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Have
a question on or need to purchase quality Severe Service Valves? Our
Sponsors MOKVELD are Experts in this area!
Contact them
here.
Selecting Mokveld axial severe service control valves with proven reliable performance will help to reduce costly maintenance and lost production time; a choice that will ensure the safe and reliable operation of your plant.
Severe Service Valve General Information
Severe Service Valves are required where the process can cause damage to conventional valves through erosion, high noise, cavitation, high vibration, possible mechanical damage to the valve trim, other components and the process equipment around the valve. These valves are generally specialist designs that overcome these issues by "smart" design. They are generally used for such applications as;
Wellhead Choke
Anti-surge - compressor recycle
Papers and Applications
The following technical papers, articles and application examples are from our sponsor Mokveld
5.10
Axial
Surge Relief Valve - The high-capacity proportional pilot design allows
fast response and will eliminate the dangers of a pressure surge. All components
operate solely on fluid static pressure to provide ultimate protection. Owing to
stable opening behaviour, pilot design and consequently high effective capacity,
the valve can fully protect the piping systems against dangerous and costly
surge pressure damage.
5.10
Axial
Excellence in China's Gas Transmission Network - By nature of design the
axial control valve has unique benefits that make the valve specifically
suitable for the more special and severe service control applications. In this
article, Mokveld presents some benefits of the use of axial control valves and
provides some specific project application examples.
Application Examples
Axial Surge Control Valves in Russia - Anti surge control at -60°C (-76°F)
Other Useful Links to Technical Papers and Articles
Control Valves for Critical Applications - Dr J Kisbauer, Samson A.G.- Know the causes of cavitation and how to prevent them.
5.10
Avoiding
Pressure Surge Damage in Pipeline Systems? - Pressure
surges occur in all fluid pipeline systems. There arise two types of damage from
the surge phenomenon, fatigue and catastrophic failure. This paper addresses
this phenomenon from the viewpoint of the available solutions rather than the
mathematics and modelling involved in determining the quantum of the surge
pressure - from www.pipingdesign.com
5.10
Are
You at Risk from Not Considering the Potential for Surges in a Piping System?
- Geoffrey D Stone - This article raises a number of issues in respect of the
risks you may be exposed to from the requirements to consider the pressure
transients in a piping system design. The risks not only relate to physical
damage but also the consequential risks that arise from such damage whether it
is contractual, branding or loss of use. Piping systems are designed in
Australia and overseas to a number of National Codes and Standards. In addition
to this there are industry bodies that publish design guides and codes that are
referred to in contract documents. These require that design for surge are taken
into account to determine the loads and stresses in a piping system. This paper
only addresses surge events from a liquid pressure transient. Events arising
from condensate in steam or gas lines are not covered here. These events may be
even more catastrophic as the velocities of the liquid column are much higher
than in a liquid system. If nothing, read the section on Contract Requirements
and consider the risks you run by being ignorant of this engineering topic -
from www.pipingdesign.com
5.10
Diffusing Bubble Bombs
- Proper Valve Sizing for Severe Service Can Help Lessen Wear and Damage from
Cavitation - Gerald Liu, PE - Instrument technicians are often called by
their instrument engineers to look at repeated control valve failure problems
during plant shutdowns. From a maintenance point of view, the definition of
"severe service" in control valves can be based on how long the valves
last - From the excellent www.controlglobal.com
5.10
When
all Else Fails - A Kinetic Energy Criterion for Control Valves via Trim Retrofit
is the Final Solution - Herbert Miller, Laurence Stratton, and Mark
Hollerbach -The retrofits took place because the valves were not performing
their intended control function. The database shows that after retrofit and
using trim that limits the kinetic energy below 70 psi (480 kPa), a valve
application results that meets or exceeds the user's expectation - from InTech
and the ISA
The Following links are from CCI Valves.
