Locating the Beam Index Point (BIP)
Verifying the Refracted Angle
Velocity and Zero Calibration
Conclude the calibration process as described in the instrument manual.
Recheck the two echoes and verify that distance measurements are accurate.
Identify the echo representing the 225 mm or 9”sound path from the small radius reflector located behind the wedge and peak it up. It may be necessary to increase gain in order to see it since it will be much smaller than the first echo, and it may be preceded by a still smaller echo representing a multiple of the 100mm/4” path. Move the measurement gate to that echo and set the echo height to a level such that it can be clearly seen. Initiate a velocity calibration as described in the instrument operating manual. Enter the known sound path length of 225 mm or 9.000 inches.
Place a measurement gate on the radius echo and set the echo height to approximately 80%. Initiate a zero calibration as described in the instrument operating manual. Enter the known sound path length of 100 mm or 4.000 inches.
Set the instrument range to 10” or 250 mm. Couple the wedge to the test block as shown below, so that the beam index point is directly over the zero mark. Identify the echo from the 100 mm or 4” radius and peak it up.
In angle beam setups it is necessary to establish a zero offset that compensates for the portion of the sound path that falls inside the wedge, and also calibrate for material sound velocity as in any other flaw detector setup.
This is commonly done as a two-step calibration using two reflectors in an IIW-type block or a similar reference standard that provides two reflectors at known distances.
With the echo peaked up, note the degree mark on the test block that lines up with the BIP established in the first procedure. This is the actual refracted angle for that wedge assembly in metal whose shear wave velocity matches that of the test block. It may differ slightly from the angle marked on the wedge. Enter this measured angle in the instrument as the angle value to be used for depth and distance calculation.
Move the wedge forward and backward and locate the point at which this echo peaks. The peak memory function available in most instruments can be used to draw the echo envelope for confirmation.
For 45 degree and 60 degree wedges, couple the wedge to the block as shown below and identify the echo from the large hole.
For 70 degree wedges, turn the block over and couple to the opposite side, again aiming at the hole.
All commercially offered wedges are marked with a nominal angle, which is normally verified by the manufacturer to be within +/- 2 degrees or better based on typical shear wave velocities.
Aside from the manufacturing tolerance, this angle can vary with wedge wear, and because it is based on wave refraction it will vary whenever the shear wave velocity in the test material changes.
Many test procedures call for verifying the wedge angle as part of initial calibration.
Observe the echo from the 100 mm or 4 inch radius of the block. Move the wedge forward and backward and locate the point at which this echo peaks. The peak memory function available in most instruments can be used to draw the echo envelope for confirmation. Note that if velocity and zero calibration have not yet been performed, this peak will not appear exactly at the 100 mm/4” point on the screen scale.
Observe the echo from the 100 mm or 4 inch radius of the block. Move the wedge forward and backward and locate the point at which this echo peaks. The peak memory function available in most instruments can be used to draw the echo envelope for confirmation. Note that if velocity and zero calibration have not yet been performed, this peak will not appear exactly at the 100 mm/4” point on the screen scale.
The beam index point is the point at which the center of the sound beam exits from the wedge, often used as a reference point for distance measurements.
Commonly available wedges have the nominal BIP marked on them, however this can move slightly with wedge wear and small variations in acoustic properties, so many test procedures call for verifying the BIP as part of initial calibration.
Beam Index Point (BIP)
INTRODUCTION
STEP
Set the zero offset to zero and set velocity to the approximate shear wave velocity of the test material. If the velocity is unknown, you can start with a generic value of approximately 3.420 mm/uS or .1280 in/uS for typical steel alloys. Set the range to a value large enough to cover the largest calibration sound path.
Couple the transducer to the calibration block and observe the echoes from the reference reflectors. Adjust the instrument’s pulser and receiver settings as required to obtain clean echoes. Settings typically include pulse frequency, energy, damping, receiver filtering, and gain.
General
Angle Beam Setup Procedure
Index
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