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Offshore Support Journal

Offshore Support Journal

Equipment designs redrawn to catch dropped object threat

Thu 14 Mar 2019 by Gavin Lipsith

Equipment designs redrawn to catch dropped object threat
An enhanced survey regime for equipment with drop potential helps reduce the risk of fatalities (image: OES)

In a bid to prevent equipment and components falling on crew, the offshore industry is taking an increasingly careful look at equipment design

Dropped objects are dangerous and fatalities frequent in the offshore industry. According to the National Institute for Occupational Safety and Health, ‘contact with objects and equipment’ was the third biggest cause of deaths in the workplace in the US between 1992 and 2002. The same institute looked at the US upstream oil and gas industry between 2003 and 2014 and found that, of 1,221 deaths, 171 (or 14%) were caused by falling objects.

The distress, disruption and expense caused by these incidents is extreme. But although the benefits might seem obvious, it was less than a decade ago that the offshore industry began to look seriously at reducing drops, says ABS director of corporate global business development Demetri Stroubakis. Since then, industry practice has become more standardised, aided by the introduction of ABS’ own dropped object prevention programme (DOPP) in late 2017.

“The reason we started looking into this area was because one of the main drilling contractors raised it,” says Mr Stroubakis. “Further conversations with some well-known drilling contractors revealed that they wanted a focus on the equipment side. We found a lack of improvement in equipment design and a lack of robustness in the design process.”

The result was a guide that led to a class notation for offshore utilities. Underlining the role of equipment design, the enhanced notation, DOPP+, requires classification of equipment as well as the asset itself.

The guide espouses the idea of ‘inherently safe design’. One good example is the reduction of moving parts. A drill stabiliser unit can have as many as 106 moving parts. With careful redesign, Mr Stroubakis recalls that one supplier made this equipment with just 50 parts, greatly reducing the chance of something working loose and falling. The risk caused by such a situation was cut further by the inclusion of an outer casing, meaning that components would simply fall into the casing, rather than onto the decks below.

The applicability of the guide to offshore vessels will be enhanced when it is updated to include dynamic drop risks as well as static ones; while static drops focus on equipment, including A-frames, that can fall under their own weight, dynamic drops occur when moving objects collide with each other. That brings more complicated equipment, including winches and cranes, within the remit of the DOPP guide.

“We found a lack of improvement in equipment design and a lack of robustness in the design process”

“It could include a crane colliding with another crane, for instance,” says Mr Stroubakis. “It looks at how you set up barriers where there is potential for collisions, including travelling equipment and loads, objects moving at height and in severe weather. These are more destructive incidents potentially and, because they also include the human element, more complicated.”

The updated guide will be published in April. Its expansion to cover a wider range of drop hazards and equipment design will mark a further step in improving safety for workers in the offshore industry.

Winches and cranes will come under dropped object guidance when it is expanded for dynamic drops

Meanwhile, safety at height is preoccupying a Norwegian supplier of offshore lifting equipment. Molde-based Axtech has just delivered initial equipment concept studies focused on windfarm servicing to Norwegian energy company Equinor. For a company that has forged its reputation offering lifting expertise to the subsea market, it is a rare opportunity to look up rather than down. But, says managing director Richard Myhre, the skills and expertise required for this particular problem are very familiar.

“Our technology is based on heavy lifting, understanding structures and motion compensation,” he says. “It is not just about what is happening at the seabed. We are interested in the heavy maintenance element.”

There is an unsolved challenge in the offshore wind market, says Mr Myhre. When floating windmills reach a certain size, jack-up vessels will no longer work. With some modern turbine designs reaching up to 130 m above the sea, jack-ups would need to be so big that it would be difficult to get close to the installations. Perennial troubles, notably limited weather windows and the need for careful leg planting around subsea cables, would also be magnified for large floating turbines.

“How do you lift those heavy blades when the object is big and moving,” asks Mr Myhre. “The market doesn’t have the tools for this.”

Over the past year, Axtech has been investigating several ideas about how to safely dismantle or swap 150-tonne components, including awkward shapes like turbine blades, at a height of up to 130 m above the sea. Its concept, called WindWorker, focuses on finding a method of linking the vessel to the floating turbine, both at sea level and at height. To achieve this, the company is studying concepts with two heave compensators.

“If you can create the link, you just need to work out how to get a firm grip on an object,” Mr Myhre explains. Whether working on windfarms or offshore platforms, that firm grip is not something that can be taken granted.

Are batteries best for offshore lifting?

The trend for installing batteries on OSVs is intended, at least in part, to reduce environmental impact. But according to Mr Myhre, that may not be the case when it comes to energy consumption related to lifting equipment.

“Batteries are normally installed to support dynamic positioning and vessel operation [and are] not necessarily suitable for heavy lifting,” he explains. “It can be challenging to use stored energy when power demand goes up and down rapidly, as it does for large compensation systems.”

A potential solution for minimising power demand involves transferring excess hydraulic power into accumulator systems while at the same time allowing for ‘back-driving’ of the drives. As an example of their effectiveness, Mr Myhre notes that on a decommissioning boat equipped with an accumulator system, 75% of the energy used by deck equipment can be accumulated energy, with only the remainder coming from the vessel’s installed power.

Although electric winch drives are a good solution, they mean that accumulated energy is not always available, so Axtech had to rethink how it increased energy efficiency on a growing number of hybrid vessels.

One method involves combining accumulating systems with electro-hydraulic drives. These are driven by frequency converters and instantly deliver the correct amount of oil for the current application. As Mr Myhre explains, “the drives are not standing there hammering power to something that doesn’t need it.” Also, this enables the hydraulic drives to provide active front end (AFE) power towards vessel power grids.

These secondary drives have been installed for Axtech equipment on several vessels, including the hybrid subsea construction vessel North Sea Giant, which was converted to host batteries early last year. The vessel houses two Axtech towers, with a particularly advanced energy saving configuration that offers the possibility of feeding hydraulic energy to the accumulators and back into the batteries for electrical storage.

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