A problem resulting from the findings of a boiler inspection last autumn has brought a happy conclusion for the trustees of Bancroft Mill at Barnoldswick.

Bancroft Mill's Cornish BoilerDuring the Spring of 1997, boilermakers from H.A. McEwen (Boiler Repairs) Ltd replaced the entire bottom shell plates of Bancroft Mill’s 1912-built Cornish boiler. This resulted from the boiler inspector condemning the underside of the boiler shell and also requesting extensive specialist welding repairs (reclamation of wasted metal by welding) on the furnace tube. This work was undertaken at McEwen’s Farling Top Works in North Yorkshire. During the ensuing 14 years, since the boiler was reinstalled and returned to providing steam for the William Robert’s cross compound mill engine, the insurance inspector’s 12-monthly general examination of the boiler, and particularly the underside of the shell plates, had revealed no problems.

However, the October 2010 survey revealed a localised area of shell plating wastage on the second strake, resulting from a leaking rivet. Even though the boiler is only steamed for a few weekends per year, trust chairman Jim Gill was surprised on hearing the inspector’s instructions to not only replace the one leaking rivet, but another five also, due to the heads being wasted. Additionally, a small area of fireside shell plating was discovered to have suffered metal reduction due to the scouring action caused by steam impinging from the leaking rivet.

Following Alasdair McEwen and his foreman boilermaker Michael White’s survey, and the subsequent acceptance of the quote, Michael attended Bancroft Mill and by electric arc welding, expertly reclaimed the 12in x 12in area of metal wastage from the shell plating in the flame bed (a process known as buttering).

The next job of tackling the rivet replacements was a little more tricky - the problem being due the boiler’s internal design, with the furnace tube just a few inches above the bottom of the shell plates, making access to the rivet heads on the water side very difficult. But for Michael, with over 30 years’ experience of highly specialised repairs, this was all in a day’s work.

The procedure firstly involved the cutting out by oxy propane torch of the four of the six condemned rivets. Once removed, the rivet holes were reamed fair then rethreaded using a special tap. While this procedure was under way, back at the work matching heads were machined onto six steel rivets. Michael firmly screwed these ‘boilermakers patch screws’ into place. He then cut out the last two securing rivets left in place which kept tight the lap edge. The process was then repeated and machine caulking around each patch screw head and the lap-edge of the shell strakes completed the job.

The repaired 1912 Cornish Boiler was hydraulically tested to the satisfaction of the boiler inspector and has now returned to steam.