| Applies To | |
| Product(s): | AutoPIPE |
| Version(s): | ALL; |
| Area: | Piping code |
| Date Logged & Current Version | Dec 2021 12.06.00.048 |
Problem:
Is AutoPIPE suitable for ultra-deep-water spools analysis, in particular the water depth is approximately 2800m for the Project using DNV?
Solution:
To answer the question, are AutoPIPE’s results consistent when performing an analysis using DNVGL-ST-F101 in an ultra-deep water scenario?
The definition of “deep water” may vary in the industry, however, generally deep water refers to water depths between 1,000 ft and 5,000 ft. Below the depth of 5,000 ft is referred to as ultra-deep water. For the purpose of this discussion, we will consider a depth of 3,000 meters (approximately 9,843 feet) and demonstrate applicability of subsea functionality of the program in these depth ranges. The piping standard used is the 2017 edition of DNVGL-ST-F101, current edition available in the software.
DNV is recognized as a principal advisor for the maritime industry. The DNVGL-ST-F101 standard provides criteria and recommendations for submarine pipeline systems with no limit on water depth. To verify, compare the hand calculations in the form of MathCAD PDF files, handwritten calculations, and excel spreadsheets to the output results generated by AutoPIPE.
AutoPIPE Connect v.12.06.00.048 was used to model the ultra-deep water piping, analyze using the standard’s numerical calculations, and produced output results. Features in AutoPIPE that were tested are modeling, analysis, and post processing.
Modelling
The modelling capabilities of AutoPIPE were tested with depths of more than 9,000 meters. Component insertion was successfully performed without any issues. The model navigation behaved like all other models with pan, zoom, and rotate working correctly with speed not compromised. All the view modes (single line, wire frame, and solid) were working properly. Component selection, modification, and deletion worked without presenting any issues. The coordinates (in millimeters) were working with reasonable accuracy without any failures.
Tips:
To work with large coordinates, it may be reasonable to create a copy of the unit file with proper conversion factors and use more suitable input units for coordinate fields like meters instead of millimeters. This may make it easier to work with large coordinates and also may help with loss of significant digits for very large coordinates.
Visualization
The visualization capabilities of AutoPIPE (Water surface and hydrodynamic data visualization) were tested with depths of more than 9,000 meters. The visualization functions performed correctly without any issues or performance degradation.
Tips:
On certain graphics systems, having the Water Surface being displayed may interfere with points selection. In that case, disable the Water Surface display when updating the model.
Loads
The loading dialogs were tested for models in the range of ultra-deep water. The load definitions are not directly coupled with the model geometry definition and worked correctly. Enough input characters were available on the Wave dialog for entering the depth of water down to seabed for ultra-deep water. Notice that the same depth if used for water surface visualization. No substantial loss of significant digits was noticed.
The results for buoyancy will be discussed under the analysis details. The incidental pressure calculations (Loads > Pressure > Incidental Pressure) are simple calculations which are presented in the an sheet. It was noted that the reported pressure values for P1 load case are the same as calculated in the excel sheet for all points.
Analysis
Buoyancy
There are numerous hand calculations available for verification of buoyancy application in the program that includes buoyancy calculations for horizonal and vertical pipes, with and without bends, with and without insulation, buoyancy with hydrotest, and effect of added mass for submerged and unsubmerged piping.
For this report, a horizontal pipe was modeled at a depth of 10,000 feet (more than 3,000 meters) below sea level. Buoyancy loads application worked correctly.
Wave
Numerous hand calculations and comparison to other programs available but may not be relevant to deep water.
Added Mass
See reference information in AutoPIPE help on Added Mass and how it impacts dynamic analysis for submerged piping.
DNV Result Options
DNV Result Options impact the post processed results for DNV Piping code. Verification of post processed code compliance results are provided under the subsequent section.
Post Processing
Code Compliance
Code compliance calculations are typically verified for different components like bends, tees, and run points which may have different SIF or calculations requirements. Comparison of hand calculations to model results were within a percentage error of less than 0.1%.
Conclusion
All of AutoPIPE’s results are consistent with 2017 edition of DNVGL-ST-F101 calculations for ultra-deep water pipe stress analysis.
See Also
DNV Piping Code Calculation Issues