EM&I – laser scanning could replace tank entry

Oct 15 2020


Asset integrity management company EM&I is developing laser scanning methods for tanks on offshore vessels, which could remove the need for people to enter tanks to do inspections.

Asset integrity management company EM&I is developing automated methods to inspect tanks on offshore vessels using laser scanning, to avoid the need for people to enter tanks.
 
 
 
Tank inspection is considered by many to be one of the most dangerous tasks which FPSO and tanker crew undertake, with a number of accidents reported on tankers. The spaces can be difficult to enter and exit and involve inspectors working at height. If crew have any accident or medical issue while in a tank, it can be difficult to summon help. 
 
 
 
The solution developed by a Joint Industry Project (JIP) led by EM&I uses laser scanning at a distance, instead of close up inspection by people.
 
 
 
A laser beam is fired in multiple directions and bounces back to a sensor enabling the computer to build up a 3D image of what the laser can “see”, using multiple points (known as a “point cloud”).
 
 
 
The same technology is used to make 3D models of equipment, buildings and also for navigation of autonomous cars.
 
 
 
The laser device coupled with a class approved high performance cctv camera does not have to be taken into the tank by a person but is instead located by a robotic arm through existing or purpose-made holes in the deck.
 
 
 
The laser scanner can also be mounted on a free moving robot vehicle inside the tank or can use existing bottom longitudinal structure, rather like railway lines inside the tanks.
 
 
 
‘Conventional laser scanning is quite well known but our development is unique because it allows accurate thickness measurement of the internal structure which would normally require man entry’ says Danny Constantinis, executive chairman of EM&I.
 
 
 
‘A typical scan takes about 8 minutes, where it could take several days with people in the tank to do an equivalent inspection, he says.
 
 
 
With laser scanning, it would be possible to inspect all the tanks on an FPSO with 2-3 people “in a few days” – rather than having 10-12 people onboard for 3-4 weeks, doing dangerous work which involves confined space entry and working at height, as it is done today.
 
 
 
EM&I considered drone mounted lasers inside a tank, but it proved to be not a very workable approach – it would still need someone in the tank to pilot the drone and the laser needs to be very static to take synchronous measurements, so would be better sitting on something more stable than a drone.
 
 
 
Early laser trials were held in 2019 on an FPSO in Equatorial Guinea under the HITS JIP programme managed by EM&I. 
 
 
 
EM&I is collaborating with several oil majors and class societies to validate the technology on a number of offshore installations and it should be ready for full commercial launch in late 2020 or early 2021.
 
 
 
How it works
 
Laser scanning technology has advanced greatly in the past few years, and it is now possible to “see” in enormous resolution. A laser scan shows up distortion in the steel, rusty patches and paint breaking down. Laser scanning can reveal and measure pits in steel due to corrosion, and areas where the steel is thinning or corroding. The data can also be converted into stress models, to identify where the weak areas are.
 
 
 
A big challenge when evaluating tanks is measuring the thickness of the steel (and if it has been thinned through corrosion). People used to tap the steel with a hammer, or by using a calliper (if they can access both sides of the steel), or ultrasonic technology – but all of this involves someone entering the tank.
 
 
 
EM&I is developing a technique using “synchronous lasers”, when you do laser imaging from different positions in the tank, and then put the images together. This can be used to evaluate thickness if you can ‘see’ both sides of the steel with a laser and also relate the two laser positions. 
 
 
 
If you can only see one side of a tank wall with the laser, one approach to measuring steel thickness is to use datum points, such as a point on the tank wall which can also be seen from outside the tank (such as an access point). You can use this datum point to connect together multiple images.
 
 
 
A similar technique is used in building construction to ensure (for example) different sections of piping connect together. Two pipe sections can be designed to connect at a ‘virtual’ datum point.
 
 
 
“We can measure the thickness as accurately as if a man was in there,” Mr Constantinis says,” and the robotic optical camera system is able to detect cracks which laser systems may not see’. 
 
 
 
Software can handle basic quality control over the data collection, so as to confirm that all of the tank area has been surveyed.
 
 
 
The laser data can be collected by a few specialist technicians and analysed by surveyors and engineers from their desks.
 
 
 
The remote surveyor could also review data while the survey is happening, and request that certain areas of the tank are given special attention. 
 
 
 
EM&I worked together with statistics experts to assess how much data is actually needed to get a high level of reliability in the predictions.
 
 
Automated tank cleaning 
 
The next research project may be to look at automated cleaning methods for tanks. The challenge is to find a way to remove the liquid sediment which falls to the bottom of the tank.
 
 
 
The initial efforts are based around looking for technological ways to determine which parts of the tank justify most cleaning effort.
 
 
 
“We’ve tried different [automated] technologies to go through the sludge – it can be done but it is very slow, at present but work is progressing to speed things up” Mr Constantinis said.
 

 



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