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02:37 May-05-2006
Variance in ECT results during tube inspection of stripper

We are operating Fertilizer plant at India.During Annual Turn-round 2006 one of our vertical exchanger stripper's tubes were inspected by using eddy current test .
Details of heat exchanger is as follows,
Falling film type vertical heat exchanger
Media in the tube-Ammonium carbamate
Materail of tube-Titanium gr-3
Results of eddy current were very surprising as it was found more than 60% gradual wall loss in more than 25% tube.Management had started thinking about its replacement in the coming year.As it was surprsing that after 10 year of operation results were such.But then it was decided to pull ot one of the tube to check ECT worthiness.
After pull out it was inspected from inside/outside and pieces were cut to measure its bore using bore gauge.Measurement showed that reduction is not more than 40%.
Also its wall thickness was measured using ultrasonic thickness gauge,whcih also confirmed the bore gauge results.
Calibartion tube and its artificail flaws were made as ASME section-V.
ECT instrument was confirming the calibartion tube but not exchanger tube.
I would like to no possible reasons,which caused such deviation.

05:56 May-06-2006
Re: Variance in ECT results during tube inspection of stripper

Howvever I presume that

1) You are using an absolute/external reference test at a frequency appropriate to the wall thickness.

2) Calibration and Reference Tubes closely match the Ti alloy used in the Heat exchanger.

3) Your calibration tube is representative, I.e. it contains long areas of wall reduction of say 20, 40 and 60% - Not just narrow grooves.

Even so, large even wall loss is often difficult to measure with Eddy current, since with an absolute test any variations through the tube (e.g de-alloying / heat effects etc, although this shouldn't occur with Ti) will be indistinguishable fromm wall thickness variations. 60 vs 40 % loss is not too far away from what might be considered a typical level of experimental error. It is always usfeul to have a backup method such as IRIS available to verify this type of problem.

Joe

----------- Start Original Message -----------
: We are operating Fertilizer plant at India.During Annual Turn-round 2006 one of our vertical exchanger stripper's tubes were inspected by using eddy current test .
: Details of heat exchanger is as follows,
: Falling film type vertical heat exchanger
: Media in the tube-Ammonium carbamate
: Materail of tube-Titanium gr-3
: Results of eddy current were very surprising as it was found more than 60% gradual wall loss in more than 25% tube.Management had started thinking about its replacement in the coming year.As it was surprsing that after 10 year of operation results were such.But then it was decided to pull ot one of the tube to check ECT worthiness.
: After pull out it was inspected from inside/outside and pieces were cut to measure its bore using bore gauge.Measurement showed that reduction is not more than 40%.
: Also its wall thickness was measured using ultrasonic thickness gauge,whcih also confirmed the bore gauge results.
: Calibartion tube and its artificail flaws were made as ASME section-V.
: ECT instrument was confirming the calibartion tube but not exchanger tube.
: I would like to no possible reasons,which caused such deviation.
:
:
------------ End Original Message ------------

06:17 May-08-2006
Re: Variance in ECT results during tube inspection of stripper

----------- Start Original Message -----------
: Without Knowing the precise details of the test it is difficult to be sure where the error appears.
: Howvever I presume that
: 1) You are using an absolute/external reference test at a frequency appropriate to the wall thickness.
: 2) Calibration and Reference Tubes closely match the Ti alloy used in the Heat exchanger.
: 3) Your calibration tube is representative, I.e. it contains long areas of wall reduction of say 20, 40 and 60% - Not just narrow grooves.
: Even so, large even wall loss is often difficult to measure with Eddy current, since with an absolute test any variations through the tube (e.g de-alloying / heat effects etc, although this shouldn't occur with Ti) will be indistinguishable fromm wall thickness variations. 60 vs 40 % loss is not too far away from what might be considered a typical level of experimental error. It is always usfeul to have a backup method such as IRIS available to verify this type of problem.
: Joe
:
: : We are operating Fertilizer plant at India.During Annual Turn-round 2006 one of our vertical exchanger stripper's tubes were inspected by using eddy current test .
: : Details of heat exchanger is as follows,
: : Falling film type vertical heat exchanger
: : Media in the tube-Ammonium carbamate
: : Materail of tube-Titanium gr-3
: : Results of eddy current were very surprising as it was found more than 60% gradual wall loss in more than 25% tube.Management had started thinking about its replacement in the coming year.As it was surprsing that after 10 year of operation results were such.But then it was decided to pull ot one of the tube to check ECT worthiness.
: : After pull out it was inspected from inside/outside and pieces were cut to measure its bore using bore gauge.Measurement showed that reduction is not more than 40%.
: : Also its wall thickness was measured using ultrasonic thickness gauge,whcih also confirmed the bore gauge results.
: : Calibartion tube and its artificail flaws were made as ASME section-V.
: : ECT instrument was confirming the calibartion tube but not exchanger tube.
: : I would like to no possible reasons,which caused such deviation.
: :
: :
------------ End Original Message ------------

09:45 Jun-30-2006
Re: Variance in ECT results during tube inspection of stripper

Thanking you,

Regards,

Ranjeet

Dear Mr.Joe,
Thanks for sharing your valuable comments,
You can assume there was no error in the instrument (TX4200 Tes tex USA make and 4X2 eddy current sys) as test was repeated by using another different m/c(TX2000).Test were conducted Insitu by inserting probe in ID side & using Differential,Absoulte and Multi freq.probes ie.4 channel and 2 frequency.Inst has the capability of detection of flaws in the tube(pitting,cracks) and determination of tube thickness in %.Calibration standards were fabricated on fresh tubes of same dimensions and mt'l ie Ti Gr.3 as per ASME sec V article 8 Appendix.1
On inserting probe in the calibration tube it was forming wave form as expected.
calibration tube is representative, I.e. it contains long areas of wall reduction of say 20, 40 and 60% - Not just narrow grooves.And also our calibration tube is representative, I.e. it contains long areas of wall reduction of say 20, 40 and 60% - Not just narrow grooves.
We are suspecting problem in the tube materail ie its thermal conductivity and magnetic permeabilty might have changed being in service for 10 years.And ECT depends on these properties.We got this particular pulled out tube piece analysed
matellurgiucally and found that TiH2 has formed .Its micrograph shows long flake thread like of TiH2 .
Now we want to confirm whether TiH2 can effect ECT results.

----------- Start Original Message -----------
: Dear Mr.Ranjeet
: Can you please tell me the material on the shell side and also the dimensions of the tube as well as your technique of inspection , I mean to ask differential and absolute and weather with impedance plan or only with stri chart ? Your calibration tube is from the same heawt treatment lot or is it differ ? Can you pls send me the calibration detail and the signal capture you are getting from the defect?
: Thanks.
: Ikesh Patel
: (ISNT ET III)
------------ End Original Message ------------