Ultrasonic Testing (UT)
Weld inspections are the main application for the ultrasonic testing or ultrasonic scanning method known as shear wave testing, sometimes referred to as angle beam inspection. Shear wave testing, which comprises positioning a probe to the side of a weld and generating beams at an angle toward the weld, is typically required for complicated weld geometry and the presence of a weld crown or bead. Ultrasonic scanning inspection is an alternative volumetric inspection method for radiographic testing and its widely used in API 653 Inspection of Storage tank as well as API 570 Inspection for pipeline Inspection.
Ultrasonic Scanning Procedure Requirements: Variation from this ultrasonic testing procedure shall only be undertaken with the prior written approval of Client. Each variation shall be noted on the ultrasonic report and a relevant test technique or procedure produced if required. Coupland’s such as SAE 40 oil, Ultra gel, cellulose paste or equivalent may be used. Specific consideration shall be given to the service and material of the component tested. Such considerations shall include but are not be limited to oil or ‘raw’ water where such could be injurious or hazardous in certain applications and materials. The rate of search unit movement for examination shall not exceed 150 mm / second unless calibration shall be verified at the intended scanning speed. The volume shall be examined by moving the search unit over the examination surface to scan the entire examination volume. Each pass of the probe shall overlap a minimum of 50% of the probe (piezo-electric element dimension perpendicular to the direction of the scan). For weld testing, scanning shall be done from both the sides of the same face of the material. In case both the sides of the same face are inaccessible the information shall be recorded in the report. The entire volume of the weld needs to be covered, if necessary two or more angle beams need to be used to ensure full volume coverage. For plate lamination testing, using a straight beam probe, the area to be tested shall be scanned in a grid pattern. The grid dimensions shall be 225 mm width by 225 mm breadth unless otherwise previously specified and agreed with the Client. UT Scanning Service shall be performed at a gain setting of at least two times the primary reference level. The evaluation shall be performed with respect to the primary reference level. UT Scanning surface shall be free of weld spatter, dirt, and corrosion products. Forged or rolled surfaces having reasonably smooth surfaces are acceptable. UT Scanning of adjacent base metal using straight beam probe. The scanning of the adjacent base metal shall be performed to detect reflectors that might affect the interpretation of angle beam results and is not to be used as an acceptance-rejection examination. Locations and areas of such reflectors shall be recorded. Scanning for reflectors oriented parallel to the weld using an angle beam probe. The angle beam shall be directed approximately at right angles to the weld axis from two directions where possible. The probe shall be manipulated so that the ultrasonic energy passes through the required volumes of weld and adjacent base metal. Scanning for reflectors-oriented transverse to the weld using angle beam probe. The angle beam shall be directed essentially parallel to the weld axis. The search unit shall be manipulated so that the angle beam passes through the required volumes of weld and adjacent base metal specified by the referencing code section.