The fluid flow equations and formulas presented thus far enable the engineer to initiate the design of a piping or pipeline system, where the pressure drop available governs the selection of pipe size. (In addition, there may be velocity constraints that might dictate a larger pipe diameter. This is discussed below in the section on velocity considerations for pipelines.

Once the inner diameter (ID) of the piping segment has been determined, the pipe wall thickness must be calculated. There are many factors that affect the pipe-wall-thickness requirement, which include:

The maximum and working pressures

Maximum and working temperatures

Chemical properties of the fluid

The fluid velocity

The pipe material and grade

The safety factor or code design application

If there are no codes or standards that specifically apply to the oil and gas production facilities, the design engineer may select one of the industry codes or standards as the basis of design. The design and operation of gathering, transmission, and distribution pipeline systems are usually governed by codes, standards, and regulations. The design engineer must verify whether the particular country in which the project is located has regulations, codes, and standards that apply to facilities and/or pipelines.

The basic formula for determining pipe wall thickness is the general hoop stress formula for thin-wall cylinders, which is stated as

RTENOTITLE (Eq. 1)

where

HS = hoop stress in pipe wall, psi,

t = pipe wall thickness, in.,

L = length of pipe, ft,

P = internal pressure of the pipe, psi,

and

dO = outside diameter of pipe, in.