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The Case of the Fractured Sprinkler Heads

Fractured Sprinkler Head &  PartsThe Problem:

A sprinkler head frame arm failed and the observed arm fracture surface features were assessed. The project specifications required visual inspections of the installed sprinkler heads, however, there was not a requirement for nondestructive tests to examine damaged or bent sprinkler head frame arms. The Owner requested assessments of the fracture surfaces on one broken head. These concerns prompted the manufacturer to refute the claims of alleged non-compliant and defective manufacturing workmanship.

Fractured Sprinkler Head	FractureMy Assessment:

In the laboratory, the frame arm fracture surfaces were cleaned and examined at 200X. There was no evidence of internal casting porosity or inherent defects. Alloy analysis of the non-magnetic frame arm metal alloy indicated the primary elements were Nickel 65%, Copper 28%, and the remainder was Zinc, Tin and other trace elements. The fracture surfaces indicated directional stresses that coincided with the tightening direction of the sprinkler head threads onto the support pipe pendant. Overstressed longitudinal fissures were observed in the outer regions of the frame arms near the fractures and smeared flats on each frame arm. These fissures were considered initiation sites for the failed sprinkler head arms.

Surface Features Close UpThe Consequences:

All the sprinkler heads were visually inspected at the jobsite on the completed system. The Project Engineer’s visual requirements were stringent. The Contractor was not informed in advance of the surface protection requirements from nicks and gouges with improved head installation techniques.

The Lessons Learned:

The fracture surfaces indicated directional stresses that coincided with the tightening direction of the sprinkler head threads onto the support pipe. There was a failure to communicate between the Owner and the Contactor about guidelines for tightening the sprinkler head during installation onto the pipe pendants. The dispute addressed the possibility of an imposed requirement for 100% replacement of sprinkler heads on the project after the sprinkler system installation was completed and tested. The heads were not all replaced, though several heads with distinctive pipe wrench marks were replaced for preventative assurances.

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Welding Failures I Have Known, Interesting cautionary tales from Metals & Welding  expert, Dr Jesse A Grantham, PE