4.0 Pneumatic Tubing


Copper tubes are primarily used for pneumatic connections. Earlier pneumatic instruments were more popular and used (controllers, transmitters, indicators etc.). Thus pneumatic tubing was used widely. However now-a-days most of the instruments that are used are electronic instruments, thus the use of pneumatic tubing is limited. Still, at present this is used to connect the pneumatic actuator and its accessories viz. positioners, I/P converters, solenoid valves etc. which are quite important from plant operation point of view. Pneumatic instruments are still prevalent in hazardous areas. Even though the
pneumatic instruments are passé, they still provide a very reliable alternative to electronic instruments.

4.1 Advantages of using copper tubes
Strong, corrosion resistant, copper tube is the leading choice for pneumatic piping. There are seven primary reasons for this:

1. Copper is economical. Easy handling, forming and joining permits savings in installation time, material and overall costs. Long-term performance and reliability mean fewer callbacks, and that makes copper the ideal costeffective tubing material.

2. Copper is lightweight. Copper tube does not require the heavy thickness of ferrous or threaded pipe of the same internal diameter. This means copper costs less to transport, handles more easily and, when installed, takes less space.

3. Copper is formable. Because copper tube can be bent and formed, it is frequently possible to eliminate elbows and joints. Smooth bends permit the tube to follow contours and corners of almost any angle. With soft temper tube, particularly when used for renovation or modernization projects, much less wall and ceiling space is needed.

4. Copper is easy to join. Copper tube can be joined with capillary fittings. These fittings save material and make smooth, neat, strong and leak-proof joints. No extra thickness or weight is necessary to compensate for material removed by threading.

5. Copper is safe. Copper tube will not burn or support combustion and decompose to toxic gases. Therefore, it will not carry fire through floors, walls and ceilings. Volatile organic compounds are not required for installation.

6. Copper is dependable. Copper tube is manufactured to well-defined composition standards and marked with permanent identification so you know exactly what it is and who made it.

7. Copper resists corrosion. Excellent resistance to corrosion and scaling assures long, trouble-free service, which means satisfied customers.


4.2 Different types of copper tubes
Table 4-1 below identifies the six standard types of copper tube and their most common applications2. The table also shows the ASTM Standard appropriate to the use of each type along with a listing of its commercially available lengths, sizes and tempers.

Types K, L, M, DWV and Medical Gas tube are designated by ASTM standard sizes, with the actual outside diameter always 1/8-inch larger than the standard size designation. Each type represents a series of sizes with different wall thicknesses. Type K tube has thicker walls than Type L tube, and Type L walls are thicker than Type M, for any given diameter. All inside diameters depend on tube size and wall
thickness.

Copper tube for air-conditioning and refrigeration field service (ACR) is designated by actual outside diameter.

“Temper” describes the strength and hardness of the tube. In the piping trades, drawn temper tube is often referred to as “hard” tube and annealed as “soft” tube. Tube in the hard temper condition is usually joined by soldering or brazing, using capillary fittings or by welding. Tube in the soft temper can be joined by the same techniques and is also commonly joined by the use of flare-type and compression fittings.

It is also possible to expand the end of one tube so that it can be joined to another by soldering or brazing without a capillary fitting—a procedure that can be efficient and economical in many installations.

Tube in both the hard and soft tempers can also be joined by a variety of “mechanical” joints that can be assembled without the use of the heat source required for soldering and brazing.

Table-4-1

1. There are many other copper and copper alloy tubes and pipes available for specialized applications.
2. Individual manufacturers may have commercially available lengths in addition to those shown in this table.
3. Tube made to other ASTM standards is also intended for plumbing applications, although ASTM B 88 is by far the most widely used. ASTM Standard Classification B 698 lists six plumbing tube standards including B 88.
4. Available as special order only.


4.3 Recommendations for selection of a type of copper tube
It is up to the designer to select the type of copper tube for use in a particular application. Strength, formability and other mechanical factors often determine the choice. Plumbing and mechanical codes govern what types may be used. When a choice can be made, it is helpful to know which type of copper tube has and can serve successfully and economically in the following applications:

a. Underground Water Service: Use Type M hard for straight lengths joined with fittings, and Type L soft where coils are more convenient.

b. Water Distribution Systems: Use Type M for above and below ground.

c. Chilled Water Main: Use Type M for all sizes.

d. Drainage and Vent System: Use Type DWV for above- and below-ground waste, soil and vent lines, roof and building drains and sewers.

e. Heating: For radiant panel and hydronic heating and for snow melting systems, use Type L soft temper where coils are formed in place or prefabricated, Type M where straight lengths are used. For water heating and low-pressure steam, use Type M for all sizes. For condensate return lines, Type L is successfully used.

f. Solar Heating: See ‘Heating’ section above. For information on solar installation and on solar collectors, write CDA.

