Designing Bellows in Cryogenic Pipes: Advice Needed

[skyqwerty]

Any pro here know how to design bellows in a pipe? especially cryogenic pipes, which have a -196 degree celcius of liquid nitrogen flowing inside.. i m out of idea and info... limited resources online..

Kindly give some advices... million thanks

 

[Danger]

With no offense intended, my suggestion is that you hire an expert to come in and check out your plant. That sort of system can be incredibly destructive if it goes bad.

 

[Q_Goest]

You don't need to design your own bellows, they are readily available off the shelf. That includes short lengths made up with ends that can be bolted, screwed or welded into a piping system. If your intent is to figure out what lengths of these expansion joints are required to compensate for thermal contraction of the piping, that's covered by various piping codes which are unique to the country you live in.

 

[skyqwerty]

You don't need to design your own bellows, they are readily available off the shelf. That includes short lengths made up with ends that can be bolted, screwed or welded into a piping system. If your intent is to figure out what lengths of these expansion joints are required to compensate for thermal contraction of the piping, that's covered by various piping codes which are unique to the country you live in.

so i juz find out d length and choose from market? type of bellows? location of it in a pipe?

 

[Q_Goest]

There's always a reason for going to the expense of putting in an expansion joint. Generally, there are 2 reasons for installing such a joint, vibration and thermal contraction/expansion. I'm assuming your case is the latter since you're dealing with liquid nitrogen. It's not cheap to install these joints and it's not easy to determine exactly what type and length you need. In fact, if you can do away with them, you'll be much better off. But to get out of using them, the piping has to be flexible enough to prevent stresses in excess of what is allowed by the piping code for your country. Therefore, someone is going to have to do a piping stress analysis for your liquid nitrogen system and they'll need to accommodate thermal contraction of the piping, so an expansion joint is a common method. Today, most companies use a computer program to analyze stresses in piping, and that analysis is done in conformance with the applicable piping code for the country in question. For the US, that piping code will be ASME B31.3, but in other countries, other codes will apply.

You can't determine the type and location of the expansion joint yourself, you need someone that can provide the stress analysis per the applicable code for your country. Once you have requirements from that person, you can go off and determine what suppliers can provide that expansion joint.

Sorry if that sounds like I'm avoiding your question, but I have to assume this is an industrial application, not a college project.

 

[skyqwerty]

There's always a reason for going to the expense of putting in an expansion joint. Generally, there are 2 reasons for installing such a joint, vibration and thermal contraction/expansion. I'm assuming your case is the latter since you're dealing with liquid nitrogen. It's not cheap to install these joints and it's not easy to determine exactly what type and length you need. In fact, if you can do away with them, you'll be much better off. But to get out of using them, the piping has to be flexible enough to prevent stresses in excess of what is allowed by the piping code for your country. Therefore, someone is going to have to do a piping stress analysis for your liquid nitrogen system and they'll need to accommodate thermal contraction of the piping, so an expansion joint is a common method. Today, most companies use a computer program to analyze stresses in piping, and that analysis is done in conformance with the applicable piping code for the country in question. For the US, that piping code will be ASME B31.3, but in other countries, other codes will apply.

You can't determine the type and location of the expansion joint yourself, you need someone that can provide the stress analysis per the applicable code for your country. Once you have requirements from that person, you can go off and determine what suppliers can provide that expansion joint.

Sorry if that sounds like I'm avoiding your question, but I have to assume this is an industrial application, not a college project.

million thanks for ur guide Sir! but in fact , my boss hope i can come out with some papers or results, if i can't do it, den i juz telling wat u have guided me : )

 

[skyqwerty]

anything i can tell my boss else? actually i am a degree mechanical student... now having internship, but my boss assigned me that.. and i have no idea exactly how to do that

 

[Q_Goest]

Can you provide any more details regarding this liquid nitrogen system you're working on? What pressure? Size of the pipes? How large is it? Drawings?

 

[skyqwerty]

process pipe ( inner ) diameter : 1 ''

Vacuum jacketed pipe ( outer ) : 2.5''

working pressure around pn16 or pn10 : 10 bar or 16 bar

length varies: can take it as 6meter

bellow brand : Vadeb-Witzenmann

reference book : design for thermal stress and cold fact magazines

but stil hard to choose the availabe bellows..d length of bellows, number of corrugations, location of bellows in pipe, and other factors are unknown.. nid help !

