Step one for safe hose assemblies is selecting components that meet your needs. Compromises in hose and component selection may create situations of danger as well as affect the performance and durability of the system.
An effective way to properly specify a hose assembly is to use the simple acronym STAMPED, which stands for the seven major information areas required:
Size — Inside diameter, length, any outside diameter constraints.
• Overall length, includes fittings.
• Tolerances if special requirements exist.
• Inside diameter of the hose must be adequate to keep pressure loss minimum, maintain adequate flow and avoid damage to the hose due to heat generation or excessive turbulence.
Temperature of the material conveyed and environmental conditions.
• Average, minimum and maximum environmental temperatures.
• Hose routing issues if hot manifolds or other heat sources; a heat shield may be necessary.
• There is a substantial pressure derating for both rubber and PVC hoses as the ambient temperature increases.
A pplication — the conditions of use.
• Configuration/routing. Is the hose hanging, lying horizontally, supported, unsupported? When routing up or down hills, specify any pressure calculations (feet of incline, etc.) or head pressure requirements; pull forces if vertical routing is included; any external load on the hose (other things attached); bend radius requirements, flexibility.
• Immersion in the material being conveyed.
• Intermittent or continuous service.
• Indoor or outdoor use.
• Unusual mechanical loads (vehicle traffic, etc.).
• External conditions — abrasion, oil (specify type), solvents (specify type), acid (specify type and concentration), ozone, salt water, ultraviolet (UV) radiation (sunlight), geographic temperatures (e.g., Alaska versus Louisiana).
• Non-flexing applications (static), flexing applications (dynamic).
Material or Media being conveyed, type and concentration.
• Any agency or special requirements that need to be considered (e.g., FDA, API).
• Media velocity, flow rate. Will the material be continuously flowing or sit in the hose for long periods of time?
• Weight of media (specific gravity).
• Chemical name/concentration (MSDS).
• Solids, description and size.
• Fluid compatibility — Specialized oils or chemicals conveyed through the system must be compatible with the hose materials and components (hose ends, o-rings, etc.).
• Corrosiveness of product, potential corrosiveness of mixed media (resulting from improperly cleaned hoses).
P ressure to which the assembly will be exposed (or vacuum for negative pressure)
• System pressure, including pressure spikes. Hose assembly working pressures must be equal to or greater than the system pressure.
• Temperature of the media or the environment the hose assembly is being used in will impact the system pressure.
• Maximum operating pressure the system should be exposed to in normal operating conditions. This pressure should be dictated by the relief setting of the system. Both the hose and hose ends should not be rated to a pressure less than the maximum operating pressure of the system.
• Pressure spikes — When a system is subjected to a large load in a short period of time, the system pressure can overshoot the relief setting and exceed the maximum operating pressure. Frequent pressure spikes can reduce the life of hose assemblies.
• Impulsing — Applications involving pressure changes (e.g., turning off and on) at a fast rate, usually many times per minute, may require specially designed hose.
• Vacuum requirements.
• Hose routing (will the hose be straight or bent for the application?). Some hoses will hold a vacuum while straight but will collapse if bent.
Ends — style, type, orientation, attachment methods, etc.
• Materials and dimensions (steel, stainless, etc.).
• Conductivity requirements.
• Attachment method (banding, crimping, etc.).
• Sleeves and ferrules.
• Impact of any pull forces, if vertical routing of hose assembly is anticipated.
Delivery — specific to customer requirements.
• Testing and certification.
• Special packaging.
• Special shipping.
• Tagging.
A properly specified hose assembly is the first step toward safe, reliable operations.
For more information, contact Debbie Mitchell at dmitchell@nahad.org or (410) 940-6361, or visit www.nahad.org.
