In October 2003 during a night time examination of a railway bridge built in the
1870's, an inspector become so alarmed about the severe corrosion that he
was finding that he immediately phoned his manager for advice.

The inspector became particularly concerned with the condition of the bridges
east main girder. On the external surface of the web plate he found a series of
corrosion holes.

At the end of the his shift the inspector issued an urgent defect report describing
six defects that the he was most concerned about: five related to corrosion of the
east main girder that resulted in holes and severe thinning of its web plates.
The other defect concerned corrosion of the webs of several cross girders.

Just over 5 years later on the 27th January 2009 as a ten-wagon dangerous goods
train carrying full tankers of gas oil, diesel and kerosene crossed over the old
rusting bridge, it finally gave way and collapsed, derailing ten of the tankers,
spilling over 220,000 litres of diesel and kerosene into local rivers, killing fish
and wildlife, with one wagon catching fire.

The bridge at Stewarton before and after its collapse

The Bridge was located at Stewarton in Ayrshire , north of Kilmarnock and had its
girders fabricated from wrought iron plates, angles and T-sections, held together
with wrought iron rivets.

An investigation carried out by The Rail Accident Investigation Branch (RAIB) found
that "the bridge collapsed due to the catastrophic structural failure of its east and
centre main girders. Heavy corrosion had so significantly weakened the girders
that they were no longer able to carry the loading from trains that ran over the bridge".

	Photograph of a section of the east main girder after the collapse showing corrosion of the web plate.

The report listed several factors that led to the bridges failure.

The bridge had been modified over the years and this had resulted in a hidden
corrosion trap that affected the inner surfaces of the main girders, resulting in a
significant loss of web plate thickness and hence to the formation of holes.

The inner surfaces of the main girder web plates were not formally reported as
a potential hidden corrosion trap. No-one made any special arrangements, or
modified the bridge, so that they could be inspected.

No evidence was found that Network Rail took any action in relation to the 2003
urgent defect report, such as investigations that could have led to the structural
significance being fully appreciated.

Images of the corrosion from the 2003 urgent defect report

Subsequent annual visual examinations continued to raise concerns regarding
the corroded condition of the main girder webs. However, these also did not
result in any further action.

In February 2005 a visual examination was carried out by the same inspector
who had made the 2003 report, who again reported the bridge's condition as
corroded and poor.

Two other examiners carried out the next two visual examinations, in March 2006
and March 2007. They both raised similar concerns regarding corrosion on the
web plates of the east main girder and recommended steelwork repairs. They
both gave the bridge an overall condition of ‘poor’.

Photographs of web corrosion from a report in November 2007

Following the accident at Stewarton, Network Rail has been investigating the condition
of its metal bridges that are of similar construction.

Weblinks:

Download RAIB report in full:
100203_R022010_Stewarton.pdf (7,029.42 kb)

Images: Crown Copyright and Network Rail