Transcript
OmniScan MX2 Training Program Velocity Calibration Wizard Wizard
OmniScan MX2 Training Training – Phased Array Array Velocity Cal Overview Overview
The velocities of the wedge and component material are two of many parameters that must be known to the part and group set up wizard prior to the formation of the focal laws. No velocity correction can be made without recreating the focal laws. Like conventional UT, velocity is directly related to beam angle. (Snell’s law) When the velocity of the material or wedge is other than what was input into the group set up wizard the result is that the beam angle is not what it is supposed to to be and cannot be corrected. (The 70 degree beam is really 68 degrees) A material velocity tolerance error of no more than 25mm per second must be entered into the calculator to maintain a refracted steering angle within +\-- 1 deg +\ degre rees es..
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OmniScan MX2 Training – Material Velocity Overview cont.
The material velocity is a fixed parameter and does not change from one digital instrument to the next. It is measured one time and is recorded for future use. There is no need to perform repeated measurements to account for different instruments. For a known material velocity, the number can be directly input into the software with the same results on all OmniScan MX2s, or any other digital instrument.
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OmniScan MX2 Training – Wedge Velocity - Rexolite
Phased array wedges purchased from Olympus are typically made of Rexolite. Rexolite is an isotropic material that has a constant velocity in each axis of 2330 meters/sec that is critical to precise beam formation. Use of wedges made of Lucite and other lower grade plastics will result in greater beam angle error. Rexolite can be machined with tolerances much tighter than Lucite or low grade plastics that affect beam angle accuracy. For these reasons Rexolite is an ideal material for phased array wedge manufacturing.
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OmniScan MX2 Training – Velocity Management in MX2 Software
The velocity parameter can be set in the OmniScan MX2 software in 2 places: 1. The part\weld set up wizard by selecting material with a fixed velocity from the database. (Probe\Part>Part>Material) 2. The UT>General sub menu by entering a custom velocity value.
Modifying the velocity will remove any calibration that has been completed in the wizards because the focal laws must be rebuilt. Using the velocity calibration wizard will also automatically populate the value.
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OmniScan MX2 Training – Shear Wave Material Velocity
The velocity of a given material differs slightly for each angle for both shear and longitudinal propagation modes. For a shear wave beams in 1016 carbon steel the velocity deviation is less than approximately 15 meters per second between 45-70 degrees. For this reason, different angles within the same sector scan are calculated using one fixed velocity. A different velocity can be used for different groups in the MX2, but not within the same group.
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OmniScan MX2 Training – Shear Wave Material Velocity cont.
The preferred method for obtaining the velocity in the group set up wizard is to select the material from a fixed database using a default value. When the material velocity is unknown, the MX2 has a velocity calibration wizard that measures the velocity of a component based on two fixed reflectors at known positions. (Side drilled hole, radius or backwall) Use of the velocity calibration wizard for shear wave inspection is only beneficial if a suitable calibration block made of the exact same material has been manufactured. This a common practice in pipeline jobs but rarely available for typical ASME, API, AWS, and similar inspections.
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OmniScan MX2 Training – Shear Wave Material Velocity cont.
The velocity calibration is not related to the probe and use of velocity calibration block designs such as pictured at right require a zero degree shear wave probe. The velocity is measured at 0, 45, and 90 degrees in the material. Zero degree shear wave is not possible with a typical 1D linear phased array probe design. Because shear waves do not propagate through water or UT couplant, honey or another viscous liquid must be used for coupling. Panametrics nominal angle shear wave couplant is also available. (Panametrics part # SWC)
Velocity calibration block
Panametrics 0 degree shear wave probes
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OmniScan MX2 Training – Material Velocity Tolerance
For one degree angle accuracy in carbon steel the velocity input to the group set up wizard (Calculator) must be within +\- 20 meters\second. If measuring velocity on a calibration block, 1 degree angle accuracy is only achieved when the sound path measurement is +\- .1mm of the actual value Only precision measurements to this tolerance made on a block of the exact same material will result in velocity accuracy better than a default value taken from the MX2 database.
