Pipes

In American standard, the pipes are covered under

a) ASME B 36.10 – Welded and Seamless Wrought Steel Pipe

b) ASME B 36.19 – Stainless Steel Pipe

Stainless steel pipes are available in schedule 5S, 10S, 40S and 80S whereas carbon steel pipes are available in schedule 10, 20, 30, 40, 60, 80, 100, 120, 140, 160, STD,XS, XXS.

The figures indicated in these standards are the nominal thickness and mill tolerance of 12.5% is applicable to those values.

Generally the thicknesses are specified by schedule numbers. B36.10 covers pipe sizes upto 80 inch (2000mm) NB and B36.19 covers pipe sizes upto 24 inch (600mm) NB. The thickness specified in these standards match except for the following:

• 10″ SCH80 / SCH80S
• 12″ SCH40 / SCH40S
• 12″ SCH80 / SCH80S
• 14″ SCH10 / SCH10S
• 16″ SCH10 / SCH10S
• 18″ SCH10 / SCH10S
• 20″ SCH10 / SCH10S
• 22″ SCH10 / SCH10S

Pipe Ends

Based on the material of construction and the pipe to pipe joint, the ends of the pipes are specified as follows.

Bevelled ends, Plain ends, Screwed ends, Flanged ends, Spigot/Socket ends

Butt Weld Pipe Joints

Advantages

1. Most practical way of joining big bore piping
2. Reliable leak proof joint
3. Joint can be radiographed

Disadvantages

1. Weld intrusion will affect flow
2. End preparation is necessary

Socket Weld Pipe Joints

Advantages

1. Easier Alignment than butt welding
2. No weld metal intrusion into bore

Disadvantages

1. The 1/16″(1.5 mm) recess pockets liquid
2. Use not permitted by code if Severe Erosion or Crevice Corrosion is anticipated.

Screwed Pipe Joints

 Advantages

1. Easily made at site
2. Can be used where welding is not permitted due to fire hazard

Disadvantages

1. Joint may leak when not properly sealed
2. Use not permitted by code if severe erosion, crevice corrosion, shock or vibration are anticipated.
3. Strength of pipe is reduced as threads reduce wall thickness
4. Seal welding may be required
5. Code specifies that seal welding shall not be considered to contribute for strength of joint

Flanged Pipe Joints

Advantages

1. Can be easily made at site
2. Can be used where welding is not permitted due to material properties or fire hazard.
3. Dismantling is very easy

Disadvantages

1. It is a point of potential leakage
2. Cannot be used when piping is subjected to high bending moment.

Spigot Socket Pipe Joints

Advantages

1. Can be easily made at site.
2. Can accept misalignment upto 10^oat pipe joints.

Disadvantages

1. Suitable for low pressure application.
2. Special configuration at pipe ends required.

Types of Pipes:

Based on the method of manufacture pipes could be classified as;

• Seamless
• Welded
• Electric Resistance Welded (ERW)
• Electric Fusion Welded (EFW)
• Spiral Welded
• Furnace Butt welded
• Double Submerged Arc Welded
• Forged and Bored

Pipe Materials:

