There are watertight specifications for plastic and concrete pipes but no standard for metal pipes.
AASHTO M 198 is a joint method that can be used to seal with gasket materials and coupling systems. However, it will only be possible with low pressure.
Lots of silicone? They use polyurethane adhesives to fit windscreens in modern cars. These seal against water at 150km/hr with severe vibration. CMP is large diameter so it wont be cheap but you didnt mention that cost was a problem.
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you have not given the operating conditions. however, unless your pressure is very low (under 10 feet of head) than no, you really can't make it completely water tight. If you want to reduce leakage, there are mastic wraps that you can use on the joints that will help. Or use a different type of pipe.
I worked on a wood stave penstock replacement. The only economical pipe was spiral rib steel pipe. We used bolted angle flange joints with rubber gasket. The flange joints were welded to the sprial rib pipe. This job was 20+ years ago, but as I recall the pipe was 60" bituminous coated, backfilled to springline (half way). I remember the leak test we performed. No leaks except very minor amount at a one two locations, where the fabricated flange was welded to the pipe. All we could surmise was that the leaks occurred at locations where the flange to pipe weld ran across the heliccal joint. We think the weld burned/melted the sealant between in helical crimp. This is the company we bought the pipe from, they even mention the use of it in their brochure. They used to have a flier on the specific job. I would post it if I could find it.
