Pipeline pigs are used to clean pipelines. Pipelines run the hazard of forming accumulations or deposits on the interior. Such deposits accumulate over a period of time from the product flowing through the pipeline. In some instances, this is no problem whatsoever. The deposit may form very slowly and, even after formation, may be removed easily because it is relatively soft. In other circumstances, the deposit placed on the interior of the pipeline may be very hard. Depending on the locale, artesian water will include a significant mineral content. The formation of internal pipe scale is accelerated where the water is hot. Where highly mineralized artesian water is heated and flows through a pipeline, scale coating in the pipe is accelerated. It is possible to coat a pipe on the interior to almost totally plug the pipeline. The internally coated pipe scale must be cleaned. Sometimes, cleaning can be achieved with other types of pigs. However, it has been found that the pig described in this specification is superior in many cleaning operations. It is particularly able to break up the scale on the interior of a pipe so that it can be removed in large pieces.
Pigs equipped with thousands of small points have been known before, and they will eventually remove pipe scale from a pipe. One such pig is supplied by the firm Polly-Pig by Knapp, Inc., of Houston, Tex., and is sold under the trademark "Superjavalina." It is a very good pig for many purposes. One of its virtues arises from the incorporation of thousands of small, relatively short metal chisels which cut the pipe scale away. So to speak, they collectively cut away a cloud of dust. By contrast, the pig of this disclosure cuts the scale only in a few places, but it tends to cut deeply and breaks away large pieces or chunks of the pipe scale. As the large pieces are broken from the unwanted pipe coating, they are flushed by the fluid flow which propels the pig through the pipeline. This enables the line to be cleaned and flushed with just a few passes of the pig. This enables the pipeline to be restored to full service more promptly.
One advantage of the highly inventive pig of this disclosure is that it appears to work even better with coatings which are relatively harder than most coatings. Indeed, the relative hardness and brittleness of the coating enhances the operation of the pipe cleaning pig of this disclosure. Enhancement is obtained in that soft, pliant coatings will permit the sharp, pointed stud to dig and gouge, but will not necessarily initiate cracks running through the coating which break the coating free. By contrast, a brittle pipe coating which is cut in a vigorous fashion by the chiseling point of the stud associated with this pig tends to break loose in large pieces as cracks and fissures are propogated from the line of contact of the stud with the pipe scale. This breaks up the pipe coating and permits it to flake away in larger pieces. It has been suprisingly learned that it is, therefore, better to reduce the number of metal chisels striking against the internal scale. This is borne out by the reduction in points of contact against the internal scale from the "Superjavalina" pig which approximates hundreds, or perhaps thousands, of points per square inch to the present disclosure which utilizes only a few metal chisels on the entire pig. This reduction of several hundredfold to a few stud points on the body of the pig enables the hard internal pipe scale to break up in large pieces and permits its removal more rapidly.
The present apparatus has the further advantage of removing other kinds of hard coatings. For instance, highly irregular coatings are easily removed. One kind of highly irregular coating is that found in pipelines which carry seawater and which do not have sophisticated water filtration apparatus. Such pipelines (for instance, communicating with a cooling tank) often accumulate aquatic shell deposits of a very random distribution, thickness and hardness.
The improved pig of the present apparatus undergoes significant stress in operation. The tip of the stud may undergo significant bending as it impacts a brick-like pipe scale deposit. The brick-like deposit may break and shatter, but only if the stud maintains its relative position in the pig as the pig traverses the pipeline. It is important that the stud be firmly anchored in the pig to resist the wear and tear of operation. Failure of the pig can be manifested by tearing the stud out of the pig body. One important advantage of an embodiment disclosed herein is the incorporation of an enlarged shoulder or facing area near the bottom end of the stud which anchors the stud in position and prevents its tearing free. Thus, the tip of the stud may be violently deflected, but the resilience of the body of the pig enables the stud to accommodate such deflections while the stud remains intact with the body. The transverse shoulder anchors the stud in position.
The present invention has as one of its objects the provision of a pipeline pig which is pressure propelled through a pipeline with a plurality of studs mounted in spaced locations and including spirals thereon which tend to rotate the pig as it traverses a pipeline, the studs gouging and chiseling away hard pipe scale.