User Report: On-deck Joints

By MarEx 2012-06-18 14:16:09

Topics
Seaworthy securing of valuable maritime cargo such as the components of wind-power installations; mechanical loading and securing; parameters for welding the holder-fixtures; welding processes and systems; higher quality and economy in ‘rack’ mode

Securing cargo using welding systems

Offshore wind-power installations (WPI) and their individual components have to be safely transported to the installation sites by ocean freight. The cargo has to be fixed to the ship’s deck solidly and reliably, as any errors risk serious injury and damage, not to mention considerable financial losses. Based at Leer, in Northwest Germany, Seatight is a specialist company that uses its practical, ‘hands-on’ know-how to control and manage these risks. The work carried out by the welders, and the equipment they use, is of very great significance here.

Business focus: the high seas
Angelo Pennacchia first trained as a ship’s mechanic, then qualified as a navigational watchkeeping officer before going on to found Seatight, of which he is now a Managing Director. His company provides advisory and practical services related to cargo-securing and transportation safety to a clientele that includes shipping companies, charterers, logistics firms, shipping agencies and manufacturers of wind-power installations.

From Pennacchia’s explanations, it soon becomes clear that mastery of the forces exerted by the ocean requires wide-ranging knowledge of nautical science and physics: he explains the motions of a ship’s hull in terms such as roll, heave, pitch, sway and yaw, summing it up by noting that “The greater the amplitude or the frequency of the motions, the greater the accelerations that they produce. The further away the centres of gravity of the cargo items are from the centreline of the vessel, the greater the acceleration stresses become, and the greater the precautions needed to secure the cargo. On deck, the wind pressure and wave-impact forces need to be taken into account as well.”

Welding – the preferred solution
The cargo has to be secured in such a way as to create a durable connection between the ship and the cargo item. This connection will be made either of tensioned flexible elements or welded stoppers. Lugs in the walls of the cargo hold are used for attaching the tensioned elements such as chains, steel cables and textile lifting slings, whereas on the smooth ship’s deck, D-rings (lashing eyes) or lashing plates are welded onto the deck. Stoppers made from flat-bar steel or double-T sections secure items against slippage, while clamps fabricated from shaped steel plates prevent slippage, tipover and lift-up.

“Welding is normally faster and can cost up to six times less than lashing”, explains Roland Barow, the second Managing Director of Seatight. Fastening-welding on ships’ decks is governed by rules and regulations laid down by the International Maritime Organisation (IMO). An ‘a’ dimension of 6 mm is stipulated for fastening-welds. For a 1 cm length of seam, this corresponds to a load capacity of around 1.2 t and a failure load (including safety margin) of 1 t. The ‘Maximum Securing Load’ (MSL) is specified as 50 % of these loads. Accordingly, a stopper with a 20 cm long seam reaches an MSL of 10 t, while a double-T section with a 20 cm long welded join on both sides has an MSL of 20 t.

Here, ‘narrow-gap’ refers to the welders’ workspace rather than to the welding groove!

WPI cargoes
To explain the welded joints needed, Angelo Pennacchia takes a WPI  (wind-power installation) as an example. Its approx. 400 t weight is distributed between the nacelle (approx. 130 t) containing the gearbox and generator, the rotor hub (40 t), three rotor blades (13 t apiece) and three tower elements weighing 65 t each. Cargo space and deck space are expensive, and so are used as densely and efficiently as possible. On the decks, the gaps between cargo items – and thus the workspace for the welders – can be very narrow. Before the joining operations begin, all paint, rust and water must be removed from the join location.

To secure the nacelles, the technicians weld 30 clamps totalling 8 m of seam-length. These clamps sustain a total MSL of 400 t. 12 clamps are sufficient to secure the rotor hub; they comprise 2.4 m of seam-length, equating to an 120 t MSL. For each rotor blade, fastened in a support frame, the fixing-points comprise 10 clamps and 5 D-rings; and for each tower element, 12 clamps and 16 D-rings. All in all, the resulting length of welded seam totals approx. 50 m. A team of 6 Seatight employees accomplishes this in an average of one workday.

