Hose design factors
NAHAD’s Hose Safety Institute is committed to hose assembly Safety, Quality and Reliability. The Institute provides industry-leading hose assembly specification, fabrication and design Guidelines, employee training resources, online exams and powerful marketing tools to help members build stronger relations with their current and potential customers. The Institute is served by an Advisory Council of major end-users, academics and industry leaders who work with NAHAD members to address critical hose assembly practices and safety issues.
NAHAD HOSE SAFETY INSTITUTE WHITEPAPER: Hose Design Factors
Editor: D. Mitchell (see Participating Companies in this paper for a list of contributors) Hose Safety Institute©, NAHAD – the Association for Hose & Accessories Distribution, Inc., Annapolis, Maryland
This whitepaper represents an on-going effort to document best practices for ensuring safety and reliability of hose assembly applications. It is intended to represent the consensus of contributing companies and organizations as to the recommended best practices regarding hose design factors, subsequent hose labelling, and implications for end user safety. Topics addressed include:
• Definition of Hose Design Factors, what they mean, and implications for fabricators and end users of hose assemblies
• Technical information on hose testing to clarify the differences between different design factors (e.g., 3:1, 4:1, 2:1) – and subsequent implications for hose assemblies
• Examples and test data illustrating the implications of hose design factors on advertised hose working pressures
• List of guidelines for manufacturer hose labelling and associated documentation
• A list of definitions to clearly spell out what is meant by different terms or labels
Market trends – manufacturers and importers are offering hose constructions that may not meet the Association of Rubber Products Manufacturers (ARPM) standards (listed on page 8) opening the door for a “buyer beware” environment. Fabricators and users of hose assemblies need a clear understanding of what they are specifying, purchasing and how it will perform. Hose design factors in line with ARPM standards are intended to provide clear guidance for the design, specification, fabrication and testing of subsequent hose assemblies and what can safely be expected for assembly usage.
Hose design factors need to be clearly identified and documented, supported by appropriate testing and verification. End users and consumers of hose assemblies need to understand the implications of hose design factors, and ask the right questions of their supplier(s) to make sure they receive what their application requires.
Competitive pressure on hose pricing is driving companies to deviate from industry standards published by organizations such as the Association for Rubber Product Manufacturers (ARPM) for hose design factors, potentially creating safety issues.
Hose assemblies designed and fabricated based on misleading hose design factors have the potential to create serious accidents affecting worker safety, user operations, and environmental issues through things like spills of toxic materials, and related concerns. Applications with severe safety and personal injury implications, compounded by intense regulation, ups the stakes considerably.
This white paper is part of a comprehensive approach to improve worker safety and environmental stewardship through driving a clear understanding of the capabilities of the primary component of hose assemblies – the hose. Hose couplings and fittings will be addressed inasmuch as fittings should be rated to a minimum of the maximum working pressure of the hose assembly unless application requirements dictate otherwise.
Intended benefits of this paper include:
• Providing a common lexicon – ensuring that the hose industry and the end user understand what the other is referring to
• Helping end users get the right hose for the application – and understand the variables involved
• Understanding the criticality of pressure ratings – investment up front in purchasing the right hose for the job will be cheaper than the costs downstream of cleaning up a spill or dealing with an accident; regulatory issues/costs can be hugely important and relevant
Implications for the industry:
• Top line impact – Clients are attracted to vendors who can provide service in the most safe, environmentally sound and cost efficient manner. Providers who can demonstrate processes and strategies which insure the highest standards of hose integrity will gain more business opportunities and consequently grow their top line revenue.
• Bottom Line Impact – Injuries, environmental impacts and downtime due to hose failures lead to costly direct and indirect expenses, including liability insurance claims and subrogation, which will erode any top line revenue gains. Hoses that have higher integrity – and serve their intended purpose – protect profits.
• Environmental Impact – In certain applications, hose failures can lead to environmental losses which can range from relatively minor to reportable quantity (RQ) level. RQ losses can significantly impact the environment and lead to EPA inspections, regulatory penalties, fines and work delays.
