Is it worth doing a 'Pipe Leak Detection' PhD (industrywise)?
I think it sounds awesome.  Huge connection to industry, society.  Both directly with the method and then tangentially with pipes in general (water, oil, gas, sewage).  The basic things you do in acoustics, mechanics, fluid flow will be good training also. 

And then the integrative learnings from putting a "fancy" technique onto a basic problem.  And this is whether it "works" or not (in terms of physical results or economic feasibility).  For you, it's all upside in the learning and the connections.

Jump on that thing.  Like yesterday!