Underground Chilled Water Distribution Piping
The Engineer must approve the contractor performing the underground chilled water work. Submit contractor qualifications and references for five (5) similar projects performed in the last 5 years. The contractor must also meet the following minimum requirements:
- Performed a minimum of three (3) underground ductile iron pipeline installations for 24” pipe and larger within the last 5 years.
- Has been in the underground pipeline utility business and has been performing this type of work for a minimum of 5 years.
- Is licensed to perform work in the State of North Carolina.
Submittals (Copies to Chilled Water Engineer)
Submit shop drawings for all pipe sizes including, but not limited to, the following:
- Pipe: ASTM/ANSI/AWWA number, grade if known, class, type, wall thickness, material.
- Fittings: ASTM/ANSI/AWWA number, grade if known, class, type, wall thickness, material.
- Flanges: ASTM number, grade, class, type, material.
- Valves: Manufacturer, type, model number, materials of construction, manufacturer’s data sheet (clearly cross-referenced).
- Isometric drawings showing all piping installed with joints, fittings and thrust blocks, as required for installation.
- Test Pressure and media.
- Pipe cleaning method
Prior to acceptance of installation and use, contractor shall deliver two (2) copies of survey quality as built construction drawings for UNC to review and approve. Drawing to include GIS survey of points including change of directions, valves and tie-in locations. A photograph library of the installation prior to backfilling is required. Photographs should include changes in direction, thrust block installation, pipe restraints and other pertinent information. The photographs must include background landmarks to verify location, orientation and physical attributes of the installation.
Product Delivery, Storage and Handling
Furnish all pipes with plastic end-caps/plugs on each end of pipe. Maintain end-caps/plugs through shipping, storage and handling to prevent pipe end damage and eliminate dirt and construction debris from accumulating inside the pipe.
Ductile Iron Pipe
The pipe and fittings shall be suitable for a minimum working pressure of 300psi, ANSI C151/A21.51, with asphalt coating and cement mortar lining ANSI/AWWA C104/A21.4. Nominal piping wall thickness shall be as follows:
|Piping Diameter (in)||Wall Thickness (in)|
|4 – 8||0.25|
Fittings shall be ductile iron mechanical joint type manufactured in accordance with ANSI/AWWA C110/A21-10, rated for 250 psi working pressure. Straight pipe joints and fittings are to be restrained joint-type. Joints and fittings shall be flexible and shall be designed to provide positive restraint against end-wise separation due to thrust.
Piping shall be US Pipe TR-Flex® or American Cast Iron Pipe Flex Ring® or approved equal. American Cast Iron Pipe Fastite® joint or US Pipe Tyton™ joint with EBBA Iron Series 1100 for new piping or Series 1700 harness type restraints may be provided for existing piping. All joints must be restrained for permanent piping. Pressure rating of 250 si minimum.
All bolts shall be low alloy, high strength steel bolts having minimum yield strength of 45,000 psi and which are cathodic to the pipe, meeting requirements of AWWA C111.
Restrained type joint fittings shall be equal to EBBA Iron Series 1100 Megalug® restraint systems for mechanical joint ductile iron piping, fittings and valves. Series 1100 solid ring restraints shall have a rated working pressure of 350 psi up to 16” pipe and 250 psi for 18” to 36” pipe. Series 1100 split ring restrains shall have a rated working pressure of 300 psi up to 16” and 200 psi for 18” to 36” pipe. Gasket material shall be SBR.
When piping is installed and to be left unattended or overnight, installation of non-pressure pipe plugs is required, or permanent plugs must be installed. Non-pressure plugs shall be equal to Taylor Made Plastics Bell End or Spigot End Plugs. The plugs shall be polyethylene with gaskets designed to keep pipes clean.
