Page 1 of 11 TECHNICAL COMMITTEE REPORT TCM 18/01 Failed bolt, San Vito Sicily Incident Ref. 01/18/O.FRE SUMMARY This report details the failure of a bolt on a sport climbing route in San Vito lo Capo, Sicily. Author: Isabel Hadley Checker: Wil Treasure Date 29/01/2019 Approved by the Technical Committee
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Failed bolt, San Vito Sicily Incident Ref. 01/18/O Failed Bolt.pdfSan Vito lo Capo, Sicily. The leader sustained minor injuries, and it is understood that a local climber later replaced
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Page 1 of 11
TECHNICAL COMMITTEE REPORT TCM 18/01
Failed bolt, San Vito Sicily Incident Ref. 01/18/O.FRE
SUMMARY This report details the failure of a bolt on a sport climbing route in San Vito lo Capo, Sicily.
Author: Isabel Hadley
Checker: Wil Treasure
Date 29/01/2019
Approved by the Technical Committee
Technical Committee Report 18/01
Page 2 of 11
1. INTRODUCTION A BMC member has made the committee aware (see incident report in the Annex) of the failure of a bolt as a result of a leader fall on the route ‘Non ė main troppo tardi’ at San Vito lo Capo, Sicily. The leader sustained minor injuries, and it is understood that a local climber later replaced the casualty bolt with a p-bolt. The retrievable part of the bolt was sent to the BMC Technical committee for examination. 2. EXAMINATION One part of the fractured bolt, along with the associated hanger and a maillon, was received for this investigation, as shown in Figure 1. The bolt was visually inspected, and photographed in the as-received condition. The fracture surface was examined after degreasing ultrasonically in acetone, using scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) micro-analysis. The fracture surface was further examined by SEM/EDX, after being cleaned in an inhibited solution (pyrene) to remove corrosion products. One metallographic section was prepared by cutting the bolt in half longitudinally, Figure 1b. The section was examined, using light microscopy and SEM/EDX. Vickers hardness measurements were carried out on the same metallographic section, at a load of 1kg, and compared with the specification for a widely-used austenitic stainless steel, ie type 304. The chemical composition of the bolt was also determined quantitatively, using ICP (inductively coupled plasma) spectroscopy and compared with the specification for a type 304 stainless steel. 3. RESULTS & DISCUSSION Figure 2a) shows the fracture appearance in the SEM, whilst Figures 2b)-2d) show examples of the EDX spectra obtained from various regions of the fracture surface. Figure 3 shows SEM images and Figure 4 the light micrographs. The results of the chemical analysis (Table 1) and the hardness test (table 2) show the composition and properties of the bolt to be broadly in line with those of a type 304 stainless steel, although it should be noted that there is no documentation or marking to suggest that the bolt claimed to meet this specification. What is clear from the chemical analysis is that the Mo content (0.01wt%) is outside the specification limits for type 316 stainless steel, which contains around 2% Mo, and generally confers higher resistance to pitting corrosion compared with the more commonly-used type 304 grade. The micrographs in Figure 4 show branched cracking, characteristic of stress corrosion cracking (SCC). This is a very common time-dependent cracking mechanism in austenitic stainless steels subjected to an environment containing sodium chloride and warm temperatures, and is entirely consistent with the environment in which the failure occurred. It is understood that several such failures
Technical Committee Report 18/01
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have occurred in climbing equipment elsewhere, especially in tropical coastal environments, and that replacement by a resistant alloy (such as Ti) is the best solution – if the bolt is replaced with a similar bolt, there is nothing to prevent SCC occurring again. 4. CONCLUSIONS & RECOMMENDATIONS 1. The composition and properties of the broken bolt were broadly consistent with those of a type 304 austenitic stainless steel. 2. Failure occurred by a process of stress corrosion cracking, which is consistent with the environment (warm coastal cliff) in which the failure occurred. 5. ACKNOWLEDGEMENTS The author is grateful to her colleague Dr Qing Lu for carrying out the work described in this report.
Table 1 Results of chemical composition analysis of the bolt (TWI analysis No.
S/18/63), and the relevant material specification.