E!8996 Subsea detection of corrosion

The focus of the SEADEC (SubsEA DEtection of Corrosion) project is the development of a system for the health monitoring of subsea pipes, pipeline systems and risers. It is especially suitable for ageing subsea assets which are decades old and hence more at risk of structural integrity failure. The principle of operation of SEADEC is based on the propagation of low frequency electromagnetic (EM) waves in sea water to give remote indication of the site of damage, ingress of water and sites of corrosion. The innovative part of SEADEC is that pipe-in-pipe systems, with concentric pipes, insulation and armour are electrically equivalent to co-axial conductors and can carry electromagnetic (EM) signals great distances. SEADEC injects an amplitude modulated EM signal at the terminus of a pipe. When a breach occurs in the outer mantling of a pipe, water enters and corrosion starts. It can continue for years later undetected, and great damage can occur before detection is possible with current methods. However, when water enters, the EM signal escapes and is conducted away by the seawater. High frequency EM signals rapidly attenuate, but the low frequency wave envelope does pass. The sea water act as a low pass filter and the lower the frequency the further the distance the electrical signal travels in sea water. Large sections of offshore piping remain untouched since the day of its installation and its current condition is largely unknown. The target is to offer a solution with positional accuracy of defect location, ability for non-contact detection, speed of scanning and low cost of hardware and minimal human intervention.

The main aim of this project is to develop a robust and practical new NDT system (SEADEC) that remotely detects from the surface of the ocean, breaches and ruptures in subsea pipes and risers on the sea floor. The three separate hardware embodiments of the leakage detection system are: - A system mounted in a surface vessel that can scan for such defects in pipelines very rapidly at scanning rates of up to 100 km per day with a positional accuracy of plus or minus 30 metres. - A Remote Operated Vehicle (ROV) scanning for breaches obscured by marine growth in subsea pipes and risers at a rate of several kilometres a day to a positional accuracy of plus or minus several centimetres even in conditions of total darkness. - A signal injection unit (located at either the shore or offshore terminus of the pipeline/riser system) which introduces the signal into the pipeline which leaks out at the site of any breach in the outer subsea pipe. The SEADEC system has two hardware components: - A signal generator unit which is attached to the pipeline terminus and injects a signal into the pipeline (or riser) which traverses the entire length of the pipeline, even if it were many kilometres long. This signal escapes into the sea at the site of a breach in the outermost wall of the subsea pipeline or riser and it is this leaked/escaped signal which is picked up by the detector unit and allows it to precisely locate the position of the breach. - A detector unit that can be mounted on either a ship or a Remote Operated Vehicle (ROV) The SEADEC subsea breach detection system is based on the propagation of low frequency electromagnetic (EM) waves in sea water to give remote indication of the site of damage, ingress of water and sites of corrosion. This methodology has never been used before in this industrial way.