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Steam & Excursion > Flannery staybolt testing..
Date: 02/07/24 10:42
Flannery staybolt testing..
( re-posted from "3985" thread, below..)
Is the current practice for firebox staybolts to be threaded in
the firebox sheets, then seal-welded (for thermal conductivity enhancement)?
Or, is the current practice to properly recess the staybolt holes and install
un-threaded bolts, secured by welding-only in the firebox sheets?
Are there vendors that can supply replicas of Flannery Flexible staybolts,
with telltale holes to a depth of 1/3 the diameter of the ball head?
For continuity testing, Flannery bolts were supplied with copper plating
on the inside of the telltale holes. Are today's replicas of Flannerys
equipped with copper plating for continuity testing?
( Flannery bolt's telltale holes were copper plated for reasons relating to obstruction
detection. Flannery sold test & cleaning equipment that was used in verifying
unobstructed telltale holes.
Flannery Flexible staybolts were long bolts and were formed with ball-heads.
They were mounted, in the outer sheets, in capped sockets, which were
welded to the outer firebox sheets.
The steel caps for the sockets, were fitted with copper gaskets.
With the caps, failing, or replacement bolts were easily renewed).
During hydrostatic testing, firebox sheets are forced apart from each other.
The hydrostatic tests' purpose is to open-up any partial cracks in staybolts
in the firebox side sheets. The telltale holes extend the entire length of the
Flannery flexible staybolts. Not all staybolts are Flannerys, many shorter stays
are also drilled --- to a depth of 3" or 4", and are not plugged.
After hydrostatic staybolt testing, the firebox ends of the Flannery telltale holes
were plugged with tapered, pourous staybolt plugs..... prepped for the next
At boiler and firebox inspections, the Flannery bolts had the plugs chipped & removed.
The telltale holes are blown clear with a compressed air lance.
Then testing personnel probed each Flannery telltale hole with a battery powered
test light. The test light was fitted with a long, slender, electrically insulated
test probe, with only the tip exposed. The tester was inserted into each
opened Flannery bolt, and a brightly illuminated test lamp verified that
the bolt hole was unobstructed, for it's entire length. Ready for the 'stretch test'.
Failure to get a positive test-light result is considered a "broken bolt."
A plugged staybolt hole condemned the bolt, and any bolts failing the
'lamp-test' must be replaced. The tell-tale holes were capped after
each hydrostatic test with pourous plugs. Pourous, so that if a staybolt that
gets 'torn' or broken, it will spray water and steam into the firebox, but in a
The purpose of the hydrostatic test* is to have the firebox sheets stretched
apart, and to open-up any staybolt cracks ( that extend into the telltale holes).
Any staybolt telltale holes leaking water during the hydrostatic test, condemns
the leaky staybolts, and they must be renewed.
( *It takes deliberation and care to eliminate ALL the air from the filled boiler,
including filling to 100%, the steam dome..... which can become a 'trap' for air.
It's a good idea to blank-over the dry pipe leading to the superheater units
and eventuallly to the pistons.
Often, removing the vertical dry pipe extension up in the
the steam dome enhances the free access to the bolier interior ---
with the vertical section removed. On older locos, that vertical section
also contains the throttle mechanism ---- getting that out of the way
makes entering the boiler easier for the inspectors ....)
When today's crews are preparing the staybolts for hydrostatic stretching,
it's crucial that NO electric drilling of the holes be permitted, while cleaning
the telltale holes --- you risk ruining the copper plating, and resulting
in test-lamp failures... Remember that if the lamp test fails, its considered
a "broken bolt"....
Its interesting to speculate how today's crews and inspectors comply
with the original Flannery testing procedure. Luckily, an NKP boilermaker
kept his testing instrument, and in 1968, while in Conneaut, Ohio, and
getting ready to test 759's boiler, we were able to buy the extremely rare
Flannery testing tools. And add them to our collection of rare boiler tools.
The reason for the electric test is to verify for federal inspectors that
each telltale. is open its entire length, and not blocked by compacted
fly ash obstructing the telltale hole.
The pourous plugs are crucial to keep the telltale holes open while the loco is
in daily service. They're pourous so that any thread-damage, leading to a tear
into the telltale hole, will blow water and steam into the firebox, and water will
leak during the hydrostatic tests.
And, NO, you don't drill holes in the staybiolt caps!
AND , you don't clean telltale holes with an electric drill: You'll risk stripping
the copper plating, and your bolt will fail any electric continuity-test....
Test Failure requires that any defective bolts must be replaced.
Beacuse firebox sheets are necessarily 'thin' they lack the strength to withstand
boiler pressures. The sheets are 3/8" thick....thicker than that, and the steel exposed
to the fire's intensity softens and melts. Steel at 1,000 F is 8-times weaker than at
cooler temperatures. Water is what conducts heat from the sheets, and thicker
material cannot convey heat quickly enough to prevent exposed areas from melting,
and eventually the pressure on the steel forces it's collapse, and resulting boiler
explosion. The roof of the firebox is commonly known as the "crown sheet" ,
and is exposed to the hottest flame temperatures of 3,000 F., the hottest of
Staybolts supprt the inner sheets, since the outer shell is made of materials
generally thicker than one-inch thick. The stays are nominally spaced on 4" centers,
closer, as pressures approach 300 PSI operating pressure.
Because of severe pounding and bouncing-around, the threaded stay bolts are
subject to metal fatigue, and become weakened.... The threaded areas in the
thin firebox sheets are where 95% of the breakage occurs.
At risk, & weakened staybolts are best revealed when inspected while being
stretched under 'solid' water pressure. ( NO trapped air bubbles in the boiler
during the testing) --- the hydrostatic tests.
On paper, all the materials, threaded fasteners, etc. are proportioned
to be "structurally sound" , for pressures 4-times 'operating pressure'...
A boiler intended to operate at 250-PSI, is built as if the operating boiler pressure
was 1000PSI ..... That 4:1 ratio is called the Factor of Safety..
But, boilers are never actually subjected to the hypothetical 4X's
( interestingly, steel heated to a barely-visible dark red color,
is 8- times weaker, than when at safe operating pressures and temperatures.
What happened to our safety factor of 4:1?).
Edited 11 time(s). Last edit at 02/09/24 10:26 by wcamp1472.