B31.4 and B31.4 Chapter XI - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II Version
12

Calculate pressure stiffening using B31.4

Pressure stiffening is defined by default in the code. You can exclude pressure stiffening on bends in the analysis by including the Use Pressure Stiffening on Bends in the setup file.

Flanged end modifications using B31.4

Modifications resulting from flanged ends are permitted in the code providing the bend is not a widely spaced miter.

B31.4 girth butt welds default value

The default SIF value for a girth butt weld is 1.0. This is also Markl’s original basis for SIFs.

Calculate stress intensification factors (SIFs) for intersections using B31.4

In-plane and out-plane SIFs for intersections are separate and unique.

Calculate the B31.4 stress allowables

B31.4 uses EFF, (found in the Allowable Stress auxiliary field). B31.4 uses EFF in the Hoop allowable. For more information, see US Code Stresses in the CAESAR II Quick Reference Guide.

Calculate effective section modulus using B31.4

B31.4 has no provision for using an effective section modulus calculation at intersections.

B31.4 reducer default values

The default SIF value is 1.0. The default Flexibility Factor value is 1.0.

Calculate Code Stress (B31.4 only)

The B31.4 code standard defines allowable values provided in the table Allowable Values for Pipeline System Stresses. The table also indicates that the code classifies stresses as restrained, unrestrained and inland riser and platform. CAESAR II (version 9.0 and beyond) uses this table and the allowable stresses with the exceptions explained below.

Offshore liquid pipeline, discussed in Chapter IX of the code, has its own stresses and allowable values. For more information, see B31.4 Chapter IX.

Chapter XI of the code covers slurry pipeline systems and follows the stress calculations of the main body with some differences in the allowable values. For more information, see B31.4 Chapter XI.

You can select the following options through the Allowable Stress Indicator field for B31.4 and B31.4 Chapter XI jobs:

Restrained Pipeline

The software calculates the stress in that particular element as fully restrained.

Unrestrained Pipeline

The software calculates the included elements as unrestrained.

CAESAR II Determines

The software selects a stress equation based on the calculated axial load in the piping system. The software applies the fully restrained stress calculation when the axial pipe lo ad is within 2.5% of the limiting load or otherwise applies the unrestrained stress calculations. The limiting load is the load to fully constrain the pipe axially against the linear superposition of thermal expansion and pressure elongation (when the Bourdon pressure effect is selected in the Configuration Editor or in Special Execution Parameters). The restrained/unrestrained status can change from element to element.

The software uses the following loads:

  • Local axial force

  • Thermal force: E*a*AREA1

where AREA1 = p(Ro2-Ri2)

  • Bourdon force: (1-2*s)*P*AREA2

where AREA2 = pRi2

and determines the stress equation based on:

  • Limiting Force = Thermal Force + Bourdon Force

  • Delta = Limiting Force + Local Axial Force

  • When |Delta| / |Limiting Force| £ 0.025, then use the fully restrained stress calculations.

  • Otherwise, use the unrestrained stress calculations.

    This option is most suitable with the Underground Pipe Modeler or when modeling soil/pipe interaction using restraints.

Inland/Riser Platform

The software calculates the included elements as unrestrained. This option is not available for B31.4 XI.

Allowable Stress Indicator defines the calculated stresses and the allowable values. For more information, see US Code Stresses in the Quick Reference Guide. The B31.4 code standard also provides examples of restrained versus unrestrained conditions.

  • The software treats the elements as unrestrained if the indicator field is set to Inland/Riser Platform.

  • When the pipe element is buried in the Underground Pipe Modeler the software sets Allowable Stress Indicator to CAESAR II Determines.

For the primary load case types (SUS, OCC, OPE and HYD), the software calculates hoop stress, longitudinal stress, and equivalent combined stress and their respective allowable limits. CAESAR II reports the stress and allowable limit for the largest (stress/allowable) ratio. If the code standard does not specify a stress or an allowable, or the allowable is zero, then the software excludes that stress from the code stress determination. When all allowables are zero, the software sets the code stress to the largest stress.

The software reports zero equivalent combined stress for unrestrained elements. It also treats the HYD stress type as unrestrained for any Allowable Stress Indicator selection.

In accordance with the piping code, the software calculates the longitudinal stress by considering both positive and negative values of the bending stress in the analysis for both restrained and unrestrained pipe. CAESAR II uses the largest longitudinal stress in the code stress determination.

When calculating equivalent stresses or strains, the software considers the most critical combination of sustained, occasional, construction, and transient loads that can be expected.

The software calculates hoop stress according to the code standard, which indicates it should be based on the D/t ratio.

The Base Hoop Stress On (ID/OD/Mean/Lamé) configuration setting is not applicable in this situation.

For slurry pipelines (B31.4, Chapter XI), see the C403.2 section of B31.4 2016 for the hoop stress allowable, which is used for both restrained and unrestrained pipe. For other stresses, the allowable is according to the table in the design section of the standard.

The code provides the following exceptions to the allowable values:

  • For B31.4, CAESAR II calculates the hoop allowable (0.9Sy) for the HYD stress type according to section 437.4.1 of the B31.4 2016.

  • For B31.4 XI, CAESAR II calculates the longitudinal allowable for the OCC stress type (0.88Sy) according to section C403.3.1 of B31.4 2016 and calculates the Hoop allowable (0.9Sy) for the HYD stress type according to section C437.4.1 of B31.4 2016.

For more information, see US Code Stresses in the CAESAR II Quick Reference Guide.

The software calculates code stress for the EXP stress type according to section 402.5.1 of B31.4 2016 for restrained pipe and per section 402.5.2 for unrestrained pipe. The software computes the allowable expansion stress for unrestrained pipe according to section 403.3.2of B31.4 2016 (Criteria for Allowable Stress Due to Periodic or Cyclic Loading). In this situation, SL (stress due to sustained loads) used in the allowable calculation is the minimum between the maximum of sustained stress and the additive longitudinal allowable stress for unrestrained pipe (0.75Sy). Sy is the minimum yield strength.

The New Job Liberal Expansion Stress Allowable configuration setting is not applicable in this situation.