Page 51 - Pipelines and Risers

24 Chapter 2

The main design principle in these two codes is that the pipeline is assessed as a pressure
vessel, by limiting the hoop stress to a specific fraction of the yield stress. A brief outline of
new design codes is given below:

- IS0 Pipeline Code
A new pipeline code for both offshore and onshore applications is currently under
development by ISO-International Standardization Organization (IS0 DIS 13623, 1996). A
guideline being developed as an attached document to this IS0 code allows the use of
structural reliability techniques by means of limit state based design procedures as those
proposed by SUPERB (Jiao et al., 1996). This code and guideline represent a valuable
common basis for the industry for the application of new design methods and philosophy.

- APIRPllll(1998)
The recommended practice for offshore pipelines and risers containing hydrocarbons has been
updated based on limit state design concept to provide a uniform safety level. The failure
mode for rupture and bursting is used as the primary design condition independent of pipe
diameter, wall thickness and material grade.

- DNV Pipeline Rules
The first edition of DNV Rules for the Design, Construction and Inspection of Submarine
Pipelines and Pipeline Risers was issued in 1976 and the design section was mainly based
upon the ASME codes although it was written for offshore applications only.
The safety philosophy in the DNV’96 Pipeline Rules is based on that developed by the
SUPERB Project. The pipeline is classified into safety classes based on location class, fluid
category and potential failure consequences. Further, a limit state methodology is adopted and
its basic requirement is that all relevant failure modes (limit states) are considered in design.

- ABS (2000) Guide for Building and Classing Undersea Pipelines and Risers
A new guide for building and classing undersea pipelines and risers is currently being
completed. The Guide uses Working Stress Design (WSD) for the wall thickness design. The
Guide optionally allows use of Limit-State Design and risklreliability based design. It does
contain new criteria for defect assessment. Criteria for other failure modes relevant for the in-
place condition, installation and repair situations, as discussed by Bai and Damsleth (1997)
have been evaluateddeveloped based on design projects, relevant JIP’s and industry
experience.

2.2 Material Grade Selection

2.2.1 General Principle
In this section selection of material grades for rigid pipelines and risers are discussed.