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One of the most important jobs before fabricating an assembly is to accurately calculate the correct length that the hose and braid must be cut to, or the hose assembly “cut length.” The hose cut length is the assembly overall length (OAL) minus the total length of all of the fittings to be welded or threaded onto the assembly.

Here are several of the most common assembly types:

• Type A – An assembly with one straight hose section and a single solid (non-swivel) fitting welded each end.
• Type B – An assembly with one straight hose section and a single solid (non-swivel) fitting welded each end and an additional threaded fitting (such as a pipe union or a threaded flange) threaded to one, or both, of the welded fittings.
• Type C – An assembly with one straight hose section and an elbow fitting welded to one, or both, assembly ends.
• Type D – An assembly with one straight hose section and a swivel female fitting (such as a JIC) welded to one, or both, assembly ends.
• Type E – An assembly with two hose sections joined by an angled (45° or 90°) elbow. (Also called a “dog-leg” assembly).

In this Bulletin we`ll take a look at how to calculate hose “cut length” for Type A, B, C and D assemblies.

Type A – Assembly with one straight hose section and a single solid (non-swivel) fitting welded each end.

Where:

• Overall length (OAL) = The total length of the assembly
• Cut length = The length that the hose and braid are cut to before assembly fabrication
• Live length = The length of the hose between the inner edges of the braid collars. This is the portion of the hose which can actually move to take up assembly bending and vibration in service.
• Fitting 1 length = The total length of the fitting on assembly end 1
• Fitting 2 length = The total length of the fitting on assembly end 2

To calculate the hose cut length for a Type A assembly we need to:
1. Determine the Fitting 1 length.
2. Determine the Fitting 2 length and
3. Calculate Hose cut length = OAL – (Fitting 1 length + Fitting 2 length)

Example: OAL as ordered by customer = 24″
Fitting 1 length = 3″
Fitting 2 length = 2-1/2″
Hose cut length = 24 – (3″+ 2-1/2″) = 18-1/2″

Type B – An assembly with one straight hose section and a single solid (non-swivel) fitting welded each end and an additional threaded fitting (such as a pipe union or a threaded flange) threaded to one, or both, of the welded fittings.

Where:

• Fitting 2+3 length = The total length of fitting 2 + fitting 3, tightly threaded together

To calculate the hose cut length for a Type B assembly we need to:
1. Determine the Fitting 1 length
2. Determine the Fitting 2 + 3 length by tightly threading the fittings together and measuring the total length
3. Calculate Hose cut length = OAL – (Fitting 1 length + Fitting 2+3 length)

Example: OAL as ordered by customer = 24″
Fitting 1 length = 3″
Fitting 2+3 length = 4-1/2″
Hose cut length = 24 – (3″+ 4-1/2″) = 16-1/2″

Type C – Type C – Assembly with one straight hose section and an elbow fitting on one or both ends.

Where:

• Fitting 1 length = The total length of the fitting on assembly end 1, measured from elbow end to the centerline of the fitting other end
• Fitting 2 length = The total length of the fitting on assembly end 2, measured from elbow end to the centerline of the fitting other end

To calculate the hose cut length for a Type C assembly we need to:
1. Determine the Fitting 1 length
2. Determine the Fitting 2 length
3. Calculate Hose cut length = OAL – (Fitting 1 length + Fitting 2 length)

Example: OAL as ordered by customer = 24″
Fitting 1 length = 3″
Fitting 2 length = 3″
Hose cut length = 24 – (3″+ 3″) = 18″

Type D – Type D – An assembly with one straight hose section and a swivel female fitting (such as a JIC) welded to one, or both, assembly ends.

Where:

• Fitting 1 length = The total length of the fitting on assembly end 1
• Fitting 2 length = The total length of the fitting on assembly end 2

To calculate the hose cut length for a Type D assembly we need to:
1. Determine the Fitting 1 length
2. Determine the Fitting 2 length
3. Calculate Hose cut length = OAL – (Fitting 1 length + Fitting 2 length)

Example: OAL as ordered by customer = 24″
Fitting 1 length = 3″
Fitting 2 length = 3″
Hose cut length = 24 – (3″+ 3″) = 18″

We’ll take a look at how to calculate hose “cut length” for the Type E – assembly with two hose sections joined by an angled (45° or 90°) elbow in the next Engineering Bulletin.

If you have any questions or comments, please contact us.

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Quite often our distributors are asked by end-users for a copy of inspection documents according EN 10204 (especially for the inspection Certificate 3.1 “type 3.1”). In this little bulletin we want to explain what those documents are.

