Shiprepair & Maintenance: 3rd Quarter 2018
The Metalock stitching technique has been available as a means of delivering permanent repairs to marine equipment, in-situ, and without needing to carry out hot work, for over 60 years. However, the Metalock International Association (MIA) believes that many recently trained engineers are not aware of the technique and so turn to welding as a solution, despite the many drawbacks that entails.
As such, the MIA is concerned that the industry has a lost generation of engineers who have received little or no training in a procedure which requires easily transportable equipment and can be completed within a few days, and in some cases hours. The finished repairs can achieve up to 90% of the strength of the original metal piece and, since no hot work is involved, repairs can be made to machinery without needing to remove it, and without concern for the presence of flammable or explosive materials.
According to MIA president, Andre Mortimer: “In the field of ship repair the ability to repair the cast components of machinery without removal, even while at sea, is a technique that should not be overlooked. We want to make sure the Metalock process is a vital tool in all Chief Engineers’ tool boxes.”
To relaunch the concept, and raise its profile within the marine sector, the MIA has recently published a white paper, The Benefits of the Metalock Process. This document highlights what the association believes is a significant loss to shipping caused by unfamiliarity with the Metalock technique.
Cast iron repairs
Many of today’s engineers, says the white paper, believe their only option to deal with cracked machinery is welding or replacement. Since welding cast iron is at best a sticking plaster approach, the paper suggests, owners can be faced with enormous replacement bills and long periods off-hire. A new campaign by MIA, heralded by the publication of the white paper, now aims to fill the knowledge gap regarding Metalock.
The process can be applied to other metals besides cast iron, including steel, and aluminum. It is, however, with cast iron that Metalock really comes into its own, claims the MIA. Mortimer says: “Between 70 and 90% of Metalock repairs by our members are done over previous welding attempts. Welding is notoriously fragile on cast iron.”
As per the white paper: “Cast iron is the most difficult of all common cast metals to weld. All electric welding methods for cast iron have proven less than satisfactory and in many cases have created even more cracks. Failures such as a cracked engine bed plate or a fractured cylinder are almost certain to have a catastrophic effect on operations and forced unscheduled delays are potentially damaging to a ship’s profitability.”
Mortimer adds: “When a weld does fail it is always more difficult to achieve a successful repair subsequently, as the parent material around the weld has to be replaced. Sometimes a weld may work for a while, but it is far better to call an approved Metalock engineer first for a proper assessment.”
According to MIA, welding has some significant common disadvantages, including inherent weakness along the line of fracture. It is also often necessary to dismantle equipment before carrying out a repair and if carried out onboard ship requires adjustments to the surrounding area to remove potentially flammable or explosive materials. Furthermore, a welded repair can increase the risk of permanent distortion and brittleness of the metal, so that when machinery is returned to normal operation there is a high risk of it cracking again.
Welding does of course have its merits and MIA says that Metalock technicians are trained to recognise the best approach for every circumstance. Where, for example, a weld in steel is more appropriate, then that option will be recommended.
Each fracture is unique, the MIA points out, and Metalock engineers are equipped with extensive knowledge of different fracture situations, both through their own work and that of fellow technicians within the MIA membership worldwide. A key element of the work of MIA is to share experiences and solutions amongst its members. “Being armed with this information and experience allows Metalock technicians to approach repairs with absolute confidence in the result, and the time it will take to complete the repairs,” says Mortimer.
The process
With Metalock, groups of holes are drilled across the line of fracture and are then joined to align to the shape of Metalock keys which are inserted into the aperture. Further holes are then drilled along the line of the fracture and these are filled with studs, each biting into its predecessor to create a pressure tight joint. The studs and keys are then ground down to a polished finish.
Mortimer adds: “The basic technique of stitching can be expanded with the insertion of a tailor made matching cut-out from the machinery being repaired, and a bespoke ‘master lock’ would be used when there is a requirement for extra strength. But where we are performing a repair on an area that has no great load bearing or force acting on it, keys are more than adequate.”
The repair dampens and absorbs compression stresses, and provides a good ‘expansion joint’ for cylinder liners, diesel heads or any components subject to thermal stresses. The technique also distributes tension loads away from fatigue points while the fact that no heat is required means there is no distortion. Most repairs can be carried out in-situ with consequent time savings and limited disruption.
The white paper gives a case study example of a repair to a damaged main engine cylinder casing on a vessel which returned to service, after a repair operation lasting just seven days. The shipowner, faced with an eight-month replacement estimate for the engine, called in local Metalock engineers who worked to perform a full repair. The entire operation took one technician only a week and was conducted without the removal or disassembly of the engine.
Publication of the white paper coincides with an educational campaign aimed at Chief Engineers and ship owners. MIA is naturally also keen to promote the value of using companies that have Association membership or certification.
“Like any repair technique, there are many wrong ways to do it, but the training provided by MIA is thorough, and our members share knowledge continually through our seminars and conferences,” says Mortimer. “We would recommend only approaching a member company.”
