Alasdair Murrie looks at remotely operated vehicle developments for the underwater industry.
Remotely operated vehicles (ROV)are an increasingly critical element of the underwater industry. Helping to automate a range of processes and making tasks such as inspection and maintenance not only safer but also more efficient, it's easy to see why these vehicles are proving so popular among underwater operations experts.
ROV manufacturer SeaBotix designs and develops versatile ROV platforms - or 'Little Benthic Vehicles' as they are known.
The company's innovative and versatile approach is achieved through sophisticated design and proof-of-concept processes, often including collaboration with fellow innovators to deliver these robust and practical subsea solutions to market.
One particularly relevant example of this versatility can be seen in the tracked, vectored Little Benthic Crawler (vLBC), and its smaller sibling, the wheeled LBC.
By fitting a standard SeaBotix vLBV300/950 or LBV300-5 ROV with the non-magnetic Vortex Generator integrated on the vLBV's tracked or the LBV's wheeled skid, it is possible to crawl horizontally or vertically along any reasonably flat and solid surface in a very precise and controlled manner at speeds of up to 35m (115ft)/min. The impeller creates a low-pressure pocket or venturi effect beneath the vehicle yielding up to 28kg (62lb.) of attractive force. This is sufficient to maintain precise operations whilst a vessel is underway at sea or anchored in strong currents. Power is applied to the skid's drive axle for movement on the structure under maximum control. This means a survey can be conducted faster, more economically and in far more hostile environments than would be the case if diving teams were employed.
One immediate benefit is that cameras, imaging sonars, etc. are kept at a consistent distance from the structure with absolutely no relative motion. Therefore, excellent quality images and data are achieved. Additionally, the ability to set the ROV operator control unit down and focus solely on the incoming data allows the pilot to analyse the information, free from distraction in a 2D rather than 3D environment.
With its introduction to the military and security markets for inspection, damage survey and limpet mine clearance, a natural progression was then inspection, repair and maintenance (IRM) tasks, including more advanced non-destructive testing (NDT). Other missions for the crawler include harbour or hydro dam walls and offshore salvage operations - as in 2009, when a grounded container ship stuck on a reef in the Singapore Strait was surveyed in currents of 5+ Kts down to the seabed by an LBC, to determine if the hull had been breached. Additionally, these systems have been employed internally, in bilge tanks, sea chests and fresh water supplies.
FPSOs and ballast tanks of semi-submersible platforms are other ideal work environments for this system, plus there are numerous applications within the nuclear industry.
An integrated approach
The latest example of innovative partnership and development of capability is a project with Sonasearch, headquartered in the US state of Washington. This involves the integration of the storage tank surveyor (STS) acoustic camera on a vLBC for internal wall and weld NDT inspection in water, fuel and other liquid storage containers. The clear advantage is that this is achieved without needing to drain the tanks - thereby potentially saving a client millions of dollars annually and removing the obvious inherent danger of diver intervention in potentially volatile liquids.
By fitting a standard vLBC with a 'dozer' blade (to loosen settled sludge, sand, wax paraffin and other detritus), the STS is mounted on the vehicle for precise inspection of the tank.
Using phased-array 3D imaging, the STS incorporates an electronically beam-steered, multi-element scanning head, measuring the tank thickness and weld integrity at an ultra-high resolution of up to 113 microns and mapping returns passing bi-directionally through the tank wall.
With the provision of power and communication channels to the acoustic camera via its tether, real-time data is extracted at the surface as the vLBC traverses a pre-planned survey path, thus ensuring complete and accurate coverage; the result being inspection point, ≤ 6.35mm (1/2-in) accuracy to reliably detect corrosion areas measuring 25.4mm (1-in) in diameter in order to provide an accurate prediction of when corrosion has reached the point of intervention or replacement.
The advantage of this method over others is threefold:
* The physical overlap between two consecutive beams that are electronically adjustable depending on the size of the defects being detected;
* The large helicoidal pitch covered by only one phased-array probe rather than several mechanical-interlacing inspection heads;
* The optimised beam profile with less than 2dB drop between apertures, obtaining a very high density of energy in the tank floor and improving repeatability performance (missing rate = 0%).
The first customer trials of this latest SeaBotix package with an oil major are due to begin in Q3 2014. This will soon be followed by deployment in fuel storage tanks, oil tanker and FPSO hulls (inner and outer).
For more information at www.engineerlive.com/iog
Alasdair Murrie is vice president of sales, SeaBotix, San Diego, California, USA.
