Dear Mehdi Ohadi

Every structure is subjected to length- and volume changes caused by temperature changes.

If these length changes are blocked, material stresses are generated.

For ducting and piping, the length change is the most important.

The way to handle this issue is to install one fixed support for a straight section and the rest of the supports is executed as sliding supports, allowing longitudinal movement.

For steel, the increase in length is calculated as dL = heat expansion factor * d(T) * Length,

where the heat expansion factor for steel = 0.000012

A compensator or expansion joint is situated at the end of a free expanding pipe section, coping with the calculated possible expansion.

Perpendicular pipe sections (connected by a bend) are treated the same way or the length change in one pipe is absorbed in the bending of the other (perpendicular) pipe.

Also the thermal expansion or force induced shape variations of the support structure must be considered.

Thermally induced forces and stresses can be calculated by equalizing the calculated thermal expansion with the force induced compression.

Basic structural engineering

Success

Teus ■

Dear Mr. mehdiohadi

Refer to EJMA standard

Expansion Joint Manufacturers Association

Best regards ■

Originally Posted by Teus Tuinenburg

Dear Mehdi Ohadi

Every structure is subjected to length- and volume changes caused by temperature changes.

If these length changes are blocked, material stresses are generated.

For ducting and piping, the length change is the most important.

The way to handle this issue is to install one fixed support for a straight section and the rest of the supports is executed as sliding supports, allowing longitudinal movement.

For steel, the increase in length is calculated as dL = heat expansion factor * d(T) * Length,

where the heat expansion factor for steel = 0.000012

A compensator or expansion joint is situated at the end of a free expanding pipe section, coping with the calculated possible expansion.

Perpendicular pipe sections (connected by a bend) are treated the same way or the length change in one pipe is absorbed in the bending of the other (perpendicular) pipe.

Also the thermal expansion or force induced shape variations of the support structure must be considered.

Thermally induced forces and stresses can be calculated by equalizing the calculated thermal expansion with the force induced compression.

Basic structural engineering

Success

Teus

Sir

I perceive the initiator has trigerred very imp quiry

I take this oppurtunity to take this subject forward in context of today adopted engineering practice . Apparantly iam referring fly ash hadling system and below is my quiry

1) Every pipe section is subjected to thermal expansion , now how do i determine the location to provide expansion joint in ash conveying pipe? . Emphatically every pipe section will have some thermal expansion , but there must be engineering guideline to determine the location of expansion(on basis of magnitude of expansion) joint which is required to damper the possible expansion due to thermal gradient

2) I presume you are referring the dt ie temperature gradient within pipe for particuar length , which is attributed to convective,radiative,conductive heat transfer

3) You said A

, would you please make it more conceivable ?

4) You stated

would you please make it more conceivable ?

5) You stated

would you please make it more conceivable ? ■

Dear kj,

Determining where the fixed supports of a conveying pipeline are positioned, is a matter of engineering skill.

The arrangement of fixed points and expansion joints is then designed for as little as possible flexible joints and the prevention of lateral movements of pipe sections.

A lateral movement can be absorbed by a bend with a compensator at the beginning of the bend and at the end of the bend.

In pneumatic conveying lines, the expansion problem is easy to solve with small sections, consisting of short (reinforced) rubber hoses, which can also take some lateral deflection without any problem of extensive wear.

d(T) is meant as the increase of the pipe temperature, causing the length increase.

Example:

Pipe length 150m

Temperature out of operation = 25 degrC

Operational temperature = 40 degrC

heat expansion factor = 0.000012

length increase = 150 *(40-25) * 0.000012 = 0.027 m # 2.7 cm # 27 mm

It is obvious that the expansion of a pipe line manifests itself at the longest distance from the fixed support. That is the location to absorb this expansion in the most efficient way.

Between two fixed supports, the location does not matter as the total expansion to absorb by the compensator is then split in two smaller lengths.

Imagine a pipe section without a compensator, fixed supported at one end and with a bend at the other end.

Then the bend would move away and perpendicular at the next pipe section.

That movement creates bending stresses in the next pipe section, which might be acceptable.

The formula is: Elastic modulus = Stress*Length/d(Length)

or

Stress = Elastic modulus * d(Length) / Length

or

d(Length) = Stress*Length/ Elastic modulus

d(Length) = Length*d(T) * heat expansion factor

hence:

Stress*Length/ Elastic modulus = Length*d(T) * heat expansion factor

or

Stress / = Elastic modulus *d(T) * heat expansion factor

Elastic modulus for steel = 200 Gpa

In the example:

Stress = Elastic modulus * d(Length) / Length

Stress = 200 * 0.027 / 150 = 0.036 Gpa

0.036 Gpa = 360 kgf/cm2

This is for what an engineer is trained for.

