Hazards Analysis, Code Compliance & Procedure Development

Services to identify process safety hazards and facilitate compliance with established standards and codes.

Combustible Dust Testing

Laboratory testing to quantify dust explosion and reactivity hazards

Flammable Gas & Vapor Testing

Laboratory testing to quantify explosion hazards for vapor and gas mixtures

Chemical Reactivity Testing

Laboratory testing to quantify reactive chemical hazards, including the possibility of material incompatibility, instability, and runaway chemical reactions

ISO Accreditation and Scope
Fauske & Associates fulfills the requirements of ISO/IEC 17025:2017 in the field of Testing
DIERS Methodology

Design emergency pressure relief systems to mitigate the consequences of unwanted chemical reactivity and account for two-phase flow using the right tools and methods

Deflagrations (Dust/Vapor/Gas)

Properly size pressure relief vents to protect your processes from dust, vapor, and gas explosions

Effluent Handling

Pressure relief sizing is just the first step and it is critical to safety handle the effluent discharge from an overpressure event

Thermal Stability

Safe storage or processing requires an understanding of the possible hazards associated with sensitivity to variations in temperature


Classification of hazardous materials subject to shipping and storage regulations

Safety Data Sheets

Develop critical safety data for inclusion in SDS documents


Model transport of airborne virus aerosols to guide safe operations and ventilation upgrades


Model transport of contamination for source term and leak path factor analysis

Fire Analysis

Model transport of heat and smoke for fire analysis

Flammable or Toxic Gas

transport of flammable or toxic gas during a process upset

OSS consulting, adiabatic & reaction calorimetry and consulting

Onsite safety studies can help identify explosibility and chemical reaction hazards so that appropriate testing, simulations, or calculations are identified to support safe scale up

Mechanical, Piping, and Electrical

Engineering and testing to support safe plant operations and develop solutions to problems in heat transfer, fluid flow, electric power systems

Battery Safety

Testing to support safe design of batteries and electrical power backup facilities particularly to satisfy UL9540a ed.4

Hydrogen Safety

Testing and consulting on the explosion risks associated with devices and processes which use or produce hydrogen

Spent Fuel

Safety analysis for packaging, transport, and storage of spent nuclear fuel

Decommissioning, Decontamination and Remediation (DD&R)

Safety analysis to underpin decommissioning process at facilities which have produced or used radioactive nuclear materials

Laboratory Testing & Software Capabilities

Bespoke testing and modeling services to validate analysis of DD&R processes

Nuclear Overview

Our Nuclear Services Group is recognized for comprehensive evaluations to help commercial nuclear power plants operate efficiently and stay compliant.

Severe Accident Analysis and Risk Assessment

Expert analysis of possible risk and consequences from nuclear plant accidents

Thermal Hydraulics

Testing and analysis to ensure that critical equipment will operate under adverse environmental conditions

Environmental Qualification (EQ) and Equipment Survivability (ES)

Testing and analysis to ensure that critical equipment will operate under adverse environmental conditions

Laboratory Testing & Software Capabilities

Testing and modeling services to support resolution of emergent safety issues at a power plant

Adiabatic Safety Calorimeters (ARSST and VSP2)

Low thermal inertial adiabatic calorimeters specially designed to provide directly scalable data that are critical to safe process design

Other Lab Equipment and Parts for the DSC/ARC/ARSST/VSP2 Calorimeters

Products and equipment for the process safety or process development laboratory


Software for emergency relief system design to ensure safe processing of reactive chemicals, including consideration of two-phase flow and runaway chemical reactions


Facility modeling software mechanistically tracks transport of heat, gasses, vapors, and aerosols for safety analysis of multi-room facilities


Our highly experienced team keeps you up-to-date on the latest process safety developments.

Process Safety Newsletter

Stay informed with our quarterly Process Safety Newsletters sharing topical articles and practical advice.


With over 40 years of industry expertise, we have a wealth of process safety knowledge to share.

Recent Posts

Some Plain Talk Regarding Water Hammer

Posted by The Fauske Team on 05.22.17

By: Kevin Ramsden, FAI Chief Engineer, Fauske & Associates, LLC

Previous Technical Bulletins have discussed computational methods to address specific types of water hammer (waterhammer) event analysis. In this bulletin we will discuss the various types of water hammer events and their impacts on plant systems. The goal is to provide the reader with some guidance regarding what to look for and what potential effects are likely following a water hammer event.

Water hammer events come in several classes. The most common types of water hammer involve a column closure. This occurs in a system that has the potential to drain down following a pump trip, forming a vacuum at elevated high points. When the pump is restarted, the system will refill and a water- water impact will occur when the high points refill. This type of event is common in cooling water systems where the water supply is at a low elevation, and the cooling system feeds components at elevations 33 feet or higher.

FAI Water HammerA Typical Example of Water
Hammer Damage
to a Heat
Exchanger Channel Head

This type of event can be characterized by the Joukowsky equation, which relates the pressure rise due to water hammer to the product of the density, the velocity of the fluid at impact, and the acoustic velocity of the fluid, all divided by a factor of two to account for a water-water impact. These types of events typically experience runout of the pump, causing the closure velocity to be 10-30% higher than nominal operating velocity.

Another variation of this occurs in Boiling Water Reactor (BWR) Emergency Core Cooling Systems (ECCS). Since these systems typically have a suction supply from the suppression pool, they normally employ a “keep fill” system consisting of a pump that maintains a positive pressure on the system preventing any drain back. If this system fails, a drain down of the upper elevations is possible and if an ECCS injection signal occurs, a water hammer will result when the ECCS pump starts and rapidly refills the voided piping.

