CFRP Reinforcement and Repair of Steel Pipe Elbows Subjected to Severe Cyclic Loading

In order to ensure safe operation and structural integrity of pipelines and piping systems subjected to extreme loading conditions, it is often necessary to strengthen critical pipe components. One method to strengthen pipe components is the use of composite materials. The present study is aimed at investigating the mechanical response of pipe elbows, wrapped with carbon fiber-reinforced plastic (CFRP) material, and subjected to severe cyclic loading that leads to low-cycle fatigue (LCF). In the first part of the paper, a set of LCF experiments on reinforced and nonreinforced pipe bend specimens are described focusing on the effects of CFRP reinforcement on the number of cycles to failure. The experimental work is supported by finite element analysis presented in the second part of the paper, in an attempt to elucidate the failure mechanism. For describing the material nonlinearities of the steel pipe, an efficient cyclic-plasticity material model is employed, capable of describing both the initial yield plateau of the stress–strain curve and the Bauschinger effect characterizing reverse plastic loading conditions. The results from the numerical models are compared with the experimental data, showing an overall good comparison. Furthermore, a parametric numerical analysis is conducted to examine the effect of internal pressure on the structural behavior of nonreinforced and reinforced elbows, subjected to severe cyclic loading.</jats:p

Δομική ακεραιότητα αγωγών υδρογονανθράκων με τοπικές παραμορφώσεις τοιχώματος

Local distortions in the form of dents or buckles on the wall of steel hydrocarbon pipelines may constitute a threat for the structural integrity of the pipeline. In the present study, experimental research supported by numerical simulations has been conducted to investigate the structural integrity of smoothly dented and buckled steel pipes. A series of sixteen (16) full-scale experiments on 6-inch-diameter X52 pipes has been carried out, and numerical simulations have also been conducted. At first, the pipe specimens are dented or buckled. Subsequently, the dented/buckled steel pipes are subjected mainly to cyclic loading (bending or pressure) in order to estimate their residual strength and remaining fatigue life. Some specimens are also monotonically pressurized to burst. The finite element analyses simulate the experimental procedure for each specimen and loading case, in order to calculate the local stress and strain distributions at the dented region. Small-scale tests in bent strips are also conducted, and correlate very well with the experimental and numerical results. Based on the numerical results, a damage factor is computed and the fatigue life is predicted and compared successfully with the experimental results. The results of the present study are aimed at evaluating existing guidelines and methodologies towards proposing a simple and efficient assessment of local wall distortions in steel pipelines.Τοπικές παραμορφώσεις στα τοιχώματα των αγωγών με τη μορφή υβώσεων ή εγκολπωμάτων συνιστούν απειλή για τη δομική ακεραιότητά και τη λειτουργία τους. Στην παρούσα έρευνα, πειραματική και αναλυτική διερεύνηση έχει πραγματοποιηθεί για την μελέτη της δομικής ακεραιότητας αγωγών που έχουν υποστεί ομαλές οδοντώσεις και υβώσεις στα τοιχώματά τους. Δεκάξι (16) πειράματα μεγάλης κλίμακας σε δοκίμια σωλήνων X52 6-ιντσών έχει πραγματοποιηθεί, και αριθμητικές προσομοιώσεις έχουν επίσης διεξαχθεί.Τα δοκίμια, αφού έχουν πρώτα υποστεί εγκολπώματα ή υβώσεις, υποβάλλονται σε κυκλική φόρτιση (κάμψη ή πίεση), προκειμένου να εκτιμηθεί απομένουσα αντοχή τους και η υπολειπόμενη διάρκεια ζωής. Παράλληλα πραγματοποιήθηκε ανάλυση πεπερασμένων στοιχείων για την προσομοίωση της πειραματικής διαδικασίας για κάθε τύπο παραμόρφωσης και κάθε περίπτωση φόρτισης, προκειμένου να υπολογιστεί η κατανομή των τάσεων και η συγκέντρωση παραμορφώσεων στην κρίσιμη περιοχή. Με βάση τα αριθμητικά αποτελέσματα, εκτιμάται η αντοχή σε κόπωση σε σύγκριση με τα πειραματικά δεδομένα. Ο απώτερος στόχος της παρούσας έρευνας είναι η χρήση των πειραματικών και αριθμητικών αποτελεσμάτων για την ανάπτυξη αξιόπιστων μεθοδολογιών οι οποίες μπορούν να χρησιμοποιηθούν για τον έλεγχο αγωγών και την αξιολόγηση τοπικών παραμορφώσεων μορφής εγκολπώματος ή ύβωσης με στόχο την πιθανή επισκευή τους στο πλαίσιο μίας βέλτιστης διαδικασίας συντήρησης και της διατήρησης ενός αξιόπιστου επιπέδου λειτουργίας και ασφάλειας

HITUBES PROJECT DESIGN AND INTEGRITY ASSESSMENT OF HIGH STRENGTH TUBULAR STRUCTURES FOR EXTREME LOADING CONDITIONS - D4

D4.1: Materials and fracture-mechanic properties including loading rate and corrosion D4.2: Test data on welded tubular connections D4.3: Performance of advanced post-treatment welding techniques D4.4: Test data on bolted tubular connection

ATTEL PROJECT PERFORMANCE‐BASED APPROACHES FOR HIGH STRENGTH TUBULAR COLUMNS AND CONNECTIONS UNDER EARTHQUAKE AND FIRE LOADINGS - D2

D2.1: Report on the design of specimens D2.2: Definition of practical solutions for the selected typologies of column bases, of HSSCHS columns and HSS‐CFT columns and of HSS‐concrete composite beam‐to‐column joint

ATTEL PERFORMANCE-BASED APPROACHES FOR HIGH STRENGTH TUBULAR COLUMNS AND CONNECTIONS UNDER EARTHQUAKE AND FIRE LOADINGS - D6

Design Guidelines and proposal for EC3, EC4 and EC

HITUBES PROJECT DESIGN AND INTEGRITY ASSESSMENT OF HIGH STRENGTH TUBULAR STRUCTURES FOR EXTREME LOADING CONDITIONS - D1

D1.1: Report on tubular structures of interest subjected to extreme repeated loadings. D1.2: Report on current design procedures for welded/bolted HSS materials, members and connections. D1.3: Report on Bayesian estimations in probabilistic reliability assessment. D1.4: Report on Output-only structural identification techniques

HITUBES PROJECT DESIGN AND INTEGRITY ASSESSMENT OF HIGH STRENGTH TUBULAR STRUCTURES FOR EXTREME LOADING CONDITIONS - D2

D2.1: Actions on foot- cycle-bridges and railway bridges and stresses on critical elements. D2.2: Validation of MB and FE software and estimation of stresses on critical elements

HITUBES PROJECT DESIGN AND INTEGRITY ASSESSMENT OF HIGH STRENGTH TUBULAR STRUCTURES FOR EXTREME LOADING CONDITIONS - D7

D7.1: Report on design guidelines and recommendations for HSS for tubular structures D7.2: Report on design guidelines and recommendations for tubular members and connections D7.3: Report on maintenance and durability of HSS tubular structure