This article is in response to a call that came into today about a 4 year old water heater tank leaking. I dispatched a plumber to the call and found that the water pressure in the house was 150 PSI (pounds per square inch). Normally allowable water pressure is the range of 40-65 PSI (recommended), and/or under 80 PSI. Water heater tanks, fixtures, supply lines, toilet parts, valves are mostly designed to work under 80 PSI, but may have failure (burst or leak) pressure slightly higher.
Todays customer asked why so little pressure increase could cause a tank to fail. Basically a little pressure adds up over a large surface area. Here are some basic calculations. Force equals pressure multilplied by area (LB=PSI x SF). A 40 gallon water heater is aproximately 50" tall and 18" wide. Therefore the internal surface area is about 23 square feet. At 50 PSI the force of the water on the tank is aproximately 166, 750 lbs or 83 tons. At 150 PSI the force of the water on the tank is 500,250 lbs or 250 tons. The tank is designed to withstand some high pressure but the welded seams can only hold so much.
The water heaters welded seams are subjected to cyclical thermal expansion and contraction as the water heater heats the water. The glass lining of the tank also wears with this movement and eventually raw metal is exposed. The water will eat the metal slowly and the anode rod will help to slow the slow the corrosion.
At any rate, high will cause a water heater to fail before its time. We installed a new pressure regulator and replaced the water heater. Hopefully, the customer will get 8-10 years (average life according to the insurance adjuster) out of this new heater.
Michael Whitman
Atlantis Plumbing
770-505-8570