Criteria, welding processes & systems
The deep-see freighter ‘Dynamogracht’ has space for 70 components for 14 WPI. The client needs to keep loading-times as short as possible, a requirement that Seatight fulfils by fielding two teams of three certified, tested welders. In addition to their professional qualifications, they also bring other vital knowledge and skills into play. The quality of their welding-results is checked by a neutral expert. The criteria here are compliance with the parameters specified in the stowage plan, weld-seam appearance and – in special cases – dye-penetrant and magnetic-particle inspection testing. The inspectors also look out for welding spatter that could damage the valuable components. The great care taken with electrode stubs is just one expression of the conscientious work ethic at Seatight, as these can cause fires on decks below the welding site.

On-board welding means manual-electrode (MMA) welding. Wind and weather, the distance between the power source and the workplace, and of course rugged, powerful and portable welding systems are the main factors affecting working practices here. In view of the distances of 75 m to 150 m that are usual between the power source and the electrode holders at the workplace location, a stable arc is absolutely critical. This is why Angelo Pennacchia set out in search of high-quality welding systems – and found just what he was looking for at Fronius: “They provided test systems for us at very short notice, which really impressed us – as did the extremely positive results that we got. It didn’t take long for the investment to pay off. When we set 180 amps on the TransPocket 2500 Comfort, that’s the value that we get – practically unchanged – at the other end of the cable a hundred metres away.”

This is thanks to a technology called ‘Resonant Intelligence’, in which continuous automatic feedback from the arc responds instantly to every change, keeping the power parameters in line with those of the ideal characteristic. This ensures maximum arc stability at all times, even with long mains supply leads or voltage fluctuations.

The valuable cargo being gently lifted into the hold.

More plus-points
Unlike conventional remote-control units, the lightweight (only 120 g) TP09 remote-control is cable-less. It allows the six welding systems to be regulated separately from one another using only a single TP09. With the TP09, every welder can respond individually as the situation demands. Among the other advantages: ‘Hot Start’ facilitates ignition of cellulose and rutile electrodes; the ignition means that less post-weld machining is needed; the anti-stick function detects any sticking of the electrodes in a short circuit; the welders can call up just the right job for e.g. vertical-up or vertical-down welds, as and when the situation requires.

Twenty TransPocket 2500 Comfort machines form the ‘backbone’ of Seatight’s fleet of welding systems. For special cases requiring extremely high power, there is a TransPocket 4000 unit, including a remote-control unit.

Says a satisfied Angelo Pennacchia: “Using electrodes from four millimetres’ diameter upward, and working at between 180 and 220 amps, we can get a 100 percent duty cycle. Our old system used to cut out every quarter of an hour! This meant that in practice it was much more expensive, even though the initial investment costs were lower. And with the TransPocket 2500, a good welder achieves top-grade seams.”

Rack mode
On the pier, six TransPocket 2500 Comfort units are aglow in a special device known as a ‘rack’. Seatight owns the first serial-production rack from the Automation Department at Fronius. Among its advantages are shorter set-up times, as it is simply lifted out of the delivery van by fork-lift and set down on the pier, and the fact that it can be wheeled along the quayside to be close to the workplace. Being run on centrally connected – and much cheaper – onshore power, the welding systems are subjected to fewer current fluctuations, and there is less wear-and-tear on their mains filters. This operating mode also reduces the length of the individual cables, thanks to the central connector, and the safety and availability of the welding systems are enhanced by the equipment being housed in the rack. The IP54 power distributor, with 6 weatherproof outlet sockets and a primary external mains socket, has 125A of fuse protection.

The practical benefit is so great that in the medium term, Seatight is aiming to deploy further racks of TransPocket 2500 Comfort appliances at five European ports, in addition to its main facility in Leer.

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Box 1:

Seatight: Sustainability-oriented and dynamic

In July 2009, the 29-year-old Roland M. Barow joined with 28-year-old Angelo Pennacchia to found Seatight GmbH Port & Cargo Securing Service in Leer, NW Germany. Barow is a captain with an engineering degree; Pennacchia a technician and nautical officer. With their combined technical and nautical expertise, they aim to make a professional and lasting impact on the field of securing high-value maritime cargoes. This philosophy has helped the young company to make it to the top of this market niche in a very short time. After less than two and a half years in business, they had boosted their headcount from 3 to around 20. Their stock of transport vehicles, container storage space and technical equipment has increased several times over – starting with just 6 welding systems, for example, they now have over 20. As well as its own workshop building in Leer, Seatight now has a subsidiary in Spain.

In an average week, Seatight now secures the cargo of two ships. After over a hundred and fifty sailings, not one single accident or damage incident has occurred. Thanks to offshore wind-power installations, Barow sees continued growth-potential in the market niche of securing high-value maritime cargo.