• Human cost – Employees who work for companies with strong hose management programs enjoy higher confidence in their equipment which leads to higher morale and productivity. In certain applications, hose failures can lead to significant injuries, restricted or lost workdays and large medical costs.
This whitepaper can be added to over time, and delineates recommended best practices to provide guidance to end-users, distributors, manufacturers, and others involved in this business.
• Hose assembly fabricators and accessories distributors
• Hose manufacturers and manufacturers of affiliated products
• Client sales and purchasing personnel
• Risk Management Managers
• Environmental Health & Safety Managers
• Client Maintenance Managers
Scope: This paper is chiefly focused on industrial hose, and will not address hydraulic, composite, corrugated metal or fluoropolymer hose. It will also not address Hose Design Factors specifically addressed by other groups and/or standards bodies such as API, SAE, ISO, or specialized applications such as LPG, Anhydrous Ammonia, or Waterblast/Hydroblast applications.
Note: Higher design factors may not always translate into longer service life in an application. Once the hose becomes fatigued to the point of failure it can fail at a much lower pressure than it was “designed” for. This results from how each assembly is used in any specific application and is impacted by more parameters than can be put into this white paper (e.g., temperature, pressure pulses, damage, storage conditions, length of time the hose was stored before put into use, and more).
NAHAD and ARPM recommend minimum design factors as listed on page 8.
The published working pressure or working pressure branded on a hose or assembly may not be a correct indicator of the actual working pressure of the hose or assembly based on industry design factors. Hose manufacturers, suppliers and fabricators should communicate any exceptions to current industry standards; otherwise, the end user customers cannot be certain that the hose assembly will perform as required.
Always use a coupling and attachment method that is rated to the actual working pressure of the hose.
If not, the actual working pressure of the assembly should be indicated based on the lowest rated component of the assembly.
ARPM – Association for Rubber Products Manufacturers; formerly the RMA Engineered Products Group
Burst – a rupture caused by internal pressure; the destructive release of hose pressure.
Burst Pressure – the pressure at which rupture occurs.
Burst Test refers to a destructive test that determines at what pressure the assembly fails, and whether the finished assembly meets appropriate design factors.
Design Ratio or Factor – a ratio used to establish the working pressure of the hose, based on the burst strength of the hose; the higher the ratio, the less risk the end user assumes that the hose will burst at the specified working pressure. (Ex: a hose with a minimum burst pressure of 600 psi and a design factor of 4:1 would have a maximum working pressure of 150 psi.)
Hose Assembly – a general term referring to any hose coupled with end fittings of any recommended style attached to one or both ends.
Hose Assembly Components
• Hose – a flexible conduit consisting of a tube, reinforcement, and usually an outer cover
• Coupling – also known as “fitting” – a device attached to the end of a hose to facilitate connection
• Attachment – the method of securing a coupling (end attachment) to a hose (e.g., band, crimp, bolt clamp, etc.)
Hose Assembly Working Pressure – pressure to which a hose assembly is subjected; application dependent and impacted by a variety of factors such as temperature, impulsing, etc.; cannot exceed the maximum working pressure of the lowest rated component of the assembly
Hose Labelling conventions and abbreviations
• Lay line: runs the length of the hose with information to assist in the re-ordering of an existing hose. May include the manufacturer, part number and the size (inside diameter), designed application (e.g., air, suction), maximum working pressure, industry standards that the hose meets and the manufacturing date.
• BAR, PSI, MPa: refers to the units of pressure used to rate the hose
Note on testing: Hose and hose assembly testing are done for a variety of purposes, primarily to “prove” that the product or finished assembly meets the requirements of the purchaser. For hose assemblies, testing is generally geared around the lowest rated component in the system being tested, plus some Fitting Assembly safety factor; clearly defining that safety factor, what’s correct, etc. is a key part of the process and should be clarified.
