تعيين تجربي چقرمگي شكست در درز جوش مارپيچ لوله فولادي ترمومكانيكال

ارزيابي چقرمگي شكست به عنوان مقاومت ماده در برابر شروع ترك ترد در درز جوش لوله هاي فولادي انتقال گاز براي مهندسين و طراحان خط به دليل شرايط بحراني منطقه جوش بسيار حايز اهميت است. از سوي ديگر آزمون هاي تعيين چقرمگي ماده بر اساس مباني و اصول مكانيك شكست، دشوار، زمان بر و پرهزينه مي باشند. هم چنين انجام اين آزمون ها بعضا بدليل محدوديت در اندازه (خصوصا ضخامت ماده) غير ممكن است. در تحقيق حاضر كه براي نخستين بار در داخل كشور صورت گرفته است، آزمون خمش سه نقطه اي بر اساس آزمون چند نمونهاي مطابق استاندارد ASTM(با طراحي خاص نمونه و قيد و بند آزمايشگاهي) انجام ميشود. هدف تحقيق تعيين چقرمگي شكست درز جوش مارپيچ لوله APIX65 (به عنوان يكي از پركاربردترين انواع لولههاي فولادي انتقال گاز طبيعي در ايران) مي باشد. روش هاي تجربي استفاده شده در تحقيق حاضر شامل دو روش تعيين چقرمگي مواد نرم است. يك روش بر اساس محاسبه گشودگي بحراني نوك ترك (CTOD) و روش ديگر محاسبه JIC است. بر اساس روش اول مقدار CTOD برآورد شده 23/0 ميلي متر و مقدار KIC معادل آن MPa?m 265 اندازه گيري شد. همچنين طبق روش دوم JIC برابر kJ/m2396 و KIC معادل آن MPa?m 332 محاسبه گرديد. بمنظور تكميل موضوع تحقيق، بحث و بررسي در خصوص دلايل تفاوت مقادير KIC از دو روش و مقايسه نتايج با داده هاي محدود در مقالات مشابه ارايه مي شود. Assessment of fracture toughness in pipe weldment is important for pipeline engineers and designers as welded zone is the most critical site for crack initiation and propagation. Also the measurement of fracture toughness based on the Fracture mechanics tests are difficult, time consuming and expensive.Even in some cases, according to the geometric limits (especially the thickness of material) test fulfillment seems impossible.This research reports the determination of fracture toughness in spiral weld seam of API X65 pipe steel. The pipe has vast usage in Iran’s gas transportation projects. To measure fracture toughness, single edge notch bend (SENB) specimens were machined from the pipe. Two techniques of evaluation of fracture toughness based on multi-specimen tests in ASTM E 1820 standard were used. These techniques were based on determination of crack tip opening displacement (CTOD) and JIC. So 0.23 mm determined for CTOD and its equivalent KIC was 265 MPa?m, JICwas also 396 KJ/m2 and its KIC measured 332MPa?m.In addition, the reasons of the difference in KIC values of the two methods are discussed and comparing of the results with limited similar data in the literature isaccomplished.

Assessment of fracture toughness in pipe weldment is important for pipeline engineers and designers as welded zone is the most critical site for crack initiation and propagation. Also the measurement of fracture toughness based on the Fracture mechanics tests are difficult, time consuming and expensive.Even in some cases, according to the geometric limits (especially the thickness of material) test fulfillment seems impossible.This research reports the determination of fracture toughness in spiral weld seam of API X65 pipe steel. The pipe has vast usage in Iran’s gas transportation projects. To measure fracture toughness, single edge notch bend (SENB) specimens were machined from the pipe. Two techniques of evaluation of fracture toughness based on multi-specimen tests in ASTM E 1820 standard were used. These techniques were based on determination of crack tip opening displacement (CTOD) and JIC. So 0.23 mm determined for CTOD and its equivalent KIC was 265 MPa?m, JICwas also 396 KJ/m2 and its KIC measured 332MPa?m.In addition, the reasons of the difference in KIC values of the two methods are discussed and comparing of the results with limited similar data in the literature isaccomplished