On Jul 15, 1:05*pm, Andy Dingley wrote:
On Jul 15, 11:54*am, Andy Breen wrote:

Boiler explosion or firebox collapse? Actual (external) explosion of the
boiler barrel seems to have been (commendanbly rare for over a century
- the benefits of elfandsafety gorn madde, of course..).

It actually seems to have had a single cause - the avoidance of
grooving, longitudinally inside the boiler barrel. Much of this was in
turn down to one simple design change - boilers went from being
wrapped with an overlap (then riveted) to being rolled as a butt joint
without any overlap, and the joint strengthened by an external cover
plate instead. Despite now being two joints and actually weaker (in
terms of simple strength) the old design had a problem of being non-
circular. Under pressure, flexing was concentrated in the groove of
this joint, which in turn led to erosion localised here.

We used to have our boiler welded joints Xrayed,. The weld penetration
was astonishingly poor. But the experts said it was OK