Combustible Dust Testing

Laboratory testing to quantify dust explosion & 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

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

UN-DOT

Classification of hazardous materials subject to shipping and storage regulations

Safety Data Sheets

Develop critical safety data for inclusion in SDS documents

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

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

Fire Analysis

Model transport of heat and smoke for fire analysis

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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

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

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

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Products and equipment for the process safety or process development laboratory

FERST

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

FATE

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

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Recent Posts

Eliminating Oversizing and Valve Instability (Valve Chatter)

Posted by The Fauske Team on 09.27.16

By: Hans K. Fauske, D.Sc., Regent Advisor, Fauske & Associates, LLC (FAI)

Typical causes of valve chatter (instability and potential valve damage) include: https___www.fauske.jpg

• Excessive inlet pressure loss (3% rule)

• Excessive back pressure (10% rule)

• Oversized valve

Considering Tempered Reactive Vapor Systems, given uncertainties related to vapor disengagement and two-phase flow regime, valve sizing based upon two-phase flow can lead to significant oversizing and the potential for valve instability.

In order to eliminate oversizing it is recommended to calculate the required vent area based upon all vapor venting evaluated at a practical relief set pressure well below Maximum Allowable Working Pressure (MAWP). Also to be considered, there are finite number of standard valve-nozzle sizes to choose from, and the calculated vent area may not correspond exactly to one of these sizes. The practice to select the standard size nozzle area which is closest to the calculated value on the high side, may lead to potential oversizing of more than 50%. Here it is recommended to change this practice and select the relief set pressure resulting in vent area equal to the standard size nozzle on the low side.

Following the above recommended procedure based upon all vapor vent sizing, the valve is initially undersized and the pressure will continue to rise as the relief valve remains open, due to the occurrence of two-phase flow, but the resulting overpressure will not exceed MAWP.* The allowance of significant overpressure will have the following benefits:

• Assure the smallest valve size

• Eliminate oversizing and valve instability

In summary, to simply assure valve stability select the relief set pressure sufficiently below MAWP. In this regard, while plant people are reluctant to give up the practice of setting relief pressure equal to MAWP, it is time to change. Setting pressure relief activation for all reactive systems (vapor, gassy and hybrid) at practical level below MAWP, is always beneficial and does not violate any standards.

* Hans K. Fauske, "Revisiting DIERS Two-Phase Methodology for Reactive Systems Twenty Years Later," Process Safety Progress (Vol. 25, No. 3) 2006.

 

Dr. Hans K. Fauske is an original founding partner of Fauske & Associates, LLC and currently serves as Regent Advisor.  For more information, please contact Ken Kurko at Kurko@fauske.com, 630-887-5226, www.fauske.com

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Topics: valve chatter, valve instability, valve damage, tempered reactive vapor systems, mawp, reactive systems, maximum allowable working pressure, oversized valve

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