Mechanically Lined Pipe

Key details

  • Wrinkle detection

  • 1 mm scanning along the entirety of the pipe

  • Accurate to 0.05 mm

  • 3-D model of the pipe ID

Why?

For a number of years the major pipe lay companies have been spooling mechanically lined pipes onto huge drums and taking multiple kilometres of pipe offshore and unreeling into the sea. Mechanically lined pipe (MLP) is, as the name suggests, a pipe with an inner liner of corrosion resistant alloy (CRA). This type of pipe is needed for areas where the fluids and gasses are highly corrosive. The choice of pipe is normally between metallurgically bonded liner pipe and weld overlay pipe. In all cases a layer of about 3 - 3.5 mm of alloy is used to prevent corrosion. Why should such pipe need inspection? This is because the act of bending can cause the inside of the pipe to come away from the carbon pipe leaving a gap between the two and a bump in the pipe. Such areas are considered very undesirable in a pipe.

Solution

OMS has been involved in mapping the inside of such pipes for many years and has developed the tools which allows the topography of the liner to be measured. Any area where there is an anomaly (typically referred to as a wrinkle as in a wrinkled cloth) can be visualised. By conducting many simulations and trials it is feasible for the pipelaying company to determine whether their design of pipe is fit for a particular project. The process of testing is called “simulated reeling” or often a “reeling trial”.

Data surf.jpg

How?

A laser triangulation device is used to measure the internal profile of the pipe where the measurements are spaced around 1 mm apart around the circumference. The tool is then moved along the pipe by any desired distance from 1 mm to 20 mm to collect another profile. A set of these profiles are then joined together in the software to develop a 3-D model of the inside of the pipe. In order to analyse the measurement data the information is unwrapped to form a flat surface. At this point the entire structure of the pipe through its manufacturing and bending becomes visible and measurable. Any areas of wrinkle formation are then visible as vertical bumps in the surface and can easily be distinguished from any manufacturing or bending artefact. The most desirable outcome is to determine that no bumps or wrinkles exist and the process can be passed as fit-for-service. Normally it is wise to define what is meant by a wrinkle and the normal metric is to be able to say that no feature larger than 0.5 mm or 1 mm was found after the reeling trial completion.