Non-Destructive Testing – Continuous Scanning X-Ray System, An Alternative to Film Radiography for Weld Inspection

The European and worldwide non destructive testing (NDT) market is continually seeking new developments that can fulfil its need for real time, high resolution welding inspection of pipes in onshore and offshore applications, as well as for online welding inspection during steel pipe production. The aim is to find a substitute for film radiography and to reduce time and inspection costs, while obtaining increased defect detection reliability.

Film Radiography

Film radiography is often used for welding inspection in offshore and onshore pipe laying, and for checking the reliability of defect detection using ultrasonic testing. However, it can be slow and often cannot be carried out on 100% of pipe welds. To overcome the limitations of existing systems and to satisfy user needs of lower exploitation and production costs, and higher inspection process reliability, X-Tek Industrial Ltd recently launched its second-generation FFRESHeX digital, continuous scanning system.

X-Ray Detection Systems

The X-ray detection system uses new technology, which has been specifically designed for the inspection of welds and other long, thin objects. The sensor technology is unique in its ability to scan continually along the weld at high speed, presenting high quality digital image data.

Capabilities and Suitability

The system offers film quality resolution with the cost and time saving benefits of real time digital outputs. It has already been used to inspect pipelines onshore and offshore, spool yards, tie-ins, pressure vessels, tanks, and shipbuilding.

System Features

‘FFRESHeX offers continuous, real time X-ray scanning of welds at high resolution, high speed and high contrast,’ says Stephen Drake, Managing Director of X-Tek Industrial. ‘Since our first generation system, we have improved its sensitivity, re-packaged it for ease of deployment and made it lighter.’ The system’s main features are:

        Scans welds continually at speeds of up to 50mm per second at 2% sensitivity

        Resolution of 54 micron/pixel as standard (>7 line pairs/mm)

        Detector width of 55mm with >4000:1 dynamic range

        Contrast sensitivity (wire IQI) typically better than 1 %

        Uses narrow X-ray fan beam, which increases safety by reducing scatter

        Detector can be more than 100 metres from the control station.

Key Components

At the heart of the detection system is a custom-designed, sensitive X-ray multi-line detector. Configured with its own powerful control and processing software, the detector is ideal for analyzing linear, circumferential and spiral welds. ‘The special radiation tolerant, multi-line detector is a unique feature of FFRESHeX’s sensor technology,’ says Drake. ‘It has two resolution modes, 54μm and 27μm, and a choice of scintillators for different resolutions and applications.’ The detector head is shielded up to 300kV, environmentally sealed and rugged enough for heavy-duty applications.

Typical Applications

Typical applications include seam weld inspection of line pipes during mill production and percentage weld, or large diameter circumferential weld inspection for tank vessel and large tubular fabrication. Linear weld inspection applications include pipe weld seam and plate weld inspection, as well as applications within the aerospace, automotive and shipbuilding industries. The higher resolution version of the detector (27μm) can give results similar to fine grain film, especially with the addition of a custom scintillator. With accurate performance on aerospace tube welds (wall thickness down to 0.006”), the system is proving to be a fast and viable alternative to X-ray films of industry standards, such as D4. ‘Its film quality resolution depends on the film type and technique required,’ says Drake. ‘The system can be configured to match fine grain film, medium speed and fast films by choice of scintillator and scan mode.’

Advantages over Existing Weld Inspection Systems

Compared with existing weld inspection systems, FFRESHeX doesn’t require film, so no chemicals are required. It provides instant results from the welding process and scans continually at high speeds of up to 50mm per second. ‘There’s no stopping and starting, or noisy fluoroscopy imaging,’ says Drake. ‘Because of its speed it allows 100% inspection. It also provides better image quality than existing real time techniques.’ Configured with X-Tek’s image processing software (IMPS), FFRESHeX can produce high-resolution images better than 1 % in the Indicator of Quality Image (IQI). It also allows image data to be displayed, analysed and archived.

System Limitations

Currently, its application potential is limited to a maximum scan width of 55mm. Nonetheless, the official launch of the system was well received at ECNDT. ‘Numerous trials of the system have been requested in the UK, France, Canada, Australia and Greece,’ says Drake. ‘Prior to its launch, it was trialed at Statoil in Norway, and trials are currently taking place with a major UK company’.

Summary

Clearly, with such a broad range of potential users, FFRESHeX’s latest digital system seems set to have a significant impact on the non-destructive testing market by offering a viable film replacement system for high-resolution X‑ray weld inspection at a greatly reduced cost.

Source: Materials World, Vol. 10, no. 8. pp. 32-33 August 2002.

For more information on this source please visit The Institute of Materials, Minerals and Mining.

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