	Applies To
	Product(s):	AutoPIPE
	Version(s):	V8i
	Area:	Results
	Original Author:	Bentley Technical Support Group
	Date Logged & Current Version	Aug. 2015 09.06.02.06

Problem:

For CAN-Z662 (2007), When reviewing the code equation Equiv1, appears that the value is exactly the same as Hoop. Why is AutoPipe not considering the longitudinal term of the equation in 4.7.1. In some cases there isn't any stress in the expansion cases, so this makes sense, however various nodes do have significant expansion stress, which is as much as or more than the hoop stress, however AutoPipe is still only reporting the hoop stress for Equiv1 results.

Answer:

Please see the following AutoPIPE help section:

Help > Contents> Contents Tab> Reference Information> Code Compliance Calculations> CAN-Z662 (2007)

From the online help:

For those portions of restrained pipelines that are fully restrained axially, the equivalent tensile stress (seq) is calculated per the code in Section 4.7.1 as the maximum Tresca effective stress (refer to the discussions on Principal Stress and Maximum Shear Stress in the General Stress Calculations section of the Appendix), excluding bending stresses and shear stresses

Principal Stress:

The principal stresses are calculated considering the longitudinal stress (Sigma a), the hoop stress (Sigma h), and the torsional shear stress (Tau). from the following equations:

In case of Z662 - Equivalent Tensile stress, the shear stress (Tau) is set to zero and there is no bending stress considered for longitudinal stress. If you enter shear stress as zero in equation above, you would get

Where Sigma (a) is the longitudinal stress from pressure (P*Ap/As). AutoPIPE reports the maximum stress as:

In cases where the net longitudinal stress comes out as a positive value (tension), the maximum stress would be either Hoop or Longitudinal Stress and not (Sigma 1 - Sigma 2). We can relate this to the note provided by the code:

In cases where the axial stress due to axial forces by Gravity, Pressure and thermal expansion are high, the net longitudinal stress would become negative and then we will see a value of equivalent tensile stress which is greater than the hoop stress.

01. When reviewing the code equation Equiv1, appears that the value is exactly the same as Hoop. Why

Problem:

Answer:

See Also