BS EN 10204:2004 is a British Standard that supersedes standard BS EN 10204:1991 and specifies the different types of inspection documents supplied to the purchaser, in accordance with the requirements of the order, for the delivery of all metallic products e.g. plates, sheets, bars, tubes, forgings, castings, whatever their method of production.

Inspection certificate 3.1 “type 3.1” – is simply a document issued by the manufacturer in which he declares that the products supplied are in compliance with the requirements of the order and in which he supplies test results. The test unit and the tests to be carried out are defined by the product specification, the official regulation and corresponding rules and/or the order. The document is validated by the manufacturer`s authorized inspection representative, independent of the manufacturing department.

Manufacturer may transfer on to the inspection certificate 3.1 relevant test results obtained by specific inspection on primary or incoming products he uses (such as – for example – results of chemical composition analysis or mechanical properties of the strip, provided on the Material Test Reports supplied by the vendor of strip)

Summary of inspection documents according BS EN 10204:2004

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Sometimes our customers, who are making assemblies for a heat generating system, ask if corrugated hose which they consider for an application will be able to handle a certain number of BTUs. Though it seems like unrelated question, there still should be an answer to it…

First let’s look at the definition of a BTU. BTU – stands for British Thermal Unit and – is the amount of heat energy needed to raise the temperature of one pound of water by one degree F. This is the standard measurement used to state the amount of energy that a fuel has as well as the amount of output of any heat generating device or system. All combustible materials have a BTU rating – that is amount of heat energy they produced when burned. For instance:

• 1 cubic foot of natural gas yields about 1,030 BTU;
• 1 pound of coal yields about 10,150 BTU;
• 1 gallon of diesel fuel yields about 138,000 BTU;

So, if a heat generating system (working on natural gas) has rating of 8 Million BTUs/hour it means that it uses (or burns) 7,767 ft³ of natural gas in one hour (8,000,000 / 1,030); Therefore a hose used in the pipe system that supplies gas to a “burner” in such a system would have to transfer 7,767 ft³ of natural gas in one hour or – in other words – to “handle” 8 Million BTUs/hour. Such transfer corresponds to a Flow Rate of about 130 ft³/min ( 7,767 / 60 ), and the answer to the above-mentioned question comes to finding if a given Flow Rate is acceptable for the hose in question.

For maximum permissible flow rates for a given size of hose, please refer to the table below:

Maximum Permissible Flow Rates in Corrugated Hose

Where the flow rates exceed those in the table, an interlocked metal hose liner or larger hose I.D. is recommended.

If you have any questions or comments, please contact us.

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In a couple earlier Engineering Bulletins we showed how Chloride / Chlorine Levels in aqueous environments affect alloy selection and how PREN (Pitting Resistance Equivalent Number) is used to determine pitting corrosion resistance in the face of chloride attack.

Here, we consider another dimension in chlorine piping systems. Dry chlorine is defined as chlorine with its water content dissolved in solution. It could be a liquid or a gas. If the water exceeds its solubility and forms a second aqueous liquid phase, the chlorine is defined as wet chlorine, and becomes extremely corrosive.

The Chlorine Institute’s Pamphlet 6 details how moisture most commonly enters a dry chlorine system.

• Start-up and shutdown
•  Wet pad purge gases
• Exposure to atmosphere

Dry chlorine is not corrosive to steels at ambient temperatures and is commonly shipped and handled in carbon steel equipment, with higher-alloy materials such as Monel 400 and Hastelloy C-276 used for critical parts.

However, temperature and pressure changes can affect the moisture content of the solution, ushering the change from dry to wet chlorine. For this reason, it’s important to monitor these operating conditions.

Corrosion rates of different alloys in dry chlorine and temperature (°C) at which given rates are exceeded are presented in the table below. Keep in mind that moisture will greatly accelerate the attack of any of these materials with the additional danger of SCC (Stress Corrosion Cracking) of stainless steel.

Corrosion of some common alloys in dry Chlorine (Cl₂)

Disclaimer: The info presented here has been compiled from sources believed to be reliable. No guarantee is implied or expressly stated here and the data given is intended as a guide only.

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Penflex Corporation wants to let our customers know that our P3 corrugated hose is manufactured and tested in accordance with the ISO 10380 International Standard as Type 1-10 hose. ISO 10380 conformity is another example of Penflex’s commitment to provide exceptional products to our customers.

ISO 10380 is an International Standard which specifies the requirements for the design, manufacture and testing of corrugated metal hoses and hose assemblies for general purposes.

The Standard covers sizes from DN 4 to DN 300 (1/16″ to 12″), Working Pressures from PN 0.5 bar to PN 250 bar (7 psi to 3625 psi), specifies pressure derating factors for elevated temperatures, two methods of construction and three types of flexibility of hose assembly.

