Limit States Design

A limit states design approach has been developed for geotechnical loads. The approach uses a strain based design format and requires the user to develop probability distributions for the maximum strain demand and minimum strain capacity.

Checks are provided for both local buckling and tensile rupture, which are calibrated to meet specified risk-consistent reliability targets. The safety factor and the criteria used to define the characteristic strain demand and capacity are defined as functions...

A limit states design approach for onshore pipelines has been developed with reliability-based design rules for geotechnical loads. In consideration of the modelling complexity of the soil movement mechanisms and pipe-soil interaction, and to allow for flexibility to incorporate future model developments, the design rule formation is directly based on the distribution parameters of the strain demand and capacity of the pipeline.

Working as part of a joint industry project, we used the structural...

Abstract

The reliability-based design and assessment (RBDA) methodology has gained increasing acceptance in the pipeline industry, largely due to a multi-year PRCI program aimed at establishing RBDA as a viable alternative for the design and assessment of onshore natural gas pipelines. A key limit state of buried pipelines that operate at elevated temperatures is upheaval buckling. The elevated temperatures generate large compressive axial forces that can cause Euler buckling susceptibility....

Abstract

In 2005, guidelines for the application of reliability-based design and assessment (RBDA) to natural gas pipelines were developed under PRCI sponsorship. The methodology underlying these guidelines has since been adopted as a non-mandatory Annex in the CSA Z662 standard (Annex O). The benefits of reliability-based methods include consistent safety levels, optimized solutions that make best use of available resources and flexibility in addressing non-standard problems. The key...

Abstract

In 2005, guidelines for the application of reliability-based design and assessment (RBDA) to natural gas pipelines were developed under PRCI sponsorship. The methodology underlying these guidelines has since been adopted as a non-mandatory Annex in the CSA Z662 standard (Annex O). Because the methodology is based on the concept of consistent risk, it is more restrictive than current design standards for some pipelines and less restrictive for other pipelines. Specifically, the RBDA...

Abstract

Reliability-based design rules have been developed for the key serviceability limit states applicable to onshore pipeline including local buckling due to thermal expansion and excessive plastic deformation under hydrostatic test pressure. The design rules are characterized by three elements: the formulas used to calculate the characteristic demand and capacity; the criteria used to define the characteristic values of the key input parameters to these formulas (such as diameter and...

Abstract

Reliability-based design rules have been developed for the key ultimate limit states applicable to onshore pipeline, including burst under operating pressure and failure due to equipment impact. The design rules are characterized by three elements; the formulas used to calculate the characteristic demand and capacity; the criteria used to define the characteristic values of the key input parameters to these formulas (such as diameter, material strength, pressure and impact load); and...

Abstract

A limit states design approach for onshore pipelines has been developed as part of a three-year joint industry project. The approach covers both natural gas and low vapor pressure (LVP) liquid pipelines and addresses key design conditions, including burst, equipment impact loads and plastic deformations during hydrostatic testing. The results are described in a set of design guidelines that can be used as a basis for a limit states design standard.

The design methodology is based on...

The Industry Challenge:

Gas pipelines in Arctic regions pass through areas of continuous and discontinuous permafrost. The segments where the pipeline is buried in discontinuous permafrost are subject to freeze-thaw cycles that can cause uplift on the pipeline.

Where the ground transitions from discontinuous to permanently frozen ground, the uplift forces can cause severe bending loads that can exceed the yield strength of the pipe, resulting in permanent deformations.

If the pipe yields, the...