PSI - Issue 5

S. Sahnoun et al. / Procedia Structural Integrity 5 (2017) 1267–1274 A.Saifi et al / Structural Integrity Procedia 00 (2017) 000 – 000

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Fig. 1. Structure studied

Inside the pipe, we considered a water flow (of the incompressible laminar type) with a velocity equal to 1.5 m.s 1 . The contact between the scale and the pipe is supposed to be perfect. We applied a thermal flux of constant density, Q = 100 Watt / m 2 , over the entire external surface of the pipe considered. To calculate the evolution of the temperature at any point of the pipe, we used commercial software based on the 3D finite element method. The calculation of the thermal response is carried out in the case of a pipe where the materials are considered to be isotropic. The mesh adopted for this structure is a mesh composed of tetrahedral elements.

Fig. 2. Mesh diagram

The water pipes in the industry are generally made of steel. The thermal properties of used materials in this work are shown in the table below (Roussel (2012), Angel (2008), and A.Elballouti (2007)).

Table 1. The thermal properties of used materials Materials ( λ (W/m.K)

ρ (Kg/m3)

c(J/Kg.K)

Steel

44.5

7850 2600 1000

475 900

Scale(CaCO 3 )

2.7 0.6

Water

4200

By its thermal properties, scale acts as an insulator which prevents the efficiency of heat exchange. It is a cause of over- consumption of energy. Our study concerns the effect of the scale thickness, the thickness of the pipe and its diameter on the thermal response of the pipe studied. This response will be expressed by the absolute thermal contrast C (t) which is defined by the difference between the temperature value of the flawed zone and that of the unflawed zone at a given time t (Moulay A. Akhloufi (2015)):

  C t T 

    t T t 

(1)

def

s

2.2. Effect of scale thickness on absolute thermal contrast.

In order to illustrate the effect of the scale layer thickness on the absolute thermal contrast, we considered three scale deposits on a pipe with the thicknesses y = 10mm, y = 30mm and y = 50mm. The pipe studied is a circular steel