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- since 1996 -
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Technical Discussions
sentho
sentho
01:30 Jul-25-2007
coverage for TOFD

I noticed that every TOFD inspection miss some datas from the upper wall thickness(approximately 1/3 T). how can we get a better quality signals from the laterwave side.


 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1282

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1282
03:11 Jul-25-2007
Re: coverage for TOFD
----------- Start Original Message -----------
: I noticed that every TOFD inspection miss some datas from the upper wall thickness(approximately 1/3 T). how can we get a better quality signals from the laterwave side.
------------ End Original Message ------------
The "missed data" would be the dead zone. This is not actually a function of the wall thickness but instead, the ring time equivalent depth of the pulse. Frequency, probe spacing and angle used can all be factors. A simple calculator is provided as a download on NDT.net to estimate the Dead Zone heights associated with TOFD setups. Go to http://www.ndt.net/article/v10n06/ginzel/ginzel.htm
For it to be 1/3 wall thickness the specimen you are working with is probably very thin.


 
 Reply 
 
sentho
sentho
05:54 Jul-29-2007
Re: coverage for TOFD
- The "missed data" would be the dead zone.-his is from your replay. How it happents? We are using one probe as transmitter and the other is a receiver.--------- Start Original Message -----------
: : I noticed that every TOFD inspection miss some datas from the upper wall thickness(approximately 1/3 T). how can we get a better quality signals from the laterwave side.
: The "missed data" would be the dead zone. This is not actually a function of the wall thickness but instead, the ring time equivalent depth of the pulse. Frequency, probe spacing and angle used can all be factors. A simple calculator is provided as a download on NDT.net to estimate the Dead Zone heights associated with TOFD setups. Go to http://www.ndt.net/article/v10n06/ginzel/ginzel.htm
: For it to be 1/3 wall thickness the specimen you are working with is probably very thin.
------------ End Original Message ------------




 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
02:31 Jul-29-2007
Re: coverage for TOFD
Sentho

The dead zone which Ed is refering to is not of the same origin as the dead zone with the single crystal pulse-echo technique which is a characteristic of the transducer vibration. The TOFD dead zone is caused by the surface or lateral wave travelling from the transmitting to the receiving probe. Any near-surface diffracted signals will be swamped by the lateral wave.

Regards

Nigel


---------- Start Original Message -----------
: - The "missed data" would be the dead zone.-his is from your replay. How it happents? We are using one probe as transmitter and the other is a receiver.--------- Start Original Message -----------
: : : I noticed that every TOFD inspection miss some datas from the upper wall thickness(approximately 1/3 T). how can we get a better quality signals from the laterwave side.
: : The "missed data" would be the dead zone. This is not actually a function of the wall thickness but instead, the ring time equivalent depth of the pulse. Frequency, probe spacing andangle used can all be factors. A simple calculator is provided as a download on NDT.net to estimate the Dead Zone heights associated with TOFD setups. Go to http://www.ndt.net/article/v10n06/ginzel/ginzel.htm
: : For it to be 1/3 wall thickness the specimen you are working with is probably very thin.
------------ End Original Message ------------




 
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