Upon review of our internal procedure covering "hot tap" connections and associated testing, I've found a lot of discrepancy on acceptable calculation methods to determine appropriate external hydro test pressure and the required wall thickness to support it.
We often perform "hot tap style" connections onto lines that are not in service to prevent loading the entire system with water during a hydro test. There is no hot tap machine: we are simply welding the reinforced attachment onto the main line and pressure testing against the exterior wall before removal of the coupon. This is pretty common across the industry. In these scenarios, the API recommendation to never exceed 10% over internal operating pressure of the main line is not accurate. The same API recommendation really really isn't reasonable for true hot tap connections made on lines that operate at low pressure with the potential for high pressure excursions (i.e. vent lines), either.
I've used various calculations at different times to confirm typical test pressures (150% design) would not damage the pipe. Many folks used the unstayed flat plate calc as a very conservative check. I've also use external pressure calculations for convex heads. Does anyone have a clean calculation to determine the maximum test pressure that can be applied to the exterior wall of an existing piping using a branch (o-let) connection. All necessary data would be know (i.e. wall thickness, material, ID of branch). I would assume the calculation would be made without considering the reinforcement as a safety factor.
We often perform "hot tap style" connections onto lines that are not in service to prevent loading the entire system with water during a hydro test. There is no hot tap machine: we are simply welding the reinforced attachment onto the main line and pressure testing against the exterior wall before removal of the coupon. This is pretty common across the industry. In these scenarios, the API recommendation to never exceed 10% over internal operating pressure of the main line is not accurate. The same API recommendation really really isn't reasonable for true hot tap connections made on lines that operate at low pressure with the potential for high pressure excursions (i.e. vent lines), either.
I've used various calculations at different times to confirm typical test pressures (150% design) would not damage the pipe. Many folks used the unstayed flat plate calc as a very conservative check. I've also use external pressure calculations for convex heads. Does anyone have a clean calculation to determine the maximum test pressure that can be applied to the exterior wall of an existing piping using a branch (o-let) connection. All necessary data would be know (i.e. wall thickness, material, ID of branch). I would assume the calculation would be made without considering the reinforcement as a safety factor.
