R-TECH Materials were supplied a short length of hose from a gun used for applying thermal sprayed coatings. The hose was from the oxygen line of the equipment, and had ruptured causing a fire to occur (see Figure 1). R-TECH Materials were requested to determine the cause of the rupture. An unused hose of similar specification was also supplied by the customer for comparison purposes.
Figure 1: Ruptured oxygen hose
The hose consisted of a blue Natural Rubber (NR) outer, and black Syrene-Butadiene Rubber (SBR) inner, with a high tensile synthetic ply reinforcement (see Figures 2 and 3).
Visually, there was no evidence of any charring of either the outer (NR) or inner (SBR) layers of the ruptured hose. Hence there was no evidence of premature failure due to combustion. Examination also showed that there was no evidence of any damage or wear on the ruptured hose.
R-TECH Materials used FTIR and GC-MS analysis of the inner and outer polymers on the ruptured and new hoses, and showed that the correct grade of materials had been used on the ruptured hoses (see Figures 4 and 5).
In the light of the evidence from this investigation, it was concluded that the rupture of the hose had been produced by a flashback event.
Figure 2: Section through ruptured hose
Figure 3: Synthetic reinforcement ply in hose
Figure 4: FTIR spectra of NR outer
Figure 5: FTIR spectra of SBR inner
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