FPSO Piping Stress analysis using CAESAR II 3

[Kastha]

I am doing the piping stress analysis as per ASME B31.3 for a FPSO. I want some guideline regading the load combinations and the load types to be used for the stress analysis.
For onshore piping stress the wind and earthquake loads are considered as occasional loads and are applied seperately. But in FPSO piping stress both these loads along with the structural displacements have to be combined together (that is what I think!) So if someone having good experience and background of FPSO piping stress can give me the load combinations and types, it will be of great help.

 

[bvi]

The B31.3 f factors are extended to an unlimited number of cycles at a minimum f factor of 0.15, as of the upcoming 2004 edition. Given that, I recommend considering dispacement stresses of wind and earthquake (and also wave motion) similar to displacement controlled stresses due to thermal expansion in determining an equivalent number of cycles for determining the f factor.

 

[LSThill]

Team Members: Kastha (Mechanical)and cb4 (Mechanical)

Regards to FPSO piping stress analysis using CAESAR II should be back check using FE-PIPE:

http://www.paulin.com/

In contrast to traditional finite element modeling, where the analyst must build the model from scratch, FE/PIPE uses pre-fabricated templates for piping and vessel components. A library of component templates is available for Piping Intersections, Nozzles (in Flat Plates, Cones, Tanks, Heads, including Hillside Nozzles), Reinforcing Pads, Stanchions on bends, Piping Supports, Lugs, etc. The Shell String Modeler allows one to model connected Piping and Vessel segments. This includes mitered elbows, bends, reducing elbows, cylindrical and conical segments, annular plates, and spherical or elliptical heads. The latest version includes templates for a shell containing multiple nozzles, a pad reinforced fabricated cross, structural elements, and API storage tanks, nozzles and base settlement. The Plate Processor allows user defined plate attachments (lugs, saddles, shoes etc) for shell and nozzle elements. Large complex geometries may be built up by combining several smaller &quot;child&quot; models to a &quot;parent&quot; model. This is done by defining common nodes between models. The recent addition of 8-node Brick Templates allows one to perform thick wall (D/t < 10) analysis. 32-bit processing and graphics have speeded up the program by 2-3 times. There is also automated animation, Quick Calc feature for WRC107/297 and N318/392, a thermal profiler for unreinforced fabricated tees, and reinforcing pad options for hillside nozzles and bends with stanchions.

What are specific areas where a FEPipe calculation is needed? In summary, the following examples illustrate areas where FEPipe can significantly improve on existing more simplified design methods.

- Validation of pressure designs in large d/D intersections
- Allowable load determination on nozzles.
- Replacement Method for WRC 107 or WRC 297
- Cyclic applications (>5000 cycles)
- Large hillside or lateral nozzles.
- Nozzles subject to high temperatures and the potential for elastic follow-up. (>800 deg.F)
- Transverse or Axial loads on saddles.
- Bends with staunchions or structural weldments
- Transient Thermal (and thermal+pressure) loading conditions.
- Stiff systems interacting
- SIF's for non-code geometries, or for geometries outside of Code limits, and geometries not addressed by the code.
- Jacketed Piping systems
- Fixed tubesheet designs
- Collapse of thin walled piping geometries
- Stress distributions around multiple openings

FEPipe is a template driven finite element program designed exclusively for the piping and petrochemical markets. FEPipe handles saddles for axial or lateral loads, a result that Zick could never do, and find stresses in lugs and attachments in the automodeller. FE/Pipe will also produce allowable loads on nozzles which can then be handed to the piping engineer for evaluation. The new version FEPipe 4.100 does a spectacular job with multiple, close proximity nozzles in heads or cylinders using unstructured meshing.

It's known that B31 Appendix D is only justified for D/T<100. For thin walled pipe, FE/Pipe is the only tool available that will make a direct calculation of the sif and flexibility. FE/Pipe handles the thermal gradient requirements of 301.7.2, and the cyclic load requirements of 301.10. This is where the real failures occur and if the structure cycles then an accurate calculation of the loads and stresses is important. If your work involves API 579 the required membrane and bending stress determinations are found directly in FE/Pipe using Pl and Qb as described by Bergreen. You can even incorporate patches of localized corrosion/erosion and dents.

Leonard@thill.biz

 

[LSThill]

API 618 COMPRESOR FPSO piping stress analysis

http://www.paulin.com/

BOS Fluids is the engineering software package that analyzes fluid transients in pipe systems and relates this information back to the mechanical piping system transferring the fluid.

