Limit load analysis and safety assessment of an elbow with a circumferential crack under a bending moment

1995 ◽  
Vol 62 (2) ◽  
pp. 109-116 ◽  
Author(s):  
J. