Hi everyone, I am a Masters degree student at Middlesex University, London Borough UK and am in need of professional advice on a new concept I am developing for my school applied project academic research work for the partial fulfillment of my dissertation.

I am conducting an academic applied project research exercise into retrofitting of a new novel Condition Monitoring and Maintenance (CBM) System for structural health monitoring of large diameter tubular steel legs of jack-up platforms/barges or Liftboats [Self Elevating Work Over Platform (SEWOP)] operating in the oilfields globally.

The problem is that these giant tubes have over the years been experiencing fatigue degradation due to extreme environmental, local and operational loads inducing fracture breakages on them thereby plunging the whole vessel into the bottom of the ocean with huge fatalities!

The area of my study is in Marine Operations Management and I am determined to find a working 'Monitoring System' that can be integrated into the legs to predict early fatigue crack propagation on them so that the crew onboard can take an informed decision to arrest the problem before it escalates.

These legs are rigid steel tube structures that are being moved up/down with hydraulic gearboxes or electric motors in a housing whenever the boat is about to carry out its functions in the oilfields. Each tubular leg is fitted with 2 'gear teeth' racks which stretches through the entire length from one end of the leg to the other end and situated opposite to each other. The leg is inserted permanently into a steel housing which is a major structure forming part of the main deck and the hull and is fitted with gearboxes driven by hydraulic system or electric motors, the legs are usually tripod or 4 in number depending on the capacity and other criteria of the vessel.

I am considering NDE (Nondestructive Examination) concept as an integrated monitoring and inspection system on the legs using either one or combination of two of the following Acoustic Emission/Ultrasonic Principles: (i) AET (Acoustic Emission Technique) Sensing (ii) AWPAU (Automated Wireless Phased Array Ultrasonic) Sensing. (iii) PAGWU (Phased Array Guided Wave Ultrasonic) Sensing.

The legs are giant hollow covered steel tubes with welded sectional halves to make it long, 200 to 600 meters long (high). I am proposing fitting these transducers on (i) the top end of the leg (either by fixing arrays to form a ring and positioned at the circumferential edges of the top cover or symmetrically forming a ring around the wall at the top edges circumferentially) and (ii) the bottom end of the leg on strategic points on the pad (shoe).

The only free parts of the leg are the top circumferential end and the bottom end which is fitted with a pad (shoe) used for standing on the ocean floor.

I am aiming for the ultrasonic signals to be exchanged from the leg's top circumferential cover or edges down into its body (longitudinal cross-sectional area) through its length (longitudinal axis) wall thickness [not breadth (transverse) wall thickness] and or through its skin (surface or skin effect) down to the bottom shoe (pad), positioning the leg as a 'conductor' of acoustic signals (i.e. the Leg is the material to be tested and a portion is immersed in the sea with pad seated on the ocean floor).

The areas I need help are:

(i) Will the ultrasonic signals travel in that direction since the legs are hollow tubes with internally built frames and stiffeners and due to the fact that concepts involving sending, directing and reflections of signals inwards unilaterally through the longitudinal thickness of a cross-sectional area of a thick-walled hollow pipe from one end through to the other end has not really been made popular? i.e. Unlike water that moves by osmosis through a membrane of plant tissue from one end through its vertical thickness and not through the breadth thickness to the other end.

(ii) I am not sure if the transducers if fitted at the top, will transmit the signals from one end to another and or reach the bottom in case of 'Ultrasonic Testing' and be picked up by receiving transducers.

(iii) If the signals are able to pass through its longitudinal thickness and or through its skin (surface or skin effect) what will be the effect of the body of saltwater on the reflected or incident signal as they pass through the portion of the legs immersed in seawater?

(iv) Or whether a crack initiation on the steel leg can be picked up in case of 'Acoustic Emission Examination' from such a very long length from one end to another by arrays of acoustic emission detecting hydrophonic transducers?

(v) A portion of the leg is also immersed in the seawater at all times and am not sure if the acoustic/ultrasonic signals will propagate nicely, distort or disperse (attenuate) in the seawater/river water or not.

I look forward to your help and support Sirs/Mas.

Best Regards

Engr. Salawudeen Kayode (MSc Student- MDX UK.)