Thank you for your help question, my name is Steve and I am a fully qualified technician with over 30 years in the trade. Hopefully I can help you.
There should not be a great deal of pressure in the leak off system and providing there isn't a blockage in one of the pipes I would suspect that the problem is a faulty injector allowing the high pressure to escape via the leak off pipe.
This would explain why the pipe keeps blowing off.
The test to do is called a leak off test, and your garage should know how to do this but i will briefly explain.
You first need to disconnect all the leak off pipes from the injectors and block the return pipe to prevent any fuel running back.
Then a short length of pipe needs to be attached to each leak off outlet and then placed in a container, so you will need 4 pipes and containers for a 4 cylinder engine all the containers should be same size, there are dedicated kits available for this test.
now the engine should cranked for around a minute, it mat start but that is not a problem, after this time stop cranking or switch the engine off.
there should be a few mm's of fuel in each container, if one or two have a greater quantity, this shows that the injector is faulty.
I hope this answers your question but do please ask me any further questions. if this does answer your question please rate me and click accept, this allows me to continue.
Even after clicking accept I can continue to answer any further questions.