Design Memorandum



TO:                  All Design Section Staff

FROM:            Bijan Khaleghi
DATE:             November 29, 2007
SUBJECT:       Pipeline Encasement


Pipelines carrying Natural gas lines through the bridge superstructure shall be designed by the utility company in accordance with the WAC 480-93. Gas Companies Safety. Pipeline encasement requirements for natural gas lines in state right of way shall be in accordance with WAC 468-34-210 as specified below and in Bridge Design Manual Sections 10.8 and 10.9:

WAC 468-34-210: Pipelines Encasement

  1. Casings will not be required for the following conditions:
    1. Pipelines conveying natural or other gas which meet the design, installation and cathodic protection provisions of the Minimum Federal Safety Standards, 49 CFR Part 192 and Chapter 480-93 WAC Gas Companies -- Safety.
    2. Local service lines and connections conveying natural or other gas which meet the design, installation and cathodic protection provisions of the Minimum Federal Safety Standards, 49 CFR Part 192 and Chapter 480-93 WAC Gas Companies -- Safety.
  2. Casings will be required for the following conditions:
    1. Pipeline crossings where casing is required by appropriate industry practice or special conditions.
    2. Pressurized carrier pipes and carriers of transmittants other than natural gas which are flammable, corrosive, expansive, energized, or unstable.
    3. Pipeline installations where local features, embankment materials, construction methods or other conditions indicate probability of damage to the pipeline that will render it unusable.
  3. Casings may be required as protection for carrier pipe from external loads or shock during existing highway improvement projects or new highway construction.
  4. Casing pipes shall extend a minimum of six feet beyond the toe of fill slopes, or back of ditch line, or outside curb unless limited by restrictive local conditions. The casing pipe need not be continuous on freeways with or without frontage roads; however, maintenance in the median shall not be required on a routine basis.
  5. Casing pipes shall be sealed at the ends.
  6. Casing pipes shall be designed to support the load of the highway and superimposed loads thereon and, as a minimum, shall equal the structural requirements for highway drainage facilities. Casings shall be composed of materials of sufficient durability to withstand any conditions to which they may be exposed.


Background:

The current practice is to require casings for all pipelines carrying natural gas. WAC 480-93 does not require casing installations, it only provides guidance should casings be installed. Natural gas pipeline encasement requirements in state right of way has recently been changed under WAC 468-34-210. This memorandum reflects this change. The Bridge Design Manual will be updated accordingly.


If you have any questions regarding these issues, please contact Joe Merth at 705-7166 or Mike Rosa at 705-7156.


cc:   Mohammad Sheikhizadeh, Bridge Construction - 47354

       F. Posner, Bridge and Structures 47340