Another hole in per pipe,why is this happening???

Got call last sat. Said mobile home had leak on hot water line at water heater,went there and found a small hole in the red pex line right below water heater,this is the third hole that I have repaired on this trailer.do not know what brand of pex they used when building mobile home but it seems much cheaper than my zurnpex that I use.there is a prv on incoming service line with about 60 lbs pressure at faucets,but there is no expansion tank or valve at water heater,I told them that an expansion tank or valve would stop this but now I’m not so sure.shouldnt the pex pipe hold enough pressure before blowing a hole that would make the t&p valve pop-off????i don’t understand why this pex pipe keeps blowing holes in it before the popoff valve releases:eek:any ideas???

Dang spell check,per should be pex