Patent GB-1452232-A (GB)
Title: Pipeline plugging apparatus and method
IPC: F16L55/128
Filed: 1974-09-03
Abstract: 1452232 Pipeline pig W A SAWYER 3 Sept 1974 [14 Sept 1973] 38429/74 Heading F2P  A pipeline pig 10 comprises a tubular body 11, closed at the forward end by a head member 12, an integral fluid by pass valve 13, a pair of cup type seal assemblies 14 and 15  and an intermediate expansible seal assembly 16.  The integral fluid by-pass valve 13, comprises a sleeve 27 moveable between a first position (Fig. 1) in which a port 19 is covered and a second position (Fig. 2) in which said port is uncovered thus permitting pipeline fluid to flow through the pig. The valve is biased towards said first position by a spring 29. With the valve 13 in said first position fluid pressure can act on said cup type seal assemblies 14 and 15 to push the pig along the pipeline.  When a section of pipeline is to be replaced three stations may be established, one upstream of said section one downstream and one intermediate said other two stations. Each station is provided with means, for stopping a pig, comprising at least one pin 53 which may be moved from a retracted position, in which the flow area of the pipe line 1 is uninterrupted, to an extended position as shown in Fig. 1. A plunger 55 comprising a rod portion 56 and piston 57 movable in chamber 58 can be extended or retracted by applying pressurised fluid to one side or other of the piston 57 through ports 59 or 60 the overall operation of the plunger being controlled by a valve 63. Said plunger may be adapted for mechanical or electrical operation. The stop means is supported in a flange 51, welded to the pipe at a hole made by hot tapping methods. Two pigs are introduced into the pipeline, each with their integral fluid by-pass valves closed, and allowed to move along the pipeline due to the action of fluid pressure on their cup type seals. The first pig is allowed to pass the upstream station, which has its pins 53 retracted, and is arrested at said intermediate station which has its pins 53 and plungers 55 extended as in Fig. 1. Said plungers engage a flange 28 and cause the valve 13 to open thus allowing fluid to flow through the pig. The second pig is then similarly arrested at said upstream station. The plungers 55, at the upstream station are then retracted to close the valve 13 of the second pig and pins 53 are further extended to lock said second pig against movement in either the upstream or downstream direction. Plungers 55 and pins 53 are then retracted at said intermediate station thus allowing said first pig to move towards said downstream station under the action of an innert fluid introduced through a vent between said upstream and intermediate stations. The first pig is then arrested and locked at said downstream station where the plungers 55 are retracted to maintain valve 13 in the closed position. When the pigs are at rest, differential fluid pressure across each pig causes the cup like seal assemblies 14 and 15 to move axially on the tubular body 11 to compress the seal assembly 16 which expands radially to seal the pipe. Seal assembly 16 may comprise a core 43 of soft material such as polyurethane foam, surrounded by an outer layer 44 of a harder polyurethane or other suitable material. After the section of pipeline has been replaced, the valve 13 of the second pig is opened and the new section of pipeline is allowed to fill, gases being vented through a vent in the section. When the new section of pipeline is full of pipeline fluid, the plungers 55 and pins 53 at said downstream station are retracted and said first pig allowed to travel down the pipeline to receiving traps. Said second pig is then similarly released. A similar method involves the use of only two stations, one upstream and one downstream of the section of pipeline to be replaced. In this case fluids trapped between the pigs have to be pumped out.