Monday, May 11, 2009

Inspection System Checks Internal Welds

A weld scanning inspects the internal size and shape of girth welds on pipes for use in subsea oil and gas applications and is available from Optical Metrology Services (OMS). The Internal Weld Scanning Tool scans welds inside pipes - both visually and dimensionally - enabling engineers to quickly assess the quality of the root weld. In oil and gas pipes, the quality of the root pass of a weld is critical to the structural integrity of the girth weld.

Oil and gas companies, therefore, have stringent inspection requirements for checking welds. Welding of clad pipe is especially challenging and requires accurate measurement of the weld area in order to ensure zero defects and to avoid the delay and cost of a weld cut out later in the welding process. The technology can be deployed onshore and offshore at different stages of the pipe welding process. The tool can be used on corrosion-resistant alloy-lined pipe to identify sour (aggressive) ingress points, in both clad butt-weld and clad weld inlay applications.

The tool can also be used to improve weld procedure development efficiency and to check the root weld and geometry before next passes are deposited. The technology provides similar uses in fatigue-sensitive applications (SCRs) where the pipe is subject to higher dynamic stresses. The system can be mounted to a purge dam, with an integrated camera for positioning and inspection. Pipe can be inspected as it is being spooled onto a pipe laying vessel or during stalk fabrication/tie-in. Here, the tool is retrieved using a winch and wire system, with weld positioning controlled by a camera and precision motorised system.

Richard Gooch, director of technology at OMS, said: 'We demonstrated the Internal Weld Scanning Tool at the Offshore Technology Conference 2009 and the response was very positive. 'Engineers said the tool gives them complete confidence that the best possible review of the root weld has been carried out quickly and efficiently. 'Our tool helps the inspector to better understand the correlation between the various welding process parameters and the resulting physical weld,' he added. In the past, some engineers would inspect the girth weld at the final stage of the welding process (AUT inspection) - if a defect were found at that stage, the delay could be in excess of four hours.

Most reported AUT defects are in the root region of the weld. 'You need to get the root weld right first time,' said Gooch. 'This ensures that there are no delays in the welding process. 'The root weld geometry can be checked before the next welding passes and any defects dealt with prior to subsequent passes. 'This results in fewer defects at the automatic ultrasonic testing stage [AUT inspection] and improves overall productivity and efficiency,' he adds. The OMS Internal Weld Scanning Tool comprises two main systems: a digital colour camera with sophisticated optics and lighting, plus a high resolution laser scanner.

The tool can be used to detect a wide range of weld features, including root penetration, root concavity, cracks, lack of penetration, discolouration, oxidisation, surface porosity and burn-through. To ensure that all these features are detected, the scanning system measures a 25mm wide cross-section, with complete profiles at millimetre intervals around the inside diameter of the pipe. The camera takes overlapping pictures around the pipe for review and archival. Software provided by OMS enables the user to document and interpret these features, as well as measure the cross-sectional data.

Scanning a typical 10, 12 or 14in diameter pipe takes around 45 seconds in total. Once the automated scanning of the root weld is complete, the OMS software enables the user to identify the features of the weld and measure them. Cross-sections around the weld, for example, can be chosen and the main features of the weld then measured. The software also acts as a traceability tool. Inspectors can choose cross-sections around the pipe at regular angles and log any defects as they are found. The software automatically records all measurements, as well as typed comments from the inspector.

This information, including sample images and cross-sectional profile data, can then be archived. Logged data can be directly imported to Microsoft Excel as part of a weld inspection record. OMS is a specialist measurement technology company that provides measurement services and precision measurement systems to the oil and gas industry. A key focus for the company is in the dimensional measurement of oil and gas pipes or other similar structures such as aero engines, process industry tubes or manufactured cylindrical objects, where dimensions are critical.

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