Osakue 1 Piping Lines and Fittings Introduction Fluids are transported under pressure through hollow materials called lines. The common three types of fluid lines are pipes, tubes, and hoses. These lines must provide leak proof passage at the required operating pressure of the system. Standard pressure rating of pressure system varies from 125 psig to 6000 psig. Test pressures are normally higher than the operating pressures. The operating pressure is greatly influenced by the operating temperature. Generally, the mechanical strength of materials decreases with increasing temperature, so operating pressures are determined by the operating temperatures. Selecting a proper line is an important function in piping system design. Pipes Pipes are rigid hollow cylinders used for transporting fluids and sometimes, solids such as pellets, powders, etc. Pipes are made of different materials such as steel, cast iron, plastic, etc. ASME B36 codes specify dimensional requirements of pipes. For example, ASME B36.10M: Welded and Seamless Wrought Steel Pipe; ASME B36.19M: Stainless Steel Pipe. Pipe Materials Pipes may be made from metals, plastic, concrete, and glass. Cast iron and ductile iron pipes are popular for underground water, gas and sewer applications. Steel is perhaps the most popular pipe material. Steel pipes are strong, durable, weldable, machinable, and can stand high temperature. They are often used to handle water, oil, petroleum and steam. Carbon steel pipes are the most popular, being cheaper than other materials. They are the natural choice if they can meet application requirements of pressure, temperature, corrosion resistance, and hygeine. Stainless steel pipes are used in corrosive environments and food processing facilities. Copper and copper alloys are corrosion resistant and are commonly used for instrument lines, food processing, and heat transfer equipment, like heat exchangers, steam, air and oil lines. However, stainless steel pipes are increasingly being used for these applications. Plastic pipes are used extensively in piping systems today, especially in plumbing. They have high resistance to corrosion and chemical degradation but cannot withstand high pressures and temperatures. Plastic pipes are used especially for handling corrosive or hazardous gases and dilute mineral acids. Concrete pipes are pre-cast and are used mainly for underground application. Glass pipes are popular in the food, beverage, chemical, and pharmaceutical plants. Their application is limited to temperatures of 450 o F (230 o C). Lined Pipe Lined pipes are made of internal surfaces different from the main pipe material. For example, a carbon steel pipe may be lined with Teflon to enhance corrosion resistance. Lined pipes and fittings are joined by flanges. Other lining materials include glass, asphalt, zinc, concrete, and different types of plastics, e.g. epoxy. Pipe Manufacture Pipes are manufactured by two main methods: seamless and welding methods. Seamless pipe production involves piercing a solid near-molten steel rod called a billet with a mandrel. The mandrel size determines the inside diameter of the pipe. Welded pipes are made from rolled steel plates and may be butt-welded or spiral-welded. Fig. 1 shows pipes of seamless, butt-welded or spiral-welded type. a) Seamless b) Rolled c) Spiral-welded Fig. 1: Pipe manufacturing methods
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Piping Lines and Fittings
Introduction
Fluids are transported under pressure through hollow materials called lines. The common three types of fluid
lines are pipes, tubes, and hoses. These lines must provide leak proof passage at the required operating
pressure of the system. Standard pressure rating of pressure system varies from 125 psig to 6000 psig. Test
pressures are normally higher than the operating pressures. The operating pressure is greatly influenced by
the operating temperature. Generally, the mechanical strength of materials decreases with increasing
temperature, so operating pressures are determined by the operating temperatures. Selecting a proper line is
an important function in piping system design.
Pipes Pipes are rigid hollow cylinders used for transporting fluids and sometimes, solids such as pellets, powders,
etc. Pipes are made of different materials such as steel, cast iron, plastic, etc. ASME B36 codes specify
dimensional requirements of pipes. For example, ASME B36.10M: Welded and Seamless Wrought Steel
Pipe; ASME B36.19M: Stainless Steel Pipe.
Pipe Materials
Pipes may be made from metals, plastic, concrete, and glass. Cast iron and ductile iron pipes are popular for
underground water, gas and sewer applications. Steel is perhaps the most popular pipe material. Steel pipes
are strong, durable, weldable, machinable, and can stand high temperature. They are often used to handle
water, oil, petroleum and steam. Carbon steel pipes are the most popular, being cheaper than other materials.
