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- since 1996 -

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Technical Discussions
Lloyd Lawson
Student
USA, Joined Sep 2009, 5

Lloyd Lawson

Student
USA,
Joined Sep 2009
5
00:25 Nov-24-2009
Guided UT

Was wondering if someone could direct me to more information on guided ut in the power industry. specifically information on detection of corrosion on the cold side of boiler tubes, potentials, limitations and the like and maybe whether an emat would be a better system to use
?

    
 
 
Len Andersen 212-839-6599
Engineering
New York City Department of Transportation, USA, Joined Nov 2009, 31

Len Andersen 212-839-6599

Engineering
New York City Department of Transportation,
USA,
Joined Nov 2009
31
16:54 Nov-24-2009
Re: Guided UT
In Reply to Lloyd Lawson at 00:25 Nov-24-2009 (Opening).

Ladies and Gentleman,
A 2007 view from a friend was, 'This must have been around for about 10 years now, and we have tried it a few times. As with all such developments, it no doubt has its place, but so far we have been disappointed with the results we get. TWI (who developed the original, known as ‘Teletest’) swore that they wouldn’t ‘over-sell’ it, but it seems to me that they haven’t been able to resist!! The chap who developed it at TWI left to set up his own company, and developed the GUL system, which is similar. We have found no particular advantage of either: neither was able on deliver what we wanted. Even on a simple insulated pipe, Teletest picked up every piece of tie wire securing the tracing, but none of the pitting. We are persevering with it as I am sure they will sort out these bugs eventually."

This was in response to
I read the article “Long Range Guided-Wave Ultrasonics: A New Age In Pipeline Inspection” in The Fall Edition of the ( www.aws.org ) AWS “Inspection Trends” magazine. I would be happy to send you the five-page article. The article indicates refinery and other down stream used with substantial savings. I look forward to hearing from you.
Personally, I am aware of such technology and believe it is evolving. The AWS engineer answering question at 305-443-9353 might be a good start point for your enquiry. I hope this is helpful.
Sincerely
Len Andersen
212-839-6599 / 914-237-7689 / 914-536-7101
POB 1529 / NYC 10116 ( $1020 per year Caller Box GPO NYC )
www.lenandersen.com
PS – http://www.ndt.net/wshop/profile/profile.php?id=4694

    
 
 
Sang Kim
Consultant, NDT Trainer
Guided Wave Analysis LLC, USA, Joined Feb 2008, 44

Sang Kim

Consultant, NDT Trainer
Guided Wave Analysis LLC,
USA,
Joined Feb 2008
44
19:38 Nov-24-2009
Re: Guided UT
In Reply to Len Andersen 212-839-6599 at 16:54 Nov-24-2009 .

Dear Len Andersen,

I really like your frank opinion about long-range guided wave technology. Your observation of only finding, “tie wire securing the tracing, but none of the pitting,“ was absolutely correct with only guided wave system using low-frequency discrete piezoelectric belt. If you tested it with high-frequency guided wave using Magnetostrictive sensor (MsS) system, the pitting corrosion can be found depending on the size and distance from the probe. The same thing happens with attached pipe support, clamp, welded pipe support, and any geometric feature attached or welded to the pipe. This phenomenon was summarized in this website (http://www.gwanalysis.com/clamp_pipe_inspection.html) with examples.

The piezoelectric guided wave system using discrete probe around the pipe circumference cannot operate at high frequency higher than 100 kHz. Most of them are using less than 50 kHz depending on pipe size and wall thickness. As shown in the website, the high-frequency guided wave can be generated with MsS probe that continuously covers the whole circumference of pipe. The high frequency guided wave is much less or no interaction with the attachment of pipe such as tie, pipe support, and clamp. The high-frequency guided wave is much sensitive to the small defect such as surface corrosion having pitting. If you use high-frequency guided wave, you will be happy with the result. If your pipe size is bigger than 24-inch-OD, I also suggest using sectional guided probe that covers section of pipe so that it increases the sensitivity of guided wave testing. The high-frequency guided wave testing is much beneficial in inspecting and monitoring pipelines in power industry, chemical and petrochemical plant because the pipelines of these facilities include many clamps, pipe supports, and ties.

