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Technical Discussions
RP Bhan
Engineering,
HPCL Refinery, India, Joined Jul 2003, 11

RP Bhan

Engineering,
HPCL Refinery,
India,
Joined Jul 2003
11
03:09 Aug-02-2003
High temperature scanning/thickness measurement

To know the present condition of one internally corroded Pressure vessel ,we are checking thickness of same in hot condition by using a high temperature probe & a flaw detector .
I will like to know what type of correction will be required to be applied to the readings taken at high temperature i.e. whether velocity of sound at high temperature decreases & whether there is any relatioship available between velocity & temperature . Also what could be the affect of material properties changing at high temperature ( in our case temp. is about 300 deg C ) . Thanks
RP Bhan
HPCL- Mumbai refinery

one pressure vessel operating


 
 Reply 
 
IceClampers
IceClampers
03:15 Aug-02-2003
Re: High temperature scanning/thickness measurement
The velocity of the material will decrease with increasing temperature. The most reliable way to compensate is to calibrate of a calibration block at the same temperature as the test piece. If this is not an option then there is a ratio (% for every 100 deg.) but I do not know what it is off hand. (5% for every 100 deg. C rings a bell though.)

You can check it by cal. on cal block at ambient, put the probe on the hot material so it reaches temp then put back on the cal block. Note the difference. The new reading will be higher. This delay causing a higher reading is due to the increased temperature.

But if possible cal off cal block at same temp. Best way.

----------- Start Original Message -----------
: To know the present condition of one internally corroded Pressure vessel ,we are checking thickness of same in hot condition by using a high temperature probe & a flaw detector .
: I will like to know what type of correction will be required to be applied to the readings taken athigh temperature i.e. whether velocity of sound at high temperature decreases & whether there is any relatioship available between velocity & temperature . Also what could be the affect of material properties changing at high temperature ( in our case temp. is about 300 deg C ) . Thanks
: RP Bhan
: HPCL- Mumbai refinery
: one pressure vessel operating
------------ End Original Message ------------




 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 524

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
524
00:09 Aug-03-2003
Re: High temperature scanning/thickness measurement
I would be very careful about following this advice.

Most 'hot' probes will only stand 300 C for a few seconds - followed by a cooling off period.

If you place the probe on a hot surface and allow it to stabilize it may never work again!

If you keep the probe reasonably cool probe delay shouldn't change too much. (although you need to check this since it may cause drift during the test sequence)

It is the test material velocity you have to be concerned with. This depends on the alloy, But 1% per 100C seems to be a commonly used 'rule of thumb'

In this knid of application you are unlikely to be looking for very high accuracy in any case, If there is significant corrosiosn then there will be a corresponding uncertainty in the values (is isn't flat) And most corrosion survey are jsut looking for areas of corrosion or checking minimum thickness. Uncorrected readings will probably be good enough for most people.

Good luck
Joe


----------- Start Original Message -----------
: The velocity of the material will decrease with increasing temperature. The most reliable way to compensate is to calibrate of a calibration block at the same temperature as the test piece. If this is not an option then there is a ratio (% for every 100 deg.) but I do not know what it is off hand. (5% for every 100 deg. C rings a bell though.)
: You can check it by cal. on cal block at ambient, put the probe on the hot material so it reaches temp then put back on the cal block. Note the difference. The new reading will be higher. This delay causing a higher reading is due to the increased temperature.
: But if possible cal off cal block at same temp. Best way.
: : To know the present condition of one internally corroded Pressure vessel ,we are checking thickness of same in hot condition by using a high temperature probe & a flaw detector .
: : I will like to know what type of correction will be required to be applied to the readings taken at high temperature i.e. whether velocity of sound at hightemperature decreases & whether there is any relatioship available between velocity & temperature . Also what could be the affect of material properties changing at high temperature ( in our case temp. is about 300 deg C ) . Thanks
: : RP Bhan
: : HPCL- Mumbai refinery
: : one pressure vessel operating
------------ End Original Message ------------




