Digital Pipeline Radiography Speeds Detection Of Corrosion And Other Anomalies

Integrity Management
By Joseph M. Galbraith and George C. Williamson; BP America Production Company; and Michael Creech, Acuren Materials Engineering and Testing, Houston | June 2009 Vol. 236 No. 6

An enhanced digital x-ray image of a valve configuration. Photo: Acuren Material Engineering and Testing

Recent developments in solid-state radiographic pipeline inspection equipment, primarily durable, mobile computers and solid-state image capturing devices, are raising the technique’s profile as a useful, capable way to find and assess corrosion.

This article discusses how the integration of computers and solid-state imaging systems have increased the power of radiography in inspecting in-service hydrocarbon pipelines.

Radiographic inspection had its beginning with the accidental discovery of X-rays in 1895 by Professor Roentgen, but it was confined to medical usage until the development of high vacuum tubes, first in 1913 and then in 1922. The modern era started in 1931 when GE developed 1MV X-ray generators. At that time, the American Society of Mechanical Engineers granted approval for the use of radiographic images to determine the quality of welded pressure vessels. This led to the acceptance of employing industrial radiography to non-destructively determine weld quality.

Until the last decades of the 20th century, radiography changed little. Although film quality and sensitivities were improved significantly, images were still captured statically on film. Film processing had evolved to an automated state which provided more consistent quality, but the basic processes were the same.

Beginning in the 1980s, the advent of computers and their adaptation as rugged, durable, field-portable machines, coupled with the development of solid-state image capturing devices, have spawned rapid changes in industrial radiography. Images can now be captured on a variety of solid-state devices that accelerate the acquisition to “real-time”.

Software is now available to directly enhance the digital images, send the images anywhere in the world for review and provide archiving opportunities with all the flexibility and capability available with many different data storage and viewing programs. Furthermore, technological advances have led to development of smaller, lighter, more portable X-ray equipment and even field-portable linear accelerators used to generate extremely short wavelength, highly penetrating radiation capable of testing thicknesses of materials that could not be efficiently inspected until recently. Gamma ray inspection has also become increasingly capable, with many man-made isotopes that are stronger than naturally occurring radioactive materials and offer a wide range of energy levels and half-lives.

Shown here is the resulting image from the digital radiography of the pipe elbow pictured in the photograph. The x-ray image reveals pitting that would not be as easily detected using other NDT techniques. Photo courtesy of John Cope, Envision Product Design, LLC and Joseph Galbraith, BP America Production.

Image Capture

X-ray film is a photographic media that consists of a radiation-sensitive emulsion coated on one or both sides of a transparent substrate. Originally, glass plates were used as a substrate, but during WWI were replaced first with cellulose nitrate and later with a cellulose triacetate base. In the 1960s stronger, more stable polyester came into use as the film base. Since the development of radiography in the 19th century, the emulsions have been composed of a form of gelatin and a silver halide, typically silver bromide with a small quantity of iodide. While photographic film is generally only coated with the emulsion on one side of the substrate, typically X-ray film is coated on both sides.