Pipe Wall Thickness

The algorithms for stress analysis in pipes can be found in Perry, "The Chemical Engineer's Handbook", any edition, as well as other places.

Per the Piping Code, schedule numbers were defined as 1000 times the ratio of internal pressure to allowable stress for the material. That is SN = 1000 * P/S. Assigning the schedule number and allowable stress you can solve for allowable internal pressure, based on your temperature (allowable stress related to temperature).

For example, schedule 40 SA-53 Gr A pipe at 100 deg. F would handle internal pressure of 480 psig { 40 * 12000 psi / 1000 = 480 psi}. Likewise, Schedule 80 SA-53 Gr B pipe would (theoretically) handle 80 * 15000 psi / 1000 = 1200 psi at 100 deg. F.

ANSI B31.1 gives the formulas.

Stress factors for pipe and allowable pressures can be derived from either Barlow's, Boardman, or Lame formulas.

Barlow--- P=(2*S*T)/D

where p= pressure

S= stress (45,000 lbs/sq. in for mild steel)

T=thickness

D= outside diameter

Please note: Stress is at maximum (ie Burst) so use at least 4:1 reduction for running, more for extra safety if needed.

Thickness is wall thickness at thinest point yes that means the root of the pipe thread.

also check ANSI B31.1 for other details ie: extended temperature, fluids etc.

The hoop stress formula you present is only valid for thin wall cylinderical shells. For pipes, the correct equation to use is the one in the reference you give ASME/ANSI B31.1 Power Piping. The safety factor used is 3:1

All the other answers given which do not take into consideration the pipe diameter are probably ''rules of thumb'' but not validated by calculation for all diameters.

Sched 40 is suitable for 40 bar. gauge pressure. Some allowance is made for corrosion. No allowance is made for TEMPERATURE which is assumed to be -10 to 80degC. A proper calc has to be done with wall thickness at the end of service (worst case corrosion to inside and outside of pipe, fatigue, mechanical load (supports) ). Piping Engineers earn their money. These calcs will also be required for insurance and proof of competence in the event of a failure causing an injury. Pipe should be designed as a Pressure Vessel. Inspection for corrosion at normally 110 yrs then 5 yr intervals should be practical by using routes that allow access. Repainting will be part of that for outside piping. For normal process piping I'd recommend thin wall stainless steel as the preferred choice, where suitable.

Your schedule 40 =40bar is not correct. No consideration is given for pipe diameter. as pipe diameter increases allowable pressure decreases. Previous formula given is valid for up to schedule 160 and also up to XXS (double x schedule)

P=(2St)/OD

as an example burst pressure of 1/8 sch 40 pipe is 20,200 PSI and burst of sch 40 12" pipe is 3,800 PSI

see ANSI B31.1