Everything else being equal, a thicker-walled pipe is stronger than a thinner-walled one.
That simple fact is often overlooked when debating the merits of pressing vs. threading for joining pipe.
Threading pipe requires cutting into one or both ends of the pipe and removing metal to create the threads. Depending on the thickness of the pipe being used, the places where the walls have been grooved can end up being only half as thick as the rest of the pipe.
This can drastically reduce the strength and durability of the pipe at that point.
Of course, most of the threaded end is covered and protected by a fitting, but not all of it. Typically, two to three threads are left exposed and that creates a weak spot for corrosion and, possibly, breakage.
By contrast, pressing does not remove any material from the pipe, but keeps its outside diameter intact. The fitting adds additional strength without subtracting anything from the pipe.
A few years ago we saw firsthand how important that can be. A heavy snow fell overnight on the sloped roof of a movie theater in Portsmouth, N.H. The theater was heated by natural gas rooftop units with pipe running up the exterior wall and onto the roof feeding the units.
The contractor had used Viega MegaPressG fittings throughout the black steel gas piping distribution system, except where the pipe joined the heating unit. That connection was threaded, not pressed.
When the heavy snow slid off the roof, it broke the threaded connection at the rooftop unit heater. When the unit started it ignited the leaking gas and started a fire.
An insurance investigation revealed that the MegaPressG fittings used to join the pipe had held, even under the tremendous weight and pressure of the shifting snow. It was the threaded connection that had broken.
That’s a dangerous and expensive way to learn that pressing preserves the strength of pipe better than threading does.
See how pressing stacks up against threading: