![Boiler Field tube, section](https://upload.wikimedia.org/wikipedia/commons/a/a7/Boiler_Field_tube%2C_section.jpg)
A Field-tube boiler (also known as a bayonet tube
)
is a form of
water-tube boiler
A high pressure watertube boiler (also spelled water-tube and water tube) is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-gene ...
where the water tubes are single-ended. The tubes are closed at one end, and they contain a concentric inner tube. Flow is thus separated into the colder inner flow down the tube and the heated flow upwards through the outer sleeve. As Field tubes are thus dependent on
thermo-syphon flow ''within'' the tube, they must thus always have some vertical height to encourage the flow. In most designs they are mounted near-vertically, to encourage this.
They are named after Edward Field, their inventor, and were originally developed for
steam fire-engines where speed of raising steam was important. More recently, Field-tube boilers have been most widely used by French manufacturers, either for small
vertical boiler
A vertical boiler is a type of fire-tube or water-tube boiler where the boiler barrel is oriented vertically instead of the more common horizontal orientation. Vertical boilers were used for a variety of steam-powered vehicles and other mobile ma ...
s, or as a marine boiler. The use of this type of Field tube has also been researched for the transfer of heat from
nuclear reactors
A nuclear reactor is a device used to initiate and control a fission nuclear chain reaction or nuclear fusion reactions. Nuclear reactors are used at nuclear power plants for electricity generation and in nuclear marine propulsion. Heat from nu ...
,
vacuum condensers and
heat exchangers
A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...
.
[
The thimble-tube boiler has some similarities, in that its water-tubes are also single-ended. The simpler thimble tube does not have the inner tube of the field-tube, therefore its flow is mixed, turbulent and dependent on random boiling. For this reason, thimble tubes can only be short, so are used in large numbers, and usually horizontally as their flow is not coherent enough to benefit from a gravity gradient. Field tubes are however more complex and expensive to manufacture. Field-tube boilers therefore use fewer and longer tubes (giving the same heating area for a reduced number of tubes).
Field-tubes are always ''submerged'', i.e. the upper end of the tube is mounted into the boiler ''below'' the water level, otherwise flow into the cold side of the tube cannot be replenished.
The principal advantage claimed for Field-tube boilers is that there are none of the expansion problems experienced in boilers with simple tubes. Secondly, as Field-tubes are connected from just one end, their replacement and maintenance is simpler.][
One drawback of the field-tube is a tendency for ]mud
A MUD (; originally multi-user dungeon, with later variants multi-user dimension and multi-user domain) is a Multiplayer video game, multiplayer Time-keeping systems in games#Real-time, real-time virtual world, usually Text-based game, text-bas ...
and scale to accumulate in the bottom of the tube, potentially blocking circulation. The closed tube ends are also difficult to wash out. Providing an excessive dead space there as a mud reservoir would have poor circulation, thus risking local overheating. Efforts must thus be made to ensure that all tubes are equally heated and that all have strong circulation within them, encouraging enough flow to scour the tubes free of sludge.
Field-tubes as thermic syphons
Where a simple vertical boiler
A vertical boiler is a type of fire-tube or water-tube boiler where the boiler barrel is oriented vertically instead of the more common horizontal orientation. Vertical boilers were used for a variety of steam-powered vehicles and other mobile ma ...
requires additional heating surface, particularly where this is directly exposed to the furnace so as to raise steam more rapidly, field-tubes may be installed in the roof of the firebox
Firebox may refer to:
*Firebox (steam engine), the area where the fuel is burned in a steam engine
*Firebox (architecture), the part of a fireplace where fuel is combusted
*Firebox Records
Firebox Records was a Finnish record label based in S ...
, almost down to the level of the firebed. They thus act as a form of thermic syphon
Thermic siphons (alt. thermic syphons) are Heat-exchanger, heat-exchanging elements in the Firebox (steam engine), firebox or Combustion chamber#Steam engine, combustion chamber of some steam boiler and steam locomotive designs. As they are dire ...
. As they are only mounted at one end and are free to expand in the heat, many of the usual expansion problems of thermic syphons are avoided. To encourage adequate circulation though, tubes should not be closer than 30° to horizontal, and longer tubes may need to be steeper than this.
