MOE Guidelines on Surge/Transients

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Annis Morrison
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Corporate Office Hydratek & Associates Inc. 216 Chrislea Road, Suite 501 Woodbridge, Ontario L4L 8S5 Canada www.hydratek.

1 Corporate Office Hydratek & Associates Inc. 216 Chrislea Road, Suite 501 Woodbridge, Ontario L4L 8S5 Canada MOE Guidelines on Surge/Transients Introduction The Ministry of the Environment (MOE) in the Province of Ontario is responsible for setting guidelines and regulations for water and wastewater systems in Ontario. The MOE advises designers to take transients (surge or water hammer) into account when designing such systems. The following document summarizes any transient or surge related guidelines or requirements found within existing MOE documents. MOE Statement The ministry does not have explicit guidelines or regulations on transients/water hammer for transmission mains, distribution systems or wastewater systems. It is up to the engineering consultants to check that the transients/water hammer conditions are in accordance with the manufacturer s design specifications. Both of the MOE design guidelines, Design Guidelines for Drinking Water Systems (2008) and Design Guidelines for Sewage Works (2008) only advise designers to ensure that the water and wastewater systems are designed properly, including the partial consideration of system transients/water hammer. Transients in Design Guidelines for Drinking Water Systems, 2008 Chapter 2: Project Design Documentation : Stage 3 Documents, Design Brief/Basis of Design, Design Brief Major Facilities Detailed process and hydraulic design (or sizing) calculations, including surge analysis (where required) for all facilities, treatment units and equipment; (Page 32) Chapter 3: General Design Considerations : In-Plant Piping, General The design of the piping should allow for proper restraint under all anticipated conditions, particularly where surges may occur and high transient pressures could result or where different temperatures occur seasonally (Page 66) Chapter 4: Source Development 4.2.4: Surface Water, Intake Structures All designs should be checked for transient pressure problems, particularly if the intake pipe is long or has high design velocities. (Page 84)

2 4.5.2: Wells, Well Pumphouse Design If high static water levels exist, the designer should consider the use of a by-pass to waste from the pump to avoid transient high discharge pressures on start-up. (Page 91) Piping should be properly anchored to prevent movement and be protected against transient pressure. (Page 92) Chapter 5: Treatment : Straining Filtration Processes, Membrane Filtration, Ancillary Equipment Select piping materials, restraints, and actuator speed controls suitable for the intended materials, service and to prevent water hammer (page 123) 5.7.3: Straining Filtration Processes, Bag and Cartridge Filtration A slow opening and closing valve should be included upstream of the filters to reduce flow surges (page 126) Chapter 7: Pumping Facilities 7.3.9: General Design and Considerations, Controls Equipment should be provided, or other arrangements made, to prevent hydraulic surge pressure from activating controls which switch on pumps or activate other equipment outside the normal design cycle of operation. (Pages ) 7.4: Pumping Considerations Pumping station headers should be adequately protected from transient pressure surges which may occur if pumps stop on power failure. Protection may be provided either by appropriate valves or hydraulic transient surge tanks. If pump discharge valves are provided, they should be slow acting type and properly controlled to avoid high transient pressures in the system on opening or closing. (Page 199) 7.4.1: Pumping Considerations, Raw Water Pumping For raw water pumping stations remote from the treatment plant, the designer should consider the use of slow opening pump discharge valves to minimize hydraulic transients. The raw water wet well should be provided with an overflow of sufficient size or adequate surge volume to handle intake surges which occur on power failure (when all pumps stop). When designing to handle intake surge, a minimum Hazen-Williams coefficient of one hundred and fifty (150) should be applied (Pages ) Provisions should be made to prevent downsurge during hydraulic transients after power failure, which may cause problems if pump sections become exposed and air becomes entrapped in the raw water pump suction piping. (Page 200) 7.7.3: Appurtenances, Suction and Discharge Piping

3 Piping should be protected against surge or water hammer and provided with suitable restraints where necessary. (Page 208) 7.7.4: Surge Arrestor Systems A hydraulic transient analysis should be undertaken during the design of pumping stations to ensure that the transients resulting from events such as pumps starting, stopping and full load rejection during power failure do not adversely affect either the customers on the water system or the piping in the station or the system. Methods of surge protection that can be used to protect stations include: - Surge anticipator systems that dissipate over-pressure from the discharge lines; - Slow closing and opening control valves on pump discharges; - Hydropneumatic surge tanks on discharge headers; or, - Variable speed pumping units. Any discharge from such a system may be connected directly back to the water well or storage reservoir or may discharge to a drainage system provided that, in treated water situations, an adequate air gap is included to prevent backflow. Surge relief valves or slow acting check valves should be provided to minimize hydraulic transients. Slow closing check valves should operate during or immediately after power failure. The type and arrangement of check valves and discharge valves are dependent, in some part, on the potential hydraulic transients that might be experienced in the pumping station. In smaller pumping stations, mechanically operated check valves should be adequate. In large stations, consideration should be given to the method of starting and stopping the pumps. An electrically operated butterfly or hydraulically activated globe style valve, coupled with a check valve on the discharge, should be utilized for the stopping and starting sequence on a pump. Other types of valves may incorporate both the isolating valve and check valve characteristics into one common valve; however, suitable isolating valves should be available in the event that maintenance is required on combination type valves. (Page 210) Chapter 9: Instrumentation & Control 9.3: Control Systems The design should minimize pressure transients in the water distribution system following shut downs. (Page 233) 9.5: Reliability & Security The designer should consider methods of improving reliability through transient protection wherever possible (e.g., mains, filters and transient surge protectors). (Page 236) Chapter 10: Distribution System : Hydraulic Design, System Pressures, Transient Pressures

