How To: The Top 10 things to consider when selecting ...
How To: The Top 10 things to consider when selecting ...
So you have been tasked with selecting industrial valves for project or maintenance work and given a list of what valves, sizes and specifications. Great!!
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However, how much thought has been given to whether the specification is right, the valves will be suitable, and if they will be right for the job?
There are many assumptions around valve selection, the most common of which are:
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&#;this is what we used before&#; &#; on an entirely different process
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&#;contractor x said this is what we need to use&#; &#; based on what?
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&#;the site standard is x&#; &#; but what if that type of valve wont work on this application
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&#;this is what we have always used&#; &#; but have been experiencing downtime and regular failures
Getting your valve selection right from the get go is really important and in this article I will walk you through a simple 10 step process to help you ensure your valve selection is based on facts rather than assumptions.
Basics of Industrial Valve selection – 10 point check-list
Introduction:
I&#;m fully aware that there are already many check-lists for valve selection available on the market. Some of them quite simple and unfortunately also incomplete, others are so complicated that a &#;normal brained&#; person like me has trouble understanding the whole picture.
Through the years, and working in different valve-application fields such as Oil & Gas, Power Generation and Waterworks, I have built up my own check-list. It covers all the most important points to be considered when selecting on-off valves. I tried to include some personal experiences, tips and external links that might help to reduce mistakes while selecting valves.
Nothing really new for the experienced valve specialists out there, but maybe a real help for any &#;Newbie&#; getting involved in the valves selection process.
THE 10 POINTS VALVE SELECTiION CHECK-LIST (by Michel F. Bolle - )
1 ) Applicable main standard &#; DIN (EN)/ASME and or other?
While often forgotten, this is one of the most important points to clarify in the valve selection process. There are two main standards on the valves market EN (European) and ASME (American).
Depending on the location where a plant is built or located one or the other standard might be used. Usually, this information can be found in the technical specification of a project.
Other standards might be applicable such as GHOST (Russian) or AWWA (Amercian Water Works Association) among many others. In the EU, for example, most valves fall under PED standard requirements. So it would be impossible to install I the EU, a big size high-pressure gate valve made in the USA without CE marking and the related PED approval.
TIPS:
According to EN standards pressure class indication is given in PN and size in DN, while according to American standards we speak about #(lbs) for pressure class and &#; (Inches) for the size. When working on a new project, or a replacement project to not take this as a rule. A Valve specified as DN 400 and PN100 does not necessarily mean it is according to EN standards. There is a lot of confusion on the market, people mix up EN & ASME and there also many &#;hybrid&#;(mix of standards) valves on the market. Better check twice!
2) Type of Valve?
The type of valve needed is usually given by the process and the main function of the valve. Do we want to use the valve only for isolation (on-off) or do we need to control a certain flow? Might the valve be used to prevent back-flow or as a safety valve? Do we need a valve for steam (most likely a gate valve for isolation) or for water (most likely a Butterfly Valve).
Another important point de define from the beginning is to decide if you need a valve that seals in both directions (Ex. soft seated centric butterfly valve), or a valve that needs to seal only in one direction (Ex. double eccentric butterfly valve)
If working on replacement projects the choice is quite easy as usually the existing valves are replaced by the same type.
TIPS :
A very good source for information about different types of valves and their applications are the catalogues of the valve manufacturers. Usually, they state the main applications for each type of valve. Example: &#;Gate / Globe Valves excellent for Steam&#;
3) Size of Valve?
Usually, a valve is mounted in a piping system where the size of the pipe is already given. In this case, it is quite easy as the size of the valve will be the same as the piping size. Nevertheless, there are some factors which can influence the choice of the size of the valve such as:
- Max Allowable pressure drop (if any)
- Max Flow rate (if any)
While defining the size of the valve, these two factors have to be considered. There are some exceptional cases where the size of the valve might be bigger than the pipe size or smaller (which can be an important costs saving factor).
TIPS :
Consider that for many valve types such as globe valves or Ball Valves there are two options available on the market; Full Bore or Regular Bore (Reduced bore). In order to choose the right one, it is important to know if there is any requirement for max allowable pressure drop?
As an example: If you have a valve at a bottom of a pipe just to drain water, the pressure drop might not be so important and you can use a reduced bore valve. On the other hand having a valve in a steam system that brings steam to a turbine, pressure drop requirements might be crucial for the performance of the turbine.
4) Pressure Class?
In many cases, the pressure class for a valve is already given by the pressure class of the defined piping system.
Otherwise, the pressure class of a valve is the result of the combination of Pressure, Temperature and main body/bonnet materials used.
Here is a great example of a table for pressure classes definition according to ASME B16.34 (Source: Globalsupplyline):
http://globalsupplyline.com.au/wp-content/uploads//10/Valve_Material_Temperature.pdf
TIPS:
In order to define the right pressure class it is very important to know the &#;design&#; pressure & temperature for the piping system. If you define a pressure class according to &#;operating&#; conditions your selected valve might not withstand the &#;worst case&#; scenario.