Hydrostatic Proof Test – see “Proof Testing”
Hydrostatic Burst Pressure Test (Destructive) – indicates at what pressure the hose assembly fails (the hose bursts, or the fittings come off or leak); done by increasing the pressure in the test equipment until the hose bursts; refer to industry standards such as ISO 1402 and ASTM D380
Material Safety Data Sheet (MSDS) – see “SDS”
• Rated or System Working Pressure: the maximum pressure to which a hose will be subjected, including the momentary spikes in pressure, which can occur during service. Abbreviated as WP
• Surge Pressure (Peak): maximum pressure spikes seen by the system
• Burst Pressure: hose burst pressures are a multiple of the rated working pressure per specification
• Maximum Working Pressure (MWP): the maximum pressure at which a hose or hose assembly is designed to be used
• 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; typically, hose with a lower design factor will fail earlier during impulse testing; discuss specific needs with the hose manufacturer
Note on Pressure: hose selection must be made so that the published maximum working pressure of the hose and fittings are equal to or greater than the maximum system pressure. The maximum working pressure of a hose assembly is the lower of the respective published maximum working pressures of the hose and the fittings used. Surge pressures or peak transient pressures in the system must be below the published maximum working pressure for the hose. Surge pressures and peak pressures can usually only be determined by sensitive electrical instrumentation that measures and indicates pressures at millisecond intervals. Mechanical pressure gauges indicate only average pressures and cannot be used to determine surge pressures or peak transient pressures. Published burst pressure ratings for hose is for manufacturing test purposes only and is no indication that the product can be used in applications at the burst pressure or otherwise above the published maximum recommended working pressure.
Proof testing – refers to testing that “proves” the finished hose assembly meets the pressure rating required by the application for which it will be used, and that the end fittings have been correctly fitted and the assembly is leak free. Hoses are typically hydrostatically tested at Working Pressure, 1.5x Working Pressure, and up to a maximum of 2x Working Pressure; proof testing above 2x WP is considered by most manufacturers to be detrimental to the integrity of the hose assembly. For hose with a design factor of 2:1, testing at 1.5x WP may impact hose assembly integrity in the field. NAHAD’s Hose Safety Institute recommends proof testing industrial hose assemblies at 1.5x WP.
A hydrostatic test is a way in which the hose is tested for strength and leaks. The test involves filling the hose with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressurization of the hose or hose assembly to the specified pressure in the relevant product standard or other literature.
Rate of Rise – the rate at which the pressure is raised during a burst test; 1000 psi/minute for hose with a burst pressure less than 2000 psi, and 10,000 psi/minute for hose with a burst pressure greater than 2000 psi is the ASTM D380 accepted rate (raising the pressure at a faster rate can result in higher burst pressures, conversely raising pressure at a slower rate can result in lower burst pressures, both of which are very misleading); pressures are normally measured at ambient (room) temperature.
Safety Data Sheet – or SDS as referred to by OSHA – A document containing information and instruction on hazardous materials present in the workplace; SDS’s contain detail about the hazards and risks associated with the substance and the requirements for its safe handling as well as actions to be taken in the event of fire, spill, or overexposure.
Safety Ratio or Factor – see “Design Ratio or Factor”
Temperature Derating – Pressure ratings of hose and hose assemblies are typically done at room temperature. There is a substantial pressure derating for both rubber and PVC hoses as the ambient temperature increases. Higher temperatures, both of the media or the environment the hose assembly is being used in, will impact the system pressure and need to be accounted for. Hose design factors should be considered in conjunction with temperature derating as part of the assembly specification process. Please contact manufacturer for temperature derating details.
HOSE DESIGN FACTORS
Hose design factors specify the relationship between the maximum working pressure (psi, MPa, etc.) at which the hose is rated to operate and the pressure at which it is likely to burst. For example, an industrial hose rated at 250 psi with a design factor of 4:1 will typically burst if subjected to pressures of 1000 psi or higher. The design factor is intended to provide a margin in order to avoid unplanned hose bursts typically caused by a spike or sudden surge in pressure, or an increase in internal or external temperatures.
