Preventing other failures

I SUGGEST there are a number of facts not mentioned in the recent articles on the failure at Dallow Lock which are relevant to this (and similar?) failures, writes Ralph Freeman.

A few that spring to mind are listed below:

1) How old was the failed casting and/or when was it fitted?

2) What is the service life of such a casting?

3) How often were these castings replaced in the past ?

4) Would not a more modern implementation fabricated from steel make a more appropriate bracket? (It could be made to look the same as the existing units, but constructed from a modern hi-spec material.)

5) Cast iron is prone to failing catastrophically in what looks to the layman like a 'clean break'. However, a defect may have been propagating internally for a considerable length of time within the casting prior to failure, but a metallurgy lab based analysis would be required to discern the actual cause of failure.

6) The poor properties of cast iron in certain applications were known over a century ago following the Tay Bridge and other disasters involving cast iron structures. These occurred especially in the early years of the railway era. (That's why Brunel would not use cast iron on the bridges he built for the GWR. He didn't trust it!)

7) The canal builders used cast iron because before welding/steel became available, their options for high strength materials were very limited.