10 Questions You Should to Know about Flanged Flexible Metal Hose

A metal hose has several applications. Be it food processing or gas and oil distribution, there are a range of hoses and fittings to choose from. You might also have questions in your mind like: why use a metal hose or what are the uses of metal hoses? Is it safe? Is it cost-efficient for my industrial application? This blog aims to answer these questions and will provide an overview of the applications of a metal hose and the factors involved in the same.

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A] What is a metal hose?

A metal hose is flexible piping available in two basic types based on design and application. The types of metal hose are strip wound hose and corrugated hose.

• While strip wound hoses have high mechanical strength, corrugated hoses can render maximum leak tightness due to their material and withstand high pressure.
• Corrugated hoses also exhibit pressure tightness under extreme conditions like that found in space or transport of cooled liquid gas or atmospheres like aggressive seawater. They are also corrosion-resistant.
• Metal hoses have been in existence for over 100 years. They have also given rise to varied flexible line elements such as metal bellows and metal expansion joints as well as flexible metal pipes.

B] When should you use a metal hose?

One of the most frequently asked questions is when to use a metal hose. While there are different types of hose available in the market, like rubber hose, composite hose, PTFE hose, and fabric hose, the many advantages of a metal hose make it the most sought-after option.

Many industries use metal hose assemblies due to their ease and durability. Applications of metal hoses include connecting gas lines to moveable appliances and the transfer of oil, steam, or water. However, the final decision on which type of hose to buy depends on its application.

Here are a few factors that can help you determine when to use a metal hose:

1. Extreme temperatures

If the atmospheric temperature or the temperature of the media going through the hose is extremely hot or cold, then metal hose might be the only material that can withstand such temperature extremes.

2. Chemical components

Metal hoses can handle a wider range of chemicals than other hose types. A metal hose should be considered if your application exposes the hose to aggressive chemicals internally or externally. Stainless steel shows good resistance to chemicals and alloys can be used with metal hoses to make them corrosion resistant.

3. Permeation problems

With non-metal hoses, there is a possibility that gases will permeate through the hose wall and into the atmosphere. Whereas, permeation is unlikely with metal hoses when properly fabricated.

4. Catastrophic failure

In times of failure, metal hoses develop small holes or cracks while other hoses develop larger cracks or completely come apart. Moreover, the fittings are welded to metal hoses hence fitting retention problems are unlikely here. If the sudden failure of the hose is catastrophic, the metal hose will minimise the effects of a failure by making sure that the product leaks at a slower rate.

5. Overbending and abrasion concerns

A metal hose can be used as a protective cover over wires and even other hoses to prevent abrasion and overbending. Strip wound hoses are very abrasion resistant and are ideal to be used as protection. They can be applied to the outside of a corrugated hose to prevent it from overbending. One way to test the metal hose of an assembly is by bending a corrugated hose, as the strip wound hose cannot be over-bent without pulling apart the hose.

6. Fire safety

While other types of hose will melt when exposed to fire, metal hose maintains its fire resistance up to degrees F. Corrugated hoses are the better choice when it comes to fire resistance and low permeation in cases where the hose may be exposed to open flame or for applications of barge loading and unloading.

7. Full vacuum

Metal hose maintains its shape under full vacuum while other types of hose might collapse. Corrugations in a metal hose render excellent hoop strength resulting in its ability to handle a full vacuum. Helix wires are used in non-metallic hoses to improve their vacuum rating. However, collapse is still a possibility.

8. Flexibility in case of fitting configuration

Any kind of weld-able fitting can be incorporated into a corrugated hose assembly and in any configuration. Whereas, other types of hose require special collars and shanks for the same. This is an advantage over other types of hoses that would require multiple threaded connections to connect multiple hoses. Every threaded connection is a potential point of leakage. Hence, wielded fitting eliminates any leakage point and can facilitate smooth installation.

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C] What factors to consider while using a metal hose?

The factors to be taken into consideration while using a metal hose are similar to the advantages of usage and applicability it provides.

Here are the factors one must consider while using a metal hose:

1. Disastrous situations

Would a hose failure be disastrous in terms of injury or downtime? Or as we call it, a catastrophic failure in the industrial language. Generally, the fittings of a metal hose are welded as compared to clamped or crimped in a traditional metal hose. When a failure occurs, the welded fittings of a metal hose develop small cracks as opposed to large cracks and blowouts in the case of a non-metal hose.

2. Chemical affinity

Metal hoses are rated well for their wide range of abrasive and corrosive chemical compatibility. All hose fittings and other assembly components are rated to withstand chemical attacks from chemicals in the external environment as well as within the conveyed material.