4 The distribution piping system should be designed to withstand the maximum operating pressure plus the transient pressures to which it may be subjected. A thorough transient pressure analysis should be completed. Transient pressures are caused by rapid valve operation, pump start up and shutdown or power failure. Pumping systems and stations should be designed to minimize surges and transient pressure conditions including negative pressures which may allow inflow of contaminants. As a minimum allowance in the distribution system, it is recommended that pipes and joints be able to withstand the maximum operating pressure plus the pressure surge that would be created by stopping of a water column moving at 0.6 m/s (2 ft/s). The pressure created by such an event will vary depending on the diameter, wall thickness and pipe material used in the distribution system. Transient analysis should be undertaken for long transmission lines. (Page 246) : Pipe System Design, Materials, Standards & Material Selection In selecting a pipe, the designer should consider the following factors: - Behaviour of the pipe material in the event of transient pressures and catastrophic failure (Page 249) : Pipe System Design, Materials, Pipe Strength 10.9: Restraint The watermain pipe selected for a particular application should be able to withstand, with an acceptable margin of safety, all the combinations of loading conditions to which it is likely to be exposed. (Page 251) In designing thrust blocks and other restraint systems, the designer should remember that transient pressures should be added to the normal operating pressures when calculating the thrust forces (Page 255) : Separation Distances from Contamination Sources, General Water pressure in a part of the system may be reduced to a potentially hazardous level due to and negative surge pressures. (Page 257) Appendix A: Glossary Downsurge: Pipeline pressure surge, which is negative because its magnitude is below the normal operating pressure of the pipeline. (Page 293)

5 Transients in Design Guidelines for Sewage Works, 2008 Chapter 7: Pumping Stations 7.2.3: Design, Pumps When pumping stations are discharging directly to a sewage treatment plant or into a pumping station (i.e., forcemain directly into wet well of a downstream pumping station) some means of flow pacing is needed. This is provided most commonly by variable speed drives, depending upon the degree of flow pacing necessary. If even minor pump surges will have serious effects, variable speed pumps should be used. If small surges can be tolerated, two-speed or multiple speed pumps can be used. The pumps and controls of main pumping stations and especially pumping stations discharging to or operated as part of a sewage treatment plant, should be selected to operate at varying delivery rates. In addition, where practical, such stations should be designed to deliver as uniform a flow as feasible in order to minimize hydraulic surges. (Page 111) 7.2.6: Design, Valves Valves should be capable of withstanding normal pressure and high-pressure transients. (Page 113) 7.9.4: Forcemains, Design Pressure The forcemain, reaction blocking and station piping should be designed to withstand transient pressures and associated cyclic reversal stresses that are expected with the cycling of sewage lift stations. The use of surge valves, surge tanks and other suitable means (e.g. slow closing check valves) to protect the forcemain against severe pressure changes could be evaluated. The designer should be aware of the reduced reliability of air and vacuum release valves and surge control valves when applied to sewage containing grease, grit and rags. The location of the pumping station or the forcemain should be such as to minimize intermediate high points that might result in column separation. (Page 124) Chapter 8: Design Considerations for STPs 8.7.1: Essential Facilities, Emergency Power Supply Facilities Where standby power is not needed for pumping or treatment, the designer should include the provision of a small [typically 25 kw (33.5 hp)] generator set having sufficient capacity to provide the power for lighting and instrumentation, so that in the event of transient power outages, the plant will have sufficient power available for safe operation and to maintain instrumentation. (Page 155) 8.7.3: Essential Facilities, Plant Piping The design of the piping should allow for proper restraint under all anticipated conditions, particularly where surges may occur and high transient pressures could result, or where different temperatures occur seasonally. (Page 158)

6 Chapter 15: Supplemental Treatment Processes : High Rate Effluent Filtration, Backwash Surge tanks should have a minimum capacity of two backwash volumes, although additional capacity could be considered to allow for operational flexibility. (Page 294) Transients in the Pipe Data Form (for Design) Watermains: 5.7 Forcemains: 8.7 If there is a feedermain or a pipe dedicated to transporting potable water only (i.e., having no service connections), have hydraulic transients been considered? (Page 5) Have the effects of hydraulic transient been considered? (Page 9) Transients in the 1985 Version of Guidelines for the Design of Water Distribution Systems Chapter 2: Hydraulic Design 2.3.2: System Pressures, Transient Pressures The distribution piping system must be designed to withstand the maximum operating pressure plus the transient pressures to which it will be subjected. Transient pressures are caused by rapid valve operation, pump start-up and shut-down, power failures, etc. Wherever possible, the design of pumping systems should be such that surges caused by pumping station operations are minimized. As a minimum allowance in the distribution system, it is recommended that the pipe and joint strength be such that it can withstand the maximum operating pressure plus the pressure surge that would be created by instantaneous stoppage of a water column moving at 0.6 m/s. The pressure created by such an event will vary depending on the diameter, wall thickness, and pipe material used in the distribution system. When calculating transient pressures for flexible pipe materials, the designer is cautioned that celerity values given in texts, manufacturer s catalogues and other sources of information are usually for the unrestrained condition. When buried, such pipe materials may exhibit higher effective celerity values and correspondingly higher transient pressures. Celerity values utilized in transient analyses should be increased for such pipe materials for buried conditions. A rule of thumb is to use twice the value calculated from the celerity equation. (Page 9)

THE USE OF HYDRAULIC TRANSIENT MODELLING IN THE DESIGN OF RESILIENT PIPELINES

THE USE OF HYDRAULIC TRANSIENT MODELLING IN THE DESIGN OF RESILIENT PIPELINES Alistair Hancox, Grant Pedersen Harrison Grierson Consultants Limited ABSTRACT Pressure surges during the start up, shut down,