Hi all, Second time this week I've reached out on what is a pretty basic question but it is something outside my normal experience. As I said in the last post feel free to flame away on me, an engineer who is poking his head outside his normal area of competency.
Background: A client approached me with a problem. I'm likely to offer guidance and a suggestion to consult an engineer more experienced in the area, I'm not sure it is worth the risk for me, but it is a good client so I'll offer some friendly guidance on where to seek a solution. Regardless the topic has perked my interest.
The problem:The client has fabricated a bunch of pipework for compressed air with flanges rated for 7bar. The client has now found out that the the customer scope included the option to upgrade the pressure beyond this I believe up to 10bar. The fabricator doesn't want to cut and reweld dozens (possibly hundreds) of flanges and is looking for a solution.
(Under the relevant code AS it specifies specific flanges for specific pressures/temperatures. These all have predefined dimensions etc.. As I understand it ANSI has similar guidance.)
My questions:
Using some preliminary basic engineering analysis it seems to me that pipe flange design is largely dictated by deflection and sealing requirement rather than yielding or material failure.
Is this correct?
One obvious solution that occurs to me is to have half circle flanges to double up the flange. If it is thick enough then deflection and strength criteria seem to be satisfied.
Does this make sense?
The bit I don't know enough about is the local code requirement. Eg even if it works from a engineering perspective it still might not comply. Hence I'll probably stay away from the job. It likely isn't worth my time, but it does interest me.
Yes, misalignment and seal failure is critical, once you get beyond bolting patterns sufficient for axial force and wall thickness due to internal pressure.
It may be possible to solve a deflection problem with a backing ring around the flange, but as I often say, just because you can do something doesn't mean it's a good idea. The underlying flange would still not meet specifications for the increased pressure, as originally intended, and should anything happen in future, regardless of the cause, you will find yourself on the hook for it. Since design of these things is apparently not your speciality, it would put you on difficult footings to explain why you did such a thing. Plus the code apparently requires specific flanges for specific maximum pressures, a problem that is likely not going to go away with modifications. If modifications were indeed even permitted by that code, it should explain the whats and hows in detail. Plus, it's likely to be eventually rejected anyway and it would be your sole burden of proof to justify adequacy. My crystal ball says "Not worth the effort", keeping in mind that the fabricator is trying to put you on the hook for his mistake.
Your theory is correct, failure of many things is not only the result of high stress and loss of sealing is often a critical case. Take comfort in that and walk away.
--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."
-44 said:
My crystal ball says "Not worth the effort", keeping in mind that the fabricator is trying to put you on the hook for his mistake.
....
Take comfort in that and walk away.
Yes. I agree. It isn't worth the risk, I have plenty of work.
I don't mind stepping outside the norms if there is sound engineering basis for doing so. I'm used to designing bespoke structures and equipment. Particularly for temporary works and/or when I can be on site and observe and monitor things. But signing off on something like this doesn't seem to be worth the fee.
Thanks.
What Does a Pipe Flange Do in Plumbing?
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If you've got customers asking you why you need a pipe flange in a particular location, you might be wondering what the right answers are to their questions. Fortunately, we've collected the details so that you don't need to - you can just point them to this post. In this post, we'll talk about what a pipe flange is, the different types, where they tend to be located, whether they're considered fittings, and how to select the right pipe flange for your application.
What is a Pipe Flange?
Used to connect pipe sections, flange faces bolt together to create a strong, watertight connection that will hold up well under high temperature or high pressure applications. It creates a much stronger joint than simply using a coupler or other pipe fittings to connect two pieces of threaded pipe, such as fitted iron pipe systems.
However, there is a wide range of different flange types, designed to meet a range of disparate plumbing standard sections, such as ASME B16.47 or ASME B16.5. One common feature is bolt holes in the flange facing, which allow the flange to be securely fastened to the surrounding material. In the next section, we'll discuss different types of pipe flanges that you may encounter. Pipe flanges also come in several alloys some of which include: stainless steel, brass, chrome-plated brass, copper & carbon.
What Are the Different Pipe Flange Types?
