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PURPOSE
1.1 This standard defines the philosophy and criteria that shall be applied to the design of plant underground gravity drainage systems.
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SCOPE
2.1 This standard applies to the design of all sanitary, industrial wastewater, and storm water underground gravity drainage systems for all plants.
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RELATED DOCUMENTS
3.1 Air Products Engineering Documents
309734D Standard Sanitary and Process Drainage Details
4CS01004A Frost Penetration
4EQ65005A Oil/Water Separator Sizing
4ACS-640250 Underground Gravity Drainage Systems
4API-670221 Metallic Pressurized Underground Process, Potable, Utility, and Firewater Piping
3.2 American Society of Mechanical Engineers (ASME)
A112.6.3 Floor Drains and Trench Drains
3.3 General
Elwyn E. Seelye, Data Book For Civil Engineers – Design, Third Edition
3.4 International Association of Plumbing and Mechanical Officials
Uniform Plumbing Code
3.5 United States Department of Commerce
National Oceanographic and Aeronautic Administration – Rainfall Frequency Atlas of the United States
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DEFINITIONS
4.1 Catch basin: Enclosure that provides an inlet or collection point for storm water runoff. Also used to connect associated underground piping
4.2 Industrial wastewater: Any water that contains water borne waste from industrial or commercial processes, except domestic sewage. Typical examples include process condensate, blowdown water, rainwater contaminated with oil, and floor/equipment slab washdown water.
4.3 Manhole: Enclosure used to provide access to the underground drainage system for tasks such as inspection, sampling, and cleaning. Also used where there is a significant change in direction, grade, or pipe size on the piping system.
4.4 Runoff: Peak discharge of a surface drainage area due to the maximum design storm that is assumed.
4.5 Sanitary sewage: Any liquid waste containing animal or vegetable matter in suspension or solution and may include liquids containing chemicals in solution.
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MATERIAL AND USES
5.1 General
5.1.1 Solid wall pipe shall be used in the conveyance of sanitary sewage, industrial wastewater, and storm water. Perforated wall pipes are suitable for use in underdrainage, filter fields, leaching fields, and similar installations.
5.1.2 Typical materials for solid wall pipes are vitrified clay, cast iron, concrete, corrugated steel, and Acrylonitrite Butadiene Styrene (ABS)/Poly Vinyl Chloride (PVC) plastic pipe. Composite pipe or truss wall pipe is manufactured from ABS and PVC plastic.
5.1.3 ABS plastic pipe shall not be used to convey liquids with a temperature in excess of 80C (180F). PVC plastic pipe shall not be used to convey liquids with a temperature in excess of 60C (140F). Steam condensate shall not be discharged into ABS or PVC pipe. Consideration shall be given in the design of the piping system for thermal expansion due to temperature changes.
5.1.4 Piping material, wall thickness, and depth of soil cover above the pipe shall be selected to address the design surface loading for the area where the pipe is constructed. Loading that the pipe will encounter during construction activities and from other traffic shall also be considered. The minimum depth of the pipe below grade to protect against frost shall be in accordance with 4CS01004A.
5.1.5 Carbon steel pipe and fittings shall be used in special circumstances such as when high surcharge loading from roads and minimum soil coverage exist. When used underground, the pipe shall be coated and wrapped. Material and installation requirements are specified in 4API-670221.
5.1.6 Vitrified clay pipe shall not be used under buildings or equipment foundations. The loading imposed by these foundations can crush this type of pipe.
5.1.7 Manholes shall be constructed as precast reinforced concrete sections. Covers shall be solid and watertight to prohibit surface drainage water from entering the manhole. Covers shall be designed to support the anticipated traffic loading.
5.1.8 Catch basins shall be constructed of precast or cast-in-place concrete. Covers shall be designed to support the anticipated traffic loading.
5.2 Sanitary Systems
5.2.1 Drainage piping and fitting materials may be cast iron, ABS or PVC plastics, extra strength clay, carbon steel or other Code-approved materials having a smooth and uniform bore. Service weight cast iron soil pipe and fittings is preferred. It produces the lowest installed cost for most installations and the required serviceability. This material shall always be used within the limits of building and equipment foundations and for pipe extending above grade such as equipment hubs or vent lines.
5.2.2 Corrugated steel pipe shall not be used for the conveyance of sanitary sewage because the reliability of providing a system that does not experience potential fluid leakage is low.
5.3 Industrial Wastewater Systems
5.3.1 Material for drainage pipe and fittings may be cast iron, ABS or PVC plastic, extra strength vitrified clay pipe, steel pipe, or other code-approved materials having a smooth and uniform bore. Service weight cast iron soil pipe and fittings is preferred. It produces the lowest installed cost for most installations and the required serviceability. This material shall always be used within the limits of equipment and building foundations.