Fluid Kinetic Energy as a Selection Criteria For Control
Valves - Herbert L. Miller /Laurence R. Stratton - A selection
criteria is provided that assures a control valve will perform its control
function without the attendant problems of erosion, vibration, noise and short
life. The criteria involves limits on the fluid kinetic energy exiting through
the valve throttling area. Use of this criteria has resolved existing valve
problems as demonstrated by retrofitting of the internals of many valves and
vibration measurements before and after the retrofit. The selection criteria is
to limit the valve throttling exit fluid kinetic energy to 70 psi (480 KPa) or
less - from CCI Valves.
Getting Optimum Performance through Feedwater Control Valve
Modifications - Brian Leimkuehler, P.E./ Sanjay V. Sherikar, P.E. - Good
control of the feedwater system is very important for smooth operation at
nuclear power plants. The performance of the feedwater control valves, which are
the final control elements, is crucial in achieving the desired level of control
in the system. Modifications were made to existing feedwater control valves at a
565 MWe BWR nuclear power plant. These modifications were part of an overall
system upgrade, resulting in significantly improved controllability of the Feed
Water Control system. The characteristics that are critical for best performance
from the feedwater control valves are : fluid velocity control at all operating
conditions, high rangeability, proper flow characterization, high actuator
stiffness and good dynamic response. By analysis, and observed through
experience, a properly designed and maintained pneumatic control system can
provide the dynamic response and resolution necessary for feedwater control
performance - from CCI Valves.
Evaluation of Control Valve Performance is Necessary in Plant
Betterment Programs - Sanjay V. Sherikar, Ph.D., P.E. - Control
valves affect the performance of power plant in terms of output, heat rate,
reliability and availability because they are the final control elements in the
operation. Therefore, critical evaluation of control valves must to be an
integral part of any plant betterment program because the ultimate goal of such
efforts is to improve the efficiency and reduce costs. Even control valves in
the few severe service applications, which affect efficiency more than the rest
of the valve population, have traditionally not been included in such efforts.
Recent studies indicate that eliminating control valve problems
alone can improve the heat rate of power plants in the range of 2% to 5%. The
elements that are critical in realizing the potential benefits are: analyzing
the whole system and quantifying the losses, identifying the root causes of the
problems causing these losses and then, finally, eliminating the root causes of
those problems. Methods to estimate loss due to control valve non-performance
have to be judiciously applied, and sometimes developed, on a case-by-case
basis, as shown by examples in this paper. The commonly observed causes of valve
problems are discussed, followed by practical strategies for implementing
solutions to the valve problems - from CCI Valves.
Technical
Specification - Control Valve. based on “Control Valves - Practical
Guides for Measurement and Control” Published by ISA - This
specification prescribes the minimum mandatory requirements governing the
design, sizing, and selection of control valves.
Linear
Pistion Actuators - Samy, Stemler - High Reliability of
actuation is of paramount importance in the nuclear power industry. Pneumatic
actuators form the largest installed base with many in safety significant
applications. This paper addresses the issues related to actuation, such as
available Thrust, Stiffness, Sensitivity, Hysteresis, Dead band, Dynamic
Stability and a sizing example. This paper also presents comparisons between
various types of linear actuators and their relative advantages and
disadvantages. Also presented will be evaluation techniques for troubleshooting
actuator problems and improving plant performance.
Specifying
the Plant’s Control Valves - Miller - The subject of this paper is
the proper specification of the control valve to avoid
many of the problems noted above. To provide information
so that the valves’ attributes that are important for
the application are noted and that over specified needs are minimised.
Over specifying needs result in compromise and trade off
decisions in the design and result in higher initial costs.
Technology
in Severe Service Control Valves - Sherikar - Severe service control
valves are critical for safe, reliable and efficient operation of power plants.
Such critical applications must be looked at differently from general service
control valves because these applications have their own specific set of
requirements for good long-term performance. The performance limits of control
valves in such services is clearly a function of the technologies in them.
Discussion on severe service valves is presented in order to aid the application
of correct technology in such critical services.
More
technical papers on valve applications from CCI Sulzer can be found here.
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