TECHICAL Series MATHEMATICS • INFORMATICS • PHYSICS Series PHILOLOGY Series ECONOMIC SCIENCES Sereies EDUCATIONAL SCIENCES Series LAW AND SOCIAL SCIENCES Series
Lifetime Estimation of High Density Polyethylene Pipelines Based on Fracture Mechanics Principles
(Estimarea duratei de viaţă a conductelor din polietilenă pe baza conceptelor mecanicii ruperii materialelor)
Vol LXIV • No. 4/2012
Vlad Ulmanu, Gheorghe Drăghici, Virgil Aluchi
Universitatea Petrol - Gaze din Ploieşti, Bd. Bucureşti 39, Ploieşti
e-mail: vulmanu@upg-ploiesti.ro

 Keywords   polyethylene pipes; fracture mechanics; life estimation.

 Abstract
The paper presents a method for estimating the overall life of High Density Polyethylene pipes used for natural gas distribution, applying fracture mechanics principles.
The material properties - fracture toughness and the crack propagation rate are experimentally determined by testing Compact Type (CT 100) specimens machined from a polyethylene pipe wall. The crack propagation tests have been performed by tensile loading the specimens at various testing speeds, measuring the crack propagation speed and the corresponding tensile force. By applying the linear elastic fracture mechanics principles, the experimental results are used to determine the crack growth law.
The overall life of the pipe loaded by internal pressure is calculated by integrating the crack growth equation, using a specialized software elaborated by the authors, based on the procedure recommended by API 579 - 2/ASME FFS - 2 - 2009 Fitness for Service Example Problem Manual.


 Rezumat
Lucrarea prezintă o metodă de estimare a duratei de viaţă a conductelor din polietilenă de înaltă densitate, utilizate la distribuţia gazelor naturale, prin aplicarea conceptelor mecanicii ruperii materialelor.
Caracteristicile de material necesare estimării durabilităţii - factorul critic de intensitate a tensiunilor şi viteza de propagare a fisurilor, s-au determinat experimental utilizând epruvete de tip CT prelevate din peretele unei ţevi din polietilenă de înaltă densitate. S-au solicitat la tracţiune cu diferite viteze de solicitare patru epruvete, iar prin înregistrarea simultană a timpului, deplasării bacurilor şi valorii forţei s-a determinat dependenţa dintre viteza de propagare a fisurii şi factorul de intensitate a tensiunilor.
Durata de viaţă a conductei solicitată cu presiune interioară, considerată până la momentul propagării fisurii pe toată grosimea peretelui ţevii s-a determinat prin integrarea expresiei vitezei de propagare a fisurilor, elaborând un produs informatic dedicat ce are la bază procedura recomandată de standardul API 579 - 2/ASME FFS - 2 - 2009 Fitness for Service Example Problem Manual.



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