For years piping engineers have labored with simplifying hand methods, cumbersome analog computers, or user-unfriendly software products when needing basic steady state and transient fluid analysis capability. BOS Fluids was written specifically to address the need of the piping engineer for fluid reaction forces, and to provide a system whereby the fluid simulation results can be easily integrated back into the piping system design and analysis.

BOS Fluids is an interactive computer simulation package that models steady state and transient flow in liquid or gas carrying piping systems. The procedure is easy to use and interfaces with most pipe stress programs. The package contains the elements required to model most common unsteady flow conditions. The elements included in the simulation package are pipes, valves, pressure relief valves, vacuum breaker, air valves, pumps, equipment, surge vessels, inlets, outlets, and orifices. BOS Fluids makes fluid simulation simple and easily accessible and yet gives the analyst pressure transients and dynamic force results with an engineering accuracy.

Based on a number of realistic assumptions a simplified form of the time dependent conservation (Navier-Stokes) equations are solved for the internal channel flow. The assumptions made are:

1. Fluid behavior in pipes is one dimensional i.e. similarity of cross sectional distribution of properties does exist.
2. Fluid transport velocity is small compared to wave speed.
3. Wave fronts remain plane while propagating.
4. Gas simulations assume that flow velocities are below sonic, and that pressure drops through the system are less than 30%.

Based on these approximations friction effects are lumped. The present friction model used is Colebrook-White. The Darcy-Weisbach flow model is used for steady state pressure drop calculations and the basic theory applied in BOS Fluids can be found in Wylie & Streeter's &quot;Fluid Transients&quot; published by FEB Press. BOS Fluids is capable of simulating both the steady and transient behavior of liquid carrying closed conduit systems of pipes, valves, pumps and surge relief devices. The following special features are available:

1. Pipe stress models from either CAESAR or PipePak can be downloaded for fluid analysis.
2. The analyst can pick different fluids from a database or add their own fluids to the database
3. Two different models are available to simulate column separation: Concentrated Air Pocket (CAP) model and the Vapor Cavity Model (VCM).
4. Various pipe materials can be applied-both isotropic (Metals) and Orthotropic (FRP) materials are included.
5. Based on geometry typical pump properties are generated automatically.
6. Buried and above ground systems can be simulated.
7. Simultaneously the transient response of multiple sources: Pump starts, Pump Failures, Valve Operations can be simulated.
8. Harmonic option allows an analysis of the occurrence of standing waves.
9. Maximum and minimum pressures and velocities occurring during transient and/or harmonics are traced.
10. The force processor allows an analyst to survey the time history of the unbalanced forces on pipe sections and preprocesses the force time histories to be used in the dynamical module of the pipe stress program.
11. A spectrum breakdown of force time histories is available. The analyst can see the natural frequencies of the fluid response that tend to excite the piping system.
12. Both Metric (SI) and English Units can be selected.

Typical analyses using BOS Fluids include: water transmission and distribution systems, main cooling water systems for chemical plants, sewage water systems, combined power and drinking water cycle power stations, oil product transport lines, tanker loading and unloading systems and dynamical behavior of chemical liquid transport lines. Acoustic analyses for compressors and pumps.


Leonard@thill.biz

http://www.thill.biz

 

[DSB123]

lsthill,
Why not answer the guy's question instead of promoting software by the Paulin group. The forum is specifically designed to answer others queries not promote/advertise software capabilities. Where does the BOS fluids software capabilities jargon answer Kastha's question ?

 

[LSThill]

Team Members

DSB123 (Mechanical) to answer the Kastha (Mechanical) question please go to download Papers Testing, Analysis and Design of Supported Pipe and Vessels Presented at November 19, 2003 ASME Meeting in Houston, Texas. (2K) saddleppt.PDF at the following:

http://www.paulin.com/

Transportation Direction of Ship Motions FPSO
Load Combinations for Sea Force

1. dead load + sway + heave + wind
2. dead load + surge + heave + wind

For additional detail reference SEE

Leonard Thill
Leonard@thill.biz

http://www.thill.biz

 

[xhpipe]

B31.3 does not specifically adress FPSO piping. There is some albeit slow movement to adress this portion of the process piping world in the future. Currently Norske Veritas is a often used refernce.

 

[LSThill]

Team Members:

http://www.mtd.org.uk/pubs.html

THE MARINE TECHNOLOGY DIRECTORATE

http://www.mtd.org.uk/pubs.html

99/100 Guidelines for the Avoidance of Vibration Induced Fatigue in Process Pipework

lst