Hose design factors typically influence the construction of the hose, and may impact factors such as longevity of the hose, hose bend radius, durability of the hose in various applications, tendency of the hose to elongate, contract, twist, or kink. These are all factors that need to be taken into consideration when specifying the appropriate hose (and the appropriate design factor) for the application.
It is crucial that these design factors be known and documented up front in order that appropriate specification and testing of the hose assembly can be done. For example, 250 psi hose with a 3:1 design factor will typically burst if subjected to pressures of 750 psi or higher – without knowing the design factor, the fabricator or user might assume a burst pressure of 1000 psi, which could lead to improper specification of that hose for a particular application, or dangerous usage in the field. For applications other than those listed below, the application dictates the required design factor; the consumer needs to ask/understand which design factor is appropriate given the application.
NAHAD and ARPM recommend the following minimum design ratios for newly manufactured hose:
• Hose for the delivery of cement, concrete, plaster and grout, 2:1
• Water hose up to 150 psi WP, 3:1
• Hoses for all other liquids, solid materials suspended in liquids or air, and water hose over
150 psi WP, 4:1
• Hoses for compressed air and other gasses, 4:1
• Hoses for liquid media that immediately changes into gas under standard atmospheric
• Steam hose, 10:1
• Other industry design ratios exist – contact your Hose Safety Institute Distributor
ARPM requires that hose working pressures include a design factor commensurate with their intended application. Most hoses are required to meet a 4:1 design ratio, except the following: Water hose rated under 150 PSI requires a 3:1 design ratio; Steam hose requires a 10:1 design ratio; and hose conveying gas in a liquid state requires a 5:1 design ratio, or otherwise controlled by other industrial standards. (For example: a 150 PSI-rated air hose has a 4:1 design ratio and must be successfully burst tested to a minimum of 600 PSI.) Never exceed the maximum working pressure of the lowest rated component in the hose system. Maximum working pressure includes the highest pressure the system will experience, such as spikes, surges, and water hammer effects. (For example: If a system consists of a hose rated to 150 PSI and the couplings are rated to 500 PSI, the system should never be used in excess of 150 PSI.)
NAHAD recommends a 4:1 design factor (with the exceptions noted above), however we acknowledge applications not specifically listed in the above ARPM chart may be addressed by hose with a design factor other than those listed. Applications dictate the appropriate design factor.
ARPM has traditionally focused only on rubber hose; the NAHAD Hose Safety Institute HANDBOOK and related materials define industrial hose more broadly than just rubber, to include plastic, thermoplastic, etc. ISO has recently released a report confirming a 4:1 design factor for textile reinforced plastic hose for compressed air applications.
HOSE LABELLING AND HOSE CATALOG CONVENTIONS: BEST PRACTICES
Lay Line – descriptive information included on the body of the hose; may include:
Manufacturer logo, series #, construction type, WP, relevant standards, Made in [Country of Origin], etc.
Logo 7216 Translite® Tank Truck Hose 150 PSI Max WP Made in USA
REMINDER: the Maximum Working Pressure (MWP) of the hose assembly can be different than the MWP of the hose as noted on the lay line, and always reflects the rating of the lowest rated component of the assembly; all stated WP is usually at room temperature unless otherwise indicated; contact the manufacturer for derating factors for applications with temperatures higher than room temperature.
Literature/catalogs: need to include working pressure AND Design factor and/or Burst pressure, providing transparent communications to customers, particularly if design factor deviates from ARPM recommendations.
Supporting test data should be available to support MWP or design factor claims if requested.
RESULTS OF IMPROPER HOSE SELECTION BASED ON INACCURATE HOSE DESIGN FACTORS:
SAMPLE TEST DATA from Hydrostatic Burst testing of selected hose assemblies
When designing and specifying a hose assembly that will properly meet the needs of an application, an analysis of the application must first be conducted; the accepted industry guidelines for doing this is through use of the acronym STAMPED which helps guide a discussion to cover various aspects of the application. Variables include the size of the hose needed, where and how it will be used, anticipated temperatures and pressure requirements, and the material being transported; see Appendix A for a full review of STAMPED (Size, Temperature, Application, Media/Material, Pressure, Ends and Delivery).