If you are still doubt about the benefit of high-frequency guided wave, please try the MsS guided wave system by renting. The renting cost of the guided wave system is about $10,000/month to an inspection company. Then, you will find the difference of low- and high-frequency guided-wave testing just like that you will see the difference of the UT sensitivity with 1-MHz and 10-MHz UT probe.

Sincerely,

Sang

    
 
 
Charlie Jackson
Consultant, - Trainer/Inspector
Northern NDT Ltd, United Kingdom, Joined Sep 2006, 6

Charlie Jackson

Consultant, - Trainer/Inspector
Northern NDT Ltd,
United Kingdom,
Joined Sep 2006
6
16:37 Nov-25-2009
Re: Guided UT
In Reply to Sang Kim at 19:38 Nov-24-2009 .

As always the views vary widely when LRUT is mentioned and unfortunately many of the complaints are apportioned to the equipment. Accepted the various systems do have variable attributes however as with most specialist NDT systems the problems arise predominantly from operator / technician inadequacies.

As someone who had exposure to the the early Teletest system and the subsequent creation of the GUL system I understand the frustration of those today who still experience poor work.

GUL have gone some way to improving matters in their intensive qualification route but in general the training and qualification route needs the be siginificantly bolstered until improvements are evident.

Kind Regards Charlie Jackson

    
 
 
Rolf
Director,
NDT.net, Germany, Joined Nov 1998, 604

Rolf

Director,
NDT.net,
Germany,
Joined Nov 1998
604
16:54 Nov-25-2009
Re: Guided UT
In Reply to Lloyd Lawson at 00:25 Nov-24-2009 (Opening).

In NDT.net Database we have published presentations of a workshop called "Latest Developments for Ultrasonic Testing - Guided Waves, April 2008, IZFP Saarbrücken, Germany".

www.ndt.net/search/docs.php3?MainSource=78

    
 
 
Godfrey Hands
Engineering,
PRI Nadcap, United Kingdom, Joined Nov 1998, 289

Godfrey Hands

Engineering,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
289
08:32 Nov-26-2009
Re: Guided UT
In Reply to Charlie Jackson at 16:37 Nov-25-2009 .

Colleagues,

Let us not forget the purpose of Guided Wave or Long Range Ultrasonic testing.

It is designed to quickly scan large and inaccessible or difficult to access locations to identify areas where an anomaly could be.
It should always be followed up by a suplementary test to determine the origin of the signal.
The alternative to GWUT is to access the entire area and perform a conventional NDT inspection, and this frequently carries very high costs, especially with scaffolding, insulation removal and potential plant downtime whilst inspection is being performed.

Obviously as technology improves, we may be able to classify more and more of these signals without the need for access, but we have to remember that the technology is still limited by the laws of Physics, and this applies to all of the technologies, be it Teletest, GUL or MSS.
Godfrey Hands

    
 
 
Charlie Jackson
Charlie Jackson
09:00 Nov-27-2009
Re: Guided UT
In Reply to Godfrey Hands at 08:32 Nov-26-2009 .

Godfrey

Accepted the tool is predominantly used in search mode however miss calls by poor operators have resulted in poor lines being tagged as OK and good lines being stripped.

The LRUT systems in use are undergoing constant change and improvement unfortunately this cannot be said in general of operator capability.

Regards Charlie

    
 
 
Wieslaw Bicz
Engineering,
PBP Optel sp. z o.o., Poland, Joined Feb 2009, 244

Wieslaw Bicz

Engineering,
PBP Optel sp. z o.o.,
Poland,
Joined Feb 2009
244
18:24 Nov-30-2009
Re: Guided UT
In Reply to Lloyd Lawson at 00:25 Nov-24-2009 (Opening).

I have large experience with guided waves and also significant experience with LRU projects, made by TWI. My opinion concerning problems with such equipment is may be a bit curious:

The developer of such systems are mostly not checking, if the modes they are using are leaking (loosing the energy to the surroundings). I have made many experiments in modes in plates and pipes and can tell, that it is not easy to predict, which mode is leaking or not. The theory describing it apparently not really good usable. But if the mode is leaking, it must react to anything, that is in surroundings and not only to flaws in the pipe. It would be possible to excite only such modes, but it would require another equipment than this used now. I have even proposed such solution, but its realisation would require relatively large amount of work.

If the mode used is leaking it is unpossible to recognize, if the reflection is coming from the structure in the pipe or from wire insulating it or from something else.