HDPE pipe will be considered for some applications and installations, but only with the written approval of the Chilled Water Director and the Chilled Water Distribution System Supervisor. If HDPE is allowed, it must meet the specifications below:
- The carrier pipe and fittings shall be a PE3408 High Density Polyethylene (HDPE) pipe and comply with the requirements of ASTM D1248, ASTM 3350, AWWA C901 (2” through 3”). AWWA C906 (4” through 63”), and NSF Standards 14 and 61. Materials used in the manufacture of HDPE pipe and fittings shall have the following minimum physical properties:
HDPE Pipe and Fitting Material Minimum Physical Properties Property Test Method Value Cell Classification ASTM D3350 345434C Density ASTM D1505 0.955 gm/cc Flexural Modulus ASTM D790 136,000 psi Tensile Strength @ Yield ASTM D638 3,500 psi Elastic Modulus ASTM D638 125,000 psi Brittleness Temperature ASTM D746 < -180 °F Melting Point ASTM D789 260° F Hardness ASTM D2240 Shore D 64 Impact Strength (IZOD) ASTM D256 42 in.-lb/in.
- The outside diameter and minimum wall thickness shall be manufactured to Ductile Iron Pipe sizes and have a Standard Dimension Ratio (SDR) of 11 and a pressure rating of 160 psi (Class 160).
- All fittings shall be pressure rated to match the system piping to which they are joined. At the point of fusion, the outside diameter and minimum wall thickness of the fitting shall meet the outside diameter and minimum wall thickness specification of AWWA C901/C906 for the same size pipe. All fittings shall be properly rated and clearly labeled. The fitting manufacturer shall be the same as the pipe manufacturer. Molded fitting shall be made from P3408 and have fusion capability with the pipe. Fitting shall meet the requirements of the ASTM D3261 for the butt-type fittings.
- Pipe and fittings shall be joined by thermal butt fusion, flange assemblies or mechanical methods in accordance with the manufacturer’s recommendations and the requirements of AWWA C901/C906. The HDPE pipe supplier shall provide the fusion equipment necessary for connecting the pipe and fittings. All butt fusions shall be done by McElroy fusion equipment or approved equal.
- Pipe and fittings shall be marked with the manufacturer, date of manufacture, lot number, size, PE code, pressure class, SDR#, AWWA designation number, and other information as described in AWWA C901/C906.
Valves to be designed for direct buried application shall conform to latest revision of AWWA C504 in addition to the requirements listed below.
Valves shall be rated for AWWA C504 Class 250B, 250psi non-shock working pressure-minimum. Valves are to be bubble-tight at the rated pressure in either direction. They shall be suitable for throttling service and operation after long periods of inactivity. Valves must be hydrostatic, and leak tested in accordance with AWWA C504.
Ductile iron body ASTM A536, restrained mechanical joint (AWWA C111/ANSI 21.11) ends. Valves shall be furnished complete with all required MJ joint accessories (bolts, nuts, gaskets and glands).
Valve discs shall be constructed of cast iron ASTM A126, Class B, or ductile iron ASTM A536. Disc shall have ASTM A276-Type 316 continuous stainless-steel seating edge to mate with valve seat.
Valve shaft to be corrosion resistant, ASTM A276-Type 304; ASTM A276-Type 316; ASTM A564 Grade 65-45-12 or approved equal.
Resilient seat shall be natural rubber (BUNA-N). Seat shall be bonded or mechanically retained in the valve body only. The seat shall be capable of mechanical adjustment and/or replacement in the field.
Valve assembly shall be furnished with a non-adjustable, factory set, thrust-bearing, and centered to the valve disc at all times. Shaft bearings shall be contained in the integral hubs of the valve body, be self-lubricated sleeve type and be sealed in place with self-adjusting packing.
Valves to be complete with grease packed buried service gear operator in compliance with latest revision of AWWA C504. Actuator shall have adjustable open and closed mechanical position stops that can withstand input torque of 450 ft-lbs. Orient valve operator to the outside of the trench or pipe (see Appendix D). Operator shall include shaft extensions to within one foot of finished grade, centering disc(s) located on shaft extensions, and all required soil pipes. Refer to drawings for length of shaft extensions and soil pipes.
