The Chlorine Institute’s Pamphlet 6 “Piping Systems for dry chlorine” provides useful information and gives practical suggestions for the selection of material suited for chlorine piping systems. Materials of construction for chlorine transfer hoses are discussed in Appendix A of the Pamphlet. It is permitted for chlorine transfer hoses to have both metallic and non-metallic inner cores. In case of metallic hose the inner core shall be Monel 400 (UNS N04400) or Hastelloy C-276 (UNS N10276). For non-metallic hoses the inner core shall be virgin, unfilled PTFE with or without fiberglass reinforcement. So, what are the advantages and disadvantages of one material over the other?

The issue of permeability is probably the most commonly cited disadvantage for non-metallic hoses. Though certain technological advances have been made to reduce permeability in PTFE, the issue is still addressed directly in Section 7.5 of Appendix A, which states:

“Permeability: The inner core of non-metallic hoses is subject to some degree of permeability of chlorine. The braid and chafe guard shall be designed to allow chlorine which permeates the inner core to escape to atmosphere. Uses of non-metallic hose shall be limited to applications where adequate ventilation has been provided.”

Non-metallic hoses would appear to have other “limiting” characteristics as well. Although chlorine transfer hoses are only required to be designed for temperatures between -40F and 122F (which PTFE hoses can certainly handle), Monel hoses can operate from -300F to 800F. Finally, Positive Material Identification (PMI) can be used to confirm that metallic hoses are constructed from specific alloys. There is no known PMI for non-metallic materials.

Penflex designs and manufacturers Monel and Hastelloy Chlorine Transfer Hoses in complete compliance with The Chlorine Institute’s Pamphlet 6. To learn more about them, click here.

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

Note: To print this bulletin on the advantages of using 321 SS vs 304/304L SS, please click here. 

At first glance, it appears that type 304/304L SS is very similar to type 321 SS. When comparing the chemical composition of 321 SS and 304/304L SS, it is clear that the chromium (Cr) and nickel (Ni) ranges of these alloys are very similar. The difference appears when the issue of carbide precipitation in the heat-affected zone (HAZ) is discussed or fatigue strength and temperature are considered.

Carbide precipitation

The weld areas with temperatures 930°F – 1470°F are often called the carbide precipitation zone – in which Chromium (Cr) combines with Carbon (C) and precipitates chromium carbides at the grain boundaries significantly reducing corrosion resistance of steel in this zone. One of the ways to combat this phenomenon is to lower the carbon content in steel to decrease the carbide precipitation. 304L SS is an example of such steel; the “L” in 304L is for “Lower carbon” (.030% max vs. .080% max for 304 steel). An even more effective way to reduce carbide precipitation is through the addition of Titanium (Ti) to the alloy to stabilize it. The carbon is more attracted to the Titanium (Ti) and therefore it leaves the chromium alone. To be a true “stabilized” grade the 321 steel has to have Titanium (Ti) content at least 5 times than its Carbon (C) content. Reduced risk of corrosion in the HAZ is the main advantage of 321.

Fatigue strength

In dynamic applications, fatigue strength is also important to consider. And in this respect 321 SS has a slight advantage over 304 SS. Fatigue or endurance limits (strength in bending) of austenitic stainless steels in the annealed condition are about one-half the tensile strength.Typical tensile and endurance limits for these alloys (annealed) are presented in the table below:

Temperature Factors

Temperature factors could be another factor to consider in some applications. As we can see in the table below the temperature reduction factors are slightly higher for 321 than for 304L at most elevated temperatures:

The design guide by “Stainless Steel Producer’s of North America” was used for researching this answer.
Download the guide

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.

Learn about the differences between the 300 series stainless steels here.

To print, please click here. 

Note: To print, please click here. 

There was a time when Penflex used helium tracer gas for leak detection. Helium was used because its molecules are small, smaller than air molecules. We used to test each piece of metal hose under water and watched for bubbles escaping to the surface.

Although, at the time, we had determined this was the best way to identify and locate a possible leak (evidenced by bubbles), there was also a disadvantage. In this leak detection method, small leaks form bubbles at a slow rate. It takes a good eye and significant time to ensure there are no leaks. In addition the process sometimes inadvertently introduced water into the hose. We were eager to incorporate a leak detection method that was more efficient.

