PIPE THICKNESS CALCULATIONS

Pipe Thickness Calculation for Natural Gas Service Carbon Steel Pipe:

Pipe Thickness, t = (PD)/(2*Sa + P) + C.A.Where t = thickness in mm D = outer diameter of pipe in mm P = design pressure, Kg/cm2Sa= Allowable stress of pipe material at working temp, in Kg/cm2 (Refer piping codes B 31.3 / B 31.8)C.A. = Corrosion Allowance (minimum value as 1.0 mm)

ExampleTrunk Pipe line, D = 200 mm P = 40 Kg/cm2 Sa = 1050 kg/cm2 C.A. = 1.6 mmCalculate required thickness of pipeline.t = (40*200)/((2*1050)+40) + 1.6 mmt = 3.7 + 1.6t = 5.3Select the pipe of nearest schedule having higher thickness than the above value.ADOPT DN 200 Schedule 40, C.S. Pipe.

Few Field Questions

How long do I have to use the pipe?What is the residual thickness of pipe?What is the corrosion rate of pipe material under the service fluid & environmental exposures?Has the pipe material deteriorated due to exposure to service fluid & conditions? What are the mechanical & metallurgical changes? Can it be quantified?Was the piping system exposed to cyclic service loading?Has the piping material experienced creep deterioration?Has the piping material experienced stress corrosion cracking (SCC)?How much pressure can this pipe take?

Burst Pressure of PipePb = (2 Y/Su)*(Y/3)*Logn(K2)

Where,Pb = Bursting pressure, Kg/cm2Y = Yield stress of pipe material, in Kg/cm2Su = Ultimate tensile stress, in Kg/cm2 K = (OD/ID) of pipe

Hydro test PressureP (test) = 1.5 P (operating) *(Allowable stress room temp. / Allowable stress operating temp.)Safe Life of Corroded Pipe:Safe Life = (t available t safe) / (Corrosion Rate per year)Safe Working Pressure for Thick-walled Pipes:P = (((D2 d2)*S) /(3D4 + d4) 0.5)Where, D = Outer Diameter d = Inside Diameter S = Allowable Stress, Kg/cm2

HDPE Pipe

Pipe Thickness, t = (PD)/(2 Sa+ P)Where Sa = Sy/1.3Sy is the reference stress based on HDPE creep resistance in certain prefixed service life (varies from 20 year to 50 years)

ExampleLow PressureP = 2 Kg / cm2Distribution D = 200 mmBranch (Nat. Gas)Life = 50 years (Normal Pipe Temperature = 25 0C) Sy= 10 N / mm2= 100 Kg / cm2 (For Hostalen GM 5010) T2 (GM 5010)= 7.3 N / mm2= 73 Kg/cm2

Sa = (Sy /1.3) 77 Kg/cm2 (5010 T2) = 56 Kg/cm2 (5010)

Example .Wall Thickness,t = (2*200)/(2*77+2) = 2.5 mm (for Hostalen GM 5010 T2)t = (2*200)/(2*56+2) = 3.5 mm (GM 5010)Select pipe to HASTI GAS T2, CLASS..HDPE THICKNESS, t = (P*D)/ 2*S allowable + P)Where S allowable = Sv/1.3Sv is the reference stress based on HDPE creep resistance in certain prefixed service life (varies from 20 years to 50 years)

PIPE SIZE CALCULATIONPRESSURE DROP IN GAS PIPELINESHDPE PIPE: Use Weymouth Equation;Q = A*(P12 P22)0.5/(S.L.)Where A is Weymouth HDPE factor; (as listed below): O.D. (mm)Class 3Class 4Class 5 5080.569.753.6 100640.4546.8410.8 1601674.61460.71099.0 2002987.52597.31967.2 2505306.04622.23485.0Q = Gas flow rate at STP, m3/hrP1 = Upstream pressure, Kg/cm2, AbsP2 = Down-stream pressure, Kg/cm2, AbsS = Specific Gravity of gas with respect to air (0.695) or approx. 0.7L = Pipe length in Km.

PIPE SIZE CALCULATION ..GI PIPE / HDPE PIPE:For low pressure/low flow conditions:Q = 0.15228 D2.623 (h/L)0.541Where D = Inside Diameter, mmh = Pressure Drop, mm Wc.L = length of Pipe, m.M.S. / C.I. PIPE:For medium pressure / flow conditions:Q = 0.0813 d 2.6664 {(P12 P22)/(S.L.)}0.5Where d = pipe diameter, mmP1, P2 = pressures, kg/cm2, AbsS= 0.7 for Natural GasL = Pipe length, mHDPE PIPE:Q = 0.11672 * d 2.664 {(P12-P22)/(S.L.)}0.544

FOR C.S. PIPEHANDLING HIGH PRESSURE/HIGH FLOW GAS;PAN-HANDLE (REVISED) FORMULA:Q = 737 (To/Po ) 1.02 * d 2.53 {(P12-P22)/G0.061 Tf*L*Z}0.51*EQ = K*d2.53 {(P12-P22)/L}0.51 * Z-0.51Where,K = {737 * To 1.02 * Po -1.02 * G -0.49 * Tf-0.51 * E}Where,Q= Gas Flow Quantity, CfdTo= Base Temperature, F Abs.Po= Base Pressure, Psiad= Pipe Inside Diameter, In.P1= Initial Pressure, PsiaP2= Final Pressure, PsiaC= Specific Gravity of Gas (0.7)Tf= Flow Temperature of Gas, F AbsL = Pipeline Length, MilesZ = Compressibility Factor of GasE= Pipeline Efficiency Factor, (assume 0.9)