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11:38 Dec-22-2009

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
United Kingdom,
Joined Oct 1999
Mapping EXTERNAL l corrosion.

Normally, we get asked to supply equipment for internal corrosion mapping, and we have a lot of product for this, from Simple Corrosion thickness meters, to our Rapidscan system with the wheel probe.

Recently we were contacted by a customer who wants to map external corrosion. single point measurement is not to difficult, just use a thickness gauge on good metal , then measure individual points with a mechanical gauge. Mapping it is a lot more complex. Obviously anything ultrasonic is out because of the surface condition.

Anyone got any good ideas?



13:50 Dec-22-2009

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
Re: Mapping EXTERNAL l corrosion. In Reply to Joe Buckley at 11:38 Dec-22-2009 (Opening).

Hello Joe,

Usual questions - is it a pipeline or other configuration. Dimensions? What has been done e.g. pigging. Does your customer want to know remaining wall thickness or just to map the extent and depth of the corrosion.

Here is a link to EWI's laser profilometry publicity:


Hope this helps

16:46 Dec-22-2009

Dave Utrata

R & D,
Center for NDE, Iowa State University,
Joined Feb 2000
Re: Mapping EXTERNAL l corrosion. In Reply to Nigel Armstrong at 13:50 Dec-22-2009 .

Good thoughts or any thoughts? ;)

My first thought was the possible use of laser profilometry, also.

On perhaps shakier ground but in the why-not category: use a flexible medium (such as used in magnetic rubber; remember that?) to cast a replica of the surface region of interest. Then remove and take to a lab where tabletop measurement via lasers or CMM contacting probes or whatever metrology tool could be used to provide the topology of the cast sample surface.

I imagine that obtaining an absolute value would be challenging due to undulations or waviness of the rubber mold itself, but perhaps the measurements could be converted to distances relative to some known uncorroded plateau.

07:12 Dec-23-2009


Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
Joined Feb 2001
Re: Mapping EXTERNAL l corrosion. In Reply to Joe Buckley at 11:38 Dec-22-2009 (Opening).


If we are talking of a pipe or tube, we can do laser profilometry as suggested or machine vision based image processing and deduct the depth of the pit / depression from the nominal thickness.

Degradation of mechanical properties due to corrosion should also be kept in mind in such cases.



11:34 Dec-23-2009

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
United Kingdom,
Joined Oct 1999
Re: Mapping EXTERNAL l corrosion. In Reply to Dave Utrata at 16:46 Dec-22-2009 .

Thanks for the ideas. I had thought about lasers, but was not aware of the EWI system, The replica compound idea (Microset or similar) is brilliantly simple, and i reckon with a properly shaped outer mould it could be quite accurate.

I've also been contacted privately with info on an MFL system which looks promising.

I'll pass these on to the customer and see what he thinks.

BTW its an unpiggable section of a gas distribution system.

Thanks again


12:52 Dec-24-2009

John O'Brien

Consultant, -
Chevron ETC ,
Joined Jan 2000
Re: Mapping EXTERNAL l corrosion. In Reply to Joe Buckley at 11:34 Dec-23-2009 .

External profiling of damage in pipelines is now common in order to produce accurate data for use in remaining life or MAOP calculation using RSRTENG, B31G or API 579 FFS. Laser profilometry is now common and offered by a number of vendors including Applus RTD. A canadian company Creaform sells a hand held laser scanner that is also widely used. Traditional mechanical comb and bar type profilers can also be used. Some companies are also using water column probes with UT and gating on the front surface to provide corrosion profile maps. An eddy current array has also been produced by Southwest Reasearch


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