Page 428 - Pipelines and Risers

Design Codes and Criteria for Risers 395

- New concepts
- Newmaterials
- New critical failure modes

Similar to the pipeline industry, a large amount of project activities are on-going to improve
e.g. the following aspects:
- Analytical tools
- Loadeffect
- Coupled analysis
- Materials qualifications
- Failure modes
- Convert from WSD to LSD

The Limit State Design (LSD) is now a popular alternative to Allowable Stress Design (ASD)
accounting for the following limit-states:
- Serviceability Limit State - SLS
- Ultimate Limit State - ULS
- Fatigue Limit State - FLS
- Accident Limit State - ALS

In the LSD, typically Load and Resistance Factor Design (LRFD) is applied for each failure
mode, with appropriate design equations and partial safety factors.

21.2 Design Criteria for Deepwater Metallic Risers

21.2.1 Design Philosophy and Considerations
The design philosophy adopted in this chapter is to apply proved technical advances in order
to conduct safe and cost-effective design of marine risers. Load and resistance factor design
(LRFD) format is applied for riser design. This leads to reduced conservatism and uniform
safety levels.

The design of a marine riser system will require consideration of a number of factors in
relation to its functional suitability and long term integrity. Considerations should be given to:
- Consistence with Laws, Acts and Regulations
- Riser integrity: Reliability, safety and risk
- Riser functional requirements
- Riser operational requirements
- Riser structural design criteria