Date of last change Reference/Name of Presentation/SN 1

IBR THICKNESS CALCULATION

Definition:

IBR piping covers: • Boiler feed water piping and • Steam pipes with pressures above 3.5kg/sq cm (g) or pipe internal dia above 254 mm, what ever applicable

Thickness calculation:

IBR pipes - As per IBR thickness formula

Non IBR pipes - As per ASME B31.1 thickness formula

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Date of last change Reference/Name of Presentation/SN 2

IBR THICKNESS CALCULATION

THICKNESS CALCULATION AS PER IBR

IBR pipe thickness formula (OD based)

WP x Dt = ------------------------ + c 2 x f x e + WP

IBR pipe thickness formula (ID based)

WP x dt = ------------------------ + c 2 x f x e - WP

Pipe thickness formula as per B 31.1 (OD based)

WP x Dt = ----------------------------+ c 2 x ( f x e + WP x y)

T<=482 deg C; y=0.4T>=538 deg C; y=0.7

Date of last change Reference/Name of Presentation/SN 3

IBR THICKNESS CALCULATION

Where:t = Calculated mimimum pipe thicknessWP = Max working pressureD = Outside diameterd = inside diameterf = Allowable stress as computed from formulae below. Allowable stress values as specified in the code of the country of manufacture are acceptable in lieu of the figures computed from the formulae below provided they fall within limits specified by these formulae.e = Efficiency factorc = 0.75 (Corrosion allowance)

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IBR THICKNESS CALCULATION

Allowable stress (IBR):

For temperatures upto 454 oC, Min of: R/2.7 and 0.67 Et

For temperatures above 454 oC, Min of: 0.67 Et, 0.67 Sr, 0.83 Sr min and 1.0 Sc

R = Specified minimum tensile strength at room temperature.Et = Yield point (0.2% proof stress at the temp)Sr = Average stress at the temp to cause rupture at the end of 100,000 hr.Sr min = Minimum stress at the temp to cause rupture at the end of 100,000 hr.Sc = Average stress at the temp to produce an elongation of 1% (creep) in 100,000 hr.

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IBR THICKNESS CALCULATION

Allowable stress as per ASME section II part D (for comparision with IBR)Min of: R/4, 1.1/4 x Rt, 0.67 E, 0.67 Et, 0.67 Sr, 0.8 Sr min and 1.0 Sc

Rt = Specified minimum tensile strength at the temperature.E = Yield point (0.2% proof stress at room temp)

* It can be seen that ASME is more conservative than IBR and hence

allowable stress values as tabulated in ASME Section II part D can be used in IBR thickness calculation.