comparative analysis of the bursting behavior on a pvc-c...

IPASJ International Journal of Mechanical Engineering (IIJME) Web Site: http://www.ipasj.org/IIJME/IIJME.htm

A Publisher for Research Motivation ........ Email:[email protected] Volume 4, Issue 11, November 2016 ISSN 2321-6441

Volume 4, Issue 11, November 2016

ABSTRACT The PVC-C pipes are increasingly used in industry, particularly in the supply and distribution pipes of hot and cold water, because of the quality of their mechanical properties at high temperatures and their corrosion resistance. Throughout the life cycle of these materials, they are potentially subject to various attacks directly impacting their original mechanical characteristics; therefore a re-estimation of their residual life would be required under the predictive maintenance strategies. This article is an experimental comparison between two failure modes of a PVC-C DN50 PN25 pipe under burst pressure due to a circumferential and a longitudinal defect. We chose to materialize the defects as a groove machinated on a lathe to control and increment the different depth of the failure. This will give to the maintenance services concrete results confirming that the longitudinal defect on a PVC-C pipe is more dangerous than a circumferential one. Keywords: PVC-C, circumferential groove, longitudinal groove, bursting pressure, crack propagation, critical depth.

1. INTRODUCTION Polyvinyl chloride is a widely used polymer, amorphous or poorly crystalline, main representative of the chloropolymer family. It’s made from two materials: 57% of sea salt (NaCl) and 43% of petrol. it is the only plastics material constituted by more than 50% of mineral raw material [1]. Rigid PVC is used primarily for making profiles and pipes by extrusion. Soft PVC or plasticized PVC is manly used in clothes and tapestry industry. The interest of PVC-C (chlorinated PVC) is in its heat resistance: with high chlorine levels, it does not deform like PVC in boiling water; this is a known quality which finds its application in the manufacture of plumbing tubes. Outfits sufficiently high temperatures are obtained for neighboring chlorine content of 65% (PVC chlorine rate is 56.5%) [1]. PVC-C pipes manufacturers and design offices, generally evaluate these materials lifetime to 50 years, but during the storage process, installation and even during operation, some notches (groove for example) can occurs and be dangerous from a certain depth (critical) from which the crack propagation becomes brutal and unpredictable even under operating pressures. In this paper we chose to study a groove (as harmful model) 5mm wide, on the circumference of a diameter 50 mmm tube and 5.6 mm thick, by varying each time, according to its depth a 0.5 mm and 0.25 mm (see figure 2 and 4).

2. EXPERIMENTAL METHODOLOGY

2.1 REALIZATION OF TEST SPECIMENS 2.1.1 Blank specimens: Blank samples used are prepared according to EN ISO 15877: Plastic piping system for hot water systems and cold water chlorinated polyvinyl chloride (PVC-C) [2].

Comparative analysis of the bursting behavior on a PVC-C tube DN 50 PN 25 with both

circumferential and longitudinal defect

Mohamed SAFE1 Zineb AZIF2 Jilali Nataj2 , Mohamed EL GHORBA2

1laboratoire de contrôle et de caractérisation mécanique des matériaux et des structures, ENSEM Casablanca, Morocco.

2 1laboratoire de contrôle et de caractérisation mécanique des matériaux et des structures, ENSEM Casablanca, Morocco..




Table 1: the dimensional characteristics of virgin specimens

Figure 1: Preperation of virgin specimens.

2.1.2 Specimens with circumferential groove: The modeling of the damage is to provide a circumferential groove 5mm width and variable depth of 0.75 to 3.5 mm with a pitch of 0.25 mm and 3.5 mm to 5 mm with a step 0,5mm. A number of damaged specimens is 15 test pieces with groove at different depths. The grooves was machined in a lathe with a grooving tool of 5mm width.

Figure 2: PVC-C specimens with circumferential groove at different depths.

Quantity

External diameter Internal diameter Thickness Length

3 tubes 50 mm 38.8 mm 5.6 mm 400 mm




Figure 3: Machining of specimens with circumferential groove. 2.1.3 Specimens with longitudinal groove: As the last section, we modeled a longitudinal groove default on circumference of 5 test tubes of PVC-C PN25, 5mm in width, 100 mm in length and in defect depth which varies from 1 to 3.5 mm with pitch of 1 mm.

Figure 4 : Preparation of PVC-C specimens with longitudinal groove.

