FROM: Bijan Khaleghi
DATE: November 29, 2007
SUBJECT: Pipeline Encasement
TO: All Design Section Staff
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:
468-34-210: Pipelines Encasement
- Casings will not be required
for the following conditions:
- 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.
- 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.
- Casings will be required for
the following conditions:
- Pipeline crossings where
casing is required by appropriate industry practice or special
- Pressurized carrier pipes
and carriers of transmittants other than
natural gas which are flammable, corrosive, expansive, energized, or
- Pipeline installations
where local features, embankment materials, construction methods or other
conditions indicate probability of damage to the pipeline that will
render it unusable.
- Casings may be required as
protection for carrier pipe from external loads or shock during existing
highway improvement projects or new highway construction.
- 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
- Casing pipes shall be sealed
at the ends.
- 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.
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.
F. Posner, Bridge and Structures – 47340
cc: Mohammad Sheikhizadeh, Bridge Construction - 47354