g. Fuel Oil, L.P. and Natural Gas Services: Use Type L or Type ACR tube with flared joints in accessible locations and brazed joints made using AWS A5.8 BAg series brazing filler metals in concealed locations.

h. Nonflammable Medical Gas Systems: Use Medical Gas tube Types K or L, suitably cleaned for oxygen service per NFPA Standard No. 99, Health Care Facilities.

i. Air-Conditioning and Refrigeration Systems: Copper is the preferred material for use with most refrigerants. Use Types L, ACR or as specified.

j. Ground Source Heat Pump Systems: Use Types L or ACR where the ground coils are formed in place or prefabricated, or as specified.

k. Fire Sprinkler Systems: Use Type M hard. Where bending is required, Types K or L is recommended. Types K, L and M are all accepted by NFPA.

l. Low Temperature Applications – Use copper tube of Type determined by rated internal working pressures at room temperature as shown in Tables below. Copper tube retains excellent ductility at low temperatures to –452°F and yield strength and tensile strength increase as temperature is reduced to this point. This plus its excellent thermal conductivity makes an unusual combination of properties for heat exchangers, piping, and other components in cryogenic plants and other low temperature applications.

m. Compressed Air—Use copper tube of Types K, L or M determined by the rated internal working pressures as shown in tables 4-2 to 4-9 below. Brazed joints are recommended.

Table-4-2: Rated Internal Working Pressures for Copper Tube: TYPE DWV*

Table-4-3: Rated Internal Working Pressures for Copper Tube: TYPE K*

Table-4-4: Rated Internal Working Pressures for Copper Tube: TYPE L*

Table-4-5: Rated Internal Working Pressures for Copper Tube: TYPE M*

Table-4-6: Rated Internal Working Pressures for Copper Tube: TYPE ACR*


NOTE: * Based on ‘S’, the maximum allowable stress in tension (psi) for the indicated temperatures (°F).
** When brazing or welding is used to join drawn tube, the corresponding annealed rating must be used.
***Types M and DWV are not normally available in the annealed temper. Shaded values are provided for guidance when drawn temper tube is brazed or welded.


4.4 Technical Requirements of Copper tube
Following parameters are to be specified while preparing the specifications for copper tubes for pneumatic piping.

1. Type : Annealed Copper, Seamless copper tubes as per ASTM-B-68M.

2. Length: 15 m< L < 80 meters

3. Size (mm):


4. Fluid: Air /oil / water

5. Max. Pressure: 8.5 kg/cm2(g)

6. Max. Temperature: up to 100oC

7. Hardness: Rockwell F50

8. Ovality Variation : < 0.7% Of O.D.

9. Surface Finish : Better than 8.2 Microns For O.D & I.D

10. Mechanical Properties:
a. Tensile Strength: 2200 kg/Cm2 (g)
b. Yield Point: 650 kg/cm2 (g)
c. Elongation (%) in 50 mm Gauge Length: 40%

11. Tests

11.1 Type Tests
a. Hardness Test: On one test piece of each size and each batch as per ASTM-E-18
b. Expansion Test: On one sample piece of each size and each batch as per ASTM-B-153
c. Tensile Test: On one sample piece Of Each Size And Each Batch As Per ASTM-E-8M
d. Flattening And Doubling Over Test: On One sample piece Of Each Size and Each Batch As Per BS-2871 & ASTM-E-255
e. Chemical Analysis: one sample of each batch as per ASTM-E-53 & ASTMB-55M

11.2 Routine Tests
a. Dimensional Test: Required to be done on 10% of the lot
b. Hydrostatic Test: At pressure of 50 kg/cm2(g); for 10 min. Required to be done on each size each batch
c. Pneumatic Test: At a pressure 8.5 kg/cm2 (g); for 10 min. Required to be done on each size each batch.


4.5 Applicable international standards for copper tubes
Besides NPCIL specifications following international codes and standards may be referred while specifying copper tubes.

ASTM-B-68M: Standard specification for seamless copper tube, bright Annealed [metric]
ASTM-E-8M: Standard test Method for tension testing of metallic materials [metric]
ASTM-E-18: Standard test method for Rockwell hardness and Rockwell superficial hardness of metallic materials
ASTM-E-53: Method for chemical analysis of copper
ASTM-B-153: Standard test method for expansion [pin test] of copper and copper alloy pipe and tubing
ASTM-E-243: Standard practice for electro-magnetic [eddy current] examination of copper and copper alloy tubes.
ASTM-B-251M: Standard specification for general requirement for wrought seamless copper and alloy tubes [metric]
ASTM-E-255: Practice for sampling copper and copper alloy for determination of chemical composition.
BS-2871: Copper and copper alloys tubes

4 comments:

  1. The explanation is perfect and include all technical points related to Pneumatic Tubing and its statistical figures shows the availability in measurement of these respective tubes.

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