Hi Aslam
I do not know whether you are really asking about locking or critisiging some fellow member.
Sometime if spring is used for gas line operating/sustain load means almost only the piping load.
When hydrotest is done load at that point is piping + water weight.
There could be lot of difference between that two weight.

Spring may not take that load variation.
So there is a lock pin in spring If you lock that it will work as normal hanger rod.
Site people are responsible to lock it before hydrotest.
For preparation of data sheet we need to mention hydrotest weight, vendor will design spring to take care of it at locked condition.

Regards

Habib