In welding, calibration implies the adjusting and evaluating the accuracy of measurement tools. Various systems of calibration must happen during ultrasonic testing. Basically, all equipment should be calibrated for excellent performance. For meaningful information to be obtained there must be reference standards, which are of various kinds and enable an inspector to detect flaws.
1. What is IIW Block in Ultrasonic Testing?
There are several procedures of calibration that must occur in the process of ultrasonic testing. Apart from calibration there are also reference standards that come in various sizes and shapes. The IIW type block is one of the references used in this process. This equipment has a similar design with the “true” IIW block although its construction materials vary from the original one. The true IIW blocks are made of steel while the IIW type blocks are made from various selected materials. Also their dimensions differ as in true IIW blocks, the measurements are in metric entities whereas the IIW type blocks have English units. Further, the IIW type blocks feature notches and circular groves. They are available in full sizes as well as in mini versions. They are widely used in angle beam inspection, determining the thickness of the metal as well as the position of sound exit.
2. What is Angle Beam Calibration?
This type of calibration uses blocks that were designed for the US Air Force to use while in field. Although they perform similarly as the IIW blocks, they are much lighter and smaller. Angular beaming is mostly preferred as there is no echo received. The calibration uses wedges and transducers which produce a refracted wave into the scan material. With the angled sound line, sound beams arise from the side and flaws are easily detected around the welded areas. The probe has a circle segment with two cuts made on the arc. These cuts enable production of a second echo thus creating a double reflection of the sound waves. The transducers have a frequency ranging from 500 KHz to 10 MHz. This high frequency is effective in detecting and resolving small flaws. In most cases, angular testing is done at 45, 60 and 70 degrees. However, the choice of the wedge to use depends on the thickness of metal. For a metal of thickness 25mm or less, 60 degree and 70 degree wedges are used. A wedge of 45 degree is used when the thickness of a metal exceeds 50mm.
3. How to Use IIW Block for Ultrasonic Angle Beam Calibration?(Procedure)
- Position the UT probe towards the large curve on the IIW reference block
- Set the zero offset to zero
- If the velocity is known, set it in estimation to that of scan material. If it is unknown, start with a standard value of 3.420 mm/uS or .1280 in/uS
- Set a proper range in the instrument which is considerably large to cover the prevalent calibration sound line.
- On the IIW NDT calibration block, pair the transducer. Scan the transducer back and forth to peak the signal
- The beam angle indicated on the IIW reference block in line with the transducer is the exact beam angle.
- Examine the echoes arising from the reflectors.
- For a second reflection, set an appropriate range in the instrument. A large curve is used for distance calibration
- For clear echoes, adjust the pulsar as well as receiver setting. This will ensure the accuracy of detecting weld discontinuities.
- To attain meaningful analyses, instrument settings like probe angle and gate should be accurately selected.
The IIW block calibration is an approach widely used by inspectors in welding. The IIW type block varies from the IIW true block in several ways. A major difference is noted on the materials used to construct these blocks. Angle beam calibration is also a reference standard used by inspectors in welding. It uses the IIW blocks for improved accuracy in detecting flaws. In most cases, inspectors prefer this calibration as it is accurate in resolving flaws.