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Pipe Stuff ExplainedWhat your mother never told you about pipe and schedule thickness. |
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Pipe Stuff ExplainedWhat your mother never told you about pipe and schedule thickness. |
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Dimensions General Information In sizes from 1/8-inch thru 12-inch, pipe is known by its nominal inside diameter, which differs somewhat from its actual inside diameter. Early pipe manufacturers made the walls in the smaller sizes much too thick, and in correcting this error in design, they took the excess from the inside to avoid changing the sizes of the companion fittings. To distinguish pipe sizes from actual measured diameters, the terms iron pipe size (IPS) or nominal pipe size (NPS) are usually used. For sizes larger than 12-inch, pipe is known by its actual outside diameter. For all pipe sizes, the outside diameter (O.D.) remains relatively constant; the variations in wall thickness affect only the inside diameter (I.D.). To distinguish different weights of pipe, three long standing traditional designations are used: standard wall (Std.), extra strong wall (XS), and double extra strong wall (XXS). These last two designations are sometimes referred to as extra heavy wall (XH), and double extra heavy wall (XXH). For the purpose of standardizing pipe dimensions, the American National Standards Institute (ANSI) sponsored by the American Society for Testing Materials (ASTM) and the American Society of Mechanical Engineers (ASME), published ANSI B36.10. To broaden the range of wall thicknesses, schedule numbers from schedule 10 (S.10) thru schedule 160 (S.160) were adopted for steel pipe. These schedule numbers indicate approximate values for 1000 times pressure-stress ratios. Later, stainless steel schedule numbers from Schedule 5S thru schedule 80S were published in ANSI B36.19 for sizes thru 12-inch. The addition of the letter "S" after the schedule number identified it as pertaining to stainless steel. Certain relationships exist among the traditional designations of Std., XS, and XXS, the ANSI schedule numbers, and the actual wall thicknesses. Std. and S.40 are the same in sizes thru 10-inch; in sizes above 10-inch, Std has a wall of 3/8-inch. XS has a wall thickness of 1/2-inch. XXS has no corresponding schedule number, but in sizes thru 6-inch, XXS has a wall thickness twice as thick as XS. Stainless steel schedules 40S and 80S are identical with carbon steel designations Std and XS, respectively, thru 12-inch. Unless otherwise designated, references to pipe wall thickness always mean the nominal, or average, wall thickness. Most ASTM tolerances on regular pipe products specify that wall thickness of pipe at any point is to be no more than 12 1/2% under the nominal wall thickness specified. This means that a minimum wall of 0.875 times the nominal wall could apply for regular mill rolled steel. Materials Construction Information The vast majority of pipe is made from Carbon Steel in a variety of chemical compositions. and methods of manufacture. Carbon steel pipe, in some specifications, is available in either Grade A or Grade B and in a few cases Grade C. Due to a higher carbon content, Grades B and C have a higher tensile strength than Grade A, but are less ductile. The American Society for Testing Materials (ASTM) publishes most of the specifications for piping materials. Some of the most common specifications for carbon pipe are listed below. ASTM A-53B This general service carbon steel pipe is electrical resistance welded. This grade is typical Schedule 40 and 80 pipe. It is well suited for fabrication, and may be used for pressure vessels with pressure and temperature limitations. ASTM A-52F This material is for ordinary uses in handling water, oil, or gas. Under the specifications, this material is not suitable for bending, pressure vessel or high temperature service. Only continuously welded is commonly manufactured. This grade is typically used for plant water service. ASTM A-106 This is seamless pipe suitable for high pressure, high temperature service and is available in either Grade A or B, and in some walls Grade C. Grade C is considered a special product supplied only by special order at the mill. Available to Schedule 100.
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