5) Body/Bonnet Material?
The choice of the material of construction of the main parts (body/bonnet) of your valves depends on the medium. It is part of the job of the valves specifying engineer to check first material compatibility (resistance) with the medium (gas, steam, fluide, etc). In addition to this the design conditions of the piping system have to be considered (for example castings in WCB has a limit of temperature at 425C)
If the material of the piping system has already been defined, then you are lucky, as for the valve you can choose the same grade material.
TIPS :
Do not forget that the ambient conditions, can also be an important factor for the choice of the valve material. While A105 carbon steel might be a great material to be used in central Europe for a globe valve , in Russia (due to the low winter temperatures) you might have to use LF2 material instead of A105. Very salty ambient conditions might let you choose Aluminium Bronze as Valve Body Material instead of Stainless Steel.
6) TRIM Materials?
The choice of trim (stem/seat/disc or ball) materials are most likely to be in line with the chosen body/bonnet materials and will depend also on the medium, design conditions, as well on the leakage rate we want to reach.
While speaking about the trim, here should also be included the choice of all sealing material directly connected to the trim (Ex : Gaskets, Packings, etc)
Additional reading:Top 10 questions you should ask when purchasing a ...
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Other factors to consider are who often a valve is used and for how long it should last. Depending on this we might choose a higher grade for trim materials
TIPS:
If there is the possibility of having a vacuum condition while the valve is in service trim materials & design might have to be different (Example : Lantern ring on gatevalve packings)
Widely used on the market is the API Trim chart. Here you find a useful link:
https://blog.projectmaterials.com/valves/api-trim-chart/
7) Leakage Rate (valve testing)?
Directly related to trim, but often forgotten is the &#;maximum allowable leakage rate&#;. There might be some applications where this is not important, but when we start talking about this requirement, it gets quite tricky and we need to be sure which standard is applicable. Checking the questions of the leakage rate will also end-up by defining the applicable valve testing standard.
Here is an excellent overview and explanation of the different standards:
http://globalsupplyline.com.au/wp-content/uploads//10/Valve_Leakage_Rates_Test_Std.pdf
TIPS :
The definition of &#;0&#; leakage doesn&#;t mean anything by itself and is often confused with &#;Bubble tight&#;&#; Always check which is the applicable standard for the maximum allowable leakage rate.
8) Connections?
The most commonly used connections for valves are ; screwed (Ex : NPT or Gaz), welded (SW or BW) or Flanged.
Usually, the choice of the of the connection is given by the philosophy of the whole piping system. Safety and emission aspects might also be considered, as well as how the maintenance should be done.
Consider also that in any case the valve connection must match 100% the pipe connection.
TIPS :
Out of experience there are some general market tendencies of the use of end-connections:
- Power Plant Steam Systems : Welded (un to 2&#; SW, larger BW)
- Raffineries : Flanged
- Gas Systems : Welded
- House heating systems : Screwed
- Water distribution / wastewater : Flanged
9) Actuation
Once we have defined our valve, we need to figure out how we want to operate it. The most common ways to actuate a valve are:
- Hand actuated (lever / Hand wheel)
- Electric Actuator
- Pneumatic Actuator
- Hydraulic Actuator
- Self Actuated (by the medium)
TIPS:
Consider that for electric actuators the voltages are different depending of the location of the installation. This has to be checked absolutely when defining the actuator. Sizes of hydraulic and pneumatic actuators depend on available min air or oil pressure.
10) Painting
One out of two NCR&#;s for valves I have seen in the past 20 years have been related to painting.
For many projects, there are available painting specifications and/or colour codes. The choice of painting can depend on many things such as temperature resistance (medium & ambience), location, colour codes, required painting thickness et&#;.
While often forgotten in the selection process of valves, it is a key element.
TIPS:
While usually stainless steel or aluminium bronze valves would be supplied unpainted, there are some installations that use piping colour codes these valves might also be painted. Better check twice.
Other points to consider for the selection of valves:
- Accessories (limit switches, solenoid valves, lantern rings)
- Noise
- Emission
- Weight
- Dimensions
- Installation (for example horizontal or vertical)
Valve selection can be quite tricky, but it must not be. Following a simple check-list ensuring that during the selection process all the important key-points are considered is a good step in the right direction.
If you are missing some knowledge somewhere, let&#;s say &#;material resistance&#; speak to your trusted valve partner. According to my experience valve manufacturers are always willing to advise.
Last but not least, consider that the time used to make the right valve selection is a very smart investment! A lot of valve problems on production sites are due to poor and wrong valve selection.
Feel free to comment and share this article. Improvements are very welcome.
Michel F. Bolle - Industrial Valve Expert - 20.6.
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