PRCI PR-244-084507

L52302

C-FER Technologies

Need: The design section of API Recommended Practice 1111 for the Design, Construction, Operation and Maintenance of Offshore Hydrocarbon Pipelines is based on limit states concepts, cast in a simple and practical framework. Some strain-based criteria exist in the recommended practice (RP), but there are a number of load cases not explicitly addressed in the RP that could benefit from strain-based design methods. Given the advances in strain-based design methodology in recent years, there is a need to prepare a supplementary document describing how strain-based design approaches may be used in connection with the RP to produce better overall solutions and ultimately serve as a basis for enhancing the RP.

Result: As a result of this work, it was found that in general the RP provides adequate strain-based design criteria for installation load cases. However, there are no criteria for addressing thermal loads or ground movements associated with the operational load cases identified above. The latest version of the draft RP does refer the designer to recently published design guides for thermal loading issues, but no further guidance is provided. Based on the results of this study, some guidance has been provided in the Appendix on using strain-based design methodologies in conjunction with API RP 1111 to supplement areas not currently covered in the RP. It is recommended that thermal loading cases use one of the two recently published design guides that specifically address these conditions. It is also recommended that ground movement analysis initially implement the use of soil-spring modeling techniques (guidance provided), enhanced by full three-dimensional finite element modeling if warranted. A summary of the current state-of-the-art in compressive strain limit guidance has been presented, along with several equations that consider a number of different variables. Methods for assessing tensile strain limits have also been provided based on the latest research advances in the area.

Benefit: The primary objective of this research project was to develop recommendations on the potential use of strain-based design methods to enhance the design methodology described in API RP 1111. The work covers the following: 1) a listing of design conditions for which strain-based methods are beneficial; 2) the use of strain-based design for each of the identified design conditions; and 3) guidance on the use of strain-based design approaches within the framework of API RP 1111. The load cases that have been identified as possibly benefitting from a strain-based design approach include the following:


Transportation and Installation Operation
Reeling Deformations
Overbend Bending
Sagbend Bending
Ovalization Due to Tie-ins,
Connections and Terminations
J-tube Pull Deformations
Thermal Loads
Seismic Loads
Support Settlement
Slope Instability
Nearshore Arctic Permafrost Thaw
Subsidence/Frost Heave
Seabed Ice Gouging


A summary of these load cases has been provided, particularly how they are currently addressed within the context of using API RP 1111 and any additional supporting design practices. These load cases were then reviewed to assess the state-of-the-art with respect to how they can be addressed outside the context of API RP 1111. Summaries of other design guidance documents have been provided, along with summaries of ongoing research to improve design methodology.

Product Details

Published:

06/01/2009

Number of Pages:

65

File Size:

1 file , 420 KB