Hose assembly safety surveys
Hose assemblies in manufacturing or processing plants can sometimes be the source of equipment malfunction, dangerous product spills, or serious personnel injury. With today's increasing need for faster and quicker fluid transfers, the demands being placed on hose assemblies are greater than ever due to increased working temperatures and pressures that can easily diminish their containing power.
Hose assemblies in manufacturing or processing plants can sometimes be the source of equipment malfunction, dangerous product spills, or serious personnel injury.
With today's increasing need for faster and quicker fluid transfers, the demands being placed on hose assemblies are greater than ever due to increased working temperatures and pressures that can easily diminish their containing power.
Hose assemblies can be made to fit practically any fluid transfer application, but care must be taken to select the correct hose, fittings, and attachment method.
Too often, hose assemblies are put into a place or service improperly. The very properties that make hose assemblies so convenient — light weight and flexibility — can also make them difficult to maintain.
In dealing with these concerns, plant maintenance engineers, safety directors, and facilities managers have an ally in hose distributors and manufacturers. Some offer inplant hose assembly safety surveys to help identify conditions that could pose risks to plant production or safety. Some of these programs are offered free of charge.
The process begins with a visit from a technician from the hose distributor or manufacturer's representative. The technician tours the facility, determines the resources that will be required to conduct a safety survey, and meets with maintenance and safety personnel to introduce the concept and answer questions about the survey process.
Next, a safety team is formed, made up of hose and fittings experts, usually the rubber/hose distributor, plus a technician from the coupling manufacturer. Plant personnel are also assigned to the team, bringing an intimate knowledge of the plant facility and its maintenance history.
During the survey process, the safety team walks through the plant, viewing and noting hose applications and assemblies. The survey methodology utilizes the acronym STAMPED (size, temperature, application, media, pressure, ends, and delivery) as the basis for the review of hose assemblies. The locations of any potential areas of concern are pinpointed, and photos are taken to help document the findings.
Once completed, the survey results and any recommended corrective actions are submitted in a formal, written document. In addition, suggestions are provided concerning the storage, inspection, and testing of hose assemblies.
Many of these recommendations are based on guidelines issued by the Rubber Manufacturers Association and National Association of Hose Accessories Distributors.
Over the years, hose assembly surveys have uncovered a variety of potential concerns and risks. Among the more commonly found conditions are:
Broken or missing cam arms on cam & groove couplings
Damage to protective hose coverings caused by vibration
Kinks in hoses, resulting in diminished flow/pressure ratings
Use of couplings or gaskets that are the wrong material for the product being conveyed
Selection of couplings that is not designed or suitable for a particular service.
Two-inch metal hose with cam & groove-type fittings used for steam service (Fig. 1). This type of coupling should never be used for steam service. When the cam arms are opened, the coupling will separate instantaneously. The resulting burst of steam is extremely dangerous.
A steam fitting must have a thread adapter and wing nut to be safe. When loosened, it leaks, serving as a warning that the line is live and under pressure.
Bolt-style clamps need attention (Fig. 2). When installing a bolt-style clamp, it is important to know that the body sections of the clamp should never be allowed to contact each other. There must always be an even showing of hose between the clamp sections to ensure a proper installation.
Bolt-style clamps must be tightened to recommended torques. The bolts will bend during tightening and can be retorqued, but they should never be reused. When clamp halves are removed from a hose, they should be discarded.
Band-style clamps improperly installed (Fig. 3). To achieve proper retention and sealing, these clamps must be properly installed. When multiple clamps are used, the buckles must be offset around the hose to eliminate straight line leaking under the buckle areas. Do not bend excess banding material over the buckle; this leaves a sharp exposed edge to the operator.
Worm gear clamps with tangs protruding (Fig. 4). Worm gear clamps provide an excellent means of holding fittings on a hose used for low-pressure air or water service. They can be hazardous when excess material protrudes from the clamp housing, posing a safety hazard.
Tape used to repair a hose assembly or protect hands (Fig. 5). Taping hose or fittings, for any reason, is unacceptable. If a hose is damaged, it should be replaced. Taping, while offering some hand protection, hides the area most susceptible to damage from visual inspection.
Tape and other expedient measures used to secure cam arms . Securing cam arms in the closed position by means of tape wire, string, etc., may be a step in the right direction. However, lockable cam arms designed for this are available. Partially or fully open cam arms are dangerous.
Universal air coupling missing safety pins . Some couplings do not incorporate a built-in safety step feature. This safety step, located under the ears of the coupling, is designed with a 90-deg. edge that, when mated with the same edge on the opposing part, reduces the possibility of accidental uncoupling
In any case, all universal air couplings must be used with a safety pin in place. This simple step ensures positive locking and eliminates the possibility of the assembly coming apart during service.
Improper clamping on steam hoses . Steam hose should never be coupled with a permanent clamping device such as a band clamp or ferrule. There is no way of servicing the hose following installation. An interlocking bolt-style clamp that can be retightened is appropriate because of the cold flow of the rubber hose. When a coupling is clamped to a hose, the tube and cover will continually flow away from the area of stress, leaving an assembly that is inadequately torqued. Many manufacturers feel compelled to install a label on their steam hose that states: tighten clamp before using.
While many of these conditions can be easily corrected, the potential risk to the plant is serious, as each of these clearly represents an accident waiting to happen. The wrong hose in the wrong application can result in serious damage to equipment or injury to the operator should the hose assembly fail.
A good hose safety program does not end with the survey recommendations. Training sessions should be set up, survey findings presented, and best practices outlined for future selection, installation, and maintenance of hose assemblies. The end result: better operational efficiencies, reduced risk of hose assembly failures, and enhanced worker safety.
A case study
Results of a typical survey reveal many of the problems commonly encountered. This survey was conducted for a large processing facility that manufactures biochemicals and organic chemicals. This plant works with a variety of media including: nitrogen, glycol, various solvents, water, air, and steam. Working pressures range from 26 psi to 100 psi.
During the survey many proper applications were noted. Among them were the practice of tagging and dating hose, tagging hose to be taken out of service, proper hanging of stored hose, as well as selective use of locking cam and groove mechanisms.
There were several potentially dangerous conditions noted and remedies recommended.
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