Swiss Approval Advanced NDT laboratory testing, is delivering advanced Ultrasonic inspection services, with use of Total Focusing Method (TFM), Phased Array Ultrasonic Testing (PAUT) and Time of Flight Diffraction (TOFD) for weld inspection applications. Our Advanced NDT Laboratory operations, are conformed with ISO 17025 requirements.

Phased Array Ultrasonic Testing

PAUT is a proven advanced ultrasonic technique utilizing array probes to perform beam steering and focusing. In weld inspection applications, commonly, angled wedges are used and shear waves are emitted and received in pulse-echo configuration. Multiple groups may be employed (Sector Scans, Linear Scans, Compound S-scans), where each group is optimized for increased sensitivity to specific defect types.

Compared to single-element ultrasonic-testing (UT), PAUT offers several advantages:

• Increased Probability of Detection
• Faster Inspection Speeds
• More Reliable Results

Total Focusing Method

TFM is an state-of-the-art advanced ultrasonic technique, used for the inspection of fusion-welded joints of metallic materials. Using Full Matrix Capture (FMC) acquisition, TFM is implemented as a post-processing algorithm, that allows the ultrasonic beam to synthetically focus at every point in the target region. The algorithm is based on the delay and sum process, essentially adding echoes from discontinuities to maximize the amplitude at a corresponding grid point.

TFM is considered a major step forward in volumetric weld inspection. The advantages of TFM technology in weld inspection activities are:

• Increased sensitivity to small defects
• Increased resolution
• Larger area coverage from a single probe position
• Easier interpretation of inspection results

The publication of ISO 23864:2021 and ISO 23865:2021 position TFM among the standardized weld inspection techniques.

Time of Flight Diffraction

TOFD is an advanced technique of Ultrasonic inspection that leverages on existing UT methodologies, thereby bringing a whole new range of testing and detection capabilities to the NDT forefront.

Whilst conventional ultrasonic uses shear/transverse waves as the primary mode of detection, TOFD uses longitudinal waves as the primary detection mode. Ultrasonic sensors are placed on each side of the weld. The emitter generates ultrasonic waves into the material and the receiver records the scatter waves from any material flaw. Using ultrasonic beam spread, TOFD provides a wide area of coverage for anomaly detection in the material being tested. When the beam impinges on a flaw tip, it is diffracted in all directions. Measurement of the time of flight of this diffracted beam, enables accurate and reliable flaw detection and sizing. This is the case even if the crack is not oriented to the initial beam direction. During typical TOFD inspections, A-scans are collected and used to create B-scan (side view) images of the weld.

While PAUT uses reflection, TOFD uses tip diffraction; and while some weld flaws produce strong reflected waves, others generate diffraction waves. This means that these techniques complement each other, and their combination assures that all flaws in the examined weldment can be accurately detected and sized.

TOFD Advantages:

• Based on diffraction, so relatively indifferent to weld bevel angles and flaw orientation
• Uses time of arrival of signals received from crack tips for accurate defect positioning and sizing
• Quick to set up and perform an inspection, as a single beam offers a large area of coverage
• Highly sensitive to all weld flaw types

Why Advanced NDT is Chosen by Swiss Approval, over Radiography

Although radiography testing (RT) was the primary NDT method suggested by the manufacturer, SWISS APPROVAL concluded that alternative advanced NDT methods, like TFM/PAUT, is definitely a more advantageous method.

• RT inspection would have required twice as many inspectors.
• Implementation of a safety zone was deemed too difficult. Inspection activities has to be performed during the night, while other employees are not present.
• It is estimated that the complete project using RT, would take five times longer than PAUT or other advanced ultrasonic applications.
• On top of all the extra costs associated with RT, are consumables such as films, photo chemicals, and waste disposal of the lead foils.
• The most important aspect of choosing PAUT or similar over RT, is related to the probability of detection. Lack of side wall fusion, which is a critical flaw to measure, is not well detected by radiography.

Swiss Approval Scanning Solutions

Depending of each particular inspection project, Swiss Approval is using the appropriate Crawler/Scanner, in order to get the best results from scanning options.

We propose either, Semi-Automatic Ultrasonic Testing (S-AUT) solutions, as well as, full Automatic Ultrasonic Testing (AUT) solutions. applications:

• Multi Probes Crawlers for flat and curved surfaces [S-AUT]
• Specific crawlers for angle welds and joints [S-AUT]
• Specific crawlers for High Diameter Pipe Line inspection, on a fixed route [S-AUT]
• Robotic crawlers for inspection of flat or curved surfaces at height, like tanks shell or similar [AUT]
• Automatic UT solution for Long-Distance Pipeline in Petrochemical Industry [AUT]
• Pipe lines and tubes inspection, with robotic or Semi-Automatic crawlers, depending on diameter and inspection position

Swiss Approval Testing Applications

Welding

• The Long Distance Pipe Lines inspection system, consists of six parts, including multi-channel ultrasonic flaw detector, PA/TOFD probe, wedge, crawler, analysis software, water irrigation device, calibration and simulation test block. Using of specific software, data acquisition and analysis can be easily completed. The weld inspection will be achieved quickly, by using the whole system.
• TFM/PAUT/TOFD on butt welds in pipes, pressure vessels, storage tanks, bifurcation lines, valve bodies, etc.
• 100% weld volume coverage at scanning intervals of 1mm,  of high pressure and high temperature piping welds at power station sites using encoded scanning  on circumferential and seam welds between 20mm to 75mm wall thickness.
• Inspection of complex geometry branch welds with variable weld profile using encoded scanning for accurate sizing of internal defects.

Other applications

• Corrosion mapping to estimate thickness at finite points in pressure vessels, pipes, tanks and structures.
• Turbine and generator components inspections with special  focus on areas of high stress concentration  such as for tree serrations of turbine blade roots and geometry changes along exciter cooling fans.
• Detection of corrosion wastage in wind tower foundation bolts or other similar HOLD DOWN BOLTS with reliable monitoring of corrosion wastage along the length of bolts up to 5 times its diameter.
• In-situ inspection of transverse cracks in shafts, axles, spindles, hold down bolts.
• TFM/PAUT scans on complex geometries including painted cylindrical, trapezoidal fuel transport tankers.
• Inspection of small bore tubes – Internal diameter of down to 38mm; having a minimum wall thickness of 5mm.
• Precise detection, measurement and reporting of smaller cracks for condition monitoring or repair.

Calibration & Reference Blocks

Swiss Approval Laboratory Staff is working consistently to guaranty the maximum efficiency and reliability of our Testing Results.

Specific Calibration Blocks for each technique, for different materials, related to different International Standards, are designed and developed within our Laboratory, in order to build in house our Know-How, necessary for service delivery of excellence.

Development of inspection capacity for this category of materials, usually includes many, if not all, of the following:

• Modelling & Simulation
• Machining of mock-ups and samples containing realistic defects
• Procedure development
• Validation and subsequent training

Such development of inspection resources and capacity represents for Swiss Approval Top Management, substantial commitments of time, high qualified personnel and significant capital investment.