De Poray boiler
The De Poray boiler is French in origin. Its defining characteristic is its patented double combustion chamber, intended to increase combustion efficiency, thus reducing fuel costs and smoke emissions. The secondary chamber is mounted adjacent to the first and consists of a refractory
In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...
ring of reduced diameter to the first combustion chamber. This ring is heated by radiation from primary combustion, thus maintaining a high temperature. Any unburned combustion gases leaving the first chamber are heated by this incandescent
Incandescence is the emission of electromagnetic radiation (including visible light) from a hot body as a result of its high temperature. The term derives from the Latin verb ''incandescere,'' to glow white. A common use of incandescence is ...
ring and together with the supply of secondary air are encouraged to ignite.
In the vertical
Vertical is a geometric term of location which may refer to:
* Vertical direction, the direction aligned with the direction of the force of gravity, up or down
* Vertical (angles), a pair of angles opposite each other, formed by two intersecting s ...
form of the De Poray boiler, the main heating surface is composed of vertical Field tubes in this secondary combustion chamber. A steel ''radiation bell'' is hung in the centre of the chamber, beneath the outlet flue, and the combustion gases are directed to pass over this, heating it. Heating of the tubes themselves is partly by convection from the gases, partly by indirect re-radiation from this heated bell. This permits a lower operating temperature
An operating temperature is the allowable temperature range of the local ambient environment at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the de ...
for the tubes, also a more even heating. This is claimed by the makers to encourage more uniform boiling within the tube, thus faster steam-raising.
An unusual feature of this boiler is that the field tubes are not rigidly attached to the boiler shell, but merely gasket
Some seals and gaskets
A gasket is a mechanical seal which fills the space between two or more mating surfaces, generally to prevent leakage from or into the joined objects while under compression. It is a deformable material that is used to c ...
ed into place. The thickened ends of the tubes are formed to a taper and the tubeplate holes are reamed to match. A paper gasket is sufficient to seal the joint. Inspection or removal for replacement is thus simplified. As the boiler is always under greater pressure than the atmosphere, the tubes self-tighten under pressure and avoid leaking. Obviously the boiler must never be placed under vacuum, so a vacuum valve may need to be provided.
Niclausse boiler
The Niclausse boiler is another French design, used for both land and marine use. It uses long Field tubes set at a shallow angle to the horizontal, as per the Babcock & Wilcox boiler
A high pressure watertube boiler (also spelled water-tube and water tube) is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-gene ...
. These Field tubes are linked into vertical sets by headers at their upper end. This header is a double pipe, with two sections linking the inner and outer waterspaces separately. Above the boiler and outside the flue gas enclosure, a steam-and-water drum links these headers together.[ Harris, Model Boilermaking, pp. 63,65]
It was notably used in some of the last pre-dreadnought battleship
Pre-dreadnought battleships were sea-going battleships built between the mid- to late- 1880s and 1905, before the launch of in 1906. The pre-dreadnought ships replaced the ironclad battleships of the 1870s and 1880s. Built from steel, prote ...
s (circa 1900) of the French, Italian, Russian[ Varyag class] and British navies. The built by the Bath Iron Works
Bath Iron Works (BIW) is a major United States shipyard located on the Kennebec River in Bath, Maine, founded in 1884 as Bath Iron Works, Limited. Since 1995, Bath Iron Works has been a subsidiary of General Dynamics. It is the fifth-largest de ...
in Maine and her launching in October 1904 with steam provided by twenty-four coal-fired Niclausse Boilers.
Although performance of this boiler has been good, washout is difficult and sludge build-up can be a problem. With careful design and regular maintenance the type gained a reputation for reliability and the quick replacement of a failed tube, which made it suitable for naval practice, less so for commercial use.
Niclausse boilers gave poor fuel economy when coupled with turbines operating at low speed, in addition to copious quantities of smoke and sparks. As such, they fell out of favor for naval shipbuilding once steam turbines became commonplace (see Danton class battleship for example).
Dürr boiler
A very similar type, used in German warships, was the ''Dürr boiler''. This did not use sectional headers, but single chambers.
By 1901, the Royal Navy
The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
had ordered eight Dürr boilers from Germany, to be installed as a trial on board the ''Marathon''-class cruiser .
See also
* Clarkson thimble tube boiler
A thimble tube boiler is a form of steam boiler, usually provided as an auxiliary boiler or heat-recovery boiler. They are vertical in orientation and would be considered a form of water-tube boiler.
Description
The characteristic feature of th ...
References
{{Boilers
Water-tube boilers
Steam boiler types
Vertical boilers