steam lines have "u" bends why?

Expansion loops may be in different shapes: U or S. They are used when the lines are long. They remove/reduce the stress due to by thermal expansion or contraction, sismic waves, wind.

Velocity of steam can be controlled by a Pressure regulator.

Condensate removal can be carried out several traps.

I have seen another shape like OMEGA in steam line.

In some circuits where the loop cannot be used and the teperature and pressure alloow it there are bellows used as compensators.

irshad ahmed, You do not say what your job is. Are you an operator in a plant? Are you a piping designer or engineer? Are you new to the process plant engineering and design profession?

You have received a number of answers to your question. All of them correct. Now your next question might be how does one size an expansion loop ("U" bend) for a hot line.

I have had a similar or related question before, the question and my answer id below.

Piping Loops

The question:

"How do I determine the location for anchors and the size of an expansion loop?"

My answer:

You want to know how to handle layout problems that involve long runs of pipe, thermal expansion, anchors, guides and ways to compensate for expansion.

This is a basic problem for all novice pipers and is one that is not easy to explain. However let me try. First, I think you need to look at the whole system and come to a solution based on that whole configuration.

There are four basic options to compensate for thermal expansion in a piping system. These options are as follows:

1. Do nothing. Just allow enough room on the pipeway and let the pipe expand and contract as it will. It will create its own friction anchors and will "snake" around as required to compensate for the expansion. This is not a highly recommended option.

2. Normal configuration. This is where there are natural changes in direction of pipeways or routing that will compensate for the thermal expansion. Natural configuration is defined as a basic "L" shape or a "Z" shape. Anchors and guides need to be installed to prevent the thermal growth in one line from interfering with another. If all the legs are the right length and the anchors and guides are placed correctly then you will not need additional methods to compensate for the expansion.

3. Expansion loops. In long straight runs of pipeways pipe expansion loops are added to compensate for the thermal expansion. Anchors and guides are required to control the pipe and insure that the loop will work as designed.

4. Expansion joints. Expansion joints of various types are made and used to compensate for expansion in piping systems where there are space limitations or natural configuration or loops are not an option. Systems with expansion joints also require pipe anchors and pipe guides to work properly.

You need to ask yourself:

Where do I have natural turns that can be used to compensate for expansion?

Where do I have branches? And do these branches create potential problems?

Where do I need to add loops?

Where can I place anchors and guides?

What is the distance between the potential anchor points?

Now!

What size loop do I need for the places where natural configuration will not work?

Now, the question is not how much pipe should you have between expansion loops but what size an expansion loop should be for a given distance between anchor points of a line.

The answer to this question is really simpler than would first appear. Let's say you are doing layout for a "Unit" which branches (west) off the main north/south offsite interconnection pipeway. The line under consideration is a medium pressure steam line with 8" schedule 40 pipes and a temperature of 450 degrees F. There are battery limits block valves at the interconnecting pipeway end and the line dead-ends at the other end of the unit.

Your pipeway (or sleeper way) has a specific spacing and width. We will use 10 pipe supports at a spacing of 25 feet each and a width of 25 feet. Number the supports from right to left as PS #1 through PS # 10. You know you need one or more loops. You also know that the loops need to be supported. You also recognize that you can use option 1 (above) for some of the header. So, start out by placing your first anchor two pipe supports in from the dead-end of the unit at PS # 8. You will let the last 55 feet (+/-) of header to "free expand." Next move to the battery limits end of the pipeway and place an anchor at PS #1 nearest to the battery limits block valve.

Now look at the distance between the two anchors. Is this distance less than 200 feet? If it is less then you should need only one loop. This loop should be as near to the halfway point between the two anchors as practical. Our distance between PS #1 and PS # 8 is 175 feet. The halfway point is between PS # 4 and PS # 5.

The line will run in the first pipeway berth at the far south side of the unit pipeway. The loop will rest on a support beam on the north side of the unit pipeway and cantilever out about 5 to 6 feet. This makes the loop with dimensions as follows: a vertical rise up 2' – 6", a leg north of 23 feet, a flat turn and a leg west of 20' – 0", then a flat turn south of 23 feet and a vertical drop of 2' – 6" back into the lines assigned berth.

You have already placed an anchor at PS # 1 and at PS # 8 so the next thing is to place guides. The guides need to be one pipe support away from the loop. So the guides are placed at PS # 3 and PS # 6.

This is what I mean by being simpler than would first appear. 90% of the time you can use the "natural landscape" to help to do the loop design instead if worrying about a lot of calculations.

Please note: this being a steam system it will still need to have a proper check and/or analysis by a qualified Pipe Stress Engineer.

Is Flexibility the only reason for the expansion loop installation? Are there any other reasons? If so plz mention!!

Thank You!!

A chemical Engineer

Flexibility is the only reason that I know of.

Thanks for asking.

please correct me if i'm wrong .

another reason, i think that "U" bend can make a restriction that can build pressure drop. Because it consist of 4 elbows. It's can make the dinamic fluctuatuion more slower, when suddenly a large pressure buid in pipingline, this loop can restrict the momentum.

thanks

I would call pressure drop, if actually desired, a serendipitous (ser'en·dip'i·tous) effect of the action of installing a loop needed for Flexibility.

Dear Mr. irshy84,

The U bend what you are referring is called as EXPANSION LOOP which will accomodate the DISPLACEMENT of pipe, due to THERMAL EXPANSION of the pipe, while steam is allowed to flow through the pipe.

The Thermal Expansion for Piping, rod, plates etc., can be calculate by using the Formula Lt = L0 (1 + Alpha T) where Lt = Length of Pipe at the given Temp. in Kelvin, L0 = The Actual Length of Pipe at Ambient Temp., Alpha = the Co.eff. of LINEAR EXPANSION denoted as INCH/INCH in FPS System, or CentiMetre/ centimetre.

Tthe Co.eff. of LINEAR EXPANSION will be different for different Metal/Materials and for Steam Piping it will be generally 7.2 x 10E-6 Inch/Inch Length of pipe or in other words 7.2/10^6 Inch per Inch Length of Pipe.

Higher the Temperature, Higher will be the Thermal Expansion and will cause tremendous force on the system and even may collapse. While opening the steam in the pipe which is at ambient temp.

and gain temp. by absorbing Heat from the steam, thereby condensation takes place and to be removed. After some time the metal attains the full temperature close to the Steam Temp. and expansion will be almost complete. For example for a temp. of 495 Deg.C Steam, a 90 Metre pipe line will expand by 210 MM which means a pipe line of 90 Metres Length requires tremendous pull force to elongate by 210 MM..

DHAYANANDHAN.S

https://whatispiping.com/expansion-loop-on-piping-system/