When an assembly comes back to us, the failure almost always has a signature that identifies its cause. This page is the diagnostic table we use, published so you can read your own failures without waiting for us.
| What you see | Mechanism | Root cause | Prevention |
|---|---|---|---|
| Longitudinal split along the hose; corrugations flattened on one side | Over-bending | Installed below the minimum bend radius, or flexed at the static radius | Design to the dynamic radius; fit a bend restrictor |
| Crack at or immediately behind the braid collar | Fatigue at a stress concentration | Bending at the fitting; no straight run beyond the end | Allow a straight tangent of at least 2 × OD; bend restrictor on dynamic duty |
| Corrugations twisted; hose stiff or shortened | Torsion | Assembly rotated during installation or in service | Use a swivel end; rotate the pipe, not the hose |
| Circumferential crack at a corrugation crest, no deformation | Flow-induced resonance fatigue | Velocity above the limit with no liner | Fit an internal liner; see flow limits |
| Fine branching cracks, brittle appearance, no thinning | Chloride stress corrosion cracking | Chlorides plus tensile stress plus temperature above ~60 °C | Review chlorides in medium, insulation and atmosphere; consider a lined assembly or higher alloy |
| Isolated deep pits, often under deposits | Pitting / crevice corrosion | Chlorides with stagnant conditions | 316L rather than 304L; avoid dead legs; drain on shutdown |
| Cracking along grain boundaries after hot service | Intergranular attack | Sensitisation from sustained exposure in the 450–850 °C range | Specify 321; see derating |
| Braid wires broken and splayed, hose intact | Braid overload or abrasion | Assembly under tension, or repeated flexing without an interlayer | Install slack; specify an abrasion interlayer on high-cycle duty |
| Bore worn thin at corrugation valleys | Erosion | Abrasive solids in the medium | Internal liner; review velocity |
| Bellows buckled sideways under pressure | Squirm / column instability | Insufficient or wrongly spaced guides | Guide per the design; first guide within ~4 pipe diameters |
| Bellows over-compressed, convolutions touching | Movement beyond rating | Movement under-estimated, or shipping bars removed too early | Recalculate movement; restraints off only after anchoring |
| Liner detached or rattling | Reverse flow through the liner | Assembly installed against the marked flow direction | Observe the flow arrow; specify double-ended liners if reversible |
Send us the failed part
Photographs help, but the part itself is far better. Most of these mechanisms are unambiguous once the fracture surface and the corrugation geometry can be examined. We will tell you what happened even where the assembly was not ours — knowing the mechanism is worth more to both of us than a warranty argument.
The three that account for most of what we see
Torsion, because it is easy to do accidentally during installation and produces very high stress at very small angles. Bending at the fitting, because the stiffest part of the assembly is exactly where a person will grab it. And chloride stress corrosion cracking, because the chlorides frequently come from somewhere nobody looked — wet insulation, a coastal atmosphere, a cleaning chemical — rather than from the process fluid.
