The art of Laser surveying 1

[Ferex]

Hi everybody, I am new to this forum as a registered user and this is my first question, I sure I will get good answers. Excuse me if my English is not perfect.
I work for a laser scanning survey company, I am however new to this work and I ask those who have experience in this field or if some of you have received survey drawings with infos excerpt with this instrument what are the advantages of this kind of technology and do you think you really obtain more precision than traditional methods?
These are two general questions, I hope to give birth to an interesting discussion, I think that the core of this work is giving the client what really needs with the accuracy he needs, because as I can notice few (10/15) millimeters don't matter in the plant industry, am I right or wrong? I need a discussion with people who use survey drawings.
Many thanks

 

[JLSeagull]

The industrial precision depends upon the application. Laser scans are popular for offshore hookup where steel fabricated onshore needs to stab precisely onto offshore steel. Similar examples exist for modular fabrication that ships to a job site for assembly.

 

[Ferex]

Ok, thanks, in this case the problems arise when the steel is a little bit bent, usually I give the distance at the basements, I never surveyed off-shore but for pipe-rack steel columns I find distances are never the same as designed, I can find 4005, 4003, 4012, 3088, as an end user do you want to have this differences in the final drawings?

 

[BigInch]

Well that depends on what the temperature of the pipe is when you got those differences! 15 mm can mean thosands of tons of load if measured at the wrong temp or the measurement is not compensated to design and installation temperatures.

**********************
"Pumping systems account for nearly 20% of the world’s energy used by electric motors and 25% to 50% of the total electrical energy usage in certain industrial facilities." - DOE statistic
"Note: Make that 99.99% for pipeline companies" -

http://virtualpipeline.spaces.live.com/

 

[Ferex]

But what if I talk about structures...
If I take the distance on the basements I think that temperature and load doesn't matter, I think it's a mistake during the construction phase, should I care about it or not?

 

[BillBirch]

The assumption that there will be differences between "as-designed" and "as-built" is one of the factors supporting your industry.

I know of offshore operators who have their platforms designed in PDMS (3D CAD), and laser survey after installation. This digitised data is then fed back into PDMS to show steel (and in particular piping) in its actual position. The updated model thus represents the as-built status of the platform. This can then be used as an accurate datum for future modifications such as flowline installation.

Another specific use offshore is for the fabrication of pipeline riser tie-in spools. Generally there will be a yard installed section of the pipeline within the topsides module, but the final position of the jacket-mounted riser will not be known until it is set. Laser surveys enable the ends of the pipe to be located in space, including the orientations of the cut surfaces to be defined, allowing the infill spool to be accurately shaped (even if both the joint surfaces are not parallel).

Clearly, t is a good tool if it provides accurate as-built information. The cost of rectifying shop-fabricated spools offshore is enormous compared to their initial fabrication cost. Similarly the cost of sending draftsmen offshore is expensive, even if we assume that they able to, or have sufficient access to measure accurately (that is another topic). Although laser surveying may be considered expensive by some, the examples given indicate the type of costs that can be used to justify the surveys.
Regards,
Bill

 

[BillBirch]

By the way. You are doing the industry no justice by referring to it as an art. This will create an impression on your potential clients that the occupation requires experienced operator interpretors, whereas your client would want a warm feeling that the data he is given is absolutely reliable, and not subject to intangible factors usually associated with "arts".

 

[Gator]

http://www.pipingdesign.com/field-fit_welds.html

Near the the bottom of this page is some writing on laser scanning written by Bruce Raymond. It's probably worth a look.

Paul
Piping Design Central

 

[Ferex]

Many thanks, I already took a reading on the article Gator suggested.
BillBirch, I said it is an art because I have to represent reality, and many times it's difficult to represent it on a drawing, many times, after 30 years the plant is very different from how it was at the beginning, (luckily I have only to represent engineering infos).
I hope you can tell me another thing, do survey operators take isometrics (without dimensions) on field, in the plant before going to the office and take distances from the point clouds??
This is just to know other's proceudures. We don't take preliminaries, but I think we should...
Many thanks