That's usually x-rayed if it's critical infrastructure AFAIK. Dad was a pipe fitter for Imperial Oil.
Depends on the size of the cracks you want to observe. For aircraft they use ultrasounds. I assume you dad used x-ray because methane and H2 are extremely small (they can’t be contained in, for example, water pipes, so the same goes for diagnostics and wavelengths).
Hot crude and hydrochloric acid under pressure are two I remember from his stories. He said they checked for hairline cracks. What that actually meant in practice for measurements I’m not sure.
I've done a fair amount of weld inspection / NDT. X-ray would be the only radiation based method used on a construction site. This would typically be done in batches and require the evacuation of an exclusion zone.