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Forging or casting?
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(Chemical)
(OP)
3 Feb 04 14:02Dear all,
Usually small steel valves (NPS<2") I have seen are forged , but lastly a manufacturer has quoted me casting body valves for those sizes. Do you think is allowable? Having a look at ANSI B16.34 it seems that, for example, materials like A-105 or A-216 WCB are exactly the same. Is forging better than casting (as I have heard sometimes) or is it just a topic? Perhaps casting require more non destructive testing? any good link or book about this?
Any help will helpful.
Best regards
(Mechanical)
5 Feb 04 03:09Forging is better than a casting bcos internal defects like blow holes, shrinkage will not be there in a forging.
Also the dimensional conformity and finish of a forging will be better.
Generally smaller size valve bodies are made from forging because of its size and good production volumes.
As the size increases the forging becomes difficult.
Depending on the severity of application different NDE techniques will be used. For forging UT and casting RT is generally employed.
(Mechanical)
5 Feb 04 16:37Forgings are better than castings as described by "bljnv" above. API 602 for small compact gate valves allows both. Lately, I have also noticed that many ball valve and needle valve manufacturers are offering cast bodies - especially in stainless steel. I believe it is a question of economics.
(Mechanical)
9 Feb 04 07:39"Better" depends on the application and the relative importance of cost and benefit. It's true that forging are not susceptible to shrinkage, porosity, etc. But you don't want to pay for more performance than you need.
API 602 defines small valves (<= 4") in Classes 150, 300, 600, 800, and , and allows both cast and forged material (but from my experience I associate API 602 with forged valves). API 602 is used carbon steel (eg. WCB or A105), alloy steel (WC9 or F22) and stainless steel (eg CF8M or F316). However, the wall thickness requirement for all valves from Class 150 to Class 800 is the same. If your application is low pressure you end up with more valve than you need.
For stainless steel only, API 603 defines valves from 1/2" to 24" in Classes 150, 300, and 600--with different wall thicknesses for each class (corresponding to B16.34). API 603 also allows both cast and forged, but at least from my experience I associate API 603 with cast valves.
JN
(Chemical)
(OP)
10 Feb 04 12:02Thak you all for your help.
So, in a critical service do you think that a casting valve with radiographic examination is as "good" as a forged one? Or even in that case you would not rely on them?
Thanks
(Materials)
18 Feb 04 12:59Good points made by your previous correspondants.
Sorry to confuse things even more, but valves can be very difficult to radiograph successfully due to their complex shape. We have had experiences with cast feed control valves on boilers that have contained defects even though they were radiographed following production. Sometimes vlaves are so complex in shape that forging isn't possible.
In our industry, our 'big' steam valves have to be shown to have a very low probability of failure. Cast valves come under intense scrutiny for such features as evidence of repairs but then we have to because of the plant we operate.
Really I think you have to put the choice into context. Provided a manufacturer is making the components fully in accordance with the specification, provides all the required documentation and has demonstrated that the required NDT has been carried out and that there are no specific requirements for YOUR plant, and if there are that you are satisfied that the NDT will detect the required defect types, then either a cast valve or a forged valve may be acceptable (provided its the right thickness and material).
If you are worried about failure then you get into a whole different ball park when you have to be concerned about whether it would leak before breaking or fracture.
I can't recall that many instances when a valve (body) has failed dramatically, but there are several instances where plant conditions (erosion etc) has caused the valve to bypass due to erosion of an existing casting defect.
I'm not familar with ANSI B16.34 so I can't be more specific about your particular application. Generally (I hope someone can back me up here) if the standard doesn't say you can't use a particular manufacturing method then it is OK to go for either and the choice then is down to either economics (along with the points I made earlier) or any specific requirements your plant or regulator might have.
Hope this hasn't made things more difficult.
Cheers
Andy
Goto kairuite to know more.
(Industrial)
21 Jun 04 18:20at that size stay with forge unless you use investment cast.look at www.aesvalves.com they make the small valves in cast.
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Published: August 1,
Last updated: December 30,
Knowing what makes a valve the right choice
Valves control gas and liquid flow in almost every process and system. As common as they are, choosing the right valve can sometimes be time consuming and confusing.
Begin valve selection by first gathering some basic information on system performance requirements. Knowing this will make it easier to find the right valve. The five tips in this article focus on how to match valve features with these requirements.
Tip 1 &#; Valve size and type
Choose the right valve type. Every valve needs to perform one or more basic functions:
Function determines the design of standard valve types. These are some of the most common valve types:
Properly sizing the valve is also important. The right valve choice means matching the valve&#;s size to expected flow through the system.
Common Valve Types at VMA, Valve Manufacturers Association of America
How to Select the Right Valve (with Pros and Cons) at Indelac Controls
Tip 2 &#; Materials of construction
Know the chemical compatibility requirements. The valve materials need to be compatible with the gases or liquids flowing through it. Plastic valves usually resist harsh or corrosive chemicals better than metal valves.
Miniature Ball Valves: Plastic, Brass or Stainless Steel? at ISM, Industrial Specialties Mfg.
Chemical Compatibility Chart at ISM, Industrial Specialties Mfg.
Tip 3 &#; Performance requirements
Determine the pressure and temperature requirements. Find out both the temperature and pressure ranges where the valve will be installed. Metal valves tend to withstand higher temperatures and pressures than plastic valves. Metal valves are also usually best for pressurized gases. This is because they tend to be stronger than plastic valves.
A Selection Criterion for Pump and Valve Reliability at Processing Magazine
Tip 4 &#; Check valves have special requirements
Be sure the new check valve will work as expected. Look at the response time needed as well as the cracking pressure required to open the valve.
Another consideration is normally closed vs normally open. There are basic check valve designs that require positive downstream pressure to open. These are usually referred to as normally closed check valves. There are other designs that require a positive backpressure to close. These are usually called normally open check valves. An appropriate choice between these two can improve check valve reliability. It is usually best to base this decision on whether the valve is usually open more or usually closed more during normal system operation.
Some check valve types may not work properly if mounted vertically instead of horizontally. Flow direction (upwards vs downwards) and fluid density both matter for check valve designs that can be mounted vertically.
Checking Out Check Valves &#; An Introduction at ISM, Industrial Specialties Mfg.
Tip 5 &#;Maintenance
Don't forget to consider ongoing maintenance. Any valve choice should include attention to maintenance requirements. This is important for both valve reliability and application stability.
A good example of this are ball valves. They resist clogging, jamming or malfunctioning. But they are not suitable for adjusting flow. Using them to control flow can lead to leaking or premature failure.
Valve connection type affects the ease and speed of repair or replacement. Each connection type (threaded, barbed, push-in, Luer, and so on) has its pros and cons.
Plant and Equipment Maintenance at HSE, Health and Safety Executive
Knowing where to start makes valve choice faster and easier
There it is. Knowing particular information beforehand, makes choosing the right valve easier and more certain. There will always be complications like application requirements, operating conditions and chemical compatibility. Starting with basic valve requirements will simplify and speed up valve selection:
Some additional resources
How ISM can help you find the right miniature valve for your application
Personalized customer service and resources available at the ISM website can be a great help when selecting a valve. Available online resources include chemical compatibility reference guides, dimensional drawings and product data sheets. Our online and PDF flow control valve catalogs provide access to a wide variety of miniature valve types, connection types, materials and sizes:
Take Advantage of Our Expertise
We offer a line of ideas, so if you don't see it - ask for it. Let us turn your ideas for pneumatic or fluidic circuitry assemblies into reality &#; from conception to finished product.
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