A sleeve of woven wires that covers the exterior of the corrugated metal hose. Braid is made to fit snugly over the hose and be welded at the ends of the assembly. Braid prevents elongation of the corrugations under pressure.


Constant Flexing: The minimum radius of a bend measured to the assembly’s centerline to be used in motion calculations.

Static Bend: The radius of a bend measured to the assembly’s centerline to which an assembly may be bent for installation. The assembly should be subjected to no further motion other than vibration.


Regular cyclic motion at a slow cyclic rate and constant travel. The dynamic Minimum Centerline Bend Radius must be doubled for calculations involving constant flexing.


Annular: Corrugations are a complete circle or ring.

Helical: Corrugations that are continuous and spiral along the length of the hose.



Abrasion: Failure caused by external damage as a result of the hose rubbing against a foreign object.

Braid Wear: Failure caused by motion between the braid and the outside diameter (OD) of the corrugations.

Carbide Precipitation (Galvanic Corrosion): Corrosion that occurs between dissimilar metals on the less noble of the metals.

Erosion: The wearing away of the inner corrugation of a hose by the media conveyed, such as wet steam, abrasive particles, etc.

Fatigue: Failure caused by flexing which results in the break down of the metal structure.

Squirm: Failure caused by excessive internal pressure that causes the corrugations to warp into an “S” or “U” shape. Often caused by off loading of the braid by compression or manual handling of the assembly.

Stress Corrosion: A form of corrosion in stainless steel normally caused by chlorides.

Torque: excessive twisting of the assembly causing metal fatigue and failure.

Velocity Resonance (Harmonic Resonance): The sympathetic vibration of corrugations caused by high velocity media often resulting in catastrophic failure.



The volume of media being conveyed in a given time period (measured in ft3/hour; lbs/second; or GPM).



The rate of vibration or flexure of an assembly in a given period of time (measured in cylces). 


The sympathetic vibration of corrugations caused by buffering the corrugations by a high velocity gas or steam flow.



Live: The length of the exposed hose and braid excluding weld rings and fittings; the flexible length of a hose assembly. Also called “exposed length”.

Overall: The total length of the assembly including end fittings. Also called “developed length”.



Angular Motion: Motion that occurs when one end of an assembly is deflected in a simple bend. In these applications, care must be taken not to unload the braid by expansion.

Axial Motion: Motion that occurs along the longitudinal axis of the hose so as to compress or expand the length of the assembly. Care should be taken to never use braided assemblies or helical assemblies for this application. Unbraided corrugated assemblies at low pressures and small axial motions are acceptable, alternatively, expansion joints are recommended.

Offset Motion: Motion that occurs when the ends of an assembly are displaced laterally to each other in a plane perpendicular to the longitudinal axis with the ends remaining parallel. The offset radius should never be greater than 25% of the minimum centerline bend radius.

Radial Motion: Motion that occurs when the centerline of the assembly is bent in a circular arc.

Random Motion: Motion that occurs non-cyclically as when an assembly is handled manually. Care should be taken to avoid abrasion and the off-loading of the braid.

Traveling Loops: An installation configuration designed for axial motion or excessive offset motion.



Pressure Drop: The amount of pressure lost by the medium as it travels through the hose; estimated at 150% higher in metal hose than in new, smooth piping. In long assemblies pressure loss is estimated to be three times that of comparably sized pipe.

Maximum Working Pressure: The maximum operating pressure to which the hose assembly should be subjected, including the momentary surges in pressure, which can occur during service.

Burst Pressure: Actual: The pressure at which the hose assembly can be expected to rupture or the braid fail in tensile. This pressure is determined in a laboratory setting at 70°F and the hose installed in a straight line. Rated: A burst value which may be theoretical or a percentage of the actual burst pressure determined by laboratory test.

Deformation Pressure: The pressure at which the hose corrugations will permanently deform regardless of the external braiding.

Test Pressure (Proof Pressure): The maximum pressure at which a hose can be subjected to without either deforming the corrugations or exceeding 50% of its burst pressure. It is not recommended that hydrostatic testing be conducted above 120% of the Maximum Working Pressure, or 150% of the actual operating pressure of the particular application, whichever is less.

Pulsating Pressure: A rapid cyclic fluctuation in pressure above and below the normal base pressure. Pulsating pressure can cause braid wear.

Shock Pressure: Also called surge pressure or pressure spike; a sudden increase in pressure which creates a shock wave through the assembly. Often causes fatigue failure.

Note: For applications that experience pulsating, shock, or surge pressures, the peak pressures should not exceed 50% of the Maximum Working Pressure and the braid must be tight to the hose with no slack after installation.



Low amplitude motion occurring at high frequency. 



Piping geometry is a primary driver in designing the routing of steam heating circuits.  Steam must be able to freely flow through the jacketing system and contact all heat transfer surfaces.  Air and condensate must be efficiently removed from the jacketing to avoid compromising the system’s heat transfer capability. The following design guidelines are helpful for dealing with elevation changes in piping systems:

1.Run circuits downhill.  In other words, the steam supply point to the circuit should be at a relatively higher elevation than the condensate return point.  This allows the condensate to gravity drain out of the circuit.  As a rule, there should not be a vertical rise in the jacketing that would force the condensate to flow uphill.  This situation can lead to condensate collecting in the jacketing, which can prevent the free flow of steam to and through the jacketing.

2.Provide a clear path for air removal.  Upon startup, the jacketing will be full of air.  The air must be removed from the jacketing since air is a good insulator and will prevent the steam from contacting the internal heat transfer surfaces of the jacketing.  At pressures above 20 psig, air removal is complicated by the fact that the density of steam is greater than the density of air.  Unless there is a clear flow path for the steam to push the air out of the jacketing, buoyancy will drive the air towards high spots in the jacketing.  Vertical dead legs in the jacketing system should be avoided since the steam will only compress the air into the dead leg but not be able to remove it.

3.Allow condensate collection in jumpers instead of the jacketing.  If the steam jacketing circuit contains more than one heating element, some condensate collection within the circuit is inevitable.  It is not desirable for this condensate to collect in the jacketing since it would impede the system’s heat transfer.  Rather, it is preferred to allow the condensate to temporarily collect in the jumpers which interconnect the heating elements of the circuit.  This will not affect the system’s heat transfer.  To allow condensate collection in the jumper, the steam inlet connection on the jacketing must be at a high elevation, and the condensate outlet connection must be at a relatively lower elevation.  The jumper must dip below the condensate outlet before entering the steam inlet of the next element.  If the connections and/or jumpers are installed in the opposite manner, the entire jacketing will fill with condensate.