By: Dave Randle, QinetiQ, UK
KobraTM is a new flexible, steerable guide tool for fibrescopes and videoscopes alike. It is a new product targeted at power plants and other industries and markets that need to carry out remote visual inspections. What makes this tool unique is its two-dimensional flexibility, which means that it can transport a fibrescope further and deeper into critical plant reaching areas that may have otherwise required component removal.
The need for better condition assessments
Maintenance personnel know that carrying out detailed internal inspections inside gas turbines, steam turbines and boilers is an essential part of any routine maintenance programme. It is also important to achieve a balance between maintenance requirements and maintaining production targets.
Deciding when to service components has an impact on both production and repairs, so a better working knowledge of a machine’s present condition, reliability and durability is vital. It is therefore essential to improve the intelligence gathered during internal inspections. In the absence of reliable intelligence most operators opt for an engine strip or component removal because they cannot risk a catastrophic failure.
There are many reasons why remote visual inspections can fail to provide such intelligence. One common cause is due to proximity limitations of an internal inspection, for example, if it is not possible to get close enough to make a distinction between what might be a crack or just discolouration. Kobra has been designed to tackle such issues and offers a solution to these types of problems.
What is Kobra?
It is a flexible, steerable guide that supports fibrescopes and videoscopes. Its unique articulated segmented link construction gives it variable flexibility. It is constructed of two flexible steerable guides, or sleeves, arranged coaxially. Mechanical controls enable the operator to steer and vary the tension of the Kobra allowing navigation and viewing angles otherwise not possible.
Construction and Design
Kobra consists of an inner and an outer section with separate control mechanisms for each. The inner section sits inside the outer section. Both the inner and the outer sections comprise a number of links which is variable and determined at the build stage to suit the inspection device owned by the user. The inner section links have a central hole to accommodate the fibrescope or videoscope. Each hole is chamfered to provide a lead-in to facilitate insertion of the fibrescope.
Using the Kobra inner and outer sleeves with a fibrescope effectively provides triple articulation
The links are threaded on to four steel wires, like beads on a necklace, 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 become detached. The wires are not crimped at the ends: they are silver soldered, which gives much greater strength and security.
Varying the tension equally on all four wires simultaneously alters the rigidity along its length. This proves a major advantage when navigating because the tension can be relaxed around corners and then reapplied for further straight sections or proceeding through larger voids. This prevents ‘bunching’ or ‘coiling’ in larger open spaces, which can be a common problem with most fibrescopes and videoscopes.
Navigation or steering of the tip is then 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 to do this: the articulation control for navigation, the tension control for handling and the position lock which maintains Kobra in position.
One of the main features is its ability to enable a fibrescope or videoscope to ‘sit up and look’. This allows better viewing angles and overcomes the constraints of gravity. It also avoids the need to remove components to gain better access, which is not always an available option. The viewing angle can be very important especially in cases where long shadows are either desired or not, or if the rise or bend at the bottom of a void limits the view using single articulation. The example diagram here demonstrates the advantage of this.
One of the problems encountered in larger voids when using a conventional fibrescope or videoscope without any stiffening devices or tailor-made guiding tools is ‘bunching’ or ‘coiling’. This is a common problem and is primarily due to the inherent flexibility of a fibrescope or videoscope. Kobra overcomes this problem because its rigidity can be increased when going through larger voids or other areas that cause this issue.
Most fibrescopes and videoscopes provide single four-way tip articulation, but using the Kobra inner and outer sleeves with a fibrescope effectively provides triple articulation. With just the inner sleeve and a fibrescope, double articulation on a single plane can be achieved. This feature opens up many more navigational routes which may have not been previously possible. The Kobra inner and outer guides can be purchased separately as some customers’ applications may not require both.
Achieving Rapid Assessment
Remote visual inspections using fibrescopes or videoscopes are used to perform component condition assessments in power plants and other industries, without the need for costly and time consuming disassembly.
More and more companies have tight outage schedules and high penalties for running outages longer than scheduled and are using remote inspections to perform quick condition assessments during brief shutdowns.
Kobra extends the range of standard fibrescopes and videoscopes so that previous ‘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 procurements and repairs, and reduces the need to replace components unnecessarily.
KobraTM is an unregistered trademark of QinetiQ.