Kobra Adds Bite to Inspection Programs

Carrying out detailed internal inspections of gas turbines is critical to any routine power plant maintenance program, but it has to be achieved without affecting production targets. Many companies have tight outage schedules and face the prospect of high penalties for longer than expected equipment downtime.

Against this backdrop, operators of power plants frequently use remote visual inspections of machinery and pipework during brief shutdowns. However, it is argued within the industry that such inspections have limited effectiveness because fiber scope and video scopes used to carry out the work can lack flexibility, and these remote visual inspections may fail to provide accurate condition monitoring, as they are unable to get close enough to potential equipment problems.

Thus,they may not clearly distinguish, for example,whether a mark inside power plant equipment is a crack or just a discoloration.This leaves doubt in the minds of maintenance engineers, who have to decide when to service components.

Kobra is made of two flexible, steerable guides,or sleeves, arranged coaxially. Mechanical controls enable the operators to steer and vary the tension of Kobra, allowing navigation and viewing angles that were otherwise impossible.

Faced with potentially uncertain information gathered during a remote visual inspection, plant operators often decide to carry out an engine strip or component removal rather than risk a potentially disastrous failure or other serious engineering problems such as gas turbine vibration. Engineers at a British company have,however, developed a new flexible, steerable guide tool, which it claimed can carry fiberscopes and videoscopes further and deeper into critical plant and reach areas that may have otherwise needed component removal.

The company behind the new product, which is called Kobra, is QinetiQ — an energy, defense and security technology company based in Farnborough, Hampshire, England. QinetiQ said the product is targeted at power plants and other industries and markets that require remote visual inspections.Kobra is a flexible, steerable guide that supports fiberscopes and videoscopes.The flexibility, QinetiQ said, is a result of what it describes as a “unique articulated segmented link construction. ”It is made of two flexible,steerable guides, or sleeves, arranged coaxially. Mechanical controls enable the operators to steer and vary the tension of Kobra, allowing navigation and viewing angles that were otherwise impossible.

According to QinetiQ, one of the most striking features of Kobra is its ability to enable a fiberscope or videoscope to “sit up and look, ” which the company said allows better angles to view areas of the power plant and also overcomes the constraints of gravity.An added attraction, said QinetiQ,is that it eliminates the requirement to remove components to gain better access,which is not always an available option.

“ The viewing angle can be very important, especially where long shadows are desired or not, or if the rise or bend at the bottom of a void limits view using single articulation, ” said Dave Randle, a gas turbine engineer at QinetiQ. “ One of the problems encountered in larger voids when using a conventional fiber scope or video scope without any stiffening devices or tailor-made guiding tools is ‘bunching’ or ‘coiling.’This is a common problem, and primarily due to the inherent flexibility of a fiber scope or video scope.

Kobra overcomes this problem because its rigidity can be increased when going through larger voids or other areas that cause this issue. ” Kobra consists of an inner and outer section with separate control mechanisms. Both sections comprise a variable number of links. The number is determined at the build stage to suit the user’s inspection device. The inner section links have a central hole to accommodate the scopes, and each hole is chamfered to provide a lead-in to facilitate insertion of the fiberscope. The links are threaded onto four steel wires similar to beads on a necklace, said QinetiQ, with four wires for the outer section and four for the inner section.

Each steel wire has three combined functions — navigation, tension and safety.To safeguard against breakage, each wire carries a 57 kg breaking strain and all four wires would have to break before any links could become detached, according to QinetiQ.The wires are not crimped at the ends but are silver soldered, which the company said gives much greater strength and security. Varying the tension equally on all four wires simultaneously, alters the rigidity along its length,which QinetiQ said is beneficial when navigating because the tension can be relaxed around corners and then applied for further straight sections or proceeding through larger voids.

QinetiQ said that Kobra extends the range of standard scopes so that previously beyondinspection
areas become accessible.

Navigation or steering of the tip is achieved by tensioning two wires on one side while relaxing the tension on the two wires on the opposite side.The control assembly incorporates all of the controls needed — the articulation control for navigation, the tension control for handling and the position lock,which maintains Kobra in position.

“Most fiber scope and video scopes provide single four-way tip articulation, but using Kobra inner and outer sleeves with a fiberscope effectively provides triple articulation,” added Randle. “With just the Kobra inner sleeve and a fiber scope, double articulation on a single plane can be achieved. This feature opens up many more navigational routes which may not have been previously possible. The inner and outer guides can be purchased separately, as some customers’ applications may not require both.“Kobra extends the range of standard scopes so that previously ‘beyond-inspection’ areas become accessible. This leads to increased levels of confidence about the condition of the inspected components, and the information gathered can be used to enhance effective parts procurement and repairs and reduces the need to replace components unnecessarily.” visit www.dieselgasturbine.com