Case Histories » Insurance

Plastic Hot Water Tank Valve

Failure analysis of a plastic valve which was overthreaded into a metal socket
Failure analysis of a plastic valve which was overthreaded into a metal socket
Expelled material on overthreaded plastic valve
Expelled material on overthreaded plastic valve

Specimen

Plastic hot water tank valve.

Material

White polymeric plastic.

Background

The plastic hot water tank drain valve was originally installed in a hot water tank located in a residential home. The tank leaked into the home, causing approximately $50,000 worth of damage.

Service Life

The water heater would have been in service for less than five years.

Findings

The valve was poorly installed and had been over-tightened past the as-manufactured length of the threads. This action abusively tapped further threads in the body of the valve, resulting in undue stress on the valve, and displaced the plastic of the body. The stress created a mushroomed ridge of plastic around the circumference of the valve, which initiated cracking in the valve that led to the failure and water damage to the residence.