A correctly specified assembly installed badly will fail early, and it will look like a manufacturing defect when it does. These rules are short, and each one has a mechanism behind it.
Before installation
- Check the assembly against the drawing — size, length, material, end connections, flow direction.
- Confirm the line is clean. Weld spatter and grit left in a new line will erode a corrugated bore.
- Check that the pipework is aligned. A hose is not an alignment tool.
- Leave shipping restraints on an expansion joint until the anchors and guides are complete.
The rules
| Rule | Why |
|---|---|
| Never twist. Rotate the pipe or use a swivel end to bring flange holes into line | Torsion produces very high stress at low angles and fails suddenly. On interlock, the helix unwinds |
| Never install taut. Allow slack | A hose in tension has nothing left to absorb movement and loads the braid and welds directly |
| Never bend at the fitting. Allow a straight run beyond each end | The fitting is the stiffest and most stressed point on the assembly |
| Never exceed the bend radius. Use the dynamic figure if it moves | Over-bending flattens corrugations and concentrates stress |
| Support the weight. Hose plus medium is heavy | An unsupported horizontal run will sag below its minimum radius |
| Install the liner the right way round. Flow into the liner | A reversed liner chatters, wears and can detach |
| Do not use the hose to correct misalignment beyond its rated offset | It becomes a permanent stress rather than an absorbed movement |
| Do not weld near a fitted assembly without protecting it | Arc strike and spatter on a thin corrugated wall are through-wall defects |
| Earth PTFE-lined assemblies in flammable service | Flow over PTFE generates static charge |
Expansion joints specifically
- Anchors and guides first. A joint installed in an unguided line will squirm under pressure. The first guide goes within about four pipe diameters, the second within about fourteen.
- Shipping bars come off last, after the line is anchored, guided and supported — and they are not reused as supports.
- Check the pre-set. Where the joint is supplied cold-sprung, it must be installed at the stated installation temperature and length.
- Orientation matters on hinged and gimbal joints. The plane of rotation is fixed by the hardware.
- Do not use the joint to close a gap. Face-to-face must be within tolerance before the bolts go in.
Interlock hose specifically
- Install at mid-position. An interlock hose has a length range, not a length, and between compressed and extended that range can be fifteen to forty-five per cent.
- Never stretch to fit or crush into a short gap.
- If cut on site, restrain the cut end immediately — an unrestrained helix unwinds.
Storage and handling
- Store coiled at or above the static bend radius, off the floor, dry.
- Do not drag assemblies across concrete; the braid abrades and the fitting takes the load.
- Keep end caps on until installation. Most bore contamination happens in the store, not the plant.
- Do not lift by the hose. Lift by the fittings or with a sling under the body.
Failure modes shows what each of these rules prevents.
