PRCI PR-220-9123


Evaluation of Ultrasonic Inspection Techniques for the Root Region of Girth Weldsvan der Ent, J.; Dijkstra, F.H.Pipeline Research Council International / 01-Jan-1996 / 523 pages

RTD Quality Services (Rontgen Technische Dienst bv)
(e-book version)Need: A system for mechanized ultrasonic inspection of girth welds during pipeline construction, the RTD Rotoscan, has already been available for almost twenty years. In fact, its development started back in the seventies, after initial trials going as far back as the fifties. First commercial use started in the beginning of the eighties. Today, RTD Rotoscans are being used all over the world whereby, for a number of pipeline projects, it replaces radiography as a sole girth weld inspection technique. It has been known for many years, that the main difficulty in mechanized ultrasonic inspection of pipeline girth welds is in a reliable inspection of the root region. On one hand, the possibility exists that serious planar defects are over-looked (missed defects) because they are interpreted as geometry signals, on the other hand geometrical echoes (caused by e.g. hi-lo) can easily give rise to interpretation as defect signals false calls). This difficulty is mainly caused by the fact that defect signals and geometry echoes are received with only very small differences in transit distance, and thus are difficult to separate by means of a gating system.
Benefit: This project was initiated to evaluate the performance of the existing system(s) / method(s) and the improvements contemplated. It was decided to build the project around a number and variety of representative test welds. These were inspected with Rotoscan 1990, also using improvements and radiography, and then destructively tested for correlation with the NDE results. This document reports improvements to the RTD mechanized ultrasonic inspection system for pipeline girth welds. Describes how the addition to the ROTOSCAN 1990 system of ROTOMAP AND ROTOTOFD have led to improvements in the accuracy of the inspection of the girth welds in the root region.
Result: The work done within this project shows, that by proper implementation of improvements such as Rotomap and RotoTOFD (here still used in early prototype versions) the initial drawbacks of mechanized ultrasonic inspection in the root can be overcome. Together with the technology and experience that form the basis for the existing Rotoscan 1990, mechanized ultrasonic inspection of pipeline girth welds can now be considered as a mature technique, capable of replacing radiography in many cases.

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