مهندسی سازه و ساخت

مهندسی سازه و ساخت

مقاومت لوله‌های جداره ضخیم فولادی دارای خوردگی حفره‌ای تحت فشار محوری و لنگر خمشی

نوع مقاله : علمی - پژوهشی

نویسنده
استادیار، دانشکده مهندسی عمران، دانشگاه صنعتی شریف، تهران، ایران
چکیده
در این پژوهش رفتار لوله‌های فولادی دارای خوردگی تحت اثر نیروی محوری و خمش مورد مطالعه قرار گرفته است. لوله‌های فولادی به طور گسترده در ساخت سازه‌های ساحلی و فراساحلی همچون دکل‌ها و سکو‌های نفتی و همچنین خطوط انتقال نفت و گاز به کار گرفته می‌شوند. هدف از ‌این مطالعه بررسی تأثیر نوع خاصی از خوردگی تحت عنوان «خوردگی حفره‌ای» بر مقاومت لوله‌های فولادی است. رویکرد اصلی در پژوهش حاضر روش تحلیل عددی با استفاده از نرم‌افزار اجزا محدود ABAQUS است. بدین ترتیب با استفاده از مدل‌های صحت‌سنجی شده، اثر همزمان سه عامل خمش، بارمحوری و خوردگی بر مقاومت لوله‌های فولادی ارزیابی شده است. در این خصوص با درنظرگیری مشخصات ابعادی متداول در پایه‌های لوله‌ای شکل سکوهای فراساحلی، اقدام به انجام تحلیل‌های پارامتری شده است. اثرات خوردگی حفره‌ای نیز براساس شاخص کاهش جرم نسبی لوله‌ها و در ارتباط با شاخص‌های ریخت‌شناسی خوردگی حفره‌ای، شامل چگالی و عمق خوردگی در تحلیل‌ها لحاظ شده است. مبتنی بر نتایج و با استناد به معادله آیین‌نامه آمریکا در تخمین ظرفیت لوله‌های فولادی فاقد خوردگی تحت فشار محوری و لنگر خمشی، دو ضریب اصلاح تراز باربری محوری و خمشی لوله‌های خورده شده پیشنهاد گردید تا با مقیاس کردن معادله آیین‌نامه آمریکا، اثر زوال مقاومت برآورد شود. ضرایب اصلاح حاصل به ازای شاخص کاهش جرم نسبی 10 الی 30 درصد، متوسط کاهش ظرفیت باربری 20 الی 50 درصد را نسبت به نمونه فاقد خوردگی نشان دادند. همچنین لازم به توضیح است که در یک شاخص یکسان از کاهش جرم نسبی، خوردگی عمیق‌تر اثرات زوال مقاومت بیشتری را حاصل داد. آزمون روش پیشنهادی طی دو سناریو خوردگی مختلف، بیشینه اختلاف تا 11 درصد را در مقایسه با نتایج تحلیل اجزا محدود حاصل داد. بدین ترتیب قابلیت کاربست روش پیشنهادی نشان داده شد.
کلیدواژه‌ها

موضوعات


عنوان مقاله English

Strength of thick-walled circular steel tubes with pitting corrosion under axial compression and bending moment

نویسنده English

Alireza Moazezi Mehretehran
Structural Engineering Division, Civil Engineering Department, Sharif University of Technology, Tehran, Iran
چکیده English

In this research the behavior of thick-walled Circular Steel Tubes (CSTs) with corrosion under axial compression and bending moment have been studied. There are several factors leading to corrosion in steel structures, especially in marine structures that results in strength reduction of whole structure. Steel tubes are widely used in construction of on-shore and off-shore structures such as, oil rigs and platforms, oil and gas transmission lines. Current study focuses on strength reduction of steel tubes with “pitting corrosion”. To this end numerical analyses using finite element software, Abaqus, have been performed. Therefore, utilizing verified models, the simultaneous effects of bending, axial load and corrosion on CSTs have been evaluated. Accordingly, by considering the dimensional characteristics of typical tubular legs of off-shore jackets, a set of parametric study has been undertaken. Pitting corrosion has been characterized in the analyses by relative mass loss ratio index, in companion with morphological indexes of the corrosion, i.e. density and depth of the pits. In accordance with the results obtained and based on the AISC360-22 formula for calculating the load bearing capacity of uncorroded CSTs under combined axial compression and bending moment, two adjustment factors were introduced to scaled down the AISC360-22 formula for accounting the degradation due to the pits. The obtained factors for the relative mass loss ratios vary between 10 to 30 percent showed an average lost bearing capacity of 20 to 50 percent as compared with intact CSTs, with a more profound detrimental effect for deeper pits. The comparison of the proposed method for estimating the lost capacity of the corroded CSTs under combined aforementioned actions in two distinct scenarios, revealed the maximum difference of 11 percent with those obtained from finite element analyses. This showed the applicability of the proposed method.

کلیدواژه‌ها English

Circular Steel Tubes (CSTs)
Axial compression
Bending moment
Pitting corrosion
Finite element analysis
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  • تاریخ دریافت 09 شهریور 1402
  • تاریخ بازنگری 22 مهر 1402
  • تاریخ پذیرش 26 آبان 1402