 

[Q_Goest]

This helps a bit. At least we now know the pipe is a vacuum jacketed affair which is generally treated a bit differently than unjacketed pipe. Nevertheless, the piping codes applicable in your country still apply and you are legally responsible to make sure your design meets those codes. Those codes should cover design, analysis, documentation, construction, testing, inspections, etc…

For VJ piping, there are 2 common approaches to installing an expansion joint. The first and most common is to put the expansion joint in the outer pipe. The second and still very common method is to put it on the inner pipe.

Installation on the outer pipe allows the inner pipe to be free of those expansion joints and the problems associated with them. For one, the bellows has to accommodate the pressure stresses. A bellows in the outer line is only exposed to a vacuum on the inside and ambient pressure on the outside, so they generally do not need to be reinforced with a braided covering. If they are under internal pressure they will generally need to have wire reinforcement (braiding) on the OD. Another problem with having the bellows on the inner line is that when pressurized, that pressure creates a force in the direction of the axis of the pipe which must be accommodated by the inner line supports. The braiding also has to be sufficiently lose to keep from becoming taught in the axial direction or it will restrict motion of the expansion joint. Having them on the inner line is also generally considered less safe as they are more likely to rupture than a section of pipe.

Installing them on the outer line also has problems however. When placed on the outer line, they are exposed to atmosphere so the possibility of corrosion is increased. Having them in the outer line also means the entire VJ line expands and contracts with the inner line so all of your pipe supports have to be able to accommodate that motion. Also, the inner line will be exposed to some stresses dependent on the geometry of the line and those pipe supports.

When looking at an expansion joint you’ll need to look at stresses in the expansion joint, pressure loads created by the expansion joint and stresses over the range of motion, both in the expansion joint and the adjoining piping. Perhaps a simple example would help. Consider a length of pipe X with elbows on each end going to pipe A on one end and pipe B on the other and an expansion joint on the outer line. You’ll have inner line supports on X that allows the inner line to slide relative to the outer line. You’ll also have similar supports on A and B. When the line is first built it will be at ambient temperature with a vacuum in the annulus. That vacuum will put a force on the outer line in the axial direction equal to the area of the outer line times ambient pressure, so X will be exposed to a compressive force. That force will be transmitted to the inner line via the inner line supports in A and B resulting in some bending stresses in those other lines. When the pipe is exposed to cryogenic temperature, the inner line shrinks, so A and B will now be closer to one another. The expansion joint will compress by that amount resulting in there being some change in the stress in the expansion joint.

Now if the company you work for is not familiar with the codes and has experience building vacuum jacketed lines, then you’ll never be able to do all this obviously. What you should be doing is creating a specification for the piping so that a company that specializes in building vacuum jacketed piping can manufacture it for you. That specification needs to cover the geometry, piping supports, piping code requirements, testing requirements, materials of construction, etc.

 

[skyqwerty]

Thanks a lot Goest... i have some ideas and doing now..and the one i doing in inner line bellow. One last question..if i have spring constant per corrugation, displacement of bellows, corrugation length of specific bellow, and some other info.. how can i determine number of corrugation of bellow?

 

[Q_Goest]

The further a bellows is displaced, the higher the stress on the bellows and the shorter the life expectancy. That kind of information can only be obtained from the manufacturer. I would suggest determining the displacement and forces your piping system can tolerate and then take that to the bellows manufacturer and let them size the bellows for you. They'll take into consideration how much stress is in the bellows so they don't fail prematurely.

 

[skyqwerty]

appreciate what u have told me... can i ask something more? how is a pipe stress analysis like? can be done manually? calculations?

 

[Q_Goest]

appreciate what u have told me... can i ask something more? how is a pipe stress analysis like? can be done manually? calculations?

The piping code applicable to this design will provide guidance on the piping stress analysis. It can be done by hand or by computer.

 

[jehake12]

Assess your situation, but realize that if it is a critical application you should consult an expert.

For a non critical & very safe application, I recommend picking up a copy of the following:

ASME B31.3
Pipe Stress Analysis by Sam Kannappan (read this first)
Pipe Stress Engineering by Peng & Peng (read this second)

There is commercial software available but it is very susceptible to garbage in/garbage out: consider AutoPIPE or CAE Caesar II. I believe they both allow trial versions with a limited node count. Before you use the software, make sure you can approximately analyze reaction loads and stresses in critical areas for small pipe loops by hand.