When choosing a flexible hose for your operation, it can be difficult to determine which option is best for your needs. Every flexible hose is designed to meet different specifications or to handle different substances, so it is crucial to choose a product that is suitable for your application. Choosing the wrong hose can drastically increase the risk of various safety hazards and equipment damage while reducing system performance and efficiency. That is why the experts at Flextech Industries have compiled some information to help you determine how to choose the right flexible hose and ensure the highest level of safety and efficiency for your system.
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Learn about 4 important components of a flexible hose.
When looking at your options for flexible hoses, it is crucial to consider the following factors before making a final decision:
When choosing a flexible hose, you will need to consider the intended application. For example, hoses that transfer air will differ in many ways when compared to hoses that transfer water or gasoline. Other application-related considerations include the frequency at which the hose will be used and whether it needs to meet certain industrial or government standards. The environmental conditions that the hose will be exposed to will also affect which type of flexible hose is suitable for your needs, so it is crucial to consider each of these elements before making a final purchase.
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The common working pressure of your application will have a direct impact on your options for flexible hoses. Whether the application calls for positive (PSI) or negative (Hg) pressure, choosing an inadequate hose can result in bursting or equipment damage. Be sure to understand your working pressure requirements to ensure that you are only looking at hoses that meet these specifications.
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The selected hose must meet the diameter and length requirements of the job. Incorrect sizing will often result in clogs if the hose is too small or leaks if it is too large. This can be especially dangerous if the hose is used to transport fuel, hazardous materials, or substances that are extremely hot.
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All flexible hoses have a temperature rating that determines their resistance to extreme heat or cold. Failure to match these requirements with your application can result in frozen or melted hoses. Internal and external temperatures directly impact the type of hose that should be selected for the job, so be sure to consider both before selecting a product.
To learn more about our selection of flexible hoses and other specialty products, get in touch with the team at Flextech Industries. We can be reached through our online contact form and will work with you to provide the perfect solution for your needs.
Unless specified, you may be wondering when you need to consider a metal hose versus a rubber or plastic hose for your assembly. One specification that stands out as an indicator for needing a metal hose is temperature. On one side, we have very hot applications, up to °F. On this end of the spectrum, we have two considerations: outside environmental conditions, such as an assembly near a furnace in a steel mill; or, internal process conditions, like combustion gases or hot air for test facilities. Metal hose performs great at elevated temperatures, but be aware, stainless steel’s strength declines gradually as temperatures rise.
On the other hand, you may need to consider a metal hose for very cold (cryogenic) temperatures, -325°F and lower. Stainless steel improves mechanical properties as temperatures drop, even to cryogenic levels. The colder the temperature, the better they get. When thinking about your end connections, remember that carbon steel has an effective temperature range of 0-800°F; outside this range, its properties diminish quickly.
Another property of metal hose is low permeation—zero leak rate. All rubber and plastic hoses will permeate molecules through the tubing over time. Functionally speaking, the metal hose has a zero leak rate.
Vacuum is another condition that could sway your decision between rubber and metal hose. Because of the low permeation, metal hoses can also be uniquely qualified for vacuum-rated applications. If you need to guarantee the highest level of vacuum rating, a metal hose is a great choice! Because of its corrugated design, it also handles full vacuum from a structural perspective.
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Because metal hose can be made from the most chemically resistant metals, this can be another consideration point when deciding to choose metal hose. Metal hoses can withstand the most corrosive of environments. Keep in mind: One aspect of chemical resistance is thickness; a thick component has more material to corrode away and will inevitably last longer.
Finally, it’s important to remember that metal hose is not particularly good with abrasion resistance, contrary to what you might think. The braid wires found in metal hose construction are only a few thousandths of an inch thick; if they’re put in an application where abrasion exists, they can quickly abrade and weaken until they eventually fail. In a scenario such as this, another layer of protection is required, such as a plastic spiral wrap or a strip-wound metal guard welded over the top of the assembly.
Metal hoses can also see this type of degradation from the high frequency of vibration in the system itself. The braid can cause abrasion on the crests of the corrugations. You can address an issue such as this by adding a sacrificial bronze braid layer in between the tube and stainless-steel braid; this softer bronze braid acts to protect both the tube and braid from degrading.
Metal hoses can be manufactured with improved bend radius and flexibility. A compressed hose with a high number of corrugations per inch allows for greater flexibility and reduced force to bend.
Keep in mind that a metal hose does not play well with torsion or twisting; this is something that can be avoided by proper installation. Using two wrenches to tighten a swivel nut will keep the hose free from torque. Proper routing is important too. Bending should occur in a single plane, as multi-planar bending creates torsion and decreases the service life of your hose.
The high velocity of the process fluid can be another consideration when looking into metal hoses. When referring to metal hoses, velocity is considered high at 75 ft/s or more. When your velocity goes above 75 ft/s, the media becomes turbulent, and the hose begins to whistle and vibrate. A flow liner of stripwound hose will smooth out the surface the media flows against and reduces turbulence.
At times, customers may require certain testing requirements. In the absence of a customer spec, every metal hose assembly built by a company using NAHAD standards receives an air-under-water test for one minute to look for leaks at the weld.
NAHAD suggestions include:
High-pressure pneumatic testing has been shown to result in fewer false-positive outcomes, meaning anything higher than 75 psi. Some pinhole leaks are so small they don’t register a bubble in one minute at pressures under 75 psi; however, increase the pressure, and bubbles form quicker. You can talk with your manufacturer to decide if this increased level of testing is right for you.
This is another consideration driven by the customer. You must determine if your organization requires certification, as many do not. The most common certification for a metal hose is ASME Section IX, which tells you, as a buyer, that the weld procedure yields an effective weld, and that the welder is qualified to produce that weld. We won’t sugarcoat it: weld certifications are a labyrinth of understanding and interpretation. If you need details, give us a call and we’ll show you how deep the rabbit hole goes.
Weld inspections can also be performed by a certified inspector. Again, this is a customer-driven requirement. Inspections are normally non-destructive and simply visual. Increased levels use aids like liquid die penetrant to inspect the surface of the weld. Other non-destructive tests, like X-ray and ultrasonic, can detect discontinuities in the internal weld. There are other methods that must be discussed at the quoting and design stage but remember: visual inspection is a minimum requirement for all welds.
Metal hose is a great choice when it comes to oxygen applications, especially industrial oxygen; however, certain care must be taken to ensure the hose is clean and free of hydrocarbons prior to use. Oxygen itself is not flammable, but in the presence of a fuel—typically hydrocarbons—it allows those fuels to ignite at lower temperatures and burn hotter. Metal hose is generally safe because the manufacturing process should not introduce fuel onto the surface of the hose.
When it comes to internal cleanliness, cleaning the inside of the hose and then capping the ends after it’s been fabricated can ensure the hose is safe to use. Cleaning methods and degree of cleanliness should be discussed during the quoting and design stage.
Each size and style of hose has a minimum recommended live length, meaning the minimum length of the flexible portion of the hose must be able to flex and hold pressure, generally behaving like a hose. At lengths shorter than the minimum recommended live length, the hose tends to act more like a pipe, with little flexibility; these cannot be guaranteed to perform as expected. Most fabricators will make these short assemblies and simply state the length is shorter than recommended, which could void the warranty.
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