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Posted on Thu Dec 06, 2007 08:33 AM
Post Subject: lateral wave indication
I am using TOFD 8 channel equipment to scan welds of various thickness. I have two channels set for creeping wave scan and each acting as individual receiver and transmitter. and six remaining in the pitch catch mode.
I wonder if creeping wave travels only on the surface how the B scan display gives the through thickness indications.
Also in the tofd display if the lateral wave travels only on the surface how the receivers is picking up the pulse sent by the transmitter. What does the width of the lateral wave indication shows. How can i determine the dead zone of the lateral wave.
Also why only unrectified pulse is used in A scan display for Tofd scanning.
1. "I wonder if creeping wave travels only on the surface how the B scan display gives the through thickness indications." Using the creeping wave technique, the time axis (or usual depth axis in a B-Scan) represents the surface distance to the indication.
The calibration of the time axis is done as follows:
- Velocity : Positioning the probe at a known distance from 2 targets (ex: 10mm and 20mm between the probe and the target)
- Wedge delay can be done by the same procedure but it needs only one target.
2. "Also in the TOFD display if the lateral wave travels only on the surface how the receivers is picking up the pulse sent by the transmitter.” Not sure how to explain this one, except that the energy radiates also towards the surface boundary as the lateral waves travels towards the receiver probe. Then, a part of this energy is transmitted in the receiver's wedge.
3. “What does the width of the lateral wave indication shows.” The width of the lateral wave shows the cycle period of the pulse sent by the pulser probe. The frequency of the probe used determines the width of its pulse.
4. “How can i determine the dead zone of the lateral wave?" There are standard formulae for calculating the width of the dead zones. You can find specific programs that calculate it, but it is typically around 3 mm for a 10 MHz TOFD probe.
5. “Also why only unrectified pulse is used in A scan display for TOFD scanning?” An unrectified signal is used so that the operator can see the phases of the signals, and differentiate between the top of a defect and the bottom. The beams undergo a phase reversal under these conditions.
Posted on Wed Aug 27, 2008 03:26 AM
Post Subject: RE: lateral wave indication
jayaraj wrote:
I am using TOFD 8 channel equipment to scan welds of various thickness. I have two channels set for creeping wave scan and each acting as individual receiver and transmitter. and six remaining in the pitch catch mode.
I wonder if creeping wave travels only on the surface how the B scan display gives the through thickness indications.
Also in the tofd display if the lateral wave travels only on the surface how the receivers is picking up the pulse sent by the transmitter. What does the width of the lateral wave indication shows. How can i determine the dead zone of the lateral wave.
Also why only unrectified pulse is used in A scan display for Tofd scanning.
1. "I wonder if creeping wave travels only on the surface how the B scan display gives the through thickness indications." Using the creeping wave technique, the time axis (or usual depth axis in a B-Scan) represents the surface distance to the indication.
The calibration of the time axis is done as follows:
- Velocity : Positioning the probe at a known distance from 2 targets (ex: 10mm and 20mm between the probe and the target)
- Wedge delay can be done by the same procedure but it needs only one target.
2. "Also in the TOFD display if the lateral wave travels only on the surface how the receivers is picking up the pulse sent by the transmitter.” Not sure how to explain this one, except that the energy radiates also towards the surface boundary as the lateral waves travels towards the receiver probe. Then, a part of this energy is transmitted in the receiver's wedge.
3. “What does the width of the lateral wave indication shows.” The width of the lateral wave shows the cycle period of the pulse sent by the pulser probe. The frequency of the probe used determines the width of its pulse.
4. “How can i determine the dead zone of the lateral wave?" There are standard formulae for calculating the width of the dead zones. You can find specific programs that calculate it, but it is typically around 3 mm for a 10 MHz TOFD probe.
5. “Also why only unrectified pulse is used in A scan display for TOFD scanning?” An unrectified signal is used so that the operator can see the phases of the signals, and differentiate between the top of a defect and the bottom. The beams undergo a phase reversal under these conditions.