Approved Manufacturers: DeZurik, Pratt, or approved equal.
Valve boxes shall be 2 – piece cast iron, screw type, 5.25” shaft with stay-put heavy-duty traffic weight lid marked “CHILLED WATER”. Boxes shall be equal to figure UTL 273, as manufactured by Charlotte Pipe and Foundry Co., Dewey Brothers or Tyler.
Valve boxes to be coated with coal tar for direct buried service application.
Vent Valve Boxes
Vent valve boxes shall be 2-piece cast iron, 12-inch diameter box with a cover with a highway H20 rating. Boxes shall be located directly above the installed corporation stop. Mark cover as “Chilled Water”.
Tapping sleeves shall be manufactured from Type 304 stainless steel plate with a stainless-steel ring flange, compatible with ANSI Class 125 and 150 bolt circles. The body and outlet shall be chemically passivated after welding for maximum corrosion resistance. The side bars shall be heavy gauge stainless steel. Trackhead bolts shall be 304 stainless steel with heavy nuts with UNC thread. Nuts shall be coated to prevent galling. Tapping sleeve shall be Romac STS420, no exceptions allowed.
Flange shall be stainless steel class “D” plate flange, with proper recessing for tapping valves. Flange will accommodate tapping flanges per MSS SP-60.
Gaskets for the flange and outlet sealing gaskets shall be Styrene Butadiene Rubber (SBR) compounded for water and sewer in accordance with ASTM D2000.
Gate Valves (For Tapping Service Only)
Conform to latest version of the AWWA Standard C-509 for resilient seated gate valves. There shall be a non-rising stem. The stem shall be cast bronze. The stem stuffing box shall be the O-ring seal type with two rings located above the thrust collar. The valve shall have a smooth full diameter waterway with no recesses.
The valve body and wedge shall be cast iron or ductile iron and shall be coated inside and outside with epoxy. The epoxy coating must meet or exceed AWWA C-550. The valve shall be designed for a pressure rating of 200psig and shall be hydrostatically tested at 400psig. The wedge must be completely encapsulated with rubber. Operator shall include shaft extensions to within 1’ of finished grade, centering disc(s) located on shaft extensions, and all required soil pipes. Refer to drawings for length of shaft extensions and soil pipes.
Approved Manufacturers: US Pipe, Clow or approved equal.
When digging within 10 feet of chilled water piping and the piping is unrestrained:
Locate chilled water pipes.
If the centerline of the chilled water lines and the proposed utility are less than 8 feet apart and any part of the proposed utility is below the top of the chilled water pipe, install the utility as follows:
- Locate both chilled water lines and the proposed utility, excavate joints one at a time and install split ring megalug restraints.
- When the restraints have been installed, backfill and compact to 90%. Backfill to original grade.
- Install proposed utility section and proceed to next unrestrained joint. If required, all of the restraint work can be completed before any of the proposed work is started.
All pipe, valves and fittings shall be installed as indicated on the drawings and according to the manufacturer’s instructions and UNC Chilled Water details.
Provide a concrete stabilizing pad under all isolation valves that are 20” or greater. (See Standard Details – Appendix D).
Provide vents at all high points of pipe sections. Contractor shall make taps at these high points and install corporation cocks and vent piping to grade before testing. During the backfill of the piping, the contractor will ensure vent lines are installed per the vent detail directly above installed piping. (See Standard Details – Appendix F).
Provide a stabilizing concrete pad around all valve boxes (see Standard Details – Appendix D). Do not locate valve boxes in parking spaces or in other inaccessible locations unless approved by Chilled Water Engineer. Install utility marking tape labeled ‘Chilled Water’ 2 feet above each pipe installed.
