pipe & wall thickness calculation

PIPE & WALL THICKNESSCALCULATION

• Introduction to Pipes

•Pipe wall thickness calculation

•Pipes are thin cylindrical shells which is used for

transportation of fluids.

•ASME B 36.10 is the dimensional standard for

Welded and Seamless Wrought Steel Pipe (CS,

LTCS, and LAS).

• ASME B 36.19 is the dimensional standard for

Austenitic / Stainless

•Pipes are made of standard sizes having several range of wall thickness

or weight.

•Pipes are known by Nominal Pipe Size NPS (in inches) and Diameter

Nominal DN (in mm).

•Upto 12" NPS the Nominal diameter is approximately equal to inside

diameter of pipe.

•Above 12" NPS the Nominal diameter is equal to the outer diameter of

the pipe.

•Pipe wall thickness is designated based on weight and schedule.

• The older system designates pipe as Standard (S), Extra Strong(XS) and

Double Extra Strong (XXS) which is based on pipe weight.

• The newer system designates wall thickness by Schedules; such as Sch

10,20,30,40,60,80,100,120,140,160 for Wrought steel pipe & Sch 5S, 10S,

40S, 80S for Stainless Steel Pipe.

•Normally for all pipe sizes Sch40 corresponds to Standard (S) and Sch80

corresponds to Extra Strong (XS).

• Commercial pipes are normally available in 6m, 12m length.

•Pipes are connected through flanges, welding (both butt and socket

welding), threaded.

• Dimensional standard for flanges is ASME B16.5 upto 24" NPS, ASME

B16.47 Series B above 24" upto 60”NPS, above that AWWA C-207 which

ranges from 4” NPS to 144” NPS.

•Dimensional Standard for Butt-welding end pipe is ASME B16.9, and for

Socket welded and threaded pipe ASME B16.11.

Pipe wall thickness calculation•Pipe wall thickness design is for internal pressure.

•When calculating pipe wall thickness operating pressure and operating

temperature is always multiplied by a factor of 1.5 to get the design

parameters. This factor is called safety factor.

•The pipe wall thickness equation given in ASME B31.3 is basedon Hoop

stress; t=PD/2S, where t-thickness, P- Internal Pressure, S- Hoop Stress.

Where,

t – wall thickness of pipe in (mm)/(inch)

P- Design internal Pressure (PSI) /(MPa)/ Bar

D- Outer diameter of pipe (mm)/ (inch)

S- Allowable stress for the material of pipe (KSI) /(MPa)/ Bar

E- Weld Quality factor

W- Weld Strength reduction factor

Y – Coefficient of material used

1 inch = 25.4mm

1 bar = 14.5 psi = 100 Kpa

1 ksi = 1000 psi

Pipe wall thickness design calculation can be done by:

•Line rating condition and Flange (Full) Rating condition.

• In any plant piping falls under,

150#,300# , 600#, 900#,1500#,2500#

Line rating condition

• In this method the pipe thickness is calculated for

the each and every line according to the line rating

or

particular line design conditions.

•This is method is generally used for large diameter pipes

or special cases such as use of costly alloys Cu-Ni .

•Pipes in 900# and above.

• It is not preferred for cases where large number of pipes

procured for similar design conditions.

Flange rating condition

• In this method the pipe thickness design calculation is

done based on the flange rating.

oPipe is made stronger than flange.

• This design is made to make the procurement more

economical.

•In this case in any case only flange fails and not the pipe,

which saves a huge cost in a process plant.

• Rating/ Class of Flange as per ASME B16.5 are- 150,

300, 400, 600, 900, 1500, and 2500.

A corrosion allowance based on process data is added to design thickness

to get the minimum required thickness. Normally for CS pipe it is 3.0mm.

For SS pipes its 0.0mm.

A mill tolerance of 12.5% is added to the required thickness for seamless

and mill-rolled pipe and a mill tolerance of 0.3mm is added to the

required thickness of plate fabricated pipe. Ref Std. ASTM 01.01 formill

tolerance.

Minimum selecting thickness for CS

½” – 1.1/2”

2”- 6”

8”-14”

Sch.80

Sch.40

Sch.20

Minimum selecting thickness for SS

Sch. 40 minimum.