Diesel is the gentlest medium on this site. It does not attack stainless, it does not run hot, and the pressures on a transfer or day-tank line are usually under 6 bar. Assemblies on this duty fail for entirely unglamorous reasons: they get dragged across concrete, they get pulled on by the coupling, and they get fitted to a bowser where somebody uses the hose as a handle.
What this service does to a hose
Handling, not pressure. A genset day-tank line, a bowser delivery line or a fuel polishing loop spends its life being connected, disconnected and moved. The braid is what takes that abuse, and a braid that has been dragged on concrete has broken wires in it. Broken braid wires do not leak — they simply stop carrying load, and the corrugation underneath starts taking pressure it was never rated for on its own. A hose-only DN25 corrugation is rated 2.5 bar against 38 bar for the same hose braided. That is what the braid is doing.
Water and what grows in it. Diesel picks up water from condensation in tanks, and the interface between the two is where microbial growth lives. The organisms themselves do not eat stainless, but their metabolic products are acidic and they concentrate under a deposit. In a hose that is left full and static between uses, the corrugation valleys are exactly where a deposit sits. This is microbially influenced corrosion, and it is a pitting mechanism — see failure modes for what it looks like next to ordinary chloride pitting.
Static. Diesel is a low-conductivity fuel and pumping it generates charge. As with LPG, a welded stainless assembly is continuous metal end to end and bonds itself, which is one of the quiet advantages of metal over the alternatives on this duty.
Biodiesel blends are more polar and more hygroscopic than mineral diesel. They are still not a problem for austenitic stainless, but they hold more water, and more water means more of the mechanism above.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated. 304L is adequate on clean indoor duty and we will say so | 316L for anything outdoors, coastal, or left standing with water in it |
| Braid | 304 wire, double braid wherever the assembly is handled or dragged | The braid is the wear part on this duty, not the corrugation |
| Ends | Camlock, threaded or flanged; camlock where it is connected and broken daily | Match what is already on the tank and the bowser |
| Cover | External spring guard or a braid guard at the ferrules on dragged assemblies | It protects the transition where fatigue starts |
| Length | Long enough to reach with slack, and no longer | Excess length on a handled hose becomes something to trip over and drag |
What we would not fit, and what happens
Interlock hose. Not pressure-tight. It has a legitimate use carrying diesel-soaked air in a vapour recovery duct and none at all carrying the fuel.
Single braid on a bowser or a hand-handled line. It will survive the pressure and not the handling.
A hose used as a lifting point or a handle. The failure is always at the ferrule and it is always avoidable.
What we need to size it
| We need | Because |
|---|---|
| Where in the system it sits — suction, delivery, polishing loop or day tank | Suction duty raises collapse, which is a different question from pressure |
| Working pressure and the pump's dead-head pressure | A positive displacement pump can produce far more than its rating if it is deadheaded |
| Whether the assembly is handled daily or fitted and left | It decides single or double braid and whether we guard the ferrules |
| Whether the line is drained between uses | It decides the grade and whether we would use 304L at all |
| Fuel type — HSD, LDO, biodiesel blend, and the blend percentage | Blends carry more water, which is the mechanism here |
| End connections at both ends | Camlock families are not universal and half-couplings must match |