Pressure and temperature requirements are particularly impacted by the design factor of the selected hose. Finished hose assemblies must be able to withstand unanticipated pressure spikes or higher/lower than expected temperatures for both the media being conveyed and the surrounding environment in which the hose is being used. A margin for error is built into the assembly design and specification process through hose design factors. Hence, an application with an expected pressure requirement of 250 psi should be safely addressed with a hose rated at 250 psi and a design factor of 4:1 – it shouldn’t burst until 1000 psi is reached giving a solid margin for error. The same application with a hose design factor of 3:1 would result in a burst hose if 750 psi is encountered. Less margin for error.
Selection of proper hose is dependent on proper manufacturer labelling and accurate literature (e.g., catalogs); both the pressure rating and the design factor need to be clearly communicated.
The maximum working pressure of the hose communicated by a supplier may not reflect the actual working pressure, unless both maximum working pressure AND the design factor are considered.
Without complete communication in reference to the Design Factor of a hose, the fabricator, distributor or end user customer cannot be sure that the hose will perform as required. The Hose Safety Institute recommends that hose suppliers clearly communicate the manufactured Design Factors in all of their hose products. When using hose products that do not meet the recommended NAHAD and ARPM design factors (page 8), premature hose failure can result.
The following tests compare results obtained when testing various types of hoses, comparing the advertised working pressure with the actual working pressure as defined by the test and recommended design factors. This also underscores the criticality of pressure testing. Hose should always be used at or below the stated branded working pressure; test results below simply illustrate the possible variability in actual working pressure, depending on design factors.
Test #1 1” ID Air/Multi-Purpose Hose
Branded WP Stated Design Factor Actual Burst Required Min Burst Top Hose: 300# W/P 4:1 1515# 1200# Bottom Hose: 300# W/P Not provided 764# 1200#
Test #1 shows two hoses branded with the same (300#) working pressure. The Bottom Hose should be branded 190# W/P when using the recommended ARPM 4:1 Design Factor.
Test #2 3/8” ID Pressure Washer Hose
Branded WP Stated Design Factor Actual Burst Required Min Burst Top Hose: 3000# 4:1 12,760# 12,000# Bottom Hose: 4000# 3:1 13,620# 12,000#
Test #2 shows a hose that is supposed to be 33% higher working pressure, but is really only 7% higher based on burst test. The 4000# W/P hose does not meet the recommended ARPM 4:1 Design Factor.
Test #3 2” ID Wire Reinforced Air Hose
Branded WP Stated Design Factor Actual Burst Required Min Burst Top Hose: 500# 4:1 2819# 2000# Bottom Hose: 600# Not provided 2633# 2400#
Test #3 shows a hose with a lower specified working pressure (500# W/P) that burst at a pressure higher than the 600# W/P hose. Both hoses meet the recommended ARPM 4:1 Design Factor.
Test #4 3” ID Petroleum Suction & Discharge Hose
Branded WP Stated Design Factor Actual Burst Required Min Burst Top Hose: 150# 4:1 715# 600# Bottom Hose: 150# Not provided 580# 600#
Test #4 had two hoses with the same branded working pressure and both tested close to or above the recommended ARPM 4:1 Design Factor. The top hose burst at a 23% higher pressure.
As illustrated above, hoses may not perform in applications as expected without the proper design factor being used in the design and specification process for the hose assembly. It is up to the hose manufacturer, fabricator, and end user to properly understand and communicate true design factors in order to ensure an optimally designed hose assembly that minimizes chances for premature failure or accidents. Exceptions to the above may be warranted, but should be communicated clearly as such in order to set proper expectations for appropriate usage, maintenance, etc. of the assembly. Injuries, environmental impacts and downtime due to hose failures lead to costly direct and indirect expenses, including liability insurance claims and subrogation, which will erode any top line revenue gains. Hoses that have higher integrity protect profits.
