A jacketed hose is two pressure boundaries in one assembly: a product hose inside, an outer carrying steam or hot oil around it. It exists for media that will not survive being allowed to cool — sulphur, bitumen, molten waxes, some polymers and resins, concentrated caustic in cold weather. Get the construction right and it runs for years. Get it wrong and you have two leaks instead of one.
What this service does to a hose
Two ratings, two certificates. The inner hose has a working pressure derated at the product temperature. The jacket has its own working pressure at its own temperature, its own relief, and its own test. They are not the same number and they should never appear as one figure on a datasheet. If the tracing is saturated steam at 10 barg, the jacket is a 184 °C pressure part.
The termination is the hard part. Everything difficult about a jacketed assembly happens in the last hundred millimetres at each end, where the jacket has to be closed off, the tracing has to be brought in and out, and the product flange face has to be left clean and accessible. A jacket that runs onto the gasket face makes the joint impossible to seal. A jacket terminated too far back leaves a cold length where the product sets first, and that cold length becomes the blockage.
The two boundaries move differently. Inner and outer are at different temperatures, so they want to be different lengths. Over a long assembly that differential has to be allowed for in the design, not discovered at commissioning.
Electric trace is the other route and is often the better one on short runs: a traced and lagged assembly with no second pressure boundary, no steam trap and no condensate to manage. It is less capable at high temperature and it needs power at the hose, but it removes an entire failure mode.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Inner hose | 316L or 321 annular corrugated, PTFE-lined where the product needs a draining bore | The product decides this; see the individual duty pages |
| Inner braid | Matching grade, sized on the derated product pressure | The product pressure at the product temperature, not the catalogue figure |
| Jacket | Stainless outer with its own inlet and outlet connections, rated and tested separately | It is a pressure part and is documented as one |
| Termination | Jacket closed clear of the flange face, with the trace connections positioned to your drawing | This detail is agreed before we cut, not after |
| Testing | Both boundaries hydrostatically tested at 1.5 × their own working pressure, certified separately | Two boundaries, two certificates |
What we would not fit, and what happens
A jacket over an interlock hose. Neither boundary is pressure-tight.
A jacket terminated onto the flange face. The joint will never seal properly and the fitter will be blamed for it.
An assembly with no way to drain the jacket. Condensate sits in the low point, the low point stops transferring heat, and the product sets exactly there.
A single test certificate covering both boundaries. They are different pressures and different tests. We issue two.
What we need to size it
| We need | Because |
|---|---|
| Product, product temperature and product pressure | It sets the inner hose entirely |
| The temperature the product must not fall below | This is the actual design requirement for the tracing |
| Tracing medium, its pressure and its temperature | The jacket is a pressure part and needs its own rating |
| Overall length, and the geometry including high and low points | Condensate collects at low points and the product sets there |
| Where the trace connections must sit, and the flange standard at each end | The termination detail has to be agreed before fabrication |
| Whether electric tracing is acceptable instead | It may be the better answer and it is cheaper |