products. You cannot compare it with standard, non-explosion proof equipment. Even you might think that little damage of the thread on the cover of the electrical housing isn’t critical, it might fail,” he says. Encasing the spark-producing elements in isolating fireproof housings is one approach to spark-proofing. Another is to eliminate spark production, insofar as this can be done. Most winches worldwide are electrically powered. Offshore winches are pneumatic, powered by compressed air, thus bypassing many of the spark problems generated by electricity. Two types of air motor dominate for powering off-shore winches: the piston-type and the geartype.

The latter consist basically of two intermeshing gear wheels in a close-fitting chamber. Compressed air fed into one side of the chamber pushes against the gear teeth and generates torque, causing them to revolve. Van Zaanen of EMCÉ says there are many advantages for the latter—and he should be knowledgeable, since he helped to design them. Chief among these advantages are that they have only two moving parts, compared to a five- or sixcylinder piston-type air motor. This makes for simplicity, economy and safety. “In the past, piston motors were mainly used for winches with larger capacities,” he says. “For 40 years after the development of the piston motors more than 40 years ago, no appreciable developments occurred in the field of air-operated motors with capacities above 10 kW. It was a niche market.

“Sound mufflers are unavoidable on air-powered winches, as exhaust air expansion generates sound levels way above 115 dB(A) as normal. The valves that control the airflow cause a certain amount of back pressure, which brings appreciable capacity reduction in piston motors. The complexity of the internal airways in the piston motor, and the rotating distribution valve in combination with these components, means that this back pressure is substantially higher than in gear motors. In various tests, EMCÉ has shown that all these counteractions together result in a power loss of more than 30%. Consequently, air motors bring capacity improvements that are principally expressed in higher output speeds even under full loads and at equal operating pressure and air consumption when compared to piston motors. Simpler construction brings cost price reduction and lower need and cost for spares.” Ingersoll Rand also extol the virtues of the air gear motor: “Manufacturing and design innovations overall have increased the reliability of rig equipment and streamlined the maintenance of these assets,” says Caldera.

“The design of Ingersoll Rand hoists and winches reduce the amount of maintenance needed. This is a characteristic of our air gear motor, which has a limited number of parts and can withstand harsh conditions.”

Caldera points to an additional demand made of hoists offshore: “One challenge of offshore maintenance is that some products are not used frequently. This means equipment should be designed so it can be restarted and be ready to deliver optimum performance after being on standby for weeks.”

This is particularly so for LNG installations. LNG, Liquified Natural Gas, is a sector sometimes neglected in offshore power commentary, yet measured on an energy basis LNG production is expected to account for 10% of global crude production by 2020. Gas obtained on- or offshore is pressurised and chilled to liquefy it, and in that form is transported to its destination by ship. The procedure is used in regions where pipelines are not feasible. It requires coastal terminals for off-loading. Receiving terminals exist in about 18 countries; due to price and supply considerations several more are currently proposed or under construction on the Atlantic coast of the US.

But LNG puts even more extreme requirements on hoisting equipment. In particular, hoists required for maintenance or replacement of motors may be required to operate immediately after being idle in place for months, possibly for years, and this at very low temperatures. Kraus explains some of the operational needs: “At the bottom of most LNG tanks there is an extremely heavy pump weighing several tons. It is used to pump the cooled liquefied natural gas from the tank into the pipelines. In the case of maintenance work or faults the pump must be lifted out of the tank—a manoeuvre which, due to the immense temperature differences and risk of explosion from vaporised natural gas, places highest demands on personnel competency and equipment reliability.”

A Stahl-implemented LNG project on the Chinese east coast involved custom versions of wire rope hoists in their triedand- tested SH60ex series. These are certified according to ATEX for explosion protection zone 2. When implemented according to safety level 2, two rope drums from the SH wire rope hoist, connected permanently by a chain, are operated with a motor. The standard rope and the rope for the liquefied gas pump can optionally be interchanged using a quick fastener. The ropes of the LNG pump can be wound on one of the drums or simultaneously on both drums. The system is equipped with a single motor, hoist gear and brake. The hoists are mounted on slewing cranes on the roofs of the liquefied gas tanks, have a lifting capacity of 3.5t and a lifting height of 58m.

The hoists were optimised for use on the Chinese LNG tanks by modifying the control unit and using a special rope drum. The customer stipulated both the rope diameter and the ratio of rope diameter to rope drum diameter in its specifications. These requirements could not be met with the SH 6 wire rope hoist’s standard drum. Stahl CraneSystems therefore built a special rope drum based on the standard drum of the SH 6 but with a centre diameter of 457mm, rather than 352mm. In this way it was possible to fulfil the customer’s requirements while keeping the hoist’s frame geometry and the proven rope drum brake of the series hoist.

A special rope, permanently connected to the pump, is used to lift the pump; it is kept in the tank’s maintenance shaft during normal operation. After opening the shaft, the rope must be fastened to the LNG wire rope hoist’s rope drum with three rope claws. To simplify rope changes, Stahl equipped the wire rope hoists with additional key switches at the hoist and control pendant. The technicians are therefore able to override the hoist emergency limit switch at the touch of a button and thus unwind the last rope windings from the drum.

Due to the salty air and harsh coastal climate, a corrosion-resistant coating was necessary. A further safety precaution was taken because of the high wind forces on the coast that can cause the load to swing. The hoist stops working automatically at wind force 8. An enclosure protects the hoist against weather influences when not in operation as months, or even years, can pass between times of use. The equipment can be used at any time in temperatures between -20°C and +40°C.

More radical still, and placing even more demands on the technology, is the FLNG, or floating LNG plant; this is a complete shipboard factory which liquefies gas from subsea fields and transfers it to ships moored alongside. The first of these is currently being commissioned off the coast of Australia and is claimed as the largest floating structure ever built. As a comparison, its 260,000t make it several times the size of the largest aircraft carriers. It is intended to spend its working life permanently moored in the browse Basin over the Prelude field.

Its design life is 25 years. Neither conventional rigs nor state-of-the-art FLNG plant last forever. They need replacing, or fields become exhausted. In the North Sea in particular, decommissioning of older rigs is set to become an important factor in the near future.

“The total value of decommissioning across the North Sea to 2040 is estimated to be £46bn, with 40 platforms being decommissioned from 2017 at an estimated average annual cost of £1.8bn,” says Ingersoll Rand’s Caldera. “The figures come from a report titled ‘The RSA Great Recovery & Zero Waste Scotland Programme’ by the Royal Scottish Academy. Over 50% of the assets will come from the UK sector of the North Sea. This will require a lot of heavy lifting.

“Various lifting equipment is necessary for the different decommissioning operations. For top-side decommissioning, companies hire our winches to move equipment around the deck. A 5t pneumatic winch like our FA5i Infinity winch is often used for these types of operations. “Another area where we get involved is in the overhaul of winches and hoists to be used in drilling operations for other active rigs. A few years ago a project in Scotland called the Great Recovery provided directions on re-use opportunities for assets in a rig. Winches and hoists along with other critical equipment have been identified as products that should be reconditioned for future usage. This falls in line with Ingersoll Rand’s focus on sustainability and zero waste.

“For decommissioning work, our Authorized Service Distributors are trained and certified to rebuild winches or hoists for re-use. The process includes exterior assessment of the products, cleaning for decontamination, disassembly and rebuild, paint, and testing and certification. Generally, our products would go back to oil and gas operations, but they can be deployed for other applications.”

An EMCE air-powered hoist on board a rig
A JD Neuhaus Profil TI handling a turbine for maintenance offshore.