ARPM: Letha Keslar, Richard Batzer GHX: Jim Reilly PSC: Rick Pitman NAHAD: Debbie Mitchell Groendyke Transport: Steve Niswander Parker: Ron Moner; Ernie Pitchford ContiTech: Guy Enta, Adam McCracken, Jeff Epperson, Jeff Dodson Abbott Rubber: Terry Weiner Summers Rubber: Sam Petillo Marathon Petroleum – Roger Gautreau Smithers-Rapra: Jeff Andrasik Gates: Rob Huber Tennessee Valley Authority: Ken Wyatt BioProcess Institute: James Vogel
This whitepaper was developed under the auspices of the Hose Safety Institute©, operated by NAHAD, The Association for Hose and Accessories Distribution. The Institute provides a powerful forum for distributors, manufacturers, suppliers, end-users and industry organizations to support and promote hose assembly safety, quality and reliability, across all markets and industries.
The Institute’s core deliverables are the NAHAD Hose Assembly Guidelines; performance standards for hose assembly specification, design, fabrication, handling and management as provided by qualified NAHAD Hose Safety Institute Members.
The Institute is managed by NAHAD’s Standards Committee and supported by the end-users and industry experts serving on the Hose Safety Institute Advisory Council.
Appendix – STAMPED
Specification and Design of Hose Assemblies – STAMPED An effective way to identify application factors that need reviewing prior to defining the proper specifications of a hose assembly is to remember the simple acronym STAMPED.
The STAMPED acronym stands for the 7 major information areas required to provide a quality hose assembly for the customer, as follows:
S stands for SIZE; I.D. and length; any O.D. constraints
• overall length should be specified to include fittings
• tolerances need to be specified if special requirements exist I.D., O.D. and overall length of the assembly
• To determine the replacement hose I.D., read the layline printing on the side of the original hose. If the original hose layline is painted over or worn off, the original hose must be cut and inside diameter measured for size.
• The inside diameter of the hose must be adequate to keep pressure loss to a minimum, maintain adequate flow, and avoid damage to the hose due to heat generation or excessive turbulence.
• Length tolerances should be considered for all types of hose assemblies.
• Pressure Loss – The flow rate of the system in conjunction with the inside diameter of the hose will dictate the pressure loss through the hose. Please consult your hose supplier for specific recommended flow rates.
• Loading and unloading flow rate is impacted by the inside diameter of the hose.
• Note: hoses with a large OD will likely require special handling.
T stands for TEMPERATURE of the material conveyed and environmental conditions
• How hot is the material being conveyed
• Are there factors such as heat sources in the environment in which the hose will be used
• Continuous (average) and minimum and maximum temperatures have to be specified for the environment
• Care must be taken when routing hoses near hot manifolds and in extreme cases a heat shield may be necessary.
• In subfreezing temperatures, care must be taken to keep water flowing through hoses. All hoses must be drained on completion of the project. In starting in subfreezing conditions, hoses must be flushed to remove ice crystals prior to installing the tip.
• Other things to consider: maximum intermittent ambient temperature, fluid temperature, ambient temperature and maximum temperature.
• There is a substantial pressure derating for both rubber and PVC hoses as the ambient temperature increases. Please contact manufacturer for details.
A stands for the APPLICATION, the conditions of use
• Configuration/routing (add a sketch or drawing if applicable)
• is the hose hanging, laying horizontally, supported, unsupported (orientation and aspect of the hose); routing up or down hills – requirements for pressure calculations (feet of incline etc.) – head pressure requirements; pull forces if vertical routing is included
• what else is attached to the hose, any external load on the hose o bend radius requirements, flexibility
• Immersion in the material being conveyed
• Quantify anticipated movement and geometry of use requirements
• Intermittent or continuous service
• Indoor and outdoor use
• Unusual mechanical loads (vehicle traffic, etc.)