3. Permeability

Gas can seep in due to permeable hose walls of the non-metal hose, while the expertly fabricated metal hose assemblies do not allow gases to pass through their wall. Since there is no cross-contamination to the material of the hose, stainless steel hose can be cleaned with appropriate chemicals, hence reducing costs and extending service life.

4. External environment

One of the important factors taken into consideration while using a metal hose is that the external environment does not degrade it. Certain metal hoses are not electrically conductive and hence will not spark. Moreover, metal hoses will maintain their integrity up to degrees F even in the event of a fire. The metal hose has a higher vibration absorption than the non-metal hose, which minimises strain on connecting equipment.

5. Temperature

The metal hose can withstand extreme temperatures. If the temperature of the material conveyed via the metal hose or the external temperature is too hot or too cold, the service life of a non-metal hose will shorten and collapse. You should keep your crew safe by using metal hoses that are flexible in low-temperature applications up to -50 degrees.

6. Vacuum

The corrugation in a metal hose helps it to retain full shape even under a full vacuum, while a non-metal hose will collapse under a vacuum even when reinforced. Metal hose is not recommended for applications of high pressure, but it is a supreme choice for vacuum applications.

Find Out How Metallic Hoses Can Improve Your Operations

Conclusion

The responsibility of job safety is an important aspect for any industry and a critical task to shoulder. Hence, it is vital to choose a metal hose that not only renders efficiency, but also the safety of the crew. Even when the application might not demand the use of a metal hose, the versatility of a metal hose will come in handy most of the time.

Corrugated metal hoses come in many configurations. These tools can help ensure you select the right corrugated metal hose for your application.

There are many components in a metal hose assembly and care should be taken when selecting each of them. Moreover, the components have their own unique technical limitations so it is important to make sure each of the components is compatible with your application. In much the same way as a “chain is as strong as its weakest link”, a metal hose assembly will only perform to the limits of its weakest component.

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Once the components have been selected, the quality and skill of the fabricator assembling the components becomes important. The procedures and care used when fabricating assemblies also has a dramatic effect on the assembly’s overall performance.

Hose Master has invested a considerable amount of resources to researching metal hose fabrication and developing a state-of-the-art fabricating center. In addition, we share the welding technology we have developed with our fabricating distributors. All of this is done to promote quality and consistency in fabricating metal hose assemblies.

In this section, we will discuss the various components that make up a corrugated metal hose assembly, and what information a metal hose fabricator will need in order to make an assembly for your application. If you need assistance determining the information, we have also included an explanation of how to analyze the application and make the appropriate selections.

Specifying a Corrugated Metal Hose Assembly:

In order to make an assembly, the fabricator will need answers to the following five questions. For more information about any of these questions, or for a list of available options, click the topic heading for a more detailed explanation.

1. Hose (type, alloy, and size)
2. End Fittings (type, alloy, and size for each end)
3. Length of the assembly (either overall length or live length)
4. Fabrication options
5. Accessories

If you have the answers to these questions, a metal hose fabricator will be able to make the assembly. If you do not know the answers to all five questions, you will need to obtain them. The next section is designed to help you determine the answers.

Analyzing an Application:

To properly design a metal hose assembly for a particular application, the following design parameters must be determined. To help remember them, they have been arranged to form the acronym “S.T.A.M.P.E.D.”

1. Size – The diameter of the connections in which the assembly will be installed is needed to provide a proper fit. This information is required.
2. Temperature – As the temperature to which the assembly is exposed (internally and externally) increases, the strength of the assembly’s components decreases. Also, the coldest temperature to which the hose will be exposed can affect the assembly procedure and/or fitting materials. If you do not provide this information it will be assumed that the temperatures are 70° F.
3. Application – This refers to the configuration in which the assembly is installed. This includes both the dimensions of the assembly as well as the details of any movement that the assembly will experience. This information is necessary to calculate assembly length and required flexibility.
4. Media – Identify all chemicals to which the assembly will be exposed, both internally and externally. This is important since you must be sure that the assembly’s components are chemically compatible with the media going through the hose as well as the environment in which the hose is installed. If no media are given, it will be assumed that both the media and the external environment are compatible with all of the available materials for each component.
5. Pressure – Identify the internal pressure to which the assembly will be exposed. Also, determine if the pressure is constant or if there are cycles or spikes. This information is important to determine if the assembly is strong enough for the application. If no pressure is given it will be assumed that the pressure is low and there are no pressure surges or spikes.
6. End Fittings – Identify the necessary end fittings. This is required since fittings for the assembly must be chosen to properly fit the mating connections.
7. Dynamics – Identify the velocity at which the media will flow through the assembly. Since corrugated metal hose does not have a smooth interior, rapid media flow can set up a resonant frequency that will cause the hose to vibrate and prematurely fail. If no velocity is given, it will be assumed that the velocity is not fast enough to affect the assembly’s performance.

