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- since 1996 -
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Technical Discussions
S.Mohamed Riaz
S.Mohamed Riaz
15:50 May-01-2009
Exchanger Tube Thickness

Dear Sir,

I would like to inform that, myself working as a NDT Inspector in Petroleum Industry kuwait. I like to know about, any machine ( in ultrasonic or eddy current ) is available for getting thickness in exchanger tubes externally. we tried in ultrasonic, but the probe size is 5mm so the reading is not stable. your prompt reply is highly valuable.

 
 Reply 
 
Justin Lehmann
Consultant,
Quality Testing Services, Inc, A Premium Inspection and Testing Group Affiliate, USA, Joined Sep 2007, 22

Justin Lehmann

Consultant,
Quality Testing Services, Inc, A Premium Inspection and Testing Group Affiliate,
USA,
Joined Sep 2007
22
18:58 May-01-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:50 May-01-2009 (Opening).

Mohamed,

What type of probe are you using?
What is the surface condition you have on the tubes?
What is the nominal OD and thickness of the tubes?

I will make a couple of assumptions in the hopes of helping you more timely.
Assuming you have an acceptably surface surface and are using a dual element probe, you must place the septum (cross talk barrier) properly or your readings will be unstable and a little inaccurate. The septum is the portion of the transducer that separates the two crystal elements and prevents interference with one another.

If the septum is placed parallel to the axis of the tube the sound path will vary due to slight rocking of the transducer. The distance to the surface is actually changing and will have an effect on your reading. To receive a more stable signal, place the septum perpendicular with the long axis of the tube, such that any rocking the transducer will not change the distance from the sound entry point to the transducer face. A picture is worth a thousand words in this case but I do not have the type to sketch one out for you. Maybe someone on the forum can do this for you.

If my assumptions are correct and this does not solve your problem, you may have a very pitted ID surface. Another issue may be if you have a single element probe in conjunction with pitted ID or very small diameter tubes.

Justin

 
 Reply 
 
Roger Duwe
NDT Inspector, API-510, 570, 653
MISTRAS, USA, Joined Jan 2009, 148

Roger Duwe

NDT Inspector, API-510, 570, 653
MISTRAS,
USA,
Joined Jan 2009
148
20:08 May-01-2009
Re: Exchanger Tube Thickness
In Reply to Justin Lehmann at 18:58 May-01-2009 .

The best 'ducer we have found for accurate, reproducible readings in boiler and Hx tubes is a SINGLE-element transducer, 5 or 10 MHz, and 1/4-inch [5mm] diameter. We use them with a 'delay-line' plexiglas/perspex standoff about 7mm long. The delay line places the 'Main Bang' and resulting nearfield much earlier on the time displayed on the screen. This gives you a clean screen to see the first [and subsequent] reflections. If you will look at the reflections, and keep wiggling the 'ducer until you get at least 4 successive [decreading] echos, you will have an accurate & reproducible measurement.

The trouble with dual 'ducers is that you havew no idea what they are actually measuring. They could be 'looking' at an alloy segregation mid-wall [giving a too-thin reading], or adding in the surface contamination from the front surface [giving a too-thick reading]

The second 'secret' is to set your instrument to measure Echo-to-Echo. When you use absolute time measurements [standard on most machines], the scale and product encrustations on the tube add to the measured tube thickness, unpredictabily and unreproducibily. Echo-to-Echo only measures the actual thickness of metal between the front and back walls. Try to catch the 2nd and 3rd peak, as they seem to me to be a bit 'cleaner' than the first, and thus give a more accurate measurement from the internal electronics of your UT machine.

 
 Reply 
 
S.Mohamed Riaz
S.Mohamed Riaz
06:57 May-02-2009
Re: Exchanger Tube Thickness
In Reply to Justin Lehmann at 18:58 May-01-2009 .

Dear Mr. Justin
We are using krautkramer mini probe 5mm dia, surface condition is good and the excahnger tubes OD is 1'' & 3/4'' and the thickness is 2.77 & 2.11mm. your prompt reply is highly valuable.

 
 Reply 
 
bob sudharmin
Engineering, Reliability and Integrity Eng
Shell Malaysia Trading, Malaysia, Joined Jan 2008, 54

bob sudharmin

Engineering, Reliability and Integrity Eng
Shell Malaysia Trading,
Malaysia,
Joined Jan 2008
54
14:57 May-02-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:50 May-01-2009 (Opening).