• Excessive abrasion
• 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 vs. Louisiana)
• Hose now in use
• Type of hose
• Service life being obtained and description of failure or source of customer dissatisfaction
• strength and frequency of impulsing or pressure spikes
• non-flexing applications (static), flexing applications (dynamic)
M stands for the MATERIAL or MEDIA being conveyed, type and concentration
• Are there special requirements for this hose tube
• Any special specifications (or agency requirements) that need to be considered (e.g., FDA, API)
• Will the material be continuously flowing, or sit in the hose for long periods of time
• Media velocity, flow rate
• Weight of media (specific gravity)
• Chemical name/concentration (MSDS)
• Solids, description and size
• Fluid Compatibility – Some applications require specialized oils or chemicals to be conveyed through the system. Hose selection must assure compatibility of the hose tube. In addition to the hose materials, all other components, which make up the hose assembly (hose ends, o- rings, etc…), must also be compatible with fluid being used. Depending on the fluid, your hose supplier may lower the maximum temperature or pressure rating of the assembly. When selecting any hose assembly, always consult your hose supplier’s recommendations.
• Temperature of product
• Corrosively of product; potential corrosiveness of mixed media (resulting from improperly cleaned hoses)
P stands for the PRESSURE to which the assembly will be exposed (or vacuum for negative pressure or inches of mercury)
• System pressure, including pressure spikes. Hose assembly working pressures must be equal to or greater than the system pressure. Pressure spikes greater than the maximum working pressure will shorten hose life and must be taken into consideration.
• Temperature of the media or the environment the hose assembly is being used in will impact the system pressure and needs to be accounted for
• Maximum Operating Pressure – This is the maximum pressure that 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 end 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; typically, hoses with a design factor of 3:1 will fail before one with a 4:1 design factor during impulse testing; discuss specific needs with the hose manufacturer
• Vacuum as measured in inches of mercury (HG)
• Hose routing (will the hose be straight or bent for the application) impacts the hose requirements; some hoses will hold a vacuum while straight, but will collapse if bent.
E stands for ENDS; style, type, orientation, attachment methods, etc.
• Specify end style
• Materials and dimensions (steel, stainless, etc.)
• Conductivity requirements
• Specify attachment method – banding, crimped
• Consideration should be given to the lowest rated component (hose, fitting, and attachment) in determining overall MWP of the entire hose system.
• Clarify sleeves and ferrules (add to fabrication portion)
• Specify impact of any pull forces, if vertical routing of hose assembly is anticipated
D stands for DELIVERY
• Specific to customer requirements
• Testing and certification requirements
• Any special packaging requirements
• Any special shipping requirements
• Tagging requirements
Hose Assembly Fabrication Considerations
Fabrication of hose assemblies should be done in accordance with industry best practices such as NAHAD’s Hose Assembly Guidelines, supplemented by specific manufacturer instructions. As part of the fabrication process, assemblies should be tested to ensure the integrity of the product when first made; this is usually done through hydrostatic pressure testing, but may include vacuum testing if required by customer. Inspection and re-testing of in-service assemblies should be conducted on a periodic basis, depending on application. Field inspection should be conducted prior to each use as well as end of job use. For assembly handling, storage and shipping best practices, please refer to the appropriate sections found in NAHAD’s Hose Safety Institute Handbook©.
Documentation of assemblies should be thorough and trackable in conformance with a formal hose management program including tagging of assemblies through a formal marking scheme, and a formal tracking process. Specific remediation of hoses which have been taken out of service is beyond the scope of this document. Repair and Remediation of hoses should be done in accordance with industry best practices.
NOTE: The overall Maximum Working Pressure of the entire hose system is determined by the component (hose, fitting, and attachment) with the lowest pressure rating, regardless of attachment method used. Repeatability and consistency of the fabrication process are crucial in yielding safe, reliable hose assemblies.