Once we learned of a new method in leak detection, we were eager to incorporate it into our testing process. This detection method uses hydrogen as the tracer gas and is based on a microelectronic sensor technology known as MIS-FET. The sensor is a field effect transistor in an integrated circuit. The gate electrode of the transistor is made of a hydrogen absorbing metal alloy (metal hydride). When this device is exposed to hydrogen, the gas molecules absorb on its surface, dissociate into hydrogen ions (protons) and diffuse rapidly into the gate metal. The absorption of hydrogen ions affects the work function (surface potential) of the metal, which gives the same effect as if the gate voltage of the transistor was changed. The electrical output signal from such sensors must undergo signal interpretation in order to give reliable measurements. This is done by a microprocessor in the instrument.

Hose sizes with nominal inside diameters from 12” down to 2-1/2” are manufactured in mill lengths approximately 25 feet long. These hose sections are filled with the 5%-95% hydrogen-nitrogen mix, the ends are capped and a probe is manually moved directly along the weld seam at a rate of 5 seconds per foot.

If there should be a leak anywhere along the weld seam, the hydrogen gas from inside the hose finds its way through the hole by “diffusion.” The hydrogen detector unit is calibrated to a leak alarm level of .0088 cc/sec.

Hose sizes with nominal inside diameters ranging from ¼” to 2” are manufactured in mill lengths approximately 50 feet long. In order to test these longer hose sections more efficiently, an automated system is used. A “tram” moves a short section of PVC pipe along the entire length of the hose. A special probe “sniffs” the volume of gas which accumulates inside the PVC tube which is sliding along the hose.

If gas leaks out from the weld seam, the concentration of hydrogen in the void around the hose will increase. The hydrogen detector unit is calibrated to a leak alarm concentration of 10 ppm hydrogen. An audible alarm sounds when a leak is encountered and the moving “tram” stops. At this point, the tester uses the manual probe to locate the leak and mark it so that it can be cut out after the test.

Hydrogen leak test being administered in Penflex’s Gilbertsville, PA headquarters.

If you have any questions in regards to the leak detection method described here, please contact us.

There’s also more information about our various nondestructive leak testing methods here.

To print, please click here. 

The Penflex catalog offers you detailed information about our product line of flexible metal hose. Product descriptions and detailed specifications are included.

Penflex Catalog

We have made several changes and additions to our Product Catalog which are listed below. The printed edition of the latest version of our Product Catalog will be available in the near future. To receive free copies of the Catalog, please contact us and they will be shipped to you promptly.

PAGE 1

The pressure rating on the 2″ Series 700:

• With 1 layer of braid rating has been changed from 518 to 516;
• With 2 layers of braid rating has been changed from 829 to 826;

The pressure rating on the 1/4″ Series 700:

• With 1 layer of braid rating has been changed from 2,562 to 2,116;
• With 2 layers of braid rating has been changed from 4,099 to 3,125;

The pressure rating for two new sizes 1/4″ and 3/8″ added for Series 800:

• 1/4″ with 1 layer of braid rated at: 2,562 with 2 layers of braid rated at: 4,099;
• 3/8″ with 1 layer of braid rated at: 1,501 with 2 layers of braid rated at: 2,401;

PAGE 6

Some changes have been made to geometry of 1/4″ and 3/8″ hose Series 700:

• 7xx-004 Nominal OD changed from 0.50 to 0.48;
• 7xx-006 Nominal OD changed from 0.67 to 0.63;
• 7xx-1SB-004 Maximum Working Pressure changed from 2,562 to 2,116;
• 7xx-2SB-004 Maximum Working Pressure changed from 4,099 to 3,125;
• 7xx-2SB-004 Maximum Test Pressure changed from 6,150 to 4,687;
• 7xx-2SB-004 Nominal Burst Pressure changed from 16,400 to 12,500;
• 7xx-1SB-080 Nominal Burst Pressure changed from 754 to 764;
• 7xx-224 Carton Quantity changed from 12-15 to 10.5;

PAGE 7

Pressure rating have been changed for the following items:

• 1SB-006 Maximum Working Pressure changed from 1,848 to 1,501;
• 1SB-006 Nominal Burst Pressure changed from 7,391 to 6,004;
• 1SB-032 Maximum Working Pressure changed from 518 to 516;
• 1SB-032 Nominal Burst Pressure changed from 2,074 to 2,064;
• 1SB-096 Maximum Working Pressure changed from 207 to 135;
• 1SB-032 Nominal Burst Pressure changed from 662 to 660;

PAGE 8

Two new sizes 8xx-004 and 8xx-006 have been added to Series 800 (these are hoses formerly manufactured as 7xx-004 and 7xx-006) with the following technical data:

If you have any questions or concerns about these changes, please contact us.