Process Piping and Water Hammer


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How do you control Water Hammer, Selection of Piping materials in fluid control industry by Gobind Khiani

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Process Piping and Water Hammer

  1. 1. Keywords: Check valve • Nozzle check • Slam • Water hammer W AT E R & W A S T E WAT E RWater hammer in process piping:How to avoid this by selecting theright check valve As pipelines grow longer the swing check valves’ travel distance to closure in high volume of process flow becomes greater causing water hammer or “slam”. The industry currently utilises several types of check valves and these tend to slam upon closure in reverse direction – a common problem. Reviewing the process piping to find a more suitable check valve becomes necessary. Mr. Gobind Khiani, an AIMS Manager at Cenovus Energy Inc., shares Swing Check vs Dual Plate Spring loaded design. his know-how regarding water hammer in process piping and 3. The swing check valve is not closing Prototypes were developed and tested at the role of nozzle check valves fast enough allowing water hammer Delft Hydraulic Laboratories during the in its prevention. to slam the disc into the seat. 1960’s and have been in operation for over Continued slamming has damaged 50 years with no sign of failures in various the sealing surface preventing the industries and applications.Compact design valve from sealing fully. tested at the Utah State University and hasBy GobindKhiani, Cenovus Energy Inc. been in operation since 1975 in various The signs of excessive “swing check industries with no failures reported. slamming” include grout cracking beneathC heck valves are emergency Factors to consider in nozzle check pump and motor pads and base, damage backflow preventers typically applications include during normal or to electrical cable to the motor, and used around critical equipment. minimum operation where fluid flow is increased vibrations caused by inducedThese rely on backflow to operate shut less than 10 ft/sec, air flow is less than pump and motor misalignment. Pressureand flow to open and how much it is 400 ft/sec and saturated steam flow is less gauges and switches become abnormallyopen is dependent on the flow condition. than 200 ft/sec. Another factor is when out of calibration as well as cracked valveAmong the various types of check check valve locations are downstream seat surface, excessive piping headervalves are swing check valves. However, of pump elbows or other turbulence displacement and heat exchangerproblems arise with this type of valve, source and when said valves are located tube failures caused by pump cyclingsuch as leakage through its seat due to the downstream of the pump or compressor. activations.following reasons: In addition, nozzle check valves should1. The valve is installed in its application Nozzle check valves be in a system where pressure surges in which it is not suitable. Most swing Nozzle check valves are check valves that during flow transients and valve closure check valves cannot be installed prevent reverse flow. These have an axial produce pressure spikes approaching the vertical with the flow passing from disc movement with short stroke and system design pressure. Essentially, when through above. a venturi nozzle-style, which maximises previously installed check valves have2. The swing check valve was installed flow impact on disc and minimizes internals that are worn or damaged at the less than 10-pipe diameter away from pressure loss. The valves have better hinges, bushings or seating surface, nozzle upstream pipe fitting or pump.This dynamic response, high reliability and check valves are the best alternative; also results in turbulent flow, disc chatter and most significantly, non-slam operational in positions where check valves are known ultimately damage to the sealing surface. characteristics. for November 2012 1
  2. 2. W AT E R & W A S T E WAT E R About the author GobindKhiani, B.Sc., MEng graduated with a B.Sc. from the University of Poona in India and a Masters in Engineering from the Universityof Calgary in Canada. His career began with the Transmark Group in UK and Dubai. After 16 years, he moved to Canada and worked at VELAN Valves, Crane Energy and currently worksA cross section of Nozzle Check Valve design. at Cenovus Energy Inc. as an AIMS Manager.Why and when? and reciprocating compressors Gobind has worked in the oil & gasNozzle check valves are clean service (pulsating flow). and nuclear industries since 1992 andvalves with high reliability, low maintenance Nozzle check valves are ideal to use has been involved with valves sinceand relatively low pressure losses.These with liquids e.g. oil; water (sea, potable); day one. He has helped numerousapplication-sensitive valves have the ammonia; hydrocarbon liquids etc.; rapid users in selecting the right valvetechnology known to eliminate water deceleration systems, e.g. multi-pump product for the desiredhammer and potentially destructive surge installations, upstream of vertical column, process conditions and helpedpressures. The latter is usually associated upstream of air vessel or surge tank; gases improve asset integrity managementwith conventional check valves used with e.g. hydrocarbon, refrigerants, nitrogen, programs.centrifugal compressors when surging hydrogen etc. 2 November 2012