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#39930 - 01/06/11 01:24 PM Insulation
Raam____ Offline
Member

Registered: 05/01/10
Posts: 33
Loc: .....
Dear Friends/Senior,

I have a doubt in insulated piping and pipeline. Normally Pipes are insulated to maintain the inside medium temperature of pipe and personnal protection. Based on the purpose, temperature & fluid condition the insulations are classified into Hot Insulation, Personal protection Insulation, Cold Insulation, Anti-sweat insulation, Acoustic insulation, Heat tracing insulation and etcetra.

My doubt is,

1. When a pipe is completely insulated, it has no contact with atmospheric temperature (Ambient temp.) so the fluid temperature could be maintained, as well as pipe has also no contact with atmospheric temperature so its has the fluid temperature. Formula says whenever there is a change in temperature, change in length occurs (DeltaL = e * L) Where, e-Coefficient of thermal expansion/contraction between 70 deg. F to pipe temperature, in/100ft deg. F (ASME B31.3).

2. As per the above formula insulated pipe has no change in temperature. So will it expand or contract during operating case. If it does kindly explain me how?

3. For insulated pipe is there any special consideration for ambient temperature in the analysis?

Example problem:

Pipe dia = 30”,
Insulatation = Aerofoam,
Insulation Thick = 40 mm,
Medium = Chilled water,
Temperature(1) = 5 deg C, Temperature(2) = 100 deg C,
Ambient Temperature = 40 deg C.
Length = 100 m,

For the above temperature 1 & 2 cases the pipe will contract/expand or not?

Please clear my doubt.

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#39959 - 01/07/11 05:39 AM Re: Insulation [Re: Raam____]
MoverZ Offline
Member

Registered: 11/22/06
Posts: 1195
Loc: Hants, UK
Go back to school.

If there is a difference between the installed temperature and operating temperature there will be resultant thermal expansion or contraction, whether the pipe is insulated or not.

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#39963 - 01/07/11 06:03 AM Re: Insulation [Re: Raam____]
Vannella Offline
Member

Registered: 10/24/10
Posts: 37
Loc: IT
Dear Raam,
during the construction, first the metallic line is installed, and after the insulation is fixed on it.
During the installation the temperature of the pipe is the ambient temperature, so the dilations will occur starting from this non insulated situation.
Often in calculation the installation temperature taken in account is the minimum ambient temperature, to be more conservative.
After the ending of construction, and after the start up, the pipe heats up and reaches its operative temperature.
So, no matter if the line is insulated or not, delta T is:
(Operative or Design temperature) - (Minimum ambient T, or ambient T).
Sometimes, if the operative temperature is low, you have to take in account the effect of solar radiation that can heat the pipe during installation up to 50°C or more, and calculate Delta T as:
(Temperature caused by solar radiation) - (Minimum fluid temperature).

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#39970 - 01/07/11 08:41 AM Re: Insulation [Re: Vannella]
sillyman Offline
Member

Registered: 06/06/09
Posts: 128
Loc: Australia
Dear Mr.Raam,

As per your query "2. As per the above formula insulated pipe has no change in temperature. So will it expand or contract during operating case. If it does kindly explain me how?"

Yes.

There will be an expansion and contraction if the operating temperatures are above and below 21 deg C or 70 deg F. Since, universally it is assumed that @ 21 deg C or 70 deg F, the material will have a zero expansion or contraction. If the material is exposed above or below the 21 deg C or 70 deg F, there will be an expansion or contraction.

As in your case, since the operating temperatures are 5 deg C to 100 deg C. so there will be a contraction and expansion in your pipe irrespective of insulation.

When we talk about the insulated pipe, the ambient temperature has no effect, provided the all the parts of piping system are fully insulated.
There are some cases, particular in the gulf part, where the operating temperature is (for example) 50 deg C below the black body temperature, then the design temperature shall be 84 deg C (Black body temperature). If the piping system is insulated for the process requirement, then the piping system shall be stress analyzed for the operating temperature of 50 deg C only. Since the design temperature is selected based on the atmospheric condition, it is no effect on insulated piping system.

Hope so this may clarify your doubt. Also I request the other members to provide a solution if my suggestion seems to be not accepted.
_________________________
Knowledge is nothing unless it is shared

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#39984 - 01/07/11 11:12 AM Re: Insulation [Re: sillyman]
Raam____ Offline
Member

Registered: 05/01/10
Posts: 33
Loc: .....
Dear Mr. MoverZ, Vannella, sillyman.

Thank you very much for you valuable explanations. You Made me clear about my doubt regarding the Insulated pipe expansion/contraction. Basic concept...


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#39991 - 01/07/11 08:09 PM Re: Insulation [Re: Raam____]
pstrn Offline
Member

Registered: 02/06/05
Posts: 15
Loc: USA
This is just a small addition to Vannella's comment on solar heat gain.

I have seen for outdoor and overground pipes, carrying fuids even at ambient temperature, the design temperature of pipe is considered as 85ºC or 90ºC. The idea is, the pipe may be empty and will absorb solar heat until an equilibrium temperature is reached when incoming solar heat will equal heat lost from the surface of pipe by convection and radiation.

Thank you,
_________________________
kumar

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