2.1.4 CHARACTERIZATION: The characterization is to put under static pressure at controlled speeds bursting up the specimens in a test bed equipped with a hydraulic pump and a digital indicator with two displays: instantaneous pressure and ultimate pressure rupture. Figure 4 shows the test bench with accessories for measurement and control of various parameters. The test pieces are immersed in a water bath under an ambient temperature of 23 ° C. Both extremities of every test tube are fixed by two mandrels; the mandrel is connected with a pump bath test membrane by a high pressure flexible. For safety reasons, the test tubes are submerged in the water bath under ambient temperature before setting the pressure.




Figure 5 : Bath water hydrostatic .

Figure 6 : Presentation of specimen’s montage.

3. RESULTS 3.1.1 BURST PRESSURE AS A FUNCTION OF THE FRACTION OF LIFE ∆a/e 3.1.1.1 Circumferential groove damage:




Figure 7: Evolution of the burst pressure (Pe) according to the fraction of life (∆a/e).

3.1.1.2 Longitudinal groove damage:

Figure 8: Evolution of the burst pressure (Pe) by the fraction of life (∆a/e)

3.1.2 BURST PRESSURE DROP RATE ACCORDING TO THE FRACTION OF LIFE ∆a/e 3.1.2.1 Circumferential groove default:

Figure 9: Presentation of burst pressure drop rate as a function of the fraction of life (∆a/e).




3.1.2.2 Longitudinal groove default:

Figure 10: Presentation of burst pressure drop rate as a function of the fraction of life (∆a/e).

4. DISCUSSION / ANALYSIS: In the first case of circumferential groove,the bursting pressure falls slowly to the depth of 3.5mm for which the pressure drops suddenly (see figure 7). For the second case which corresponds to a longitudinal groove, the pressure drop is gradual with the decreasing of the groove’s until a depth of 3 mm where the pressure drop is sligthly accentuated.(see figure 8). This is clearly represented in figures 9 and 10 illustraing the pressure drop rate in function of the fraction of life for both cases. The critical depth of a circumferential groove is 3.5mm more than the critical depth of a longitudinal groove which is 3 mm for the same pipe in the same conditions. This difference between the two cases is explained by the amount of radial stresses applied on a the longitudinal groove are two times greater than those applied on the circumferential one.

5. DAMAGE CALCULATION OF STATIC TEST ON PVC-C SPECIMENS : In this section we are interested in studying the static damage which describes the material’s condition basically on the increasing of the burst pressure. The static damage is obtained by the following relationship [3]:

On other hands the reliability is defined as the probability of the success and It varies as the opposite way of the probability of failure or damage [4]:

u

a

u

ur

s

PPPP

D

1

1

1)()( DR




5.1 Circumferential groove default:

Figure 11: Static Damage’s evolution as a function of the fraction of life.

Figure 12 : Reliability’s evolution according to the fraction of life.

Figure 13 : Static Damage – Static Reliability as a function of the fraction of life.

Stadium I Stadium II Stadium III




5.2 Circumferential groove default:

Figure 14: Static Damage’s evolution as a function of fraction of life.

Figure 15 : Reliability’s evolution as a function of fraction of life.

Figure 16: Static Damage – Static Reliability according to the fraction of life.

Stadium I Stadium II Stadium III




6. CONCLUSION Experimental results of this work in particular on critical depth will allow users of PVC-C pipes to assess the harmfulness of a burst pressure failure depending on the direction and the depth of the notch. The critical depth of a default on a PVC-C pipe with a circumferential groove is more than a longitudinal one (3,5 mm for the first and 3 mm for the second). The static damage curves comparison shows that the evolution of damage is more pronounced on a tube with longitudinal defect. A longitudinal default on PVC-C pipes is more harmful than a circumferential one.

REFERENCES [1]. Contribution à l’histoire industrielle des polymères en France par Jean-Marie Michel.

[2]. Norme EN ISO 15877 : système de canalisation en plastique pour les installations d’eau chaude et d’eau froide –polychlorure de vinyle chloré (PVC-C).

[3]. Mouhib.N. Ouaomar.H.,Lahlou. M. ElGhorba. M. “Characterization of residual energy loss and Damage Prediction of 7-wire stand extracted from a steel wire rope and subjected to a static test “International Journal of Research (IJR) e-ISSN: 2348-6848, p-ISSN:2348-795X.2015.

[4]. Fiabilité du système par P.CHAPOUILLE et R.de PAZZIS.

comparative analysis of the bursting behavior on a pvc-c...

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