Pipeline pig launch apparatus

1. A pig launching apparatus comprising:

a frame including a first guide rail with a first pig supporting surface and a second guide rail with a second pig supporting surface, the first guide rail extending substantially parallel to, and spaced apart from, the second guide rail, the first guide rail and the second guide rail configured to support a pig on the first and second pig supporting surfaces;

a drop tube at an end of the frame into which the pig is positioned for dropping into a pipeline;

a drive system including a pushing finger protruding into the frame, the drive system configured to move through a cycle from a starting position through a forward stroke to move the pushing finger toward the drop tube and a rearward stroke to pull the pushing finger back to the starting position, the forward stroke moving the pushing finger to push the pig axially along the first and second pig supporting surfaces;

an extension of the first guide rail in the drop tube, the extension being moveable between (i) a support position for supporting the pig in a substantially vertical position in the drop tube and (ii) a release position wherein it can release the pig to drop out of the drop tube; and

a lock mechanism for the extension, the lock mechanism configured to alternately lock the extension in the support position and release the extension for movement to the release position, the lock mechanism configured to release the extension when the drive system moves through the rearward stroke.

2. The pig launching apparatus as defined in claim 1 , wherein the extension is biased into the support position.

3. The pig launching apparatus as defined in claim 1 , wherein the lock mechanism includes a linkage mechanically connected to the drive system.

4. The pig launching apparatus as defined in claim 1 , wherein the extension has an upper surface positioned in substantially the same plane as the first and second pig supporting surfaces.

5. The pig launching apparatus as defined in claim 1 , further comprising a pig stop configured to stop the pig from moving from the drop tube to the first and second pig supporting surfaces.

6. The pig launching apparatus as defined in claim 1 , further comprising a brake for locking the pushing device in an inactive condition.

7. A method for launching a pig into a pipeline, comprising: providing the pig launching apparatus of claim 1 ; loading the pig into the pig launching apparatus to rest on the pair of guide rails; driving the drive system to push the pig along the guide rails into the drop tube at an end of the guide rails; accommodating the pig in the drop tube on the guide rail extension, the guide rail extension holding the pig in a proper orientation, against tipping, within the drop tube; driving the drive system to move a next pig along the guide rails and into the drop tube; and actuating the guide rail extension release the pig from the drop tube to thereby launch the pig into the pipeline, wherein driving the drive system to move a next pig actuates the guide rail extension to release a pig from the drop tube.

8. The method of claim 7 , further comprising returning the guide rail extension to the releasably locked support position before the next pig is driven into the drop tube.

9. The method of claim 8 , further comprising shutting down the drive system where returning the guide rail extension fails to configure the guide rail extension in the releasably locked support position.

10. The method of claim 7 , further comprising pushing the pig past a pig stop to enter the drop tube, the pig stop preventing the pig from moving out of the drop tube back onto the guide rails.