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OmniScan MX2 Training - Velocity Calibration Wizard Overview
The MX2 velocity calibration wizard has 3 options for measuring the velocity of a component that are compatible with both shear and longitudinal beams. 1. Radius. (Angle beam on sound path radius) 2. Depth (Angle beam on side drilled hole) 3. Thickness (0 degree on component backwall)
All three options require 2 reflectors at known positions. All three options will achieve best results when used with one A-scan or focal law. Angle beam is not recommended due to angle error. Prior to entering the velocity wizard, program at least one single focal law appropriate for the calibration type or install a conventional UT probe.
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OmniScan MX2 Training - Velocity Calibration - Thickness
Select Wizard>Calibration>Type Ultrasound> Mode Velocity>Start. Select Echo Type Thickness> and enter the values for thickness 1 and 2. Select Next.
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OmniScan MX2 Training - Velocity Calibration –Thickness cont.
If using a phased array probe, select the focal law used for the measurement. Adjust the gain for a signal and ensure that neither target 1 or 2 is saturated. Adjust the range over the targets. Excessive range will result in reduced accuracy due to UT axis resolution based on a fixed point quantity. (MX2 default is 320) Select Next.
1st backwall at 25mm
2nd backwall at 50mm
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OmniScan MX2 Training - Velocity Calibration –Thickness cont.
Set the gate A start, width, and threshold over thickness 1. Select Get Position. The time of flight position of thickness 1 is recorded.
1st backwall at 25mm
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OmniScan MX2 Training - Velocity Calibration –Thickness cont.
Set the gate A start, width, and threshold over thickness 2. Select Get Position. The time of flight position of thickness 2 is recorded and the MX2 will calculate the velocity.
2nd backwall at 50mm
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OmniScan MX2 Training - Velocity Calibration –Thickness cont.
Observe the calculated velocity and ensure it is close to the expected value. Select Accept. The velocity is now set for the active group based on the wizard results.
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OmniScan MX2 Training – Velocity Indicator in MX2 Software
The OmniScan MX2 user interface displays a status indicator for velocity.
A green V indicates that the current velocity in this group was the result of a measurement made through the velocity calibration wizard. A green V is not an indicator that the velocity is within tolerance and has no relevance to code or procedure compliance. When a velocity other than that in the MX2 database is required, it is normal practice to measure it one time with a conventional probe and enter it manually for future inspections. It is normal and acceptable for inspection .Ops files that have been calibrated for sensitivity and TCG to have a red V indicating no velocity wizard calibration was performed.
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OmniScan MX2 Training – Material Velocity Measurement Question: If the material velocity for the component is unknown and no calibration block of the exact same material exits, what is the benefit of performing the OmniScan MX2 velocity wizard calibration on an IIW block? Answer: There is no benefit. Measuring the velocity of the IIW block does nothing to improve the accuracy of the inspection because it is not made of the same material as the component. Without the calibration block on the left (Or similar design) made of the exact same material, the MX2 database is just as likely to be correct as a measurement made from a similar but different component like an IIW block. These functions do not calibrate the instrument, they measure the component velocity. This is the same principle for conventional UT as well and not unique to phased array inspection.
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OmniScan MX2 Training – Material Velocity Errors Question: What is the affect on focal law creation using a wrong or inaccurate material velocity in the part and setup group wizards? Answer: The result is angle, focus, and wedge delay calculation error. Only wedge delay error can be fixed with the calibration process. Angle and focus error cannot. Slight angle error due to minor material velocity errors is normal and affects phased arrays similarly as a a single element probe. This is typical of conventional UT and can be measured using a standard IIW calibration block. IIW block angle verification is covered in detail in a later section.
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OmniScan MX2 Training – Material Velocity Measurement Question: Can the material velocity be measured with the OmniScan MX2 if it is unknown? Answer: Yes. Measurement for precise shear and longitudinal velocity requires a calibration block made of the same material. Not just same type of material or P number, but a block made from the exact same pipe or component. The measurement is taken for both shear and\or longitudinal velocity at 0, 45, and 90 degrees and is recorded for use in the calculator or instrument.
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OmniScan MX2 Training – Material Velocity Overview Question: Why do computer based calculators contain more material parameters such as frequency, density and attenuation in the material and not just velocity? Answer: Because some phased array calculators can perform beam modeling, predictive sensitivity and TCG calculation in addition to predicting the wedge delay. The frequency is also required to calculate the near field.
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OmniScan MX2 Training – Velocity Calibration Wizard Movie
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OmniScan MX2 Training – Velocity Calibration Wizard Movie
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