Hose foes
Are you using the right hose or tubing?  Is it laid out correctly?  Is it subject to abuse?  Know the facts to avoid premature failure and a huge mess.

If anything in your plant moves through flexible tubing or hose, imagine the outcome if that tubing or hose ruptured.  What would be the total cost in human suffering, lost material and productivity, any legal and governmental (such as OSHA or the EPA) ramifications, and your company’s insurance rates?  What is hose and tubing safety worth to you and your company?  Probably more than you realize.

Hose and tubing manufacturers can predict the life expectancy of their products under normal conditions.  But unexpected conditions and accidents cause premature hose and tubing failures.

Why do hoses and tubing fail prematurely?  The biggest problems are misapplication and abuse, but they certainly aren’t the only culprits.  Here are some things to watch for to avoid becoming a hose killer.

Use the right hose for the job
Hose and tubing manufacturers publish the properties, limitations and suggested applications for their various products.  Nevertheless, hose and tubing still are used in inappropriate circumstances.  Although this may not be immediately apparent, if you’re replacing hoses far more frequently than the manufacturer-stated life expectancy, or if a hose suffers a catastrophic failure, that’s a “red flag.”  Perform an analysis of the properties of the material being transferred before you place your next hose order.

Closely inspect the failed hose or tubing.  Does it appear that the hose or inner tubing material dissolved, or became brittle or cracked?  Did the hose or tubing contents leak through and cause the hose cover to blister or swell?  Is there rusted wire or worn, frayed fabric reinforcement around the area of the failure?  All of these are symptoms of an incorrect application, and deserve attention.

Sometimes, someone not attuned to the subtleties of hose performance will use “that piece of hose from the store room” for the wrong application, or run different, damaging material through hose or tubing not designed to withstand the “new” material.  If you stock and use hose for a specific purpose, always label it clearly to reduce the risk that someone will innocently misuse it.

Color-coding only works if everyone knows the code.  It’s better to label the hose’s contents and the direction of travel.

The many faces of abuse
Abuse takes many forms, from a deep cut or slice in the covering material, or constant abrasion against a non-insulated bulkhead opening, to being dragged along the floor or run over by a forklift.  It can be as subtle as incorrect storage or careless handling before installation.

Overpressure drastically shortens the life of a hose or tube, if it doesn’t first cause a catastrophic failure.  Select hose or tubing rated to withstand the spike or surge pressure, not just the working pressure.  While it’s true that hose manufacturers understate their hose maximum pressure, you cannot rely on that margin to handle your pressure spikes; that margin may deteriorate as the hose ages.

When choosing a hose assembly to be used in suction applications, be certain the hose you choose carries a sufficient suction rating.  Failure to choose properly may result in hose collapse and subsequent equipment failure.

Excessive heat hardens or melts the hose or tubing components and leads to rapid failure of the assembly.  Be conservative when you select a hose’s temperature limit.  The heat ranges quoted by the manufacturer may not apply to all materials that the hose or tubing handles.  Any ambient temperature extremes must also be accommodated.

Respect the bend radius limitations of the hose or tubing.  Bend radius is measured at the inside of the curvature.  A kink in the hose or tube may not be outwardly visible, but it can seriously damage the hose or tubing.  If you change hose types, will the new product be compatible with the old routing?  Selecting a hose assembly not designed for a tight bend is an invitation to failure.

Design the hose run to prevent or minimize hose assembly twist.  Hose twist distorts and weakens the tubing material as well as the reinforcement, and can reduce hose life by up to 90 percent.  Use the layline as a guide when you install it.  If your hose bends in normal use, be certain the range of motion causes the hose to flex in only one plane.

Hose and tubing grow and shrink with temperature, pressure and age.  If you custom fit a hose assembly, be sure to allow for hose growth, shrinkage and the movement that accompanies both.  Allow a cut-off factor appropriate for the type of end fitting, at both ends when you’re estimating or measuring hose to be cut.  If the hose assembly is too short, separation at the coupling is a possibility.  If it’s too long, there’s potential for chafing damage.

On the subject of movement, if chafing and abrasion are likely or unavoidable, purchase hose with a covering, such as braided nylon or polyurethane compositions, specifically designed to endure the punishment.  If the potential for abrasion is high, consider installing a supplementary covering such as round-wire or flat-wire spring guard or protective abrasion sleeves.

A crushed or kinked hose that exhibits an outside dimension (OD) reduction of less than 20 percent indicates internal damage.  Remove, inspect and test it before returning it to service.  An OD reduction of 20 percent or more indicates severe damage.  Replace such hose or tubing.  This damage is usually caused by driving over the hose assembly with heavy equipment.

Use end fittings suggested by the hose or tubing manufacturer for the best compatibility.  More important, both parts of a coupling should always be the same design from the same manufacturer.  Small differences in design from different manufacturers result in leakage, or an outright connection failure.

An ounce of prevention
Fortunately, the road to accident prevention is well-known, and paved with regular inspections coupled with scheduled maintenance and part replacements.

Your insurance carrier may already have a program in place within your company, or you may wish to consult with your hose distributor for recommendations.

Because many government oversight agencies require recording and reporting as part of the program, some companies are outsourcing these responsibilities to professionals, such as Boston’s Certified Chemical Hose Distributor (CCHD) product and service package.

If you perform your own inspections, or make decisions regarding scheduled maintenance and replacement, get familiar with your hoses.

If the hose or tubing came installed on a piece of equipment, the best source of information is the equipment’s operating manual.  Manufacturers know the limitations of the hose or tubing on their equipment, and they benefit from the collective experience of other owners.  If the manufacturer sees a recurring problem, it is the best source for inspection, maintenance/replacement and corrective action.

If the hose or tubing is part of a custom installation, you can turn to several sources for help.  A popular source is your hose distributor.  Reputable hose and tubing manufacturers have data and recommendations available for the asking.

The Rubber Manufacturer’s Association “Hose Handbook” is another reference resource.  The RMA also publishes technical bulletins that target hose applications.

Article provided by Boston Weatherhead Division of Dana Corporation.  Writers include Howard Aspinall, product specialist; Bill Harr, product manager; Lisa Headley, technical support manager; and Dave Wall, marketing specialist.

This article appeared in the June/July 1999 issue of MRO Today magazine.  Copyright, 1999.

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