Out of straightness measurements

This topic has 10 replies, 4 voices, and was last updated 16 years, 11 months ago by Andy Shiers.

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May 25, 2007 at 11:35 am #766

Savante
Participant

Has anyone here been engaged in out of straightness or spool piece metrology measurements – either diver or ROV based?

Just completed a 3D laser beacon system akin to the acoustic positioning systems at the moment for tracking an ROV – looking for some operational stories and methodologies as to applying it to a real job; out of straightness or spool piece metrology.

Can you please email me at grant.thomson@savante.co.uk ?

We were told by one company that 30m range would be appropriate for this sort of thing? Any comments?

May 25, 2007 at 12:06 pm #12144

Ray Shields
Participant

Out Of Straigness normally requires running a wheel along the top of the pipe with a bathy/digiquartz attached. The wheel accurately measures where it is as it goes along the pipe whilst survey log the depth readings.

The pipe can be a few km long, dont see how the laser positioner could help with that.

For metrology, at present its normally done with an acoustic LBL array although I have heard of laser range finders being used more for ranging. Again, a bathy/digiquartz is placed at a pre-determined location (flange etc.) measurements taken, then fly the route logging bathy/altimeter readings to the other end. This is usually done a few times to work out the mean.

If the laser positioning was more accurate/easier to deploy etc. then it could be useful.

May 25, 2007 at 1:51 pm #12145

Savante
Participant

Precision.
———–

in the lab I can stand on the floor next to the reciever and pick up the movement of the beacon – reading the computer screen is a pain unless I round to nearest mm – the numbers change depending on where I stand in the room!!

Position precision seems to be around +/- 30 microns. (i.e it fluctuates by +/-0.015mm if I stand still next to it). Presently around 2m from the transmitter. Room isn’t really long enough to try out further.

Angular precision, heading, pitch, roll seems to be around +/-0.009 degrees under the same circumstances.

Perhaps this is more suited to the spool piece metrology applications…..

Beacon is pretty much fire and forget – can run off 12V DC.

May 25, 2007 at 2:05 pm #12146

Andy Shiers
Participant

Through personal experience , Laser measurements underwater is a no go . Sediment and salinity being the main problem.
What you refer to as guidence and measurement on top of the pipe is a odometer either magnet or mechanical set over a pot ( complete with gubins 😀 ) and in conjunction with a bathy . The problem being with these is sufficient down thrust to keep the vehicle pressed against the pipeline , If the pressure is not enough then the whole measurement is lost. ( a major factor to consider is the accuracy of the usbl system.
I have been on a job whereby Digi quartz beacons were utilised giving position depth and distance.
The beacons have to be placed on a framework pre subsea installed-flush to the pipeline metal ( not on the weightcoat ) and a solid or fixed transducer close to or direcetly above the postioning spools (I.e platform)
Once the measurements have been taken and ‘double double’ checked then the frame and Beacons are realeased via pins or recovered via diver
All in all the mission was a success without the use of bubbleheads and the measurements were acceptable to the engineers to fabricate the spool and instaled by Sat girls later in the year 😀

May 25, 2007 at 3:29 pm #12147

Savante
Participant

kicking up crud is a total pain, but we’ve done subsea measurements up to 4m range away with the bubbleheads in the water stirring up crud into the laser path and still got to under 3mm accuracy.

cheers for the info lostboy-much obliged! 😀 were they hipap type beacons – and then is the fixed beacon like the one you have on the bottom of the ship ?

do you know what is the longest spool piece job and say average distance involved in a spool piece metrology project?

May 25, 2007 at 4:22 pm #12148

Andy Shiers
Participant

Depends on the size of pipeline and platform structures that obsruct the pipelaying facility 🙂 The vessel used was called the Maxita , I think 😕
70M was the longest I’ve ever seen which involved two workclass vehicles either end and a short 10 m close – out piece.
The metrology involved was only for the 10 m close – out spool.
So obviously the distance was not extensive and only had one ‘dogs leg’ in it.

May 25, 2007 at 4:53 pm #12149

truered
Participant

if you use the odo wheel, watch out for the damn star fish 👿

May 25, 2007 at 6:15 pm #12150

Savante
Participant

we don’t need no odo-meter – just an unburied pipe I think – no contact, no crud !

the 10m spool piece would not present a prob, but there’s a dog leg? Do you mean like this?

so the vehicles had some sort of inertial nav sensor? like the cdl system or is it strings and direction of pull?

– just run from one end to the other a couple of times and take average? do they have to run along the path of the intended spool piece (i.e is it only the ends that count or do we need to know about relief within the track of the spool piece?)

also, I’m presuming that the ends of the two pipes can be at crazy angles to each other, but do you find that spool pieces overlay existing pipes?

May 25, 2007 at 8:29 pm #12151

Andy Shiers
Participant

😕 Er no ,
Surgayers or Enginears are usually quite adept at getting the spool flange at the right angle ( Face to face ) Unless they are foriegn 😀 and as I said before the reason for having the close – out spool a certain distance is NORMALLY due to obstructions ( including other pipeplines coming into the platform )
This means that the spool has to ‘jump’ over other pipelines or manouver around ‘sleepers’ etc
The divers Metrology table gives both angles and a bog standard tape measure gives distance.
The reason why Enginears get a shed load of money is to work out these anomalies and give the measurements to the fabricators to fabricate the spool. Or F@#k it up 😀
Any small discrepancy can be rectified by lifting the pipeline via aid of lift bags and floating the load Or bagging / sleepers / Grout bag the pipeline after it has been lifted by A-frame.
And yes I have seen some pipelines overlap 🙂
The good thing is that you don’t need a close out spool …………………….
The bad thing is that someone F@#ked -up 😆

May 25, 2007 at 8:50 pm #12152

Savante
Participant

All or nothing – I like those odds! 😆

May 25, 2007 at 9:39 pm #12153

Andy Shiers
Participant

What are you up to Savante 😀
Interesting questioneys 😀
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