For Type 1-10 hoses, the bend radii for testing each hose size is defined by the Standard for both static (Pliable) and dynamic cycling (U-Bend) testing. The pressure in bars for which a hose shall meet all requirements, must be selected from one of the pressures listed in section 5.7.2 of the standard. When cycle tested in a U-bend, hoses shall have an average life of 10,000 cycles.

P3 Products: ISO 10380 Qualifications [Type 1-10 Hose]

If you have any questions or comments, please contact us.

Alternatively, you can find out more about our P3 products here.

Imagine a situation when you received a “next day delivery” order for 3″ assemblies and, by Murphy’s law, have plenty of 2″ and 4″ braid in stock but not a single length of 3″. A few questions might flow through your mind: What if I use one of those sizes on 3″ hose? Will that do? How it will change Max. Working Pressure (or Max. Load Capacity of braid)? How’s braid coverage going change? Well, let’s take a look.

Let’s recall (real quick) some basics about the braid. Braid is a flexible wire sheath surrounding a metal hose that prevents the hose from elongation created by internal pressure. It can also absorb exterior tensile stress and provide general protection of the exterior surface of the hose. Braid is composed of a number of wires wrapped helically around the hose in a basket weave fashion and fixed to the hose at both ends. The angle between crossing wires is usually called the braiding angle.

Maximum Load Capacity of braid depends on a number of parameters such as numbers of carriers, number of wires per carrier, tensile strength of wire and braiding angle. For a single layer of braid Maximum Load Capacity of braid can be calculated by the following formula:

Now, what would change in the braid construction if we put braid on the smaller or larger hose OD? As you would see from the picture below the main parameter that will change is braiding angle.

If you put larger braid on a smaller hose OD, braiding angle will become smaller and if you put smaller braid on a larger hose OD, braiding angle will open up or increase.

From the formula above we can see that if braiding angle would increase Max. Load Capacity of braid (or Max. Working Pressure) would decrease and vice versa. That is, for example, because: cos 40° = 0.77 while cos 50° = 0.64.

Note: For the same braid construction with decrease of braiding angle coverage of the braid will decrease as well, while length of the braid will increase. You should not consider to use braid on a hose OD more than one size up or down.

Table below presents some (theoretical) data for most common sizes of 700 Series Standard Braid which shows how Max. Load Capacity of braid will change if braid is used for a smaller or larger OD of hose:

Note: To see how Working Pressure, Coverage or Braiding angle would change if (for example) you would put 4″ Braid on 3″ hose – in the horizontal line for braid ID find a column for 4″ size, then move up the column until the row for 3″ size (in the vertical column on the far left) – and “read” respective numbers: 257, 78, 29.

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When a hose assembly failure occurs prematurely in service it is essential to find out what caused the problem to prevent future failure. Sometimes the problem can be easily identified and eliminated, therefore first look for common clues like the following:

• Are hose assemblies “rubbing” against anything?
• Are there any broken or scratched wires in the braid?
• Has the braid geometry been distorted?
• Has the assembly taken a permanent “set,” as in is it no longer straight?
• If there is a crack in the hose, is it a circumferential crack on the “crest” or “valley” of the corrugation, suggesting some vibration issues?
• Is there anything in the air or dripping on the outside of the hose which could cause corrosion?
• Is there any evidence of braid corrosion, things like discoloration or thinning?

When a corrosion problem is encountered, it is very important to use a replacement hose manufactured from the proper alloy. Many times a failed hose is replaced with the same alloy and likely will fail within the same time frame. Therefore use the following selection process for the most suitable alloy:

• Review the nature of the environment with respect to chemical composition of the media transferred through the hose, temperature, pH, flow velocity and such.
• Use the Corrosion Rate Charts or tables to determine those alloys with the best uniform corrosion resistance against transferred solution. If it is a solution of two or more components, then determine the corrosion rates for each component individually and assume the worst-case scenario.
• Always determine if chlorides are present-and they usually are-and select the best alloy for pitting resistance based on guidelines provided in this previous Bulletin: Chloride / Chlorine levels and Stainless Steel Alloy Selection.
• Choose the proper alloy using its PREN number. Refer to Calculating Pitting Resistance Equivalent Number (PREN) Bulletin for some guidelines.

And finally, if you are not that familiar with each alloy and its limitations, please contact us for assistance – we are here to help!

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Environmental corrosion is a naturally occurring chemical deterioration of a material due to reaction with environment and especially with oxygen. The extent of deterioration of a metal depends on the chemical nature of the material. For example, when iron is exposed to an industrial atmosphere for a period of time, iron oxide or rust forms on the surface. The rust is very porous to oxygen and water in the atmosphere and consequently the corrosion process continues until the metal is entirely consumed.