 
 Reply 
 
RP Bhan
Engineering,
HPCL Refinery, India, Joined Jul 2003, 11

RP Bhan

Engineering,
HPCL Refinery,
India,
Joined Jul 2003
11
05:11 Aug-05-2003
Re: High temperature scanning/thickness measurement
--Thanks for the information . Actually we did the calibration same way as mentioned . Our finding was that there was more than 1 mm increase in thickness of the plate ( test plate ) when it was heated to 300 deg c from ambient . We were cooling the probe regularly during the testing & the contact time was kept to minimum during every check
Bhan
.--------- Start Original Message -----------
: I would be very careful about following this advice.
: Most 'hot' probes will only stand 300 C for a few seconds - followed by a cooling off period.
: If you place the probe on a hot surface and allow it to stabilize it may never work again!
: If you keep the probe reasonably cool probe delay shouldn't change too much. (although you need to check this since it may cause drift during the test sequence)
: It is the test material velocity you have to be concerned with. This depends on the alloy, But 1% per 100C seems to be a commonly used 'rule of thumb'
: In this knid of application you are unlikely to be looking for very high accuracy in any case, If there is significant corrosiosn then there will be a corresponding uncertainty in the values (is isn't flat) And most corrosion survey are jsut looking for areas of corrosion or checking minimum thickness. Uncorrected readings will probably be good enough for most people.
: Good luck
: Joe
:
: : The velocity of the material will decrease with increasing temperature. The most reliable way to compensate is to calibrate of a calibration block at the same temperature as the test piece. If this is not an option then there is a ratio (% for every 100 deg.) but I do not know what it is off hand. (5% for every 100 deg. C rings a bell though.)
: : You can check it by cal. on cal block at ambient, put the probe on the hot material so it reaches temp then put back on the cal block. Note the difference. The new reading will be higher. This delay causing a higher reading is due to the increased temperature.
: : But if possible cal offcal block at same temp. Best way.
: : : To know the present condition of one internally corroded Pressure vessel ,we are checking thickness of same in hot condition by using a high temperature probe & a flaw detector .
: : : I will like to know what type of correction will be required to be applied to the readings taken at high temperature i.e. whether velocity of sound at high temperature decreases & whether there is any relatioship available between velocity & temperature . Also what could be the affect of material properties changing at high temperature ( in our case temp. is about 300 deg C ) . Thanks
: : : RP Bhan
: : : HPCL- Mumbai refinery
: : : one pressure vessel operating
------------ End Original Message ------------





 
 Reply 
 
N. D. Patel
N. D. Patel
03:05 Aug-08-2003
Re: High temperature scanning/thickness measurement
----------- Start Original Message -----------
: --Thanks for the information . Actually we did the calibration same way as mentioned . Our finding was that there was more than 1 mm increase in thickness of the plate ( test plate ) when it was heated to 300 deg c from ambient . We were cooling the probe regularly during the testing & the contact time was kept to minimum during every check
: Bhan
: .--------- Start Original Message -----------

I glance through some of the comments. The transducer made from any piezoelectric ceramics, piezoelectric properties does change with temperature. Most temperature dependent studies are perfomed with single crystal (quartz, lithium niobates and aluminium nitride). Thus transducer stablity as a function of temperature has to be studied before making conclusion in measurement accuracies. One can use standard piezoelectic ceramics PZT 7 or lithium niobate without backing or single crystal will survive these temperature in continous mode at 300 C. However,ceramics will deteriorate with time but single crystal will survive except lithium niobate, which can crack with thermal shocking.

Regards

Dr. Patel
: : I would be very careful about following this advice.
: : Most 'hot' probes will only stand 300 C for a few seconds - followed by a cooling off period.
: : If you place the probe on a hot surface and allow it to stabilize it may never work again!
: : If you keep the probe reasonably cool probe delay shouldn't change too much. (although you need to check this since it may cause drift during the test sequence)
: : It is the test material velocity you have to be concerned with. This depends on the alloy, But 1% per 100C seems to be a commonly used 'rule of thumb'
: : In this knid of application you are unlikely to be looking for very high accuracy in any case, If there is significant corrosiosn then there will be a corresponding uncertainty in the values (is isn't flat) And most corrosion survey are jsut looking for areas of corrosion orchecking minimum thickness. Uncorrected readings will probably be good enough for most people.
: : Good luck
: : Joe
: :
: : : The velocity of the material will decrease with increasing temperature. The most reliable way to compensate is to calibrate of a calibration block at the same temperature as the test piece. If this is not an option then there is a ratio (% for every 100 deg.) but I do not know what it is off hand. (5% for every 100 deg. C rings a bell though.)
: : : You can check it by cal. on cal block at ambient, put the probe on the hot material so it reaches temp then put back on the cal block. Note the difference. The new reading will be higher. This delay causing a higher reading is due to the increased temperature.
: : : But if possible cal off cal block at same temp. Best way.
: : : : To know the present condition of one internally corroded Pressure vessel ,we are checking thickness of same in hot condition by using a high temperature probe & a flaw detector.
: : : : I will like to know what type of correction will be required to be applied to the readings taken at high temperature i.e. whether velocity of sound at high temperature decreases & whether there is any relatioship available between velocity & temperature . Also what could be the affect of material properties changing at high temperature ( in our case temp. is about 300 deg C ) . Thanks
: : : : RP Bhan
: : : : HPCL- Mumbai refinery
: : : : one pressure vessel operating
------------ End Original Message ------------




 
 Reply 
 

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