They are the natural choice if they can meet application requirements of pressure, temperature, corrosion
resistance, and hygeine. Stainless steel pipes are used in corrosive environments and food processing
facilities. Copper and copper alloys are corrosion resistant and are commonly used for instrument lines, food
processing, and heat transfer equipment, like heat exchangers, steam, air and oil lines. However, stainless
steel pipes are increasingly being used for these applications. Plastic pipes are used extensively in piping
systems today, especially in plumbing. They have high resistance to corrosion and chemical degradation but
cannot withstand high pressures and temperatures. Plastic pipes are used especially for handling corrosive or
hazardous gases and dilute mineral acids. Concrete pipes are pre-cast and are used mainly for underground
application. Glass pipes are popular in the food, beverage, chemical, and pharmaceutical plants. Their
application is limited to temperatures of 450oF (230
oC).
Lined Pipe
Lined pipes are made of internal surfaces different from the main pipe material. For example, a carbon steel
pipe may be lined with Teflon to enhance corrosion resistance. Lined pipes and fittings are joined by flanges.
Other lining materials include glass, asphalt, zinc, concrete, and different types of plastics, e.g. epoxy.
Pipe Manufacture
Pipes are manufactured by two main methods: seamless and welding methods. Seamless pipe production
involves piercing a solid near-molten steel rod called a billet with a mandrel. The mandrel size determines
the inside diameter of the pipe. Welded pipes are made from rolled steel plates and may be butt-welded or
spiral-welded. Fig. 1 shows pipes of seamless, butt-welded or spiral-welded type.
a) Seamless b) Rolled c) Spiral-welded
Fig. 1: Pipe manufacturing methods
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In butt-welded pipes, the steel plate is heated and fed through special rollers that bend and join the ends of
the plate into a pipe. Spiral welded pipes are made from twisted strips of metals and welded in spiral form.
This is the least common of the pipe making methods. ASME B31.1.0 assigns strength factors of 100%, 85%
and 60% to seamless, butt- and spiral-welded pipes, respectively.
Pipe Sizes
The American National Standards Institute (ANSI) has standardized pipe sizes. Pipes are specified by the
nominal pipe size (NPS) in English units. It is used as a reference or designation for a pipe size. The metric
system assigns DN (Nominal Diameter) sizes to pipes. Table 1 gives pipe sizes in common use. The normal
range of pipe sizes for process pipe is 1/8” to 48”. However, stock size range is from ½” to 24”. Sizes outside
the normal ranges may be obtained by special order. Pipe sizes of 1/8” to 1½” are usually for service and
instrument lines. The common process pipe sizes are in the range of 4” and 48” in diameter.
English
(NPS: in)
Metric
(DN: mm)
English
(NPS: in)
Metric
(DN: mm)
English
(NPS: in)
Metric
(DN: mm)
1/8 6 6 150 30 750
¼ 8 8 200 32 800
3/8 10 10 250 36 900
½ 15 12 300 40 1000
¾ 20 14 350 42 1100
1 25 16 400 48 1200
1 ¼* 32 18 450 54 1400
1 ½ 40 20 500 60 1500
2 50 22 550 64 1600
2 ½* 65 24 600 72 1800
3 80 26 650 80 2000
4 100 28 700 88 2200
Table 1: Common pipe sizes (*For special applications. Not used in new designs)
NPS of 1/8” to 12” is designation for a size only. It is not equal to the outside or inside diameter of the pipe,
but is close enough to the inside diameter for most calculations. NPS above of 14” and above refers to the
outside diameter of the pipe. The outside diameter of a pipe is it’s inside diameter plus twice its wall
thickness. The NPS helps in knowing the outside diameter of pipe; usually by referring to a table of pipe
sizes. The inside diameter of a pipe is the outside diameter minus twice its wall thickness. Pipe wall
thickness is standardized in ANSI B36.10M-1985 with schedule numbers from 5 to 160. Thickness varies
with weight and size of pipe and higher schedule number represents thicker pipes. The outside diameter of all
pipe sizes is fixed (Fig. 2) but the wall thickness can vary depending on the schedule number. Pipe thickness
is also described as standard, strong and extra strong. Standard thickness corresponds roughly to schedule 40
and extra-strong thickness is about schedule 80.
a) Standard b) Extra Strong (XS) c) Double extra strong (XXS)
Fig. 2: Pipe thickness and schedules
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OD = Outside diameter; ID = Inside diameter; T = wall thickness
OD = ID + 2T ID = OD - 2T T = 0.5(OD – ID)
The pressure rating of pipes is an important parameter in their specification. Pressure standards range from
125 psig (0.862 MPa) to 4500 psig (31 MPa). Allowed pressure is greatly influenced by operating
temperature. Thicker pipes are normally required for higher pressure applications. The commonly used
schedule numbers are 40, 80, and 160. Schedule 40 or standard (SD) seamless pipes are usually used for low
pressure applications. Schedule 80 or extra strong (XS) seamless pipes are designed for medium pressure
applications; while schedule160 pipes or double extra strong (XXS) pipes are designed for high pressure