Linear thermal expansion

Thermal expansion is an important operating parameter of pipeline systems. It is caused by excitation of movements of atoms constituting a given substance as a result of thermal energy supply. This results in linear expansion of the material. Incorrectly adopted compensation of this parameters in the operated system may lead, among others, to excessive stress in the pipe, cracks, misalignment and even leaks leading to pipeline damages. To prevent this phenomenon, following steps may be undertaken:

  • build a pipeline with low thermal expansion rate

  • apply a system for compensation of linear thermal expansion


Considering the production process of TERMOTECH system, it should be noted that the conduit pipe, sleeve pipe and the foam filling the space between these pipes form a uniform piping system for which the thermal expansion for design calculation purposes is as follows:

  • α = 0.04 mm/mK - for conduit pipe made of PVC-U, PVC-C and ABS

  • α = 0.08 mm/mK - for conduit pipe made of PE-HD, PP-H and PVDF

Calculation methods

Prior to commencement of pipeline thermal expansion calculations, a very important question should be asked: "What is the temperature at which the pipeline will be erected?" This temperature is the basic temperature in reference to which the ΔT for two variants shall be calculated.

Variant I

The pipeline is not in operation but is subject to action of external factors (extreme possible high and low temperatures should be considered).

Variant II

The pipeline is in normal operation; the temperature of the medium to be flowing in this pipeline should be considered together with the influence of external factors on the entire "system".

"System" thermal expansion.

ΔL = L·ΔT · α

ΔL - length change for the entire system, mm

L - basic system length, m

α - unit expansion rate of the system, mm/mK

ΔT - temperature difference, K

temperaturowa_wydluzalnosc_liniowa
Calculation example

We shall examine the linear expansion rate for a 1000 meter pipeline made of various materials for temperature increase of ΔT=30oC.

Materials to be tested ar as follows:
  • PE 100 pipeline   

α = 0,18 mm/mK
  • TERMOTECH (PE-HD, PP-H and PVDF) pipeline system

α = 0,08 mm/mK
  • TERMOTECH (PVC-U, PVC-C and ABS) pipeline system

α = 0,04 mm/mK
Results:
  • PE 100 pipeline

ΔL = 5,40 m
  • TERMOTECH (PE-HD, PP-H and PVDF) pipeline system

ΔL = 2,40 m
  • TERMOTECH (PVC-U, PVC-C and ABS) pipeline system

ΔL = 1,20 m

Linear expansion rate

Due to the thermal expansion of the pipeline systems, they are a much better solution that the systems erected in a traditional manner. This brings following benefits in particular:

  • reduction of the required number and size of expansion joints

  • reduction of the required number of supports

  • considerable reduction of the pipeline erection time

The above factors drive the project cost reduction versus pipelines insulated in a traditional manner.