1. Seabed irregularities (unevenness) during installation(residual tension on span creation is closely linked to thepipe weight). Subsequent scouring(sand wave) and movement.Seabed topography and composition (type of soil), waveand current action and pipe properties.

2. Type of Span 3. End Condition Using in Free Span Fixed- Pinned end condition may be assumed for single spans. Fixed- Fixed may only be assumed if validated be observed support condition. "Fixed/Pinned" in this case is assumed to be the average of "Fixed/Fixed and "Pinned/Pinned" bending moments, on the basis that the end fixities of a span are somewhere between the two cases but it is difficult to determine exactly where. When calculating permissible span lengths, the assumed end conditions have a large impact on the results. The fixed/pinned assumption may not be accurate when, for example, a pipeline spans between two rock ridges. The support conditions might then be closer to pinned/pinned; though the adjacent sections of pipe will provide some restraint so that the pipe section is not truly pinned/pinned. Analytically, it is only possible to accurately determine these effects with the use of an advanced finite element analysis to accurately model the span support conditions and axial effects. It is obviously impractical to perform this type of analysis on every span along the pipeline route. However, it may be possible to build a "typical" FE model to determine the magnitude of these effects and modify the limiting span criteria. 4. A. DNV-1981II. Criteria for Span Condition Vortex Shedding Static Stress Induced Bar Buckling Fatigue.Vibration: In Line; Cross Flow; 5. 1. Static Stress Checked individual stress components, and the total combined stress condition is also limited to maximum percentage of the material SMYS (percentage is variable according to pipeline loading condition).2. Vortex Induced Vibration VIV dependent upon the pipe and span characteristics,fluid flow around a pipeline span can result in vorticesoccurring on the wake side of the pipe. If vortices areof sufficient frequency, they can produce significantpipeline oscillations. The parameter assessment VIV is Reduced Velocity(Vr ). 6. 0 < Vr < 2.2 symmetric vortex shedding producing "In- Line" oscillations, i.e. parallel to fluid flow. 2.2 < Vr < 3.5 alternate vortex shedding causing "In-Line" oscillations (unstable); 7. 4.8 < Vr < 12.0 alternate vortex shedding causing CrossFlow" oscillations i.e. perpendicular to fluid flow.3. Bar Buckling For a restrained pipeline, the pressure andtemperature induced axial force (compressive), ifof sufficient magnitude, may lead to beam modebuckling of the pipeline 8. 4. Fatigue As mentioned previously, vortex shedding induced span vibrations may be broadly divided into two categories: In-line; Cross-flow. Cross flow vibrations by their nature are almost always high amplitude and consequently their occurrence should be avoided at all costs, while in-line vibrations are generally of smaller amplitude and may be permissible. The criteria for permitting in-line vibrations fall within assessment of the pipeline fatigue and fatigue usage requirements. 9. III. CalculationPermissible span lengths for a pipelineFor each of these criteria the permissible are calculated based on each of thespan length should generally be calculatedfollowing criteria:for each of the following four load cases:Static stressEmpty Vortex shedding (in-Water filledline vibrations) Vortexshedding (crossHydrotestflow vibrations) Bar buckling. Operation 10. III. Calculation2. Static stress Due to its self-weight and lateral hydrodynamicloading. The combined stresses should be checked againstthe allowable levels of stress given in the relevantcodes, i.e.is not to exceed thepermissible value. .ep = usage factory as defined table below .F = specified minimum yeild strength What are a and b ? 11. III. Calculation Is function likes Operation ? How about Functional and environmental ? 12. III. Calculation 13. III. Calculation 14. III. Calculation 15. III. Calculation3. Vortex Sheddinga. Cross-Flow Vortex Shedding 16. III. Calculation The Reduced Velocity (Vr ) parameter see figure below: 17. III. Calculationb. In-Line Vortex Shedding Stability parameter is controlling the motion , KS 18. III. Calculation Effective mass (me) is function of Ca (add masscoefficient). Submerged Weight(Wsub) The relationship between VR and the stabilityparameter, KS 1 4.7 and Ks