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Effect of creep characteristics on pipeline durability

Mutwil K.

Journal of Achievements in Materials and Manufacturing Engineering

2011

Vol. 48, nr 1

97--102

Purpose: The paper presents an assessment of durability of a steam pipeline operating above the threshold temperature. The durability calculations take into account the creep characteristics of the material. Design/methodology/approach: The results of calculations of the degree of wear caused by the creep of a pipeline, made using numerical methods, are presented. The calculation model takes into consideration the basic geometric and material properties of the pipeline, its operating parameters, and the displacement of valve and turbine chambers which force an initial displacement of the pipeline in the cold state. Findings: As a result of the calculations made, the effect of redistribution and relaxation of stresses induced by the initial guy wire tension has been found. This leads to a rapid loss of stresses, the consequence of which is enhanced durability of the investigated object. Research limitations/implications: Due to the lack of data regarding objects operated for a long time, the calculations of their durability made under this study provide preliminary information on the expected further operational life of a specific structural element. The comprehensive evaluation of the life of an object should be supplemented by research on the material to enable determining the actual degree of material wear in the areas of the analyzed element subject to the highest effort. Practical implications: To ensure operational safety of pipelines operated for a long time, a method is presented to evaluate their durability, which takes into account the effect of additional loads on the effort of the pipeline. Originality/value: In the calculations of wear caused by creep, carried out in line with the EN-13480 standard, the criterion is the stress in the wall of a component under internal pressure. The paper presents the results of stress calculations while taking account of additional operational load, which has a significant influence on the degree of material wear.

Procesy pękania najbardziej wytężonych elementów rurociągu energetycznego

Renowicz D., Cieśla M., Mutwil K.

Zeszyty Naukowe Politechniki Świętokrzyskiej. Nauki Techniczne

2007

Z. 4

104-105

Zagadnienie prognozowania trwałości elementów maszyn i urządzeń poddanych złożonym oddziaływaniom mechanicznym i cieplnym jest obecnie przedmiotem zainteresowania wielu ośrodków naukowych. W pracy analizowano wpływ historii obciążenia obiektu oraz procesów degradacji struktury na proces inicjacji pęknięć oraz na trwałość w warunkach pełzania i zmęczenia. Przedstawiono wyniki badań staliwa 0.2C-1.2Cr-0.6Mo-0.3V stosowanego na elementy rurociągów pary świeżej, pracujące w blokach energetycznych. Należą do nich m.in. trójniki. Ze względu na ekstremalne warunki eksploatacji rurociągu rozruchowego trójniki ulegają szybkiemu zużyciu a ich stan decyduje o niezawodności i bezpieczeństwie pracy całego obiektu. Celem przeprowadzonych badań doświadczalnych było określenie stanu materiału trójnika wyciętego z rurociągu rozruchowego łączącego dwa kotły OP-140 z turbinami i określenie przyczyn niszczenia tego elementu po upływie ponad 100000 godzin pracy.

The paper presents the results of research on a live steam pipeline working in a power generation unit. Based on an analysis of the load state, it has been proved that T–connections are the pipeline elements subject to the highest effort. Due to extreme operating conditions present during a power unit’s start-up, T-connections undergo wear quite fast, with their condition determining reliability and safety of the whole power generation facility. The research objective was to identify the condition of the T-connection material cut out from a start-up pipeline connecting two boilers OP-140 with turbines and to determine the cause of its destruction after more than 100,000 hours in service.