Case Histories » Public Sector

Chloride Stress Corrosion Cracking

Pattern of corrosion had initiated in the residual stress field produced when the bolt holes were drilled
Circular rosette pattern of corrosion had initiated in the residual stress field produced when the bolt holes were drilled or punched in the web of the purlin
Multiple cracks, orientated at approximately 45 degrees
Multiple cracks (20 or more in a 9 cm length had initiated in the outer edge of the flange. Multiple cracks, orientated at approximately 45 degrees, had initialed in the outer surface of the 45 degree bend (denoted by arrows)
Climbing a flight of stairs to reach the forensic examination level
View of Carly climbing a flight of stairs to reach the forensic examination level where the roof purlins are located
Dino-Lite digital microscope
View of Carly using the Dino-Lite digital microscope in order to examine the surface of the roof purlin at 59x magnification

Specimen

Roof purlin was cold formed corner and sheared edge.

Material

Type 304 stainless steel.

Environment

Indoor swimming pool.

Background

The pool had to be closed down early due to rust falling into the pool.

Service Life

The Type 304 stainless steel roof purlins had been in service for approximately six years.

Findings

Stress corrosion cracking happened at many spots in the purlins where cold work, either by bending or punching, had been imparted into the Type 304 stainless steel. The structural designers and the persons supplying the Type 304 stainless steel purlins should have been aware that a very corrosive, high chloride environment exists at ceiling level in an indoor swimming pool. In Europe, Type 304 stainless steel structural members have been banned for approximately 20 years due to numerous cases of stress corrosion cracking in many European countries.

This investigation was featured in the Winnipeg Free Press: Portage La Prairie Suing Over Pool Roof.