By W.E. Currie, PE
There are two types of usage for hose assemblies in maritime service that run into two rather unrelated groups of problems. In one usage, the assembly is more or less built in, so that it sees the same general type of service all the time. An example is the hose assembly in a hydraulic system, where the pressure, flow, temperature, and idle time may vary greatly over time, but the assembly is not moved from place to place or put into a different situation. The other usage is when the assembly is taken out of storage and put into use wherever it is needed. Here the obvious example is the transfer hose assembly used for fueling or defueling, then used for liquid cargo transfers, and then pumps seawater.
I don’t know that there is a good term that adequately covers each type. In this article, I will refer to the first as a "fixed" hose assembly and the second as a "utility" hose. A more important point in terminology is to be sure when the word "hose" refers to the flexibility member alone versus when it refers to the whole unit, including hose fittings (couplings?), which is better termed a "hose assembly."
A real problem can arise when one person says "hose" and other understands "hose assembly".
Fixed hose assemblies have a reputation for unreliability in some circles, yet there are many applications where they consistently outlast the machine they are on. I have hurt a lot of feelings the last forty years by telling people that hydraulic control hose failures are always traceable to flawed engineering. Nevertheless, it is the simple truth, once we delete the actual defects. Every supplier’s catalog gives the limits of what each hose will take, and also reminds the user of such things as to allow a little slack so it won’t self-destruct when pressure is applied. I won’t bore you with the list. It’s an industry standard in every catalog. I will touch on what I consider the most baffling misuse, which is planning the installation to bend tighter than the minimum bend radius listed. Even the village handyman knows not to overstretch the spring on a screen door. I cannot comprehend why a graduate engineer will go to one-quarter of the minimum radius, sometimes much less, but not even consider it a factor when hose after hose fails there. This is one reason I spend more time looking than listening when on a trouble call. There really is a reason for the radius specification. In layman’s terms, bending tighter cramps the wires too much and makes them fail early. You know, that is about as flawed as engineering can get.
It doesn’t take an engineering degree to generate technical blunders. I have plenty of "war" stories about operating personnel who knew a little less than they thought they did. Here are a couple.
An innovative hydraulically operated oil assembly dripped oil where the hose went into one fitting after three years operation. The superintendent barked "Get a new high-pressure hose". That’s what the purchasing agent ordered. He really did. I saw the order when I was called in to determine why the new assembly blew off a hose fitting after two hours and started a million-dollar fire. These were two inch hoses coming off a 500-gallon pump. Sure enough, the hose assembly that was replaced was what we call four heavy spiral, this size rated for operation at 2500 pounds per square inch (psi), while the new one was double braid rated at 1125 psi. The supplier said he did his best. He did supply the very highest-pressure hose assembly from his stock. I can’t say much for his imagination. It turned out that the system pressure was too high even for the first hose. That is why the leak in the first place.
The second tale concerns a storage compound located between an oil refinery and a salt water inlet. After some years of operation, someone hooked a 1 ¼" delivery hose assembly up to the main delivery piping, which was about a mile long and mostly eight inch diameter. Tugs calling for diesel fuel tied into the small line and had the fuel pumped in by someone nudging the on-off switch to the pump ‘way back on the other end of the main line. An observer down at the tug directed the operation by telephone. Amazingly, this apparently worked well until the two workmen had a spat. The next time the pumper got a call to fuel a tug, pumping was hampered by a big air bubble in each of two spots where the pipe was raised up to clear a road, and the fuel refused to start with the usual moderate nudging. After some nasty words had been exchanged, the pumper turned her on full and swept out the bubbles. Once the fuel squeezed these out, it was going at a pretty good clip – all FORTY TONS of fuel. When the impact reached that little hose assemble, it wasn’t about to stop. Once again, blame the hose.
But fixed hose assemblies don’t really get the mususe that utility assemblies do. There is not much opportunity. When either type fails in any fashion, there are some things to check automatically. Examples: The right fittings put on right, all the numbers in the catalog and spec, a fluid that won’t attack the material, no twisting or kinking (look at nearby assemblies). There are further things to check with the utility hose assembly, because the damage may have occurred in some different service at a different time, even during storage. The weakened assembly may then have failed in light service. Lab personnel are familiar with this phenomena, where running something almost to failure will often cause it to fail early when it is then given the full test. (Incidently, this is why it is pointless to burst test a sample from a hose that has already burst).
The brake hose assemblies in your car undergo far more severe service than a utility hose does (or should), yet they stand up.
Uncertainty is the extra in the background of utility hose assembly failures. The varying service and storage create quite varied deterioration, more likely to add up against the assembly than not. In addition, the history of any one assembly may be forgotten. Some probably draw more than their share of the rough jobs. Finally, if it isn’t discarded till it fails, why complain when it does?
So, what ate the problems with utility hose assemblies? Really, just the same as with the fixed, except that all of the previous uses have to be looked into, not just the one that supposedly caused trouble. Whenever we think of hose assembly problems, we should think of the two sides of the coin. One side is an actual failure. What happened? Was it defective? Was it abused? (I’m not discussing defects here except to say that they can generally be found if the evidence is preserved). The other side of the coin is the failure that might happen to a new assembly if it is misapplied, badly installed, abused in service or storage, and certainly if it starts out defective.
The first is the bad side. Trouble occurred, maybe big trouble. The other is the good side of the coin because trouble really will not occur with good hose assemblies when the problems are understood and acted upon.
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