- Weld Neck Flange - As the most commonly-used flange in process piping, a weld neck flange provides the highest joint integrity, because the butt weld that is created with the piece protruding from the raised face provides a strong bond. However, it can be bulky and cumbersome compared to other flange types, but is also available as a long welding neck flange.
- Slip On Flange - A slip on flange matches the outer diameter of the pipe, with two locations for fillet welding to create a strong bond. With a moderate cost, it's typically used for low-pressure and temperature applications.
- Ductile Iron Backup Flange - Often used in high pressure settings, typically between 150 and 250 PSI, a ductile iron backup flange is a relatively simple flange. It features a flat flange facing paired with a beveled edge at the center hole.
- Threaded Flange - Typically used in utilities as well as in lower temperature and pressure applications for air and water, a threaded flange has a National Pipe Thread female connection and is available in thread sizes up to 4", providing a relatively inexpensive option for a number of situations.
- Socket Weld Flange - Also used in lower temperature and pressure ranges, the socket weld flange has a stopping point, from which the pipe is pulled back slightly to allow for expansion. The pipe can then be welded around its circumference to the face of the flange.
- Lap Joint Flange - If tight spaces and an expectation of frequent dismantling is a possible issue, a lap joint flange is a decent option. Consisting of two separate pieces, a ring with bolt holes and a stub that can be welded to the pipe a short distance from the ring, the butt weld created is stronger, while the stub allows the pipe to be turned while welding.
- Blind Flange - Sometimes used as manhole covers for vessels, a blind flange has no hole for air or gas to pass through. It's also commonly used to end runs of pipe, effectively isolating the run from other systems.
- Swivel Flange - Designed to speed up installation, a swivel flange makes it easy to align bolt holes on a pair of flanges. Because the flange is able to swivel around the circumference of the pipe, it can easily be moved to match a welded flange's bolt positioning.
- Expanding Flange - When a pipe needs to change to a larger size, an expanding flange provides an effective way of managing the change. It features a widening stub that the larger pipe can be joined to, making it a popular choice for retrofit projects.
- Reducing Flange - When there needs to be a change in the side of the pipe to a smaller pipe, a reducing flange has a tapered raised face for a butt weld. Providing an economical way to reduce pipe size at a particular point, they're used in a range of applications.
- Nipoflange/Weldoflange/Elboflange/Latroflange - Most commonly used in high-pressure situations, these types of specialty flanges create a unique nipple that protrudes markedly from the flange facing. Its installation requires fewer welds, while still maintaining superior strength.
- Plate Flange - An economical alternative to heavier ANSI flanges. Plate flanges are suitable for low pressure, less critical applications. They have a serrated surface to enhance sealing properties. There are several types of plate flanges: blind, tube OD slip-on, IPS slip-on bevel x square and IPS slip-on square x square.
Where are Pipe Flanges Located?
Generally speaking, a pipe flange is located at points where regular disassembly, maintenance, or cleaning will be taking place. This can include making it possible to bolt pipe systems directly to equipment, fittings, or other features quickly, easily, and securely.
Are Pipe Flanges Considered Fittings?
Pipe flanges are considered a very popular type of fitting in plumbing systems, and are often used when pipes are used for non-plumbing systems as well, such as railings, racks, and similar applications. However, they often provide an additional level of security to the fitting, because the bolt holes allow the fitting to be secured to the surrounding structure.
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How Do I Choose the Right Pipe Flange?
Pipe fittings will vary based on your application. However, by having a better grasp of how pipe flanges work, you'll be able to answer your customers' questions much more easily, improving their confidence in your ability to do the job they've hired you for. If you're looking for expert advice, contact Merit today for more details.
STILL HAVE QUESTIONS?
SOURCES INCLUDE:
https://hardhatengineer.com/types-flanges-used-piping
https://www.unifiedalloys.com/blog/flanges-101
https://www.apiint.com/resource-center/introduction-to-flanges
https://www.punchlistzero.com/swivel-flange
3/28/ 1:48:38 PM
For more information, please visit Structural Pipe Flange.