1. ASTM A53: Welded and Seamless Steel Pipe Black and Galvanized
2. ASTM A106: Seamless CS Pipe for High Temp. Services
3. ASTM A120: Black and Hot Dipped Zinc coated (Galvanized) welded and seamless pipe for ordinary use
4. ASTM A134: Electric fusion welded steel plate pipe (Sizes ≥ 16”NB)
5. ASTM A135: Electric resistance welded pipe
6. ASTM A155: Electric fusion welded steel pipe for high temperature service
7. ASTM A312: Seamless and welded Austenitic stainless steel pipes
8. ASTM A333: Seamless and welded steel pipe for low temperature service
9. ASTM A335: Seamless ferric alloy steel pipe for high temperature service
10. ASTM A358: Electric fusion welded Austenitic chrome-nickel steel pipe for high temperature service
11. ASTM A369: Carbon and ferric alloy steel forged and bored for high temperature service
12. ASTM A376: Seamless austenitic steel pipe for high temperature central station service
13. ASTM A409: Welded large diameter Austenitic steel pipe for corrosive or high temperature service
14. ASTM A426: Centrifugally cast ferric alloy steel pipe for high temperature service
15. ASTM A430: Austenitic steel forged and bored pipe for high temperature service
16. ASTM A451: Centrifugally cast austenitic steel pipe for high temperature service
17. ASTM A452: Centrifugally cast austenitic steel cold wrought pipe for high temperature service
18. ASTM A524: Seamless carbon steel pipe for atmospheric and low temperature services
19. ASTM A587: Electric welded low carbon steel pipe for the chemical industry
20. ASTM A660: Centrifugally cast carbon steel pipe for high temperature service
21. ASTM A671: Electric fusion welded steel pipe for atmospheric and low temperature service (Sizes ≥ 16” NB)
22. ASTM A672: Electric fusion welded steel pipe for high pressure service at moderate temperature services (Sizes ≥ 16″NB)
23. ASTM A691: Carbon and alloy steel pipe, electric fusion welded for high pressure service at high temperatures (Sizes ≥ 16″ NB)
24. ASTM A731: Seamless and welded ferritic stainless steel pipe
25. ASTM A790: Seamless and welded ferritic/austenitic stainless steel pipe
26. ASTM A813: Single or double welded austenitic stainless steel pipe
27. ASTM A814: Cold worked welded austenitic stainless steel pipe
28. ASTM F1545: Plastic Lined Ferrous Pipe
29. API 5L: Line pipe

Thickness of Straight Pipe under Internal Pressure:

ASME B 31.3, the Process Piping Code, in clause 304.1.1 gives minimum thickness as follows:

tm = t + c

c = sum of the mechanical allowances (thread or groove depth) plus corrosion and erosion allowances. For threaded components, the nominal thread depth (dimension h of ASME B1.20.1, or equivalent) shall apply. For machined surfaces or grooves where the tolerance is not specified, the tolerance shall be assumed to be 0.5 mm (0.02 in.) in addition to the specified depth of the cut.

D = outside diameter of pipe as listed in tables of standards or specifications or as measured

d = inside diameter of pipe. For pressure design calculation, the inside diameter of the pipe is the maximum value allowable under the purchase specification.

E = quality factor from Table A-1A or Table A-1B from B31.3

P = internal design gage pressure

S = stress value for material from Table A-1 or Table A-1M from B31.3

T = pipe wall thickness (measured or minimum in accordance with the purchase specification)

t = pressure design thickness, as calculated in accordance with para. 304.1.2 of B31.3 for internal pressure or as determined in accordance with para. 304.1.3 of B31.3 for external pressure

tm = minimum required thickness, including mechanical, corrosion, and erosion allowances

W = weld joint strength reduction factor in accordance with para. 302.3.5(e) of B31.3

Y = coefficient from Table 304.1.1 (B31.3), valid for t < D/6 and for materials shown. The value of Y may be interpolated for intermediate temperatures.

For t ≥ D/6,

Y = (d + 2c) / (D + d + 2c)

For t < D/6,

the internal pressure design thickness for straight pipe shall be not less than that calculated in accordance with below equations.

t = PD / 2 (SEW + PY)

t = P (d + 2c) / 2 [SEW – P(1 – Y)]

For t ≥ D/6 or for P/SE > 0.385, calculation of pressure design thickness for straight pipe requires special consideration of factors such as theory of failure, effects of fatigue, and thermal stress.

Thickness of Straight Pipe under External Pressure:

To calculate wall thickness and reinforcement or stiffening requirements for straight pipe under external pressure, the procedure outlined in the BPV Code, Section VIII, Division 1, UG-28 using UG-30 shall be followed, using as the design length, L, the running Centre line length between any two sections stiffened in accordance with UG-29. As an exception, for pipe with Do/t < 10, the value of S to be used in determining Pa2 shall be the lesser of the following values for pipe material at design temperature:

(a) 1.5 times the stress value from Table A-1 or Table A-1M of B31.3 Code, or

(b) 0.9 times the yield strength tabulated in Section II, Part D, Table Y-1 (B 31.3) for materials listed therein

(The symbol Do in Section VIII is equivalent to D in B31.3 Code.)