Another type of water hammer that occurs in water filled systems results from the rapid closure of a valve on a flowing system causing a fast stagnation of the flow. If the closure time is less than 10 times the acoustic path length (defined as the piping length divided by the acoustic velocity) a propagative wave (water hammer) will result. An example of this type of event is a rapid closure of a ball valve by an operator on a flowing system. If the close is in a slow and deliberate manner, there would be little or no propagative effects since the flow would be throttled gradually. If he were to snap the valve shut rapidly, a significant water hammer is the likely outcome since the flow would be stagnated immediately. The Joukowsky equation also applies to this case, but the factor of two in the denominator is replaced by unity since there is no cushioning due to a water-water impact. Thus, this type of water hammer will yield twice the pressure rise as a column closure event, for the same closure velocity. Of interest in this type of event is that the rapid closure actually causes two water hammers, one against the upstream face of the valve that propagates backwards, and a vapor pocket collapse on the downstream face of the valve that propagates forward. This type of event can be very serious in large service water or circulating water systems that employ motor operated butterfly valves. A failure in the motor operator (shaft shear or gear strip) can allow the butterfly to be forced closed rapidly by the flow, with disastrous result.

The worst types of water hammer result from steam condensation events. These types of events require a situation where a cold water slug interfaces with a steam pocket, causing rapid condensation of the steam and acceleration of the fluid into the collapsing void. These events require at least a 20˚C temperature difference between the steam temperature and the liquid interface. Examples of these types of events include a relief valve discharging to a pool of cold water. When the relief valve closes, cold water can rapidly enter the discharge line and condense the steam in the line. This type of application typically requires vacuum breakers to preclude condensation water hammer events. Another example is the refill of a steam filled line with cold water. If a long horizontal run (L/D>24) is filled with cool water, there is a potential to trap and condense a steam pocket at the top of the run, causing a rapid condensation event and resultant water hammer. It is of interest to note that these types of events can be “powered” by the condensation process, and may not require an active pressure source to drive the event. Given this, it is entirely possible to experience significant condensation water hammer in passive systems (e.g. BWR isolation condenser), as well as in active systems. Steam condensation events can be an order of magnitude greater than the previously described events, and need to be taken very seriously.

The last class of water hammer events involves non-condensable gas appearing in a system that is intended to be nominally water solid. This situation normally occurs as a result of inadequate venting following a maintenance situation. It can also occur as a result of dissolved gas leaving solution and accumulating in high points. This situation is particularly of concern in Pressurized Water Reactor (PWR) Residual Heat Removal (RHR) systems when back leakage from accumulators pressurized with nitrogen to approximately 600 psig can release significant amounts of gas to the high points. Startup of an ECCS pump with non-condensable gas accumulated in the discharge line high points can result in dynamic events due to the compressibility of the gas. These events are typically less severe than any of the previous examples, but may still result in challenges to relief valves as well as cause dynamic loads on the piping system.

Now that we have described a variety of possible water hammer events, it is reasonable to consider the effects that they have on a system. A water hammer event results in propagating pressure waves travelling through the affected piping system at acoustic speeds. This propagation yields wave loads that act axially on each piping segment as the pressure wave transits the piping. Depending on the magnitude, this will cause acceleration of the piping system against its supports. Most water hammer events will cause piping support failure prior to damage to the piping itself. Support failure can manifest itself by deformation of the embedment plates or pull out of the anchors. Subsequent damage to the piping system will be observed by flattening of the piping at elbows or other plastic deformation. Personnel in proximity to a water hammer event usually find the experience attention-getting and memorable.

While the axial forces and piping reactions are a principal result of water hammer, they are not the only issue of concern. The transient pressure wave can challenge many components in the piping system. These include relief or safety valves, heat exchangers, flange gaskets, and instrumentation. The effects depend on the magnitude and duration of the pressure wave as well as physical geometry and susceptibility of the components. A pressure wave transiting from a large pipe to a small pipe will amplify, and can double the pressure amplitude. Heat exchangers are particularly susceptible to damage at the channel head, since this structure typically is not designed with large transient differential pressures in mind. Also, heat exchanger tubes that have undergone degradation due to corrosion may fail when challenged by a water hammer event. Gasket materials at flanges can be extruded from the flange as a result of pressure surges and leakage will result. Following a water hammer event in a plant system, it is important to assess not only the piping and supports, but also any components that could have sustained damage.

Given the range of potential issues that arise from water hammer, the best practice is to mitigate or eliminate the possibility of experiencing such events. This can be accomplished with vacuum breakers in some cases, or by slowing the rate of fill of a system following a potential drain down event. Proper maintenance of valve operators can help prevent failures that can yield water hammer events. For steam condensation events, the best approach is often to modify operating procedures to preclude the conditions that can lead to an event. This requires critical review of the system and operating procedures under normal and emergency conditions.

For more information, please contact Kevin Ramsden, FAI Chief Engineer (630) 887-5260, ramsden@fauske.comwww.fauske.com

Subscribe to FAI's "Nuclear Technical Bulletins"

 #nuclear, #powerplant


Please check the Web Directory Blog to find our blog


Topics: nuclear plant, BWR, pwr, Boiling water reactor, waterhammer, ECCS, pressurized water reactor, residual heat removal, water hammer, RHR


Is My Dust Combustible?

A Flowchart To Help You Decide
Download Now