Due to the limitations of small dia tubes, thickness readings from external is best taken with the use of profile radiography. A much bigger area is gained and thickness can be computed / calculated based on reference object placed beside the tube.

 
 Reply 
 
Vignesh M
NDT Inspector, Blue Star Limited
IE , India, Joined May 2009, 29

Vignesh M

NDT Inspector, Blue Star Limited
IE ,
India,
Joined May 2009
29
13:09 May-06-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:50 May-01-2009 (Opening).

Hi, Mohamed Riaz.
I think i can help you on this if you give me some more details.
1. Wether you are using TR probes.
2. what is the problem that you are facing in the same.

Please visit the mentioned site address
http://www.olympus-ims.com/data/File/panametrics/panametrics-UT.en.pdf
see page no 6 of the same pdf file are use similar kindly of concave delaylines as per your required size. If you have any doubt please feel free to ask me

 
 Reply 
 
Vignesh M
NDT Inspector, Blue Star Limited
IE , India, Joined May 2009, 29

Vignesh M

NDT Inspector, Blue Star Limited
IE ,
India,
Joined May 2009
29
13:18 May-06-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:50 May-01-2009 (Opening).

Hi Mohammed,
Please visit the mentioned site address
http://www.olympus-ims.com/data/File/panametrics/panametrics-UT.en.pdf
see page no 6 of the same pdf file are use similar kindly of concave delaylines as per your required size. If you have any doubt please feel free to ask me

 
 Reply 
 
S.Mohamed Riaz
S.Mohamed Riaz
15:32 May-06-2009
Re: Exchanger Tube Thickness
In Reply to Vignesh M at 13:09 May-06-2009 .

Dear Mr. Vignesh

Thanks for reply. yes we are using TR probe ( 7mm dia ), this is the small probe we have. for excahngers tube OD mainly 1" & 3/4". the problem is, the reading is not stable. do u have any idea regarding small probe for 3/4" OD tube. i am waiting for your valuable answer.

 
 Reply 
 
Vignesh M
NDT Inspector, Blue Star Limited
IE , India, Joined May 2009, 29

Vignesh M

NDT Inspector, Blue Star Limited
IE ,
India,
Joined May 2009
29
11:44 May-07-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:32 May-06-2009 .

Hi Mohamed riaz,
Why don't you check the tubes with thickness guages like
MG2Xt. panametrics Make.

This would help you to get a good reading.

 
 Reply 
 
S.Mohamed Riaz
S.Mohamed Riaz
15:58 May-07-2009
Re: Exchanger Tube Thickness
In Reply to Vignesh M at 11:44 May-07-2009 .

Dear Mr. Vignesh

Thanks for reply again. the problem is not in the thickness gauge. we also having good thickness gauge, but the probe dia is big for exchanger tubes.

 
 Reply 
 
vignesh m
NDT Inspector, Blue Star Limited
IE , India, Joined May 2009, 29

vignesh m

NDT Inspector, Blue Star Limited
IE ,
India,
Joined May 2009
29
17:24 May-07-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:58 May-07-2009 .

if u get a probe of 3mm dia i thing it would work isnt it

 
 Reply 
 
Vignesh M
NDT Inspector, Blue Star Limited
IE , India, Joined May 2009, 29

Vignesh M

NDT Inspector, Blue Star Limited
IE ,
India,
Joined May 2009
29
06:12 May-09-2009
Re: Exchanger Tube Thickness
In Reply to vignesh m at 17:24 May-07-2009 .

Hi,
I Think you can use the V2325 transeducer from Panametrics for this application.

It's just 2.5 mm in dia and would serve your cause.

 
 Reply 
 
Simon
Simon
19:40 May-09-2009
Re: Exchanger Tube Thickness
In Reply to S.Mohamed Riaz at 15:50 May-01-2009 (Opening).

There may multiple reasons for getting the reading. Check for the following if your gage supports for LOS - Loss of Signal and couplant. Try to use high temp gel - which will be thick or use grease or silica gel.

I feel you should get the reading, if the above 2 options are OK with 5 mm dia probe. If you use any lesser dia probe, the scattering will be more and the reading will erratic.

Along with the above you can try out some curveture shoes - suitable for various dia of tubes, you will be able to get better contact with the tube and the reading will be good.

Good Luck
Simon

 
 Reply 
 

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