Precise words prevent expensive mistakes. Where two people mean different things by "minimum bend radius" or "length", an assembly gets built wrong. These are the definitions we use.
The terms, defined
Annular corrugation
Corrugations formed as complete rings at right angles to the hose axis. The construction we use for corrugated hose; it gives an undisturbed seat for the end fitting and produces no torsion under pressure.
Helical corrugation
A single continuous corrugation running as a screw thread along the hose, as against annular rings at right angles to the axis. We build annular, because a helix runs out at the hose end where the fitting is attached and couples axial pressure load into a twist.
Agraff / interlock profile
The profiled strip form used in strip-wound hose, where each coil mechanically locks into the one before it.
Live length
The flexible portion of an assembly between the fitting terminations — the part that actually moves. ISO 10380 calls it effective length.
Overall length
Face to face, or sealing surface to sealing surface, including the end fittings.
Pitch
The distance between the peaks of two adjacent corrugations.
Profile height
The radial distance between the inner and outer apex of a corrugation.
Ply
One layer of the pressure-bearing wall. Multi-ply construction uses several thin layers instead of one thick one.
Braid coverage
The percentage of the hose surface actually covered by braid wire.
Braid collar
The ring over the braid ends at a fitting. It contains the wires and immobilises the corrugations affected by weld heat.
Static bend radius
The tightest fixed radius at which a hose may be installed when it will not move again.
Dynamic bend radius
The radius to design to where the hose flexes in service — typically 2.9 to 5.6 times the static figure, depending on size.
Effective area
The cross-sectional area that determines the axial force produced by internal pressure, taken at the mean corrugation or convolution diameter.
Pressure thrust
The axial force produced by internal pressure acting on the effective area, tending to push a line apart at a bellows or unbraided hose.
Spring rate
The force required to deflect a bellows or hose by unit distance. Elements in series are softer than either alone; elements in parallel are stiffer.
Squirm
Sideways buckling of a pressurised bellows caused by inadequate guiding. A sudden failure, not a progressive one.
Cold spring / pre-set
Installing an expansion joint deliberately extended or compressed so it reaches neutral at operating temperature, halving the movement the bellows sees.
Tied joint
An expansion joint with tie rods that carry the pressure thrust, relieving the anchors but removing axial capability.
Universal joint
Two bellows separated by a centre spool, absorbing large lateral and, if untied, axial movement.
Gimbal
A two-axis hinge arrangement allowing angular rotation in any plane while carrying pressure thrust.
Flow liner
An internal sleeve presenting a smooth bore to the flow, preventing resonance fatigue of the corrugations and erosion by solids. Directional.
Bend restrictor
A short sleeve at the fitting preventing the minimum bend radius being violated where the assembly is stiffest.
Abrasion interlayer
An elastic layer between hose and braid that reduces friction wear under repeated flexing.
Whip check
A restraint preventing uncontrolled hose movement if a pressurised connection separates.
Duplex / jacketed assembly
A hose within a hose, both acting as independent pressure carriers, used for steam tracing, vacuum insulation or secondary containment.
Derating factor
The multiplier applied to ambient working pressure to give the permissible pressure at service temperature.
Sensitisation
Chromium carbide precipitation at grain boundaries after sustained exposure in the 450–850 °C range, leaving the material vulnerable to intergranular attack.
Chloride stress corrosion cracking
Brittle branching cracking of austenitic stainless requiring chlorides, tensile stress and temperature above roughly 60 °C together.
Cycle
One complete movement from the neutral position to the extreme and back.
Nominal diameter (DN)
The dimensionless size designation of a pipe or hose, approximately the bore in millimetres.
Nominal pressure (PN)
The dimensionless pressure designation, approximately the permissible pressure in bar at reference temperature.
Safety factor
The ratio of burst pressure to working pressure. Four is the accepted basis for corrugated metal hose.
EN 10204 3.1
An inspection certificate carrying specific test results, validated by the manufacturer's authorised inspection representative.
PMI
Positive material identification — instrumented confirmation of an alloy on the finished part.
