Page 33 - Pipelines and Risers

Introduction 7

Each stage in the design should be addressed whether it be conceptual, preliminary or detailed
design. However, the level of analysis will vary depending on the required output. For
instance, reviewing the objectives of the detailed design (Section 1.2. l), the design should be
developed such that:

Pipeline wall thickness, grade, coating and length are specified so that pipeline can be
fabricated;
Route is determined such that alignment sheets can be compiled;
Pipeline stress analysis is performed to verify that the pipeline is within allowable stresses
at all stages of installation, testing and operation. The results will also include pipeline
allowable spans, tie-in details (including expansion spoolpieces), allowable testing
pressures and other input into the design drawings and specifications;
Pipeline installation analysis is performed to verify that stresses in the pipeline at all
stages of installation are within allowable values. This analysis should specifically
confirm if the proposed method of pipeline installation would not result in pipeline
damage. The analysis will have input into the installation specifications;
Analysis of global response;
Expansion, effective force and global buckling
Hydrodynamic response
Impact
Analysis of local strength;
Bursting, local buckling, ratcheting
Corrosion defects, dent

1.3 Design Through Analysis @TA)
A recent technical revolution in the design process has taken place in the Offshore and Marine
industries. Advanced methods and analysis tools allow a more sophisticated approach to
design that takes advantage of modem materials and revised design codes supporting limit
state design concepts and reliability methods. At J P Kenny the new approach is called
“Design Through Analysis” where the finite element method is used to simulate global
behavior of pipelines as well as local structural strength (see Bai & Damsleth (1998)). The
two-step process is used in a complementary way to determine the governing limit states and
to optimize a particular design.

The advantage of using advanced engineering is a substantial reduction of project CAPEX
(Capital Expenditure) and OPEX (Operating Expenditure) by minimizing unnecessary
conservatism in the design through a more accurate determination of the effects of local
loading conditions on the structure. Rules and design codes have to cover the general design
context where there are often many uncertainties in the input parameters and the application
of analysis methods. Where the structure and loading conditions can be accurately modeled,
realistic simulations reveal that aspects of the design codes may be overly conservative for a
particular design situation. The FEM (Finite Element Methods) model simulates the true
structural behavior and allows specific mitigating measures to be applied and documented.