Development of High Speed Rotary Probe Ultrasonic Testing System of Large Diameter Seamless Pipes for the Oil and Gas Industries

Introduction
   Modern tube  mills now produce large diameter seamless pipes at relatively higher production rates and as such the demands made on testing systems are also that much greater in terms of testing speeds. To meet this ever increasing demand and also to accommodate the need for more inspection directions than just longitudinal and thickness/lamination checking, a new generation of Ultrasonic Rotary Heads has been developed. The following summary descriptions provide details of the capabilities of these new rotary test systems:

Rotary Head Mechanics
   The original operation of ultrasonic rotary heads were generally designed to test tubes with square cut ends but now more recent designs incorporate a unique probe arm lift mechanism which enables tubes with a variety of end conditions e.g. un-cut or upset ends, to be tested. The contact shoe principle has always proved to be the best technique  to use when testing hot finished seamless pipe, and this technique has been retained with improvements to probe assemblies in terms of maintainability. A range of water column probe blocks have been designed to carry novel transducer arrays and inspections for thickness, laminations, transverse and oblique (variety of angles) defects can now be carried out simultaneously and at much higher testing speeds than ever before. The rotary heads can be equipped with many more transducers and can run at faster rotational speeds; the ability to cope with off-centre pipes (± 10mm) due to hooked ends, has always been an excellent feature of the contact shoe design and this aspect has been improved still further. All the new range of rotary heads have retained the tried and tested hydrostatic bearing designs which have proved very reliable in a production environment over many years of operation. One area which is vital to the reliable operation of the system is the signal transfer system via slip rings; here the brush assembly has been simplified and re-developed in recent times to provide easier maintenance.
   The range of pipe diameters that can be tested with the contact shoe design has been extended, and the rotary heads that currently can be supplied are:

Processing Electronics
    As with the rotary head mechanics the multichannel electronics for generating and processing the ultrasonic data has recently been developed to take advantage of the advances of the new data processing technology that is now available. The state of the art electronics used in conjunction with the rotary head, can generate and process ultrasonic data at P.R.F. rates greater than 20KHz per channel and from 128 channels or more without any compromises being made or loss of data from any individual channel. The electronics is fully programmable to cater for any customisation requirements and standard software is available for a whole array of facilities and analysis; the following list (although not exhaustive) provides an idea of the new systems capabilities:

Thickness Measurement

Ancillary Equipment
   Very often, even with the best test mechanics and electronics a good reliable production test also relies on the ancillary equipment used in conjunction with the test system. Reliable operation is crucial and Unicorn have also paid particular attention to ensuring the reliable and efficient operation of items such as the tracking and paint gun marking of detected defects, water Recirculating systems, operator safety features, conveyor sensors and encoder driving mechanisms and automatic fault diagnosis for ease of maintenance.
   Good tube restraint is also a very important aspect in performing a good test, and Unicorn recommend to customers that they use two pinch rolls on both to inlet and outlet side of the rotary head.

Advantages of the New High Speed Rotary Systems
   The new generation of ultrasonic rotary test systems available today provide the OCTG pipe manufacturer with more flexibility in terms of location of the ultrasonic test systems within the production plant. The ability to test at faster throughput speeds and to test prior to end-cutting operations allows the option of siting the test system much earlier in the process route; this provides the obvious benefits of having a completely tested pipe after the pipe ends are eventually cut back. In addition the quality of the pipe produced is determined much earlier in the process route, thereby allowing possible corrective action and/or savings been made. The detailed results information for each pipe, together with the ability to carry out a defect signal profile analysis on each defect detected, can lead to genuine savings in terms of production efficiency, as well as providing a wealth of quality control information.
   With all these facilities and proven ability for the systems to work in a production environment for 24 hours 7 days a week the modern ultrasonic Rotary Testing Systems now available should be considered as an integral part of a Pipe Production Plant and not merely be viewed as a production line bottleneck which should only be used when absolutely necessary.
 

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