Fabrication Options

Corrugated metal hose is used in a very broad spectrum of applications. Just as the hose, fittings, and other assembly parts must be tailored to suit the demands of the service, so must the methods of joining these components. While standard production joining methods work very well for the majority of service demands, the following extremes may dictate special joining or fabrication techniques:

• Pressures
• Temperatures
• Corrosion
• Other conditions

Hose Master has developed specialized welding, brazing, joining, and fabrication procedures to assure the integrity and serviceability of metal hose assemblies in even the most extreme applications.

The fabrication options to be considered are:

• Specialized attachment techniques
• Testing options
• Additional cleaning requirements
• Packaging

In each of the following sections, the standard method and available options are explained. Select the options best suited for your application.

Specialized Attachment Techniques

Industry Standard

This method will be used unless another method is specified
Standard fabrication of an assembly generally consists of:

• Cutting the hose and braid through a hose corrugation valley.
• Installation of a braid collar over each end of the hose.
• Trimming of any excess braid.
• “Cap” welding the hose, braid, and braid collar together.
• Cleaning the cap weld surface.
• Placement and alignment of a fitting on the cap weld.
• “Attachment” welding the fitting to the cap weld.
• Silver brazing is also available. Consult factory.

Half-Corrugation

Standard fabrication sometimes leaves a portion of the cut corrugation, or corrugation “lip”, just under the base of the fitting. In specialized applications this residual lip may not be desirable. To prevent any exposed corrugation edges from causing damage, the hose can be specially prepared for welding by cutting the corrugation on the crest, rather than in the valley, thereby removing the lip.

Smooth Transition Weld

For applications in which corrosion is a concern, all crevices and fissures must be minimized. Specialized hose and fitting preparation, in conjunction with proprietary welding techniques, is available to provide a full penetration hose-to-fitting weld that is smooth and crevice free.

Braid-Over Construction

Assemblies operating at the upper limits of their rated working pressure or in severe service may benefit from a braid-over construction. The fitting is first welded to the unbraided hose. Then a special metal reinforcing ring is installed over the fitting and next to the weld. Finally the braid is drawn over the end of the hose and the ring, and welded to the side of the fitting. This technique reduces the amount of heat introduced into the braid wires, nearly eliminates the heat effected zones of the cap and attachment welds, and maximizes the wire strength. Braid-over construction may also be used for specific high cycle applications.

Testing Options

Note: Always test an assembly with a medium that has a smaller molecular or atomic size than the service required.

Standard Leak Testing

Every corrugated hose assembly is leak tested prior to shipment. Standard testing consists of pressurizing the assembly with air and then submerging the entire assembly under water. This method is reliable and sufficient for the majority of applications.

Hydrostatic Testing

While the standard test is designed to detect leaks, hydrostatic testing is designed to test the assembly’s strength. Testing of an assembly to its full permissible test pressure can be economically and accurately accomplished by filling the assembly with liquid while concurrently evacuating all air. The assembly is then hydrostatically pressurized using high pressure pumps. The test pressure is maintained for a predetermined period of time.

High Pressure Gas

Testing with air under water, at pressures of up to psi, is available for specialized applications. For a more sensitive test, the use of gases such as nitrogen or helium can be requested.

Dye Penetrant

Dye penetrant testing is available for both leak and for weld bead inspection, in accordance with Hose Master procedures or to customer specified standards.

Helium Mass Spectrometer

This is the most sensitive leak detection method generally available. The standard test method is to attach the assembly to a mass spectrometer and generate a very high vacuum in the assembly. The exterior of the assembly is then flooded with helium. The relatively tiny helium atoms penetrate even very small openings and are drawn into the mass spectrometer where they are detected and the leak size quantified. Helium Mass Spectrometer testing can be modified to satisfy customer or regulatory agency requirements.

Additional Cleaning Requirements

The hydroforming method of corrugated hose manufacturing inherently yields a very clean product. However, specialized cleaning for specific applications is available upon request. Contact Hose Master’s Customer Service Department for details.

Packaging

All assemblies are shipped with protectors over sealing surfaces such as threads and flange faces. Spacer bars are installed on all shorter double-flanged assemblies to prevent compression of the assembly during shipping and handling. Special packaging is available to suit customer requirements, including crating, plastic bagging, labeling, and custom fitting protectors.

Hose Master places emphasis on continual improvements within our manufacturing processes, product offering and services. Hose Master reserves the right to make changes without further notice to any products contained herein.

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