The Flannery bolts ’ tell-tale’ holes are plugged at the firebox ends with pourous plugs, that weep steam and water ( while under pressure) if their threads are torn or bolts btoken. The Flannery bolts are drilled their entire length, up into the ball head, about 1/3 of it’s diameter. These bolts are forged with spherical heads at the top, and straight threads that are screwed into the firebox sheets. Similar in purpose is a design of firebox bolts patented by the Flannery Staybolt Co, called Flannery flexible staybolts. The spherical nuts aid in allowing the crown bolts to adjust to the thermal shifts of th crown sheet. The outer ends are secured with internal threaded, spherical nuts screwed into the outer ends. Typically, because of the inverted tapers, these are ‘driven’ from the inside of the firebox out through hollow sockets of the outside of the wrapper sheets. These crown bolts are long and flexible in the extended shank portions, thus threads are relieved of the dangers of forced, lateral, strains due to shifting as a result of repeated thermal expansions and contractions. These bolts are not drilled in the threaded region. Being inversely tapered, the stretched bolt hole “catches” on the wider threads. The theory was that when dangerous, low-water conditions were allowed, by extreme negligence, the softened crown sheet, under pressure will slip down the bolt threads. Any weeping out the tell-tale hole is a failed bolt.Īnother class of bolts are the crown bolts, which are generally very long, equipped with threaded ends, that are widest at the base tapering towards the shank. If these bolts fail, they typically tear at the threaded ends, and weep hydrostatic-testing water and steam & water, if under steam pressure.

There are similar bolts that are short holes drilled into the ends of the bolts, to well inside the wall thickness of the sheets. These are referred to as rigid staybolts. Some are short, rigid bolts screwed into both the boiler shell and the firebox sheets There are several types of staybolt designs. Another examination area is the firebox interiors, particularly any drilled stay bolts.

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