Chilled Water (4” to 42”)
Contractor shall visually inspect internal portion of each length of pipe during installation. Remove all dirt and foreign matter prior to installing additional lengths.
After each major section of piping has been installed, it shall be cleaned and flushed utilizing a high-pressure water “hydro-jet” process. The hydro-jet process involves passing a high pressure, high volume spray type cleaning head through the piping. The head is inserted in each section of piping and activated with full water pressure and flow. Through hydraulic force from directional spray nozzles the head propels itself forward up the pipe section. Once the head reaches the end of the pipe section it is retracted while maintaining maximum water pressure and flow. The length of the piping section shall be determined ahead of time so that the proper amount of travel can be tracked with calibrated markings on the spray head feed water hose or a meter on the hose reel. While traveling through the piping the pressurized water spray knocks debris loose and carries it back to the open end of the piping where it is collected and removed from the system. For each section of piping the process shall be performed a minimum of two times and may need to be repeated until the water exiting the end of the pipe is clear and free of debris as determined by the Owner/Engineer.
The hydro-jet equipment utilized shall be capable of providing a minimum of 50 GPM at 2000 psi. All cleaning and flushing shall be performed so that all debris will be pulled or flushed downhill. All cleaning and flushing shall be initiated from all low points in the system and shall terminate at the nearest adjacent high point in the system.
Coordinate the limitations and requirements of hydro-jet process with the flushing subcontractor such that the piping is installed in a sequence and manner that allows every section of the new pipeline to be cleaned and flushed. Limitations may include maximum length of the pipe section, maximum number and/or degree of bends in the pipe section, maximum slope of the pipe section, equipment and excavation access requirements, and the minimum size of the openings required in the piping to allow for insertion and retraction of the cleaning head.
Contractor shall provide access at all low points through valves, tees, flanges, etc. to facilitate the cleaning and flushing process. If temporary fittings or piping are required, they shall be provided by the Contractor and removed by the Contractor after successful cleaning.
After flushing and cleaning is completed, contractor shall provide necessary pipe and fittings required to complete the piping system. Each cleaned section of piping shall be capped and protected to keep mud, debris, water, etc. from entering the piping. If a piping section is left open or unprotected, or is contaminated, it shall be re-cleaned prior to being filled and activated at no cost to the Owner.
Contractor shall provide all water for flushing and testing. Coordinate rental of fire hydrant meters with local Fire Department(s), or the University as required.
Contractor shall provide all temporary piping from water source to piping system and shall provide means for conducting cleaning water from underground piping system to the appropriate sewer; i.e. pumps, piping, hoses, tanks, etc. Contractor to remove all temporary piping, pumps, hoses, etc. from site immediately after flushing has been completed.
The pressure tests shall be sustained for not less than four hours and or long as the Chilled Water Engineer/Representative requires assuring that:
- The scale of the test gauge must be a minimum of 50 psi higher than the anticipated test pressure and the incremental reading of the gauge is 2 psi.
- No air pockets are in the line.
- No broken pipe or defective materials are in the line.
- No leaking joints have been made. Any visible leak, drip, or weeping from a joint or fitting, or pipe will cause an automatic failure of the test. The issue must be resolved, and then a new test will begin.
Before applying the specified test pressure, all air shall be expelled from the pipe. If outlets are not available at high points, the Contractor shall make the necessary taps at points of highest elevation, install corporation cocks, and vent piping to grade per the vent detail before the test is made.
Tests may be made of isolated portions of such piping as will facilitate general progress of the installation. Any revisions made in the piping systems will subsequently necessitate re-testing of such affected portions of the piping systems.
Any defective material or defects in workmanship that develop during the tests shall be remedied and the subject piping shall be re-tested.
Determine the maximum allowable amount of leakage by the following formula:
S = length of pipe tested, in feet
D = nominal diameter of pipe in inches
P = average test pressure during leakage test in pounds per square inch
|Pipe Size||Length of Pipe (Feet)|