بررسی عددی کمانش خطوط لوله ی فولادی تحت اثر بار فشاری محوری خروج از مرکز و فشار خارجی

خطوط لوله هنگام عبور از نقاط مختلف جغرافیایی، معمولاً در معرض بارهای ترکیبی مختلفی (شامل: بارهای عرضی، طولی، عمودی و فشار هیدرواستاتیک علاوه بر فشار داخلی)قرار می‌گیرند. در نوشتار حاضر، دو نوع از بارهایی که می‌توانند تاثیرگذار باشند (فشارهای خارجی و محوری)، با استفاده از نرم‌افزار آباکوس ارزیابی شده‌اند. برای ارزیابی دقیق رفتار خطوط لوله‌ی فولادی و مشاهده‌ی نوع گسیختگی ایجاد شده در اثر بارهای معرفی شده، اتخاذ ناکاملی‌ها در تحلیل به روش عددی لازم و ضروری است. جهت صحت‌سنجی پاسخ‌های نرم‌افزار، نتایج تحلیل یک نمونه‌ی آزمایشگاهی با عددی مقایسه و مشاهده شد که همخوانی قابل قبولی بین آن‌ها برقرار است. آثار فشار محوری و نسبت قطر به ضخامت (d/t) در ظرفیت کمانشی فشار خارجی تحلیل و بررسی و سپس مشاهده شد که با افزایش فشار محوری و نسبت قطر به ضخامت، ظرفیت کمانشی فشار خارجی کاهش می‌یابد.

Numerical investigation of Buckling behavior of steel pipeline affected by eccentric axial compression subjected to external pressure

The pipeline in service may be subjected to complicated loads (including lateral, axial, vertical loads and hydrostatic pressure in addition to internal pressure) when crossing complex geohazard regions. In this study, two kind of loads that cloud be more fundamental are numerically investigated using finite element method. The loads imposed on pipelines depend on the pipe content and the environment that the pipeline is passing through. Axial compression can arise within pipelines from thermal loads arising from hot hydrocarbon passage from offshore oil wells to an onshore station or can arise from anchor forces acting on pipelines and External pressure can arise within pipelines from hydrostatic pressure, sudden valve closures, and pump failures. It is very important to select suitable geometric imperfection form to exact investigation behavior of pipelines and mechanism of failures. In order to verification response of numerical analyses, one of the experimental results is compared with numerical result and concluded that there is a good agreement between results. Meanwhile, the effect of the eccentric axial compression, pipe diameter to wall thickness ratio (D/t) on the buckling external pressure are studied. The interaction between the axial load and external pressure was graphically demonstrated and compared for different geometrical ratios through numerical analysis. During analysis, the eccentric axial compression load in the pipe was primarily induced and maintained constant less than its capacity. Subsequently, the uniform peripheral pressure was gradually increased until failure, and, besides, the response of some specimens was separately investigated under pure external pressure and axial compression load. It was found that the D/t ratio is the decisive parameter to specify the buckling behavior of steel pipelines and type of created failure mode subjected to axial compression. Some significant conclusions were drawn based on extensive parametric studies. The buckling external pressure reduces with the increase of preaxial compression and diameter to thickness ratio.