High volume sensitive and repeatable inspection of Power Plant Boiler tube fabrication welds. Inspection must provide recorded data and in compliance with applied standards, on differing material types across the full boiler design and section zones (dimensions 30-50mmOD, wall thickness 3-4mm).
Boiler tube banks provide the boiler heat transfer and operate under wide temp/pressure variants. Operational boiler water chemistry is currently recognised as the major threat in contributing to the onset of potential tube failure mechanisms. If good balanced consistent chemistry management if achieved, then other threats such at thermal transients at section changes and also tube welds, are regions of inherent weakness and need to be considered and managed. Weld quality can dramatically affect boiler lifetime, resulting in massive cost implications when considering unscheduled breakdown and generation loss, and therefore weld inspection at fabrication stage is essential.
Integrity NDT Engineering offered Encoded Phased Array Small-bore scanning. The innovative systems allows for the inspection of small diameter thin wall tubing butt welds. Using high frequency low profile phased array probes, the design of the scanner allows for the inspection of closely aligned adjacent tubes in a typical boiler ‘tube bank’ configuration. The inspection is rapid and can be applied in minutes, the system providing the necessary recorded data. The data is analysed volumetrically for defects and any findings can be sized with a high level of accuracy, and code accept/reject criteria applied with confidence.
In accordance with our own written protocol, and designing project specific calibration blocks and validation test samples, Integrity NDT Engineers conducted a full code compliant procedure/technique validation exercise.
The historical standard conventional inspection application method for this inspection is Radiography (RT), as an alternative and in-lieu of RT, PA offers proven good correlation when compared with RT results, but without the numerous and well documented issues associated with radiographic inspection:
- No inherent safety issues/hazards as with RT.
- AUT does not disrupt production activities i.e. no need for planned interruptions or night shift radiography sessions.
- Immediate feedback on weld quality, unlike inherent delays in RT processes, essential for productivity and also a major advantage in managing weld repairs.
- Maximises probability of detection.
- Complete coverage and improved probability of detection (POD) of planar defects.
- Produces 3D results as opposed to RT 2D images.