The variety of materials used in the manufacture of high pressure flexible pipes provides, in the first instance, an extensive range of possible NDT methods. However their complex, composite construction imposes equally extensive constraints on the operability and potential effectiveness of many of these methods. Additionally, little detailed information is available on actual failure modes of flexible pipes and data from examinations of failed pipes is largely confidential to individual operators. Ageing of non-metallic components presents a particular problem since nearly all of the common tests for determination of material properties are of a destructive nature. In addition to the complex construction further constraints on in-service inspection are imposed by the presence of bend restrictors, anode bracelets, and buoyancy elements on risers, by the burial of flowlines, and by encasement in J-tubes. This paper addresses some of the problems of inspection and monitoring flexible pipes and describes some of the methods which are currently being considered as potential solutions to them.
There has been noticeably growing interest over the last 2 to 3 years within the offshore industry, in establishing methods for condition monitoring of flexible pipes.
With greater use, and potential re-use, of these products the need for adequate inspection techniques is increasing.
The in-service inspection of flexibles is complicated by the subsea environment in which they are used and even when access to the pipe is gained the multi-layer composite construction makes quantitative assessment of pipe condition a demanding objective.
The design of flexible pipe is a subject on which information still remains, for commercial reasons, largely proprietary to the suppliers.
Inspection during manufacture and quality control of materials is invariably monitored by the purchaser's representative and this should ensure that pipes of the highest quality are manufactured. However, for the user, his confidence in the pipers fitness for purpose can only stem from the supplier's track record of similar products in similar operating environments, and possibly from testing of small samples in simulated conditions.
