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Tubesheet Welding
The tube-to-tube sheet scanner in operation . Image courtesy of FORCE Technology .
applications within different industries . Essentially , the P-scan is a computer-based ultrasonic inspection system for automated , mechanical , or manual inspection of structures , welds and assembly of components . The P-scan system has documentation and storage facilities for all data related to each inspection operation and include visualisations of the inspection results in the form of high-quality images of the material volume examined . The P-scan system can provide different kinds of information . It has an A-scan , B-scan , C-scan , T-scan ( thickness measurement ) and TOFD ( time-of-flight diffraction ) mode . Furthermore , the system provides projection images of the object under examination . With the three projection images , called Top View , Side View and End View , any imperfection which have been detected are automatically shown at their correct 3D location . The system ’ s excellent traceability and documentation possibilities is very valuable for the operator and owner .
The tube-to-tube sheet scanner FORCE Technology tube-to-tube sheet scanner , named AHS-1 , is a handheld unit , which either can be operated by the scanner operator or remotely from
A-scan view . Green line shows ref . level : 0dB . The signals are from indication 1 on C and D scan view image . Image courtesy of FORCE Technology .
A typical mock-up . Image courtesy of FORCE Technology .
a laptop . The scanner basically consists of a motor , a shaft with an ultrasonic transducer and a keypad for local scanner control . A centring mechanism is positioned at the end of the shaft , just in front of the ultrasonic probe . The shaft is hollow and contains cables for the transducer and a hose for water supply , as water is used as coolant between transducer and inner tube wall . The motor rotates and translates the shaft together with the transducer . The scanner can be equipped with different probes , depending on the expected type of defect . Zero-degree probes are typically used for detection of lack of fusion or cluster porosity , while angled probes are used for detection of cracks in the welds . Inspection rate depends largely on the inner diameter of the inspected tube and is larger for small diameters and lower for large diameters . One-inch tubes are typically scanned with one rotation per second , i . e . a weld with a leg length of 5mm is being scanned in approximately 10 seconds . The scanner is calibrated so that the position of the artificial defects in the mock-up is well defined , enabling positioning and sizing of potential defects in the actual heat exchanger welds .
Calibration of the system Prior to inspection , the system has to be calibrated on a mock-up . The mock-up consists of 3-5 tubes in a tube sheet of identical design , as the heat exchanger that is to be examined . Full geometrical identity of diameters , thicknesses , positions and welding parameters should be ensured . Artificial defects are introduced in the mock-up welds , however , one of the welds must be kept without any welding defects . Depending on the requirements , the artificial defects can be side drilled flat bottom holes or lack of fusion defects prepared during welding of the tube in the mock-up . As the scanner needs to be prepared to fit the actual tube geometry , the mock-up must be sent to us in sufficient time before the actual testing . The screenshot on this page shows a scanning with two lacks of fusion defects . The screenshot is shown
38 Heat Exchanger World June 2024 www . heat-exchanger-world . com