Page 432 - Pipelines and Risers

Design Codes and Criteria for Risers 399

21.3.4 Design Procedure
The limit state based design approach is to define appropriate design criteria for different limit
states so that sufficient safety margins are achieved for different load conditions. The design
procedure outlined for pipelines can be applied for riser design.

21.3.5 Acceptance Criteria
With reference to the loads and limit states, different acceptance criteria need to be considered
for different design conditions. The following acceptance criteria shall be included for pipe
wall thickness sizing:
- Hoop strength acceptance criteria
- Yielding strength acceptance criteria
- Bursting strength acceptance criteria
- Buckling strength acceptance criteria
- Fracture strength acceptance criteria
- Fatigue strength acceptance criteria

21.3.6 LRFD Design Formats
The LFWD design formats for pipeline can be applied for marine riser design.

21.3.7 Local Strength Design through Analysis
Non-linear finite element methods can be applied as the tool for local strength design through
analysis. Special attentions need to be paid to the follows in computer model:
- Hydrodynamic loads
- Seabed contacts
- Interface with floater motion
- Material

21.4 Design Conditions and Loads

21.4.1 General
This chapter defines the loads and load cases used for marine riser design. First, design
conditions are specified. Secondly loads to be applied in the adopted LRFD design format are
defined. The load cases to be included in the analysis and design are defined. Special
attentions are paid to the critical loads compared to those to pipeline design. As an important
design criterion, fatigue evaluation is described separately in Chapter 22.

21.4.2 Design Conditions
The following design conditions shall be covered for structural analysis and design, namely:
- Normal operating condition
- Abnormal operating condition