Know your formulas.

Equalize them, where appropriate.

Discover the connections

Understand and apply the results

Standardized procedure.

Success

Teus ■

Originally Posted by Teus Tuinenburg

This is for what an engineer is trained for.

Know your formulas.

Equalize them, where appropriate.

Discover the connections

Understand and apply the results

Standardized procedure.

If you don't mind Teus, I'm going to use this on some of our young engineers ■

Hello designer,

Of course you can use this as a challenging remark to whom it may concern.

(Why, some of your young engineers)

I am sure, you can extend the list of oneliners.

Have a nice day

Teus ■

A not so young alleged piping engineer designed a steam line in Stanlow Refinery, UK. On start up the line pushed the pipe rack alarmingly. His response was " Nobody said owt (anything) to me about expansion!" I don't think he's still there.

As Teus and Designer say...that's what engineers are/should be trained for. I sometimes think I should have carried on with the clarinet. ■

When I were a lad, many years ago, to be a draughtsman was an honorable trade. But over the years 'draughtsman' has been transmuted into 'engineer'. Frequently this was to give the draughtsman a perceived 'higher status' (without more cash), on other occasions it was to justify more cash. There was no extra 'engineer' training.

Equally in that bygone age, few went to university (I didn't) but I was told that going to university trained you to think, and by thinking be able to solve problems in your working life. It was even suggested that training to think was more important than the actual subject you took. But now it seems the training to think has gone! Ask a young graduate to solve a problem and to often it's "we didn't cover that" or "you haven't told me how to do that" (the latter was the favorite of an eastern european 'graduate' we employed for a while).

Still, retirement beckons and I can soon put it all behind me ■

What's the difference between a draughtsman and an engineer?

DRAUGHTSMEN CAN DRAW!

I went to university. A govenment grant in the UK paid more than the apprentice wage: there were no engineering apprentichips near the little backwater where I was raised so university was the only option for me. I can't say if it tought me to think. I can say that I've learned a lot more since and that makes me think....that in this nervous new world is thinking fashionable any more? There's so much software around that the hard work is gone. Engineers have more time to analyse the big picture and yet so few bother. Result? The same mistakes get repeated but a whole lot faster. It is giving progress a bad name.■

The issue of deflection and movement is something that is glossed over in many cases. I have had experienced structural engineers boldly state that their structure does not deflect.

Well the main materials we use in engineering are Hookesian materials. That is they have a characteristic property where there is a significant area where stress is proportional to strain. Engineers exploit this property in their design.

Of course Hookes Law can be re-written in a couple of ways. One is "As the force, so the deflection". Another is "To resist it must deflect". So, a structure that does not deflect or move under load, cannot resist. Any structure must move or deflect otherwise it is of no use. As such, when there are elements that span distances in a structure, allowance MUST be made for movement (expansion and contraction). This is in addition to movement from settlement of foundations. ■

Originally Posted by mehdiohadi

Dear Friends

I would like to know when is necessary to use expansion joint for ducting system (use for dust collector), in cement and steel plant.

if you know any reference please introduce to me

Max Ambient Temperature: +40

Min Ambient Temperature: -10

Operation Temperature: Ambient

thanks in advance

Mehdi Ohadi

Hello, we also use an expansion joint in front of or right after a machine we wish to protect from stresses, such as an automatic diverter valve. We have found extreme temperatures in our Canadian weather can cause a long length of pipe to push or pull on our diverter valves, the resulting stress can distort the internal clearances, alignment, or even limit switch adjustments. The maintenance people would forever be readjusting the valve settings, without an expansion joint in place.

Hank ■

Sir

In above equation

1) Is the Temperature out of operation is atmospheric temperature ?

2) Is the Operational temperature is Tempmix at local condirion or it is shell temperature ■

Originally Posted by guddu

Sir

In above equation

1) Is the Temperature out of operation is atmospheric temperature ?

2) Is the Operational temperature is Tempmix at local condirion or it is shell temperature

It is the difference in temperature (rise or fall) that is of concern.

1)Temperature prior to the process.

2) Temperature during the process.

It is Delta T.

The same applies with ambient temperature throughout the year. As an example in Canada we get lows in the winter of -40C to highs in the summer of +30C therefore delta T = 70C. So you need to determine the worst case senario. Process or ambient. ■

Dear kj,

I am afraid that you are mixing up 2 threads.

A thread about the temperatures in pneumatic conveying and this thread about the thermal expansion of structures.

Assuming that your question is about the thermal expansion:

1)Yes.

2)Shell temperature.

Have a nice day

Teus ■