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Technical Discussions
Samuel Peebles
Consultant,
BINDT, United Kingdom, Joined Jun 2009, 8

Samuel Peebles

Consultant,
BINDT,
United Kingdom,
Joined Jun 2009
8
13:31 Mar-18-2011
Zonal discrimination coating cut back required

To err on the side of caution before the AUT system has been chosen for the project what is the recommended coating cut back that should be applied if we were to use a zonal discrimination system on a 42" dia 1" w/t on a land pipeline.

 
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CARLOS SUAREZ
Consultant, ASNT NDT LEVEL III
Integrity & NDT Solutions, Colombia, Joined Mar 2010, 9

CARLOS SUAREZ

Consultant, ASNT NDT LEVEL III
Integrity & NDT Solutions,
Colombia,
Joined Mar 2010
9
03:50 Mar-19-2011
Re: Zonal discrimination coating cut back required
In Reply to Samuel Peebles at 13:31 Mar-18-2011 (Opening).

Samuel

The cut back is depending of weld bevel. There are two posibilities, to use pulse-eco or pitch and catch technique
I recommend to use ESBEAMTOOL 4 for find the best cut back acording the probe index offset.
The weld bevel is very important

 
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samuel Peebles
Consultant,
BINDT, United Kingdom, Joined Jun 2009, 8

samuel Peebles

Consultant,
BINDT,
United Kingdom,
Joined Jun 2009
8
05:11 Mar-19-2011
Re: Zonal discrimination coating cut back required
In Reply to CARLOS SUAREZ at 03:50 Mar-19-2011 .

Carlos, Thanks for the reply but I am more concerned about the actual configuration of the scanner assembly than the weld bevel, We have a couple of AUT companies that have a band that is not suitable for our coating and require it removed, Therefore i was more interested in how much a system such as a Rotoscan from rtd would require the coating to be cut back.

 
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Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1300

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1300
16:05 Mar-19-2011
Re: Zonal discrimination coating cut back required
In Reply to Samuel Peebles at 13:31 Mar-18-2011 (Opening).

Sam
There are several coatings on a typical pipeline project. Fusion Bonded Epoxy (FBE) is usually applied directly onto the pipe. This would have about a 100-150mm cutback from the pipe end to allow UT to be used. Advice for the use of ESBT is probably useful. e.g. you can see how a Single Vee bevel with a 60° included angle requires about 95mm of standoff from the centreline of the weld but then you need extra for the back of wedge so the 100mm cutback would not be adequate for that on 25mm wall. But there is often more coating added over the FBE. Polyurathane and concrete can be added. These are also cutback...but leave the FBE and weld exposed. The cutback of these coatings will determine the mechanics of the scanner as it is mounted on the scanning band. If there is not enough room to put the band on the FBE you need to look at extender methods to extend the probes forward and down.
There is a good book "Design and installation of marine pipelines", Mikael W. Bræstrup, Jan Bohl Andersen that illustrates the materials and typical dimensions. Look for it onine

 
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P
P
01:02 Mar-25-2011
Re: Zonal discrimination coating cut back required
In Reply to Samuel Peebles at 13:31 Mar-18-2011 (Opening).

What is the coating? How thick?

The differences in bevel related requirements are too fine to be considered at this stage. You probably need to consider all bevels.

If it is simply not possible to place the band on the coating, you should leave about 15".

If there is an undercoating like FBE, for example, the 15" area could still have this coating with an undercoating cutback of 6".

If it is feasible to be able to align the pipe in a designated direction, you could specify cutbacks of, say, 15" on one end (where scanner is mounted), and 7" on the other end.

This would save on field joint coating costs, but you have to be certain that you have the flexibility when laying out pipe to guarantee that it can be aligned such that one short and one long cut-back are paired for each weld.

Ask the AUT contractors under consideration for a layout drawing of their cut-back requirements. Most have drawings prepared for this speific purpose.

After you receive the drawing, I wouldn't hesitate to let them know that you are including consideration of cut-back requirements when selecting the contractor. Maybe this will encourage them to work towards a solution to excessive AUT cut-back requirements.

Take it with a grain of salt if they offer an immediate solution for reducing their stated cut-back requirement (drop downs, etc.). I would guess that if the solution was actually effective, they would have offered it in the first place. By the time you figure out the drawbacks of their "solution" it will probably be too late.

Also, keep in mind the tolerance applied by the coaters. There is likely going to be a +/- cutback tolerance. Keep this in mind when selecting your nominal cut-back, or specify no minus tolerance, +1"/-0" for example.

As you probably are aware, if you could get away from the zonal discrimination technique, you could possibly also get rid of the band. But probably just a pipe dream (pardon the pun).


Cheers

 
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