Bore well pipe trouble

Bulging and bursting of the bore well pipe.

I am having a problem with my bore well at home. It's a new bore that we have drilled to 500ft and sent a sub motor inside up to 480ft. We get a min water for house use only. Some times 20min in the morning. The water level is low at my site. But my problem is, the very 1st pipe that connects to my Submerge moto always gets bulged and burst in the middle of the pipe. What could be the reason? My bore technician also says that he has not come across this issue in his whole experience. This has happened 2 times now in 1 month itself. The place where the submerged motor connects the pipe is good and no bulge or crack but only the centre of the pipe is bulging and bursting. I have 1st tried a 7.5kg pipe and it happened and then tried 13.3kg pipe and again it happened.