How to choose hydraulic pipes and hoses in different situations?

How to choose hydraulic pipes and hoses in different situations?

When choosing between a hose assembly and tube assembly for a hydraulic application, there are a few basic questions that must first be answered:

When would you choose a hose assembly over a metal tube assembly?
When would you choose a metal tube assembly over a hose assembly?
Can you replace a hose with a tube or a tube with a hose? 

The short answer is that each has its advantages and draw-backs. One piece of hydraulic equipment will commonly have both tube and hose assemblies on it, depending on which solution better serves each particular part of the system. For example, tube would typically be better when routed close to a heat source, and hose would be chosen for high vibration applications or when attached to moving parts.

Benefits of Tube

Lighter than hose – with a caveat
Higher heat dissipation rate
Constant dimensions under pressure
Greater temperature operating range
Typically longer service life than hose
Smaller allowable minimum bend radius
Smaller OD than hose for the same ID
Electrically conductive – good static dissipation properties
More economical than hose

Limitations of Hose

Heavier than tube
Does not dissipate heat well
Expands and shortens under pressure
Limited operating temperature range
Requires regular replacements
Greater allowable minimum bend radius
Larger OD than tube for the same ID
Often electrically non-conductive with poor static dissipation properties
Generally more expensive than tube
Metal fittings vulnerable to corrosion

Benefits of Hose

Flexible – can be used in dynamic applications, where the components on either side of the assembly do not move with respect to each other
Longer lengths
Can usually be fabricated much faster than a tube assembly by less skilled personnel.
If low quantities are required, can be less expensive than a tube to fabricate
Easier to install in tight quarters
Typically less vulnerable to corrosion
Does not transfer vibration and noise
Better heat insulator
Larger bend radius facilitates smoother flow/less flow resistance    
     
Limitations of Tube

Can only be used in static (rigid) applications, where the components on either side of the assembly do not move with respect to each other
Typically, 20’ maximum length
Specialty equipment and expertise needed to design and produce metal tube assemblies
In very low quantities, the cost per assembly can be more than a hose
Can be harder to install due to space constraints
Typically more vulnerable to corrosion
Transfers vibration through components
Poor heat insulator
Smaller bend radius (typically used) can increase flow resistance

1.flexibility

A better choice: hose
Hose-tube combination assemblies
Even small movements of connecting parts can preclude the use of tube assemblies. Even if the tube assembly works initially, movement can put stress on the end connections (causing leaks over time), and repeated movement can fatigue the tube itself.
A hose or hose combination is a better choice.

2.life

Better choice: Tube (in most cases)
This is a general rule, but it doesn’t always apply—the effects of vibration, abrasion, exposure to chemicals, UV light, heat, and other factors can diminish the benefits of a tube assembly or even make a hose assembly a better choice. Tubing is generally more durable than hose in applications involving exposure to UV rays and in high-cycle, high-pulse applications. If the equipment is subject to vibration, hose may last longer than pipe.

3.Continuous length availability

A better choice: hose
The maximum length of the assembly is limited by the availability of a continuous length of hose or pipe. Hoses are usually longer than pipes. Some types of hose can be produced in continuous lengths of 500 feet or more. In comparison, (rigid) metal pipe material is typically available in lengths of 20 feet. Longer tubing is available, but costs increase and lead times are longer. Additionally, transporting and storing the tube is more difficult because it cannot be coiled like a hose.
If long runs of pipe are required, use pipe fittings to connect multiple pipe components together.

4.Expansion considerations under pressure

Better choice: tube
When a hose is pressurized, its diameter expands and its length decreases. (When laying out the hose assembly, make sure it has enough slack so that the hose does not pull out of the fitting under pressure.) Overall, the volume inside the hose increases slightly under pressure. If enough hose is used in the system, an increase in the amount of hydraulic fluid required to complete the task may become apparent and may need to be considered during the design phase.
Additionally, volume fluctuations in the hose reduce the response time and efficiency of the hydraulic system.
In comparison, metal tubes expand negligibly, making them a first choice for applications that require precise positioning.

5.Bending radius requirements

A better choice: tubing if a small bend radius is required
Pipe assemblies can have tighter bends than hose assemblies. Having said that, choosing a smaller bend radius will increase flow resistance. While it is possible to bend tubes using large radius blocks, producing tube assemblies with multiple bend radii is tricky and adds cost and lead time. Most tube assemblies are produced using only one bend radius throughout the assembly.
With proper clamping, hose assemblies can be routed using multiple bend radii without issue (as long as the hose does not bend beyond its minimum allowable bend radius).

6.Wear resistance

Better choice: tube
Even with wear-resistant hose covers or sleeves, hoses may experience more wear than pipes in highly abrasive environments.

7.weight considerations

Better choice: It depends - if weight is important to your application, check the product specifications carefully.
When most people compare pipe and hose sizes, they compare nominal sizes, such as 1/2" pipe vs. 1/2" hose. If you do this, you will find that, generally speaking, steel or stainless steel pipe will be lighter than a hose of the same nominal size.
However, since hose is measured by the inside diameter (ID) and pipe is measured by the outside diameter (OD), the diameter of the pipe is always smaller than that of a hose of the same nominal size.
When sizing hydraulic system components, bore size is important in determining flow diameter, flow rate, etc. Therefore, when you consider which one is lighter for your application, you should compare pipes and hoses with the same diameter and required pressure rating rather than using nominal sizes.
When comparing pipe and hose with similar inside diameters and pressure ratings, the weight difference usually favors the hose - but not always.