Another problem is naturally the frequency: From the point of view of the resolution it is better to use as high frequency as possible. This is limited by the possibility of its generation. Some new ideas would be useful here.

    
 
 
Peter Philipp
Peter Philipp
07:07 Dec-02-2009
Re: Guided UT
In Reply to Lloyd Lawson at 00:25 Nov-24-2009 (Opening).

As an independent consultant for Guided Wave Testing I am interested in the different threads that have developed from the original question.

1. Firstly in reply to the original question from Lloyd Lawson re boiler tube inspection GW versus e-mat. GWT is a method that should allow tubes to be screened rapidly so that any areas that are “called” as defects can be proved up using a complementary method such as UT, radiography or evolving technology such as e-mat.
2. Another thread that has developed is the quality of operators as all 3 GWT systems are very operator dependent and this is precisely why attention is now being focussed on operator training and certification. Several major oil/petrochemical companies have either developed their own test pieces or are in the process of doing so. These blind tests in the short term are the only effective way of checking if an operator will be able to find the type of defects that are necessary. This technology is still relatively new with the all 3 equipment manufacturers delivering their first units about 10 years ago with mainstream testing over the last 5 years. The GWT method was developed primarily to find corrosion under insulation but has now developed into other areas where access is unavailable or difficult such as buried pipe, road crossings, subsea etc.
3. Another further thread is that you will see corrosion at high frequency but not at low. There are 2 issues here the first one being that a technician needs to look at the behaviour of a feature at different frequencies to gain information on the feature this is one of the areas that sorts out the good operators. It is all very well to say test at higher frequency but the down side to this is that the test range reduces as the frequency increases. All 3 GWT systems are capable of operating at higher frequency but the frequency range typically 20-100kHz is considered the best compromise between identification of features and test range.

    
 
 
Sang Kim
Consultant, NDT Trainer
Guided Wave Analysis LLC, USA, Joined Feb 2008, 44

Sang Kim

Consultant, NDT Trainer
Guided Wave Analysis LLC,
USA,
Joined Feb 2008
44
17:40 Dec-02-2009
Re: Guided UT
In Reply to Peter Philipp at 07:07 Dec-02-2009 .

zoom image
Peter,
I don’t agree on two things: 1) The test range reduces as the frequency increases, and 2) All 3 GWT systems are capable of operating at higher frequency but the frequency range typically 20-100 kHz is considered the best compromise between identification of features and test range.

1) The inspection range depends on the pipe conditions such as coating, buried or aboveground, wall thickness, and geometric features. If the pipeline includes geometric features such as clamp, pipe support, welded pipe support, spacer, and tie, the inspection range of high frequency (higher than 100 kHz) is much longer than that of low frequency. The paper, “The effect of the longitudinal welded support on the pipe for guided wave propagation,” shows how the guided wave propagation is influenced on the geometric feature and its inspection range is significantly shortened due to the trailing signals caused by the geometric feature (http://www.ndt.net/article/apcndt2006/papers/75.pdf). Please see the attached JPG file that shows the signal difference of guided waves acquired at 32-, 64-, and 128-kHz center frequencies. The data acquired at 128 kHz has the best signal-to-noise ratio in the whole inspection region. With this data we proved that there is no defect in the spacer because the high frequency is much less interaction with geometric feature. We acquire multi-frequency data for differentiating geometric features attached to the pipe. My test experience of refinery with field testing and data analysis service shows that the best center frequency for inspecting chemical and petrochemical facilities (above ground insulated pipes) is at 128 kHz (about 60 %). The next frequency is data acquired at 90 or 64 kHz (about 40 %). The data acquired at 32 kHz is only used for checking geometric feature. We need to state clearly about the inspection range and sensitivity depending on the pipe conditions.

2) MsS (Magnetostrictive Sensor) system operates at 5 kHz to 250 kHz. The commercial MsS system has band pass filters at 8, 16, 32, 64, 90, 128, 180, and 250 kHz and probes at all these frequencies. I train inspectors to use high frequencies for finding corrosion under insulation with long-range guided wave. If other 2 systems (GUL and Teletest) can operate at high frequency, please let me know what frequency of filters does the system use for high frequency job.

I also suggest one thing to personnel in major oil/petrochemical companies. If you are making own test loop for testing inspectors and guided wave systems, please put geometric features such as pipe support, clamp, and tie for simulating your facilities.

Sincerely,
Sang
    
 
 

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