API RP 1133:2005 pdf download
API RP 1133:2005 pdf download.Guidelines for Onshore Hydrocarbon Pipelines Affecting High Consequence Floodplains.
In selecting a route across a high consequence floodplain, it is vety important to address possible hazards to the integrity of the pipeline crossing: erosion of the channel bed, failure of the banks, migration of the thaiweg, damage from vessels navigating the water course, dredging and debris carried by currents—particularly during flood conditions. These risks can be managed if the hydrology of the watercourse is adequately analyzed and the pipeline crossing is located both laterally and vertically so as to minimize future exposure to these hazards.
4.1.2 Buried Crossings
In locating the route vertically, the potential for future degradation or scour of the channel should be considered by reviewing the hydrology of the channel, conducting a geotechnical investigation, as well as reviewing site records and existing topographic maps. The pipeline should be placed at a depth below the expected level of scour. Minimum burial depth of trenched crossings shall comply with U.S. Army Corps of Engineers. Department of Transportation (DOT), Office of Pipeline Safety, and other applicable regulatory requirements.
The lateral location of the pipeline should he determined after a careful review of channel hydrology. The lateral stability of the channel should be determined. Characteristics of channel instability include the following:
• Bank erosion,
• Migration of the channel within the floodplain, and
• Migration of meanders downstream.
The rate of bank erosion and migration can be projected by reviewing the hydrology and forecasting the changes in the channel for the design life of the pipeline. The lateral location of the pipeline and effective length of the crossing are then determined based on these projections. Adequate depth should he maintained to eliminate impacts from the future migration of the channel. For example, if the migration rate is 2 ft per year and the design life is 50 years, the depth below the level of scour should be maintained for at least 100 ft from the bank in the direction of channel migration. Special consideration should be given to previously existing channels that may scour as a result of secondary overhank flows during flood conditions.
Significant savings can be realized if several pipelines are bundled together in one crossing. Directionally-drilled crossings may be bundled if the diameter of the bundled pipelines does not exceed the largest diameter bore that can be installed. One or more spare pipelines within the bundle may be considered to allow for future expansion. For pipelines that arc bundied together. provisions should be made for adequate corrosion control to prevent interference of cathodic systems or to prevent one or more lines from acting as a sacrificial anode.
See the following publication for further guidelines: Installation of Pipelines by Horizontal Directional Drilling, an Engineering Design Guide (PRCI no PR-227-9424).
4.1.3 Aerial Crossings
Aerial crossings of tloodplains and watercourses can he made by using existing host bridges or dedicated bridges, and self-supporting spans that are specially designed for the pipeline crossing. The following should he considered in design of aerial crossings:
• Pipe selection (internal pressure as well as span length and ballistic protection),
• Atmospheric corrosion control (coatings and or insulaion),
• Stresses due to thermal conditions,
• Isolation of cathxlic protection,
• External loads such as wind, snow. etc.,
• Clearance for water traffic.
Physical security should he provided to prevent unauthorized access and/or damage to the crossing.
Host bridges can be the most economical method of aerial crossing of watercourses, although they are not often conveniently located along the proposed route of a pipeline. The primary design considerations for locating on a host bridge are:
• The adequacy of the host bridge to support the additional weight of the pipeline and its appurtenant support system,
• The design of the pipeline support system itself.