8.Easy to install

A better choice: In most cases, hose
Hose assemblies can "snag through" tight spaces more easily than rigid pipe assemblies. On the other hand, for the same inner diameter, the tube assemblies will have a smaller outer diameter, allowing them to fit better in certain places.

9.Availability and ease of manufacturing

A better choice: In most cases, hose
Availability is related to ease of manufacture. Generally speaking, because hose assemblies are easier to manufacture, they are easier to use. Typically, the time required to install a bending machine is longer than the time required to manufacture the hose assembly.
Bending pipe also requires special tools and trade skills that are not as common as those required for manufacturing hose assemblies. Bend pipes come from fewer sources than hose factories.
However, if we are talking about long tube assembly runs, the time required to design the tube and set up the tube bending machine is spread over a large number of components - and the time and cost required to manufacture the tube components are greatly reduced. If production volumes are high enough, pipe assemblies may be more economical than comparable hose assemblies.

10.Vibration precautions

A better choice: hose
Tubes often perform poorly when subjected to sustained severe vibration. Vibration fatigues metal, causing premature pipe failure
Sometimes a short run of hose can be used to insulate the pipe from vibration.

11.Corrosion resistance and chemical compatibility

Better choice: depends on the application
This is another area where careful research is crucial before making a decision. Typically, rubber caps protect the hose's metal reinforcements from corrosion, but the hose ends are still susceptible to corrosion. If components are exposed to moisture, sea water, etc., use stainless steel hose fittings (or aluminum if high pressure is not required) and stainless steel tubing. Sometimes painting hose and pipe assemblies is enough to prevent rust.
When considering chemical compatibility of components, each part needs to be considered individually. For hose assemblies, inner tube material, cover material, hose coupling body material and sealing material all need to be considered. For pipe assemblies, pipe and fitting materials need to be considered. Make sure your components are not only compatible with the media being transported, but can withstand exposure to chemicals in the intended environment.
If you can't find parts made from materials rated "Excellent" or at least "Good," be sure to adjust your maintenance schedule to include frequent inspections and regular replacement of affected parts.

12.Conductivity/insulation

Better choice: depends on the application
Metal pipe assemblies are conductive, but hose assemblies can be conductive or non-conductive.
In most cases, the conductivity of the hose assembly is not an issue, but in some cases, it is very important. (Read our previous blog "Electrical Properties of Rubber Hoses.")
The only time you can determine the conductivity (or non-conductivity) of a hose assembly is if the OEM specifically rates the hose as conductive or non-conductive, or if you measure the conductivity yourself. For industrial hose assemblies, there is also a method of making conductive industrial hose assemblies by attaching metal reinforcements of the hose to the ends of the hose.
A note about galvanic corrosion: Also consider using different materials for pipes and pipe fittings, or connecting pipes or hose fittings to ports made of different materials. To prevent galvanic corrosion, materials that are too far apart on the metal corrosion scale should not come into contact. For more information, see the Metal Corrosion Ratings and Pipe and Fitting Material Compatibility Charts.

13.Heat dissipation/insulation

Better choice: depends on medium and ambient temperature
If your system overheats, using a tube assembly instead of a hose assembly can help dissipate heat better and help cool the oil a few degrees.
On the other hand, if your equipment operates in a cold environment, a hose assembly will better isolate the oil and help the system reach operating temperature.

14.Resists the effects of UV rays

Better choice: tube
Steel is not affected by UV exposure. The rubber compound typically used for hose caps will break down over time when exposed to UV/sunlight. However, new compounds are being developed, and some hoses are using special thermoplastic covering materials that are UV resistant. UV-resistant covers are still not UV-resistant, but can withstand longer periods of UV exposure before damaging.

15.Temperature rating

Better choice: tube
Most hydraulic hoses are designed to operate in temperatures between -40°F and 212°F. Low-temperature and high-temperature hoses are also available and can operate in temperatures as low as -70°F and as high as 302°F. However, for some media, the operating pressure of the hose may be reduced in certain temperature ranges.
By comparison, carbon steel pipe can operate in temperatures from -65°F to 500°F, and stainless steel pipe can operate in temperatures from -425°F to 1,200°F. When using metal pipe, temperature (and severity of use) derating must still be taken into account, but the derating occurs at much higher temperatures than in the hose case. See temperature ratings for common pipe materials for more details.

16.Pressure/Vacuum Ratings

Better choice: Depends on several factors
Every hose and pipe has an operating pressure rating. For hoses, the pressure rating is usually marked on the line where it is laid, but it is also necessary to check whether the hose has been derated due to use at higher temperatures or with certain media. This information is usually available from the hose manufacturer.
For pipes, the pressure is usually determined by the specifications the pipe meets. Pipeline operating pressure also decreases at higher temperatures, although it also decreases with severity of use and high temperatures. See Parker Tube Pressure Ratings Chart.
When considering the pressure rating of a hose or pipe assembly, the maximum operating pressure is the lesser of the pressure rating of the hose or pipe and the pressure rating of the fitting. The pressure rating of pipe couplings, hose couplings and adapters depends on size, materials used and end configuration. Smaller fittings are usually rated for higher pressures. There are also differences in the pressure ratings of JICs, O-ring face seals, or fittings of the same size and material.
While many hoses have a vacuum rating of 28 inches of mercury, most tube assemblies will have a better vacuum rating than a hose assembly.

17.Maintenance precautions

Better choice: tube
Hoses typically have a shorter service life and often fail to warn of failure, making their use in hydraulic (or pneumatic) systems more demanding to maintain.

Overall, if tubing is available, it will require less maintenance/replacement than hose, and the cost of ownership over time is usually much lower than hose.