Many types of commodities are today transported by underground pipeline. For example, water, crude oil, natural gas, ammonia, and numerous other substances are transported by buried pipeline. In order to prevent corrosion of buried metal pipe, and to extend its useful life, pipe to be buried is often coated with a protective primer or coating, or wrapped with protective tape, in the field just prior to laying it in the trench and backfilling over it.
Installers of underground pipeline often have difficulty, however, with poor adhesion of coating, primer, or tape applied in the field, due to inadequate pipe surface preparation. For proper adhesion of coating or tape, the exterior surface of the pipe must be completely clean of any foreign substances, and preferably roughened by abrasion or by surface etching. Even newly manufactured and delivered pipe, however, is seldom in this condition at the time it is to be laid. New metal pipe typically is delivered with a coating of mill scale which inhibits good adhesion. New steel pipe also forms a surface layer of rust during transit and storage in the field. Environmental effects and exposure during transit and storage may leave dirt, oil, grease, asphalt, tar or a variety of other deposits on the pipe surface. Used pipe to be relaid may have previously applied coating, primer or tape that will require removal before reinstallation. Therefore, there is a need for an apparatus and method for removing previous coatings, deposits, rust, and mill scale from pipe in the field so that newly applied tape, coating or primer will properly adhere.
In recent years, several devices and methods have been used for field cleaning of pipe. One such device is a pipeline traveling knife/brush machine, as manufactured by Eagle Manufacturing Company, model no. R.C.P.T. 6"-12", or by Remco Manufacturing Company, model no. SM-DR-2"-8". These machines have a hollow cylindrical body open on both ends to receive a pipe to be cleaned. The cylindrical body houses rotary knives or scrapers that encircle the pipe and scrape the exterior surface, and rotary wire brushes that vigorously brush the pipe surface. Another such pipeline traveling device is manufactured by Cups Company. The Cups device uses high pressure water spraying in an attempt to clean the exterior surface of the pipe.
While these prior devices may be somewhat effective as a means of cleaning and preparing a pipe surface, they suffer from several inherent disadvantages. First, at best, these devices remove only approximately 70 percent of asphalt, tar, and certain types of prior coatings applied to the pipe. Second, these prior devices are relatively ineffective at removing mill scale or rust from steel pipe. The failure of these cleaning devices to completely remove these substances or deposits results in significantly reduced adhesion of field-applied tape and protective coatings, and ultimately, in reduced protection of buried pipe. Third, even when these cleaning machines are successful at removing all deposits from a pipe surface, the machines accomplish little or no surface etching of a smooth pipe surface, which is necessary to achieve lasting adhesion of tape or coating. The wire brushes in knife/brush machines tend to burnish the pipe surface, rather than roughening it. Fourth, prior cleaning methods are slow. For example, the Cups device can clean only about 2,500 feet of pipe per 8 hour day. Fifth, field cleaning by these prior devices is expensive. For instance, field cleaning a pipe with the Cups machine costs approximately $2 per lineal foot of pipe.
Consequently, a need exists for a low-cost, high-speed apparatus and method for effectively and reliably field cleaning a pipe of mill scale, rust, prior coatings, environmental deposits, and also for abrading and etching the pipe surface to maximize adhesion of field-applied tape or coating.