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Pool Ceiling Collapse

A drop-in ceiling literally dropped in! The ceiling tiles, above a swimming pool, in a retirement community periodically started falling into the pool. The drop-in ceiling aluminum grid framework was held up by stainless steel wires. Samples of the failed stainless steel aluminum grid attachment wires are shown in Photograph A.

Overall view of failed ceiling tile grid work.
Photograph A   Failed stainless steel ceiling tile grid work attachment wires.

The ends of the stainless steel wire were fractured with very little evidence of corrosion. These wires secured the aluminum grid network, which supported the ceiling tiles. A profile view of isolated pitting corrosion on a failed support wire is shown in Photograph B.

Close-up view of failed grid wire.
Photograph B   Failed stainless steel grid wire.

An end view of one of the failed ceiling grid support wires is shown in Photograph C.

End view of failed ceiling grid support wire.
Photograph C   Failed stainless steel ceiling grid wire.

A scanning electron microscopic (SEM) examination revealed a brittle fracture, typical of stainless steel, which has failed by stress corrosion cracking. A SEM view of one of the failed ceiling grid support wires is shown in Photograph D.

SEM of failed ceiling grid wire.
Photograph D   Scanning electron micrograph (SEM) of the fracture surface on the failed grid wire. (Mag 30x)

X-Ray energy dispersive spectroscopy (EDS) allows the investigator to conduct a localized chemical analysis on the sample being examined in the scanning electron microscope (SEM). The corroded area on the surface of one of the failed ceiling support grid wires was examined using EDS. The area examined is shown in Photograph E.

Area of Ceiling Grid Wire for EDS
Photograph E   Surface where energy dispersive spectroscopy (EDS) was conducted.

The EDS spectra from the area shown in Photograph E is displayed in Figure 1.

EDS on Ceiling Grid Wire
Figure 1   Energy dispersive spectra (EDS) and semi-quantitative analysis.

The semi-quantitative analysis of the EDS spectra above indicates a concentration of chlorine (Cl) of 9.6 wt.%. The chlorine is the result of evaporation of the warm swimming pool water containing chlorine and the resulting high humidity in the swimming pool room.

An X-Ray energy dispersive analysis (EDS) only tells the investigator what chemical elements are present within the area examined, in this case, on the wire surface shown in Photograph E.

An elemental X-Ray map gives the investigator a visual display or map showing the location of each element in the EDS spectra and the area or areas in which that particular element is concentrated. An X-Ray map of elements found in the EDS spectra (Figure 1) is shown in Photograph F.

X-Ray map of elements found in EDS.
Photograph F Energy dispersive x-ray maps of various chemical species found on the subject wire surface.

An EDS map for chlorine (Cl), along with an SEM image of the area examined, is shown in Photograph G.

EDS map for Chlorine
Photograph G X-ray map of chlorine (Cl) and SEM image of surface area examined.

Allowing chlorine to contact stainless steel can result in very rapid failure of the stainless steel item. The failure will exhibit corrosion product on the stainless steel.

The failure of the stainless steel in the presence of chlorine, (from chlorine being added to the pool water) is known as chloride stress corrosion cracking. The fracture is the result of the synergistic effect of chloride AND stress. Stainless steel, without the presence of chlorine in most operating environments will perform quite adequately. Stainless steel will also perform quite adequately in dilute solutions of chlorine without the presence of stress. However, when both stress and chlorine are present, failure can result.

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J.E.I. Metallurgical, Inc.

5514 Harbor Town
Dallas, Texas 75287

Phone: (972) 934-0493
Fax: (469) 737-3938

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