Flexibility Calculations
EN-13480 uses the hot modulus of elasticity in the flexibility calculations (Section 12.2.7.2). The expansion allowable stress is subsequently modified by the ratio of Eh/Ec (Section 12.1.3.2).
Flexibility Stresses
EN-13480 provides two methods of determining the flexibility stresses. The CAESAR II default implementation uses Sections 12.3.2 through 12.3.5, which perform an SRSS of all moments, including torsional moments, with a single SIF. As an alternative, determine the flexibility stresses by distinguishing between in and out of plane bending using the distinct SIFs of Section 12.3.1. See EN-13480/CODETI Use In-Plane/Out-Plane SIF in the Configuration Editor.
Stress Equation Details
EN-13480-3:2017
The code provides explicit stress equations for the single SIF method (H.1). For the alternative directional SIFs method (H.3), the code only has a generic statement about longitudinal stresses for defined conditions. Because torsion is not part of the longitudinal stress, CAESAR II does not add the torsional stress term to the primary stress calculations (such as SUS or OCC). Optionally enable it by setting Add Torsion in SL Stress to Yes in the Configuration Editor.
Additionally, the reduction of the primary (SUS or OCC) SIF in the form of 0.75i is only applicable to the single-SIF method (H.1). For the alternative directional SIFs (H.3), the code only has a generic statement that states that the factor 0.75i for moment shall be “replaced by io and ii in accordance with Table H.3.” This means that by default CAESAR II does not reduce the SUS or OCC SIFs. Optionally, set SIF Multiplier for Sustained Stress Index in the Configuration Editor.
EN-13480-3:2017/A4:2021
The code provides explicit equations for the single-SIF method (H.1) and the alternative directional SIF method (H.3). All terms (pressure, bending, axial, and torsion) are explicitly defined and intensified. See the equations in International Code Stresses in the CAESAR II Quick Reference Guide.
Occasional Load Stress
EN-13480-3:2017
The code combines stresses from the sustained (SUS) loads and from occasional (OCC) loads.
SUS loads are loads such as primary force-driven loads acting on the pipe including weight and pressure, cold as-installed hanger loads, and force sets arising due to pressure. OCC loads are loads such as wind and earthquake loads.
EN-13480-3:2017/A4:2021
Instead of traditional methods of combining stresses, the code requires using the combined SUS and OCC forces and moments for the OCC stress equation.
Alternative Expansion Stress (Sigma4)
EN-13480 defines the alternative expansion stress as:
s4 = s1 + s3 £ ff + fa
CAESAR II applies the alternative equation differently:
s3 = ff + fa - s1
These two approaches are mathematically equivalent, but the actual value for the expansion stress (s3 versus s4) and the percent allowable are different. See Liberal Stress Allowable.
Corrosion Allowance
Primary SUS and OCC stress calculations use the corrosion allowance. Secondary stresses use the nominal pipe properties.
Pressure Stiffening
The code considers the pressure stiffening effects on all bends, such as smooth, closely spaced, and widely spaced bends.
Flange Stiffening
The code always applies flange stiffening to smooth bends and closely spaced bends.
For single SIF H.1, the code does not apply flange stiffening to widely spaced bends. For directional SIF H.3, the code applies flange stiffening to widely spaced bends.
Creep
See Creep Loading.
Section Modulus
EN-13480-3:2017
For branch H.1 (single SIF), the effective section modulus is calculated using the effective thickness: SIF*Nominal thickness of the branch.
For branch H.2 (single SIF and directional SIF), the code uses the standard section modulus.
For branch H.3 (directional SIF), the effective section modulus is calculated using the effective thickness: SIF*Nominal thickness of the branch.
EN-13480-3:2017/A4:2021
For branch H.1 (single SIF), the effective section modulus includes the SIF.
For branch H.2 (single SIF and directional SIF), the Code provides special calculations for unreinforced tees and provides more geometrical considerations for calculating the section modulus and SIFs.
For branch H.3 (directional SIF), the effective section modulus includes the SIF. The software uses the in-plane SIF.
For fillet welds #8 and #9, a new formula calculates the section modulus based on the minimum between the standard value and the value using the throat of the fillet weld.