Page 460 - Pipeline Pigging Technology

Internal cleaning and coating

INTERNAL CLEANING

AND COATING

OF IN-PLACE PIPELINES

INTRODUCTION

As more and more emphasis is being placed on preventive maintenance,
methods of suppressing internal corrosion in pipelines are receiving increas-
ing amounts of attention. Internal corrosion may cause leaks, with possible
disastrous environmental effects, or may cause the product carried by the line
to become discoloured or otherwise contaminated. The costs associated with
internal corrosion can be staggering, but can usually be prevented by one of
several methods. This paper describes one such method, the "double-plug
extrusion" process for applying coating to the inside of in-place pipelines. It
will also address surface preparation for coating.
Three critical factors influence the success of any coating project: surface
preparation, coating material, and application technique. The wrong choice
in any area may cause premature failure or decease the life of the coating. This,
of course, is true of both internal and external coating, although these factors
are more difficult to control and inspect internally. For this reason, methods
must be used which offer the highest potential for success. A reputable,
experienced service company is also a must.
The first step of any coating job is to thoroughly clean the inside of the pipe
to properly prepare its surface. The preferred cleaning standard is a white-
metal blasted finish (NACE #1 or SSPC SP5), which ensures optimal coating
adhesion. The coating material, specifically selected to withstand the internal
environment of the line, is then applied by extrusion between two compress-
ible, spherical pigs.

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