بررسي عددي كمانش خطوط لوله ي فولادي تحت اثر بار فشاري محوري خروج از مركز و فشار خارجي

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

خطوط لوله هنگام عبور از نقاط مختلف جغرافيايي، معمولاً در معرض بارهاي تركيبي مختلفي (شامل: بارهاي عرضي، طولي، عمودي و فشار هيدرواستاتيك علاوه بر فشار داخلي)قرار مي‌گيرند. در نوشتار حاضر، دو نوع از بارهايي كه مي‌توانند تأثيرگذار باشند (فشارهاي خارجي و محوري)، با استفاده از نرم‌افزار آباكوس ارزيابي شده‌اند. براي ارزيابي دقيق رفتار خطوط لوله‌ي فولادي و مشاهده‌ي نوع گسيختگي ايجاد شده در اثر بارهاي معرفي شده، اتخاذ ناكاملي‌ها در تحليل به روش عددي لازم و ضروري است. جهت صحت‌سنجي پاسخ‌هاي نرم‌افزار، نتايج تحليل يك نمونه‌ي آزمايشگاهي با عددي مقايسه و مشاهده شد كه همخواني قابل قبولي بين آن‌ها برقرار است. آثار فشار محوري و نسبت قطر به ضخامت (D/t) در ظرفيت كمانشي فشار خارجي تحليل و بررسي و سپس مشاهده شد كه با افزايش فشار محوري و نسبت قطر به ضخامت، ظرفيت كمانشي فشار خارجي كاهش مي‌يابد.

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 pre-axial compression and diameter to thickness ratio.