You report 'exceptional work' welding the wrought iron girders of Cookham Bridge, Berkshire (NCE 22 November) and in the issue illustrate the Clifton Suspension Bridge - also made of wrought iron.
Some 25 years ago, it was found that the pin holes in the eyes of some of the main parts of the Clifton bridge had worn to elongated holes. A technique was developed by a skilled welder to build up the worn areas with weld metal so that a new pin hole could be drilled and a bush of weld metal fused to the iron between the oxides.
The weld metal did not fill the hole, so reducing the high risk of shrinkage cracking. Plug welds are not only prone to restraint cracking but also provide an inaccessible interface when used to join parallel members, giving rise to the risk of severe corrosion as illustrated in the article in the same issue on the reflector at Jodrell Bank.
While all kind of bolts can be installed without any qualifications, readers are reminded that welding should be carried out by approved welders using approved procedures to approved weld details.
John Judd, Tanglewood, Milford Road, New Milton, Hampshire, BH25 5PW