5.3.2 Corrugated steel pipe shall not be used for the conveyance of industrial wastewater because the reliability of providing a system that does not experience potential fluid leakage is low.
5.4 Storm Water Systems
5.4.1 Piping materials used for conveyance of storm water may be reinforced concrete, corrugated steel, and ABS or PVC plastic solid wall and truss wall pipe.
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SYSTEM DESIGN
6.1 General
6.1.1 An environmental strategy is established for each project. The project design criteria are specified in the project scope summary document. Any additional information or clarification shall be resolved with the project engineer before initiating the underground drainage system design.
6.1.2 The drainage summary prepared for the project by the project engineer provides the maximum and average discharge rates from the various point sources that the system must be designed to accommodate.
6.1.3 Information on the sizing of oil/water separators and the associated collection system can be found in 4EQ65005A.
6.1.4 The utility tie-in section of the flowsheet provides information that is to be applied to the design of the underground drainage system. The flowsheet will typically show the sources of equipment discharge, schematic routings of sewage treatment systems and the oil/water separator. The flowsheet will also show valve numbers and type of discharge piping required at chemical and oil containment areas.
6.1.5 Sewer systems shall be located below the underground electrical system and above the process piping systems such as cooling water. Care shall be taken to coordinate underground piping systems with all other underground utilities.
6.1.6 Placing any pipe beneath a foundation or the load affected zone shall be avoided. When any pipe passes through a foundation, a sleeved opening shall be installed to allow for the differential settlement between the pipe and the foundation.
6.2 Sanitary Systems
6.2.1 The governing plumbing code such as the Uniform, Basic, or Standard Plumbing Code shall be consulted for all regulations and applicable installation requirements.
6.2.2 The minimum sizes of vertical and/or horizontal building drainage piping shall always be determined from the total flow of all the fixture units that are connected to the system. In addition, vertical drainage pipes shall be sized in accordance with their length. Review the applicable tables in the governing plumbing code.
6.2.3 The recommended minimum size pipe for yard piping is 4 inch. Smaller size lines are easily blocked during construction, and cleaning is difficult.
6.2.4 Changes in direction of drainage flow shall be made with the use of approved fittings. Cleanouts to grade shall be provided in accordance with the requirements of the applicable plumbing code.
6.2.5 Horizontal drainage piping shall be run in practical alignment and with a uniform minimum slope of not less than 1/4 inch per 1 foot. Where it is not practical to obtain this recommended minimum slope, any pipe 4 inches or larger in diameter may have a minimum slope of 1/8 inch per 1 foot.
6.2.6 Nomographs titled “Flow in Partly Filled Pipes” found in the tables section of the Uniform Plumbing Code may be helpful in the design of the system. Data contained there includes information relating pipe capacity, slope, diameter, and velocity of flow. Capacity and velocity may be calculated for full and 3/4 full flow conditions.
6.2.7 Drop manholes are recommended when the difference in invert elevations is greater than 4 feet. Use of drop manholes eliminates the cost of deep sewer excavation.
6.2.8 Manholes shall be used to provide access for sampling, to house flow metering devices, and to act as a common trap and vent upstream of a tie-in to the municipal sewer.
6.2.9 Connection of private systems to the municipal collection system is made at locations called laterals. The lateral is installed at intervals along the sewer main. The lateral may extend from the sewer main to the property line. Other tie-in points may be specified by the municipality. Connections to existing sewer manholes is not recommended because of construction difficulties.
6.3 Industrial Wastewater Systems
6.3.1 Wastewater by definition will be governed by the rules and regulations of the applicable plumbing code. The requirements of the code shall be applied using good engineering judgment that provides a drain system that will effectively collect and convey all wastes.
6.3.2 Wastewater found in Air Products nonchemical facilities will be generally clear liquids that may contain some sediment. Sediment from truck wash areas, fuel islands, and exterior equipment pads where dirt from the environment gathers is conveyed into the drains by rainwater or wash water. To help convey this sediment for the piping system, drainage systems shall be designed to maintain a self-cleaning velocity of 2.0 to 3.0 feet per second. Use of a gooseneck piping inlet in the truck wash area catch basins is also recommended as a method to restrict the amount of sediment that can enter the underground piping system. Sediment is removed from these catch basins manually.
6.3.3 Pipe shall be a minimum of 4 inches in diameter. Pipe sizing and methods are discussed in paragraph 6.5
6.3.4 Changes in direction of drainage flow shall be made with the use of approved fittings. Cleanouts to grade shall be provided in accordance with the requirements of the applicable plumbing code.
