Metals and Materials Consultants
Return to Home Page
A plague of cracked and broken sprinkler heads in a cold-storage locker.
 |
The sprinkler frame at left is broken on one side and
cracked on the other side. Below: Broken ! |
 |
Even the spray dispersers were cracked. We suspected stress corrosion cracking, a common problem with highly stressed cast brass castings and in wrought brass that hasn't been stress relieved. |
 |
The wrought brass disperser fracture (seen at 200X on the
left) was partly intergranular (below, at
1000X at left) and partly ductile overload (dimple rupture - below, at
1000X at right). The scanning electron microscope revealed a great deal of sulfur in the corrosion products inside the crack in the disperser, as seen in the energy dispersive X-ray spectrum below the electron fractographs. |
 |
 |
 |
 |
At left, a typical frame crack seen close up. Below, left: Another frame crack seen in cross section with the scanning electron microscope with side branches not quite typical of stress corrosion cracking. There is much less branching than usual. Below, right: At a higher magnification, the frame crack path follows the grain boundaries of the brass. |
 |
 |
| SUMMARY:
The sprinklers were in service in a sub-freezing cold storage
locker. There was no sign of freezing
inside the sprinkler piping. The owner of
the locker disavowed any use of ammonia
or sulfur dioxide refrigerants as well as any knowledge of the usage of
ammonia based cleaners or even of non ammonium hydroxide cleaners
(which actually contain chemicals that release ammonium ion upon
contact with air without releasing ammonia). Some fruit are
treated with ammonia. ... This project remains in limbo while the
sprinkler contractor awaits further information ... The solution to
this problem may very well be to switch to sprinkler heads intended for
severe service. These are carefully stress relieved as well as
coated with a lead barrier. |