I used to think you could skip the full pressure test on a small patch job

An old guy I worked with on a job in Cleveland, Frank, told me once that if you're just doing a small patch on a low-pressure system, you can just do a soap test and call it good. He said the full hydrostatic test was overkill and a waste of a half day. I followed that for a while, until about six months ago. We patched a feedwater line on a small hotel boiler, just a 6-inch section. Did the soap test, no bubbles, looked perfect. Two days later, the plant manager called me back because the area was damp. A tiny pinhole had opened up under real operating pressure and temperature, something the soap test at room temp didn't catch. We had to shut the whole system down again. Frank's advice was wrong, and it cost us way more time and a hit to our reputation. Now I test every single weld, no matter how small. Has anyone else had a simple test fail them like that?

2 comments

2 Comments

julia2865d ago

Shortcuts always bite you later.

leo_campbell5d ago

Remember hearing that same line from a few guys over the years, and it always made me nervous. Even a small patch changes the stress on the metal around it. That soap bubble test is great for finding the big leaks right then, but it doesn't tell you if the weld itself is weak inside. I saw a fitting let go on a chilled water line after a patch passed a soap test, because the real problem was slag inclusion the bubbles couldn't show. The hydro test pushes it past working pressure and finds those hidden flaws. It's not about the size of the weld, it's about making sure the whole fix is sound.