6.3.5 Horizontal drainage piping shall be run in practical alignments and pipe gradients shall be uniform.
6.3.6 Manholes in a wastewater system shall be used to provide access for sampling and to house flow metering devices. Prefabricated fiberglass metering manholes are commercially available for this application and are specified by the Process Controls Group. The required manhole depth and pipe size information must be provided to them.
6.3.7 Pipe upstream and downstream of a metering station shall be set at a uniform gradient which will provide a uniform flow and accurate measurement. Pipe upstream of the oil/water separator shall be set at a uniform gradient of between 1 and 2 percent. This promotes uniform flow and will help prevent emulsification (foaming).
6.3.8 Underground valves used to control the flow from the curbed foundation areas shall be of the type that will accept a lock-type indicator post. The post extends above grade, has a window indicating the position, and is furnished with an angle-type operating wrench, padlock, and locking staple.
6.4 Storm Water Systems
6.4.1 Sloping of the finished grade surface in conjunction with an integrated system of perimeter drainage swales is the preferred method of surface water collection and is usually the most economical drainage alternative at the plant site. Catch basins and underground piping systems shall only be used when the site layout and/or elevations prohibit the use of a surface-type drainage system or when other local code requirements dictate otherwise.
6.4.2 The design of the storm water collection and conveyance system shall be based on the following criteria unless specific project requirements dictate otherwise.
6.4.2.1 The design storm to calculate the peak flow rate shall be the 10 year, 30 minute storm unless a different criteria is required by the state or local authorities. This rate is consistent with the method used in 4EQ65005A.
6.4.2.2 The rainfall intensity criteria for the facility site can be obtained from the United States Department of Commerce, National Oceanographic and Aeronautic Administration, Rainfall Frequency Atlas of the United States.
6.4.2.3 The calculation for rainwater flow rate is as follows:
Q = 0.0208 *I*A*C
where
Q = flow rate in gallons per minute on completely impervious surfaces
I = rainfall intensity (inches/hour)
A = surface area (square feet)
C = surface porosity coefficient
Plant sites may consist of several types of surface conditions which have a direct influence on the design flow rate. To modify the peak runoff for the different surface conditions, Q is multiplied by the coefficient C.
C = 100% for pavement, roofs, equipment pads
C = 60% for stoned yard areas
C = 30% for lawn and landscaped areas
6.4.2.4 The “Rational Method” as discussed in the Seelye’s Data Book for Civil Engineers shall be used to calculate the quantity of runoff at a given point in a storm drain system. Using this method the peak flow can be calculated at any point in the system.
6.4.3 Drainage systems shall be designed to maintain a self-cleaning velocity of 2.0 to 3.0 feet per second.
6.4.5 Pipe in a closed system shall be a minimum size of 12 inches in diameter. This size will facilitate cleaning. Reinforced concrete pipe is not made in sizes smaller than 12 inches. Pipe used as culverts (e.g., under roads) shall not be less than 18 inches in diameter. If there is limited available depth for pipe cover, pipe arches may be used.
6.4.6 Manholes shall be used at all changes in pipe direction and changes in pipe gradient. The size of the manhole may be increased to accommodate the junction of several pipes. Standard diameters are 48, 60, 72, 84, and 96 inches.
6.4.7 Pipe invert elevations at manholes shall be set to maintain a common crown elevation. The use of economical flared pipe end sections is preferred over poured in place endwalls. These sections are made to fit round concrete pipe and round or arch metal pipes.
6.4.8 Pipes that are connected with mechanical joints shall be designed with anchors when the gradient exceeds 24 percent or approximately a 1 to 4 slope.
6.4.9 Pipe sizing and methods are discussed in paragraph 6.5. Concrete pipe in 15 inch diameter may not be available in all areas. When uncertain, go to the next larger size.
6.4.10 The bottoms of catch basins shall be fashioned with smooth semi-circular channels made from concrete to eliminate any catchment area that may collect sediment or water that would become a breeding place for insects.
6.5 Pipe Sizing
6.5.1 The Manning Formula shall be used to size pipes and open channels when the flow is uniform. The design equations are as follows:
V = (1.49/n)*R2/3*S1/2
Q = A*V
Q = A*(1.49/n)*R2/3*S1/2
where
R = hydraulic radius = area of the cross section of flow divided by the wetted
perimeter
S = slope of the total head line or may be taken as the slope of the pipe or channel
expressed in feet of vertical rise per foot of horizontal distance
n = Manning roughness coefficient
Q = rate of discharge in cubic feet per second (cfs)
V = mean velocity of flow in feet per second
A = cross sectional area of the pipe or channel in square feet
Values for R2/3, S1/2, pipe cross sectional area, wetted perimeter, and other parameters are found in most drainage design handbooks.