It is generally assumed that stainless steel has a very good resistance to atmospheric corrosion and yet, when analyzing the effect of general corrosion on steel, attention has to be given to corrosivity of atmospheres. Depending on the location-rural, industrial, marine or their combination-corrosiveness of atmospheres can be significant.

Atmospheric corrosion is an electrochemical process with the electrolyte being a thin layer of moisture on the metal surface. Some locations with heavy industrial pollution in the atmosphere may have significant presence of sulfur oxides (SO_x), nitrogen oxides (NO_x), hydrogen sulfide, ammonia, carbonyl sulfide (COS) and other pollutants which amplify the “acidity” of the rainfalls and, as a result, the deposition of those pollutants on the metal surface (or in other words in electrolyte). With the “help” of some environmental factors like high humidity, high temperature, either ambient or due to solar radiation, frequent rainfalls and such, the corrosion penetration rates can lead to loss in the metal thickness. Environmental factors can cause the median thickness loss to vary by as much as 50% (!) or more in a few extreme cases.

As we are often reminded by some of the “old hands” that it is called “stainless” not “stain-free” and therefore attention should always be given to proper care in handling and storage of stainless steel assemblies and its components. To better see how environment can influence corrosion rates of the steel, please refer to the table below.

Typical corrosion rates for carbon steel in different types of atmospheres.

Note: Corrosion Rates at higher humidity and temperature, like in some places in the US, as well as in conditions with “combined atmospheres,” may be several times higher.

If you have any questions or comments, please contact us.

Disclaimer: The info presented here has been compiled from sources believed to be reliable, mostly notably “Corrosion and Protection” by Einar Bardal. No guarantee is implied or expressly stated here and the data given is intended as a guide only. 

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Vibration can be very harmful for an assembly because it may cause high fatigue stress to the metal hose, which leads to the development of cracks and premature failure of the assembly. Therefore, to decrease harmful effects of vibration, it is important during assembly fabrication to take into consideration such factors as minimum hose length requirements, operating pressure and respective derating factors for a type of vibration or dynamic stress.

If vibration is present it is especially important to follow Assembly Installation Handling Precautions which include making sure that the hose bend and the main direction of movement lie in one plain and avoiding dangerous torsions.

It is important to calculate proper length of the assembly, keeping in mind that there are some requirements as to the minimum live length of the assembly used in an application involving vibration. While minimum hose length requirements will vary based on the type and intensity of vibration experiences, suggestions are found in the table below.

Note: As been already pointed out there are some reduction factors (for published Working Pressure) that should be considered with vibration and other dynamic stresses. These factors can be as low as 0.32 in case of strong vibrations with pulsating and unsteady flow through the hose. Please consult Penflex for details.

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Since we discussed the maximum service temperatures of common austenitic steels in Engineering Bulletin #106, we’ll now look at how mechanical properties of austenitic steels are influenced by cryogenic temperatures and what types of stainless steel alloys are best suited for low temperature applications.

During World War II, experience with the brittle fracture of steel ships caused engineers to look  closely at what happens to metals in cold weather. They found that though many metals have good “room-temperature” characteristics, they do not necessarily maintain those characteristics at low temperatures.

For example, Ferritic (405, 409, 430), Martensitic (403, 410, 414, 416) and Duplex stainless steels (329, 2205) tend to become brittle as the temperature is reduced. Fracture can occur, sometimes with catastrophic results. While stretching or bulging may serve as an indicator of impending plastic failure, such signs are absent in the case of these metals. Therefore alloys for low-temperature service are those that retain suitable properties such as yield, tensile strength and ductility.

The austenitic stainless steels such as 304 and 316 retain these engineering properties at cryogenic temperatures and can be classified as ‘cryogenic steels.’ They are commonly used in arctic locations and in the handling and storage of liquid gases such as liquid nitrogen and liquid helium. Liquid helium is the coldest material known with a boiling point of -452°F (-269 °C).

The table below shows mechanical properties of stainless steels at low temperatures. Elongation is an indication of their good ductility. There is an increase in tensile and yield strengths as the temperature decreases as well.

Mechanical Properties of 304, 321 and 316 Stainless Steels at Cryogenic Temperatures.

Note: In designing a metal hose assembly for cryogenic service, care must be taken to ensure that the fittings and any accessory (guard/liner) materials are suitable for the intended operating temperatures as well.

If you have any questions or comments, please contact us.

Disclaimer: The info presented here has been compiled from sources believed to be reliable, including the American Society of Materials Specialty Handbook on Stainless Steels. No guarantee is implied or expressly stated here and the data given is intended as a guide only.

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