Vliv lokálního bodového externího zatížení na životnost polymerních trubek

Point load effect on the buried polyolefin pipes lifetime

journal article in Web of Science

en

Polymer pipe lifetime is conventionally estimated by internal pressure test. However, important for service are also other types of loading as: additional bending, different type of external loading from sand embedding, or effect of the residual stresses. One of the dangerous type of loading is so-called “point load” caused, for example, by stones in the soil. The present article is focused on the numerical prediction of this effect on the pipe lifetime. For the lifetime estimation of a polymer pipe under point loading, an approach based on combination of numerical calculation and experimental measurements was used. A special numerical algorithm, which optimizes modeled crack front shape according to the real one during simulation of crack propagation, was proposed. Finally, an analytical relationship for the estimation of fracture parameters of propagating crack across the pipe wall crucial for the pipe lifetime estimation is presented in the paper. A significant reduction of the residual lifetime was found for the cracked pipe loaded by additional point load (consideration of indentation effects of stones in the soil) in comparison with pipe loaded by internal pressure only. The approach presented contributes to the safer service of polyolefin pipes.

Životnost polymerních trubek je obvykle určována standardizovaným testem při zatížení vnitřním tlakem. Ukazuje se ale, že další zatížení, např. ohyb v důsledku uložení nebo zatížení reziduálním napětím, hraje důležitou roli právě při odhadu zbytkové životnosti. Tento článek je zaměřen na odhad zbytkové životnosti pomocí numerického modelování pro různé externí vlivy. V numerickém modelu jsou použita data z experimentů a s využitím speciálních algoritmů, např. optimalizace tvaru šířící se trhliny, jsou stanoveny vlivy jednotlivých faktorů. Tento přístup celkově pomáhá k lepšímu odhadu zbytkové životnosti polymerních trubek a k zefektivnění servisních prací na těchto již používaných systémech.

Polymer pipe lifetime is conventionally estimated by internal pressure test. However, important for service are also other types of loading as: additional bending, different type of external loading from sand embedding, or effect of the residual stresses. One of the dangerous type of loading is so-called “point load” caused, for example, by stones in the soil. The present article is focused on the numerical prediction of this effect on the pipe lifetime. For the lifetime estimation of a polymer pipe under point loading, an approach based on combination of numerical calculation and experimental measurements was used. A special numerical algorithm, which optimizes modeled crack front shape according to the real one during simulation of crack propagation, was proposed. Finally, an analytical relationship for the estimation of fracture parameters of propagating crack across the pipe wall crucial for the pipe lifetime estimation is presented in the paper. A significant reduction of the residual lifetime was found for the cracked pipe loaded by additional point load (consideration of indentation effects of stones in the soil) in comparison with pipe loaded by internal pressure only. The approach presented contributes to the safer service of polyolefin pipes.

lifetime estimation, residual stresses, polyolefin pipe, FEM, crack propagation

11.01.2016

WILEY-BLACKWELL, 111 RIVER ST, HOBOKEN 07030-5774, NJ USA

1548-2634

56

1

79–86

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