6.5.2 A nomograph is a useful tool to graphically size a pipe or waterway. Examples can be found in Seelye’s Data Book for Civil Engineers.
6.5.3 Table 2 in this standard shows the values of allowable flow in vertical leaders and horizontal storm drains. This table will aide in the sizing of rainwater and industrial wastewater piping.
6.6 Drains and Drain Sizing
6.6.1 Floor drains are primarily used for inside locations where the flow rate into the drain can be anticipated and for outside areas where the rainfall intensity dictates the sizing. Drains shall be selected with sufficient grate free area to pass the anticipated flow. Grate free area is defined as the total area of the drainage openings in the grate. The drain outlet shall be sized large enough so that it will safely pass the maximum flow through the grate without causing water build-up.
6.6.2 The following formula taken from Seelye’s Data Book for Civil Engineers is useful in determining the area of inlet grating openings:
A = Q/(C*(2*g*h)1/2* 0.667)
where
Q = quantity of runoff reaching the inlet in cfs
C = orifice coefficient
0.6 for openings with square edges
0.8 for openings with round edges
A = net area in feet2
g = 32.2 feet per second2
h = allowable head on inlet in feet
6.6.3 For most indoor locations, the grate free area shall be equal to 1 1/2 times the free cross-sectional area of the connecting pipe. The number and locations of the drains are based on the configuration of the floor plan, type of operation, and location of equipment. For areas see Table 1.
6.6.4 Floor drains or area drains, when used to drain exterior areas that are subject to rainfall, shall have a grate free area equal to 2 times the free area of the connecting pipe.
6.6.5 Drains shall structurally support the anticipated loads that will be imposed on the floor. The loading classifications as published in ASME A112.21.1M are as follows:
Light Duty – all grates testing under 2,000 pounds
Medium Duty – all grates testing between 2,000 pounds and 4,999 pounds
Heavy Duty – all grates testing between 5,000 pounds and 7,499 pounds
Extra Heavy Duty – all grates testing between 7,500 pounds and 10,000 pounds
Special Duty – all grates testing over 10,000 pounds
6.6.6 Standard floor drains shown as Details 1 and 2 on 309734 are medium duty. Grates in Details 1, 2, 3, 4 (4 inch and 5 inch size) and 5 have a grate free area at least 2 times the outlet pipe cross-sectional area. Detail 4 (6 inch size) has a 1 2/3 ratio. Detail 6 has a grate free area of less than the outlet pipe size.
6.6.7 Rainwater systems are discussed in Appendix D of the Uniform Plumbing Code. Sufficient information and examples are given to aid in the selection of the proper drain size as well as an adequate number of drains with the following exceptions:
Rainfall rate shall be as specified in paragraph 6.4 of this standard
Rainfall values shall be rounded up to the next even inch
Values given in Tables D-1 and D-2 must be multiplied by a factor of 0.5
These tables may also be applied to roof and yard drainage.
Table 1 – Recommended Grate Open Areas for Various Outlet Pipe Sizes
| Nominal
Pipe Size (in) |
Transverse
Area of Pipe (in2) |
Minimum
Flow Requirements (in2) |
Maximum
Flow Requirements (in2) |
| 1 1/2 | 2.04 | 3.06 | 4.08 |
| 2 | 3.14 | 4.71 | 6.28 |
| 3 | 7.06 | 10.59 | 14.12 |
| 4 | 12.60 | 18.90 | 25.20 |
| 5 | 19.60 | 29.40 | 39.20 |
| 6 | 28.30 | 42.45 | 56.60 |
| 8 | 50.25 | 75.38 | 100.50 |
Table 2 – Allowable Flow for Vertical Leaders and Horizontal Storm Drain
| Allowable Flow | (GPM) | |||
| Pipe Size
(in) |
Vertical Leader
|
Horizontal
1/8″ per 1′-0″ |
Horizontal
1/4″ per 1′-0″ |
Horizontal
1/2″ per 1′-0″ |
| 2 | 30 | 12 | 17 | 24 |
| 3 | 90 | 36 | 51 | 72 |
| 4 | 192 | 78 | 111 | 157 |
| 5 | 348 | 142 | 201 | 284 |
| 6 | 566 | 231 | 327 | 462 |
| 8 | 1220 | 498 | 705 | 996 |
| 10 | 2200 | 902 | 1275 | 1804 |
| 12 | — | 1467 | 2076 | 2934 |
| 15 | — | 2666 | 3774 | 5332 |