Hose Maintenance

Three steps to improved safety

By Patrick Kirk

All compressed gas and cryogenic hoses should be inspected on a regular basis. Remember, the goal is to replace the hose before it fails. This article covers PTFE, ETFE and “all metal” hoses only.

Discolorations on a hose indicate foreign matter coming in contact with the hose.

Not all hoses are constructed in the same manner. Added to that, compressed gas and cryogenic hoses are used in many different ways. It is important that you identify and address your critical applications first—high-pressure fill manifolds, tube trailer trans-fill systems and cryogenic transfer. There are a few basic maintenance steps that you can implement rather easily. In fact, a continual hose maintenance program will go a long way toward increasing the life of this important tool, while preventing the chance of serious injury or damage.

Conduct a Visual Inspection
Probably the most important thing that an operator can do as part of a maintenance program is a visual inspection. This should be conducted on a regular basis (daily, weekly or monthly, depending on the application and the useage/cycle rate). A continual visual inspection is the best way to identify and prevent a potential problem. Here is what you should look for:

Discolorations — Freckles, spotting or other markings are an indication of a foreign matter coming in contact with the hose. Often, freckles can occur from the use of a “leak check” solution. Typically, this is not a problem. However, it is crucial that leak check solutions be mixed to the manufacturer's recommended proportions. If the proportions are not correct, braid damage can occur. With ethylene glycol (a common substance used in oxygen-free leak check), the wrong proportions can negatively affect the stainless steel braid.

Kinking — A kink in the hose is an indication of over-bending, and/or over-stressing. This type of movement can compromise the overall integrity of the hose. Some fill manifolds provide no means of support for the cylinder. If the cylinder is bumped, quite often it is the pigtail or hose that stops the cylinder from hitting the ground. Unfortunately, this action will usually cause damage to the pigtail. If you find any kinks or severe bends, remove and replace the hose.

Braid Integrity — The stainless braid gives the inner core of the hose the ability to withstand pressure. There should not be breaks anywhere on the stainless steel braid. A single broken braid is a sign of a potential problem.

Inspect the Fittings — A simple visual inspection of the threads will tell you much. Look to see that the threads are uniform. You should not see any metal shavings or cross threads; if you do, remove and replace the hose. A bad thread typically will leak under pressure. Thread gauges can be purchased to ensure that fittings are in specification.

Kinks and bends compromise the overall integrity of a hose.

The above hose burst as a result of residue buildup that chemically attacked the stainless steel braid.

Pressure Test and Leak Check
It is very important to leak check the hose and fittings under pressure for any signs of leakage. Leak check solutions are commonly available and work very well under pressure. It is crucial that you not only use the correct solution, but that you mix the solution to the manufacturer's recommended proportions. Failure to do so can cause damage. Keep in mind, not all leak check solutions work for every gas service. Check with your supplier to make certain you are using the correct leak check product.

Often, a leak check is conducted while the hose is attached to the fill manifold and under pressure. The best (and most expensive) gas to use for a leak check is helium. Helium works well because the molecule is very small. As a result, helium will find a leak better than most other gases. Keep in mind that this can get a little expensive, so other inert gases can be substituted. I do not recommend compressed air or any other gas that could contain impurities.

Replace Old Hoses
All too often, hoses are overused. Contrary to popular belief, hoses do not last forever. Every high-pressure hose has a life expectancy. This is typically based on the amount of service the hose has provided and the manner in which it has been used. A good rule of thumb is a hose that sees 18 cylinder changes per day, five days a week, will operate safely for approximately 18 months. At this rate, the hose will have been connected and disconnected 12,960 times. Provided that the hose has not been abused in any other way, this is a good point of reference. The chart below can help you determine when a hose should be changed out.

This break on an all-metal hose was caused by high-velocity gas flow.

Keep in mind, hoses attached to a fill manifold can be connected and disconnected up to 20 times a day. This equates to 9,600 changes per year. At an average cost of $20 per pigtail, this tool is costing pennies per changeout.

Tube trailer hoses can get banged around and bent in a myriad of configurations. It is important to inspect all cryogenic hoses for leaks on a regular basis.

How do you choose the right hose for the right application? Patrick Kirk explains in Hose Selection 101.

One of the most common problems associated with cryogenic hose is exceeding the recommended velocity. If you exceed the recommended velocity, damage will occur.

Don't assume that just because a hose is being used for a particular application, it is the correct hose. Make certain you are using the right hose for a particular application.

To sum up, a regular hose maintenance program is a great idea. Simply conduct regular visual inspections of the hoses that you use. Perform pressure tests to ensure the hoses are in good condition. Any hoses that fail these two tests should be removed and replaced. Track the cycle rate of your current hoses and replace as required. With these three simple steps, you can maximize the life of your high-pressure and cryogenic hoses, while adding a new layer of safety for your employees and customers.