More About Pipe...

Most of the following information is from the Grinnell Supply Sales Company's P-90 catalog from 3/1990.

 

 

The pipe used by the electrical and plumbing (including gas) industries is an ASTM A-135 which comes in an A or B grade. It is an Electric Resistance Weld (ERW) steel pipe, which mean that it has a seam, and is available in sizes up to 30" diameter.

 

Did you know...

  • ...that 5" GRC (Galvanized Rigid Conduit) is the maximum conduit size allowed per NEMA, although 6" GRC can be used with a variance. Check it out: NEMA.org (still looking for the exact location to cite.)

  • ...that 6" is also frequently used as an innerduct casing.

  • ...there are several way of making pipe. Here are flow diagrams for a couple of the different methods:

    Electric Resistance Weld (ERW)

    ERW Strecth Reduced Process

Dimensions

In sizes from ⅛" through 12", pipe is known by its nominal inside diameter, which differs somewhat from the 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", pipe is known by its actual outside diameter. For all pipe sizes, the Outside Diameter (OD) remains relatively constant; variations in wall thickness affect only the Inside Diameter (ID).

 

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 variations are sometimes referred to as Extra Heavy wall (XH) and Double Extra Heavy wall (XXH), respectively.

 

For the purpose of standardizing pipe dimensions, the American National Standards Institute (ANSI), in an effort sponsored by the American Society for Testing Materials (ASTM) and the American Society of Mechanical Engineers (ASME), published ANSI B36.10M. To broaden the range

 of wall thicknesses, schedule numbers from schedule 10 (S.10) through schedule 160 (S.160) were adopted for steel pipe. These schedule numbers indicate approximate values for 1000 times the pressure-stress ratios. Later, stainless steel schedule number from schedule 5S through schedule 80S were published in ANSI B36.19 for sizes through 12". The addition of the letter "S" after the schedule number identifies 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 thickness. Std and S.40 are the same in sizes through 10"; in sizes above 10", Std has a wall thickness of ⅜". XS and S.80

Pipe/Conduit Dimensions
S.40 GRC (Rigid) Size IMC Size EMT

O.D.

I.D. Wall

O.D.

I.D. Wall

O.D.

I.D. Wall
0.840” 0.622” 0.109” ½" 0.810” 0.675” 0.070” ½" 0.706” 0.622” 0.042”
1.050” 0.824” 0.113” ¾" 1.024” 0.879” 0.075” ¾" 0.922” 0.824” 0.049”
1.315” 1.049” 0.133” 1" 1.285” 1.120” 0.085” 1" 1.163” 1.049” 0.057”
1.660” 1.380” 0.140” 1¼" 1.630” 1.468” 0.085” 1¼" 1.510” 1.380” 0.065”
1.900” 1.610” 0.145” 1½" 1.875” 1.703” 0.090” 1½" 1.740” 1.610” 0.065”
2.375” 2.067” 0.154” 2" 2.325” 2.170” 0.095” 2" 2.197” 2.067” 0.065”
2.875” 2.469” 0.203” 2½" 2.874” 2.597” 0.130” 2½" 2.875” 2.731” 0.072”
3.500” 3.068” 0.216” 3" 3.446” 3.216” 0.130” 3" 3.500” 3.356” 0.072”
4.000” 3.548” 0.226” 3½" 3.961” 3.711” 0.130” 3½" 4.000” 3.834”

0.083”

4.500” 4.026” 0.237” 4" 4.456” 4.206” 0.130” 4" 4.500” 4.334” 0.083”
5.563” 5.047” 0.258” 5"              
6.625” 6.065” 0.280” 6"              

are the same in sizes through 8"; in sizes 10" and above, XS has a wall thickness of ½". XXS has a wall twice as thick as XS. Stainless steel schedules 40S and 80S are identical with carbon steel designations Std and XS, respectively, through 12".

 

Weights for carbon steel pipe are based on a density of 0.2833 pounds per cubic inch; for wrought iron pipe, the density is 0.2777 pounds per cubic inch. Since wrought iron pipe is made to steel outside diameters and steel weights per foot, the wall thicknesses of wrought iron are necessarily slightly greater than steel pipe to compensate for this difference in densities.

 

Unless otherwise designated, references to pipe wall thicknesses always mean the nominal, or average, wall thickness. Most ASTM tolerances on regular pipe products specify that the wall thickness of pipe at any point is to be no less than 12½% of the wall thickness specified. This means that a minimum wall of 0.875 times the nominal wall could apply for regular mill rolled pipe.

 

Unless ordered to cut lengths, at a higher price, pipe is supplied in random lengths (RL). This is due to the method of manufacture where damaged ends of each length are cut away during the finishing operations. For Std pipe, a single random length usually falls in the range of 16' to 22'.

 

Threaded and coupled (T&C) pipe has threads that taper ¾" per foot on the diameter for all sizes. Threads conform to ANSI B1.20.1. End to end measurements of T&C pipe include the attached coupling.

 

Materials

The vast majority of pipe is made from carbon steel in a wide 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

Symbol

Element

C

Carbon

Mn

Manganese

P

Phosphorous

S

Sulphur

ASTM A135 Specification Data

Electric resistance welded steel pipe, NPS ¼" - 30", sch 10, sch 40, XL THD & Lightwall,  for carrying liquid, gas or vapor. Made in grades A or B.

Chemical Composition

Grade

C%

Mn%

P%

S%

Min. Yield psi

Min. Tensile psi

Grade A

.25

.95

.05

.06

30k

48k

Grade B

.30

1.20

.05

.06

35k

60k

Wall Thickness Variations: <12.5% under nominal.
Weight Variations: ±10% sch. 10, +10%/-3% sch. 40
OD Variations: ±1%
Hydrostatic Testing: Pressure held ≥ 5 seconds. Weld test
NDE Testing: Test method/practice E213, E273 or E213.

higher carbon content, Grades B and C have higher tensile strength than Grade A, but are less ductile. No extra charge is usually made for Grade B over Grade A. Generally, Grade B can be used in place of Grade A, but Grade A cannot be substituted on applications requiring Grade B.

 

Other common pipe compositions are wrought iron, chrome-moly steel (chromium-molybdenum), stainless steel (chromium-nickel) and nickel steel. A number of non-ferrous metals are also manufactured in iron pipe sizes.

 

The ASTM publishes most of the specifications for piping materials. The great majority  of the grades recognized in ASTM specifications are approved by ASME and ANSI codes. In addition, the American Petroleum Institute (API) has established materials specifications covering line pipe for the oil and gas industries.