For the In - Service - Inspection (ISI ) of welds in power plants the code requires NDE techniques. One of these techniques for volume and surface inspections is the Ultrasonic Technique (UT ). An optimized inspection procedure commits the use of several angles of incidence. Depending on the material conditions sometimes different wave modes or multi-wave modes are necessary. For fullfilling all requirements by code and procedure, probe arrangements with a large number of probes will be built. Because of geometrical restrictions the probe arrangements must be minimized in many cases. The result is a large number of scans and several changes of the probes.
For reducing scantime, time for probe changes, dose rate in nuclear plants and as result saving money, SIEMENS developed Phased Array Probe (PA ), which can substitute the standard UT-Probes. One PA - Probe replaces several standard probes.
A Phased Array Probe generates different angles of incidence by different delay times between the array elements. The delay times are controled by special electronics in the UT-device. Depending on the geometrie of the inspection speciment and on the orientation of possible defects, the arrays will be built with horizontal- or vertical angle scew. Former built PA - probes had large dimensions and were limited in there scew range. They all were fabricated as a single type only for a special application to high prices.
SIEMENS goal was to establish a Standard - PA - Probe with following features:
- Small dimensions
- Angles of incidence within 0° to 70° in steel
- Large bandwidth
- The possibility for using mode conversion and "Tandem" techniques.
- High sensitivity
- Sufficent signal to noise ratio
- Resistant against mechanical stress
The result of this development program was a Multifunction UT - Phased Array Probe
The features are:
- All points 1 to 7 are fullfilled
- High damped UT- probe based on "Composite" material
- 16 elements
- High sensitivity in the near surface area
- Stainless Steel - housing with flexible coax-cable and waterproofed connector
- Vertical scew range from 0° to 75° for long and shear waves.
Phased Array Probes
All probe characteristics like pulse, spectrum, soundfield and sensitivity are compareable to standard UT-Probes with a single function and exceed former PA - Probes.
After passing the qualification program in laboratory, the Multifunction UT - Phased Array Transducer was used in field in March 96 with great success. The very short time schedule
and a lot of geometrical restrictions were the backround conditions. The scanning areas could be optimized and the inspection volume was covered by 100%. The new technique was effective , time and money were saved.
