10 replies to this topic

[sheiko]

Dear all,

I am working in an Engineering Company.

The context is the following:
- The system is: inlet pipe + control valve + outlet pipe.
- The fluid is natural gas
- The outlet pipeline is burried.
- No outlet pipe insulation.
- The minimum allowable temperature in the outlet pipe is -20°C.
- The minimum temperature at the control valve outlet flange is about -15°C (worst scenario)

The problem is that i need to calculate the length of outlet pipe so that the fluid temperature increase to 0°C.

My data are:
- Outlet pipe material: carbon steel (L360)
- Outlet pipe internal diameter: 570 mm
- Outlet pipe thickness: 20 mm
- Outlet pipe is burried 1 m deep.
- Average air temperature: 11°C
- Wind velocity: 10 m/s

My questions are:
1/ Do you know where i can find thermal conductivity data for ground? or do you have data? I know it strongly depends on the ground composition but i don't have anything...
2/ Could you please share any Excel spreadsheet to perform that calculations?

Thank you

[djack77494]

My data are:
- Outlet pipe material: carbon steel (L360)
- Outlet pipe internal diameter: 570 mm
- Outlet pipe thickness: 20 mm
- Outlet pipe is burried 1 m deep.
- Average air temperature: 11°C
- Wind velocity: 10 m/s

My questions are:
1/ Do you know where i can find thermal conductivity data for ground? or do you have data? I know it strongly depends on the ground composition but i don't have anything...
2/ Could you please share any Excel spreadsheet to perform that calculations?

sheiko,

As I've stated elsewhere, the heat loss calculations for enthalpy changes in a warm fluid being "lost to earth" are not well handled using generalized correlations. Local conditions such as soil moisture content are very important to the pertinent properties. The best source of information for such estimates would have to be actual data from other similar pipelines. I am not sure I fully understand your situation, however. I took your questions to be based on buried pipeline heat losses. But above you mention ambient air temperature and wind velocity. Both would be irrelevant for buried pipe, so I'm not sure if I'm missing something here. I do not have a suitable Excel spreadsheet, but I know you could try using a general purpose simulator such as Hysys or ProII and look over the heat loss calculation options that they offer. Such an exercise should prove educational.

[latexman]

Are you looking for preliminary design information for a study or evaluation, or are you looking for final design information for construction and operation?

Depending on location, the variation of conditions could be small or huge. Soil type - clay, sand, loam, etc. Soil condition - wet or dry, loose or compacted, good drainage or poor drainage. I think you'll have to calculate a worst case based on historical climate data, soil type, and soil conditions.

[sheiko]

sheiko,
I am not sure I fully understand your situation, however. I took your questions to be based on buried pipeline heat losses. But above you mention ambient air temperature and wind velocity. Both would be irrelevant for buried pipe, so I'm not sure if I'm missing something here.

Thank you for the advice!
You are right as usual. My mistake.

Just to fix ideas, the gas leaves the valve at -15°C and i need to determine the length of pipe so that the fluid can reach 0°C (heated by the ground).

[sheiko]

Are you looking for preliminary design information for a study or evaluation, or are you looking for final design information for construction and operation?

Thank you latex!

We are in detailed design but the subject has not been studied durind the FEED.

[sheiko]

I do not have a suitable Excel spreadsheet, but I know you could try using a general purpose simulator such as Hysys or ProII and look over the heat loss calculation options that they offer. Such an exercise should prove educational.

Thank you so much for the advice!

Indeed i have found some data in Hysys (not in Pro/II by the way) that i share with you for info. (see attached file).

Attached Files

•  Soil_conductivity_data_by_Hysys.doc   25KB   147 downloads

[djack77494]

Indeed i have found some data in Hysys (not in Pro/II by the way) that i share with you for info.

Thanks for the feedback. I have used this calculation in Hysys, but I had a given overall heat transfer coefficient that was supplied by our client (making my problem much easier). Now comes the tough part - matching your site to the restricted listing of soil types that are defined. BTW, you'll also need to input the soil temperature. Good luck.

[JoeWong]

The soil condition varies with place. For a long distance pipeline, the soil may be treated so that it can support the pipeline. Otherwise, the pipeline need to be supported by slipper/structure. Treated soil bed may have more-or-less constant properties. However, it may changed due to soil movement, water movement, biological/chemical activities, etc. Generally soil investigation (plus necessary soil treatment) will be conducted and a range of properties will be reported. These properties including the soil thermal conductivity (instead of heat transfer coefficient - to be calculated) will be reported as design basis for pipeline design. 2.0 - 2.5 w/mK could be a good start.

Besides, the pipeline will be coated (maybe multilayer coating) for corrosion protection. The coating is generally low in thermal conductivity (can be as low as 0.1-0.2 w/mK) but with very low thickness.

[sheiko]

Thanks Jedis

[ankur2061]

Thanks Jedis

Sheiko,

Heat Loss from a buried Pipe can be calculated as follows:

Q = S*K_m*(T1-T2)

Where:
Q = heat loss from buried pipe, W
S = shape factor, m
and defined as

S = 2*Pi*L / ln(4z/D)

Where:
L = Length of pipe, m
z= burial depth or distance from soil surface to center of buried pipe, m
D = OD of pipe, m

K_m = Thermal conductivity of soil, W/m-K

T1 = Temperature at surface of pipe, K
T2= Temperature of soil surface, K

The shape factor equation is valid if L>>D (i.e L is substantially greater than D) and z>1.5D.

Since the above statement is generally true for majority of cases the above equation for shape factor holds good for majority of cases.

This information is taken from Section 3-7, 'Heat Transfer A Practical Approach' by Yunus A. Cengel, 2nd Edition.

Hope this helps.

Regards,
Ankur.

[sheiko]

Thank you Ankur!