Braided hose failure

A hose assembly in fluorine service failed because of forming a leak (Fig. 10.38). The hose consisted of a PTFE tube (liner) at its core which had been reinforced with a stainless steel braiding. The failure occurred in the PTFE tube below and near the lower edge of the collar, away from the joint. The failed hose handled fluorine that had been diluted by a neutral gas. A lengthy analysis was performed to determine the cause of the failure because of the safety concerns about fluorine service. 

A PTFE-lined, stainless steel braided hose was used to transport sulphur trioxide at a chemical plant. The hose was attached to an external tank system and was insulated and heated. One day the hose failed and sulphur trioxide leaked and caused serious environmental problems. The failed hose had one long axial crack that had split the hose open, which allowed the liquid to be released. The engineering assignment in this case was to examine the cause of the failure. 

Plastic nuts are commonly used to fasten water transport hoses to toilets, sinks, and other plumbing products. Figures 15-4-5 and 15-4-6 show a typical failure of a plastic water nut at the end of steel braided hose. The nut shows a circumferential crack that extends completely around the nut. The circumferential crack is located at the last or bottom-most thread inside of the nut. This is the area where the stresses are higher during tightening after the nut has topped out with the mating piece. 

Flexible Metal Hose Deeply corrugated thin brass, bronze, Monel, aluminum, and steel tubes are covered with flexible braided-wire jackets to form flexible metal hose. Both tube and braid are brazed or welded to pipe-thread, union, or flanged ends. Failures are often the result of corrosion of the braided-wire jacket or of a poor... 

CNG dispensing hose uses an impervious inner tube reinforced by a braided over-wrap of stainless steel wire. The inner tube can be teflon or a similar material that is not porous and will not become overly stiff in cold weather. An unusual problem that can occur with high-pressure hose is that if static electricity builds up inside the hose, it may discharge through the hose to the wire reinforcement. When this occurs, a small hole is formed in the inner tube that quickly leads to a leak through the wire reinforcement. Such incidents are rare, but they do occur, caused by the non-conducting properties of the inner tube. There have been no reported incidents of such failures in CNG dispensing hoses. 

Swing lines made up of pipe with flexible joints and provided with a counterbalance is the preferred method of transferring hazardous chemicals into or from a tank vehicle. Hoses, no matter how thoroughly reinforced, have lower pressure capability and are easily damaged in use. Rupture of transfer hose is a not uncommon cause of employee injury or spill of product. Metallic tubing with braided exterior has admirable qualities, but a sharp bend, particularly near the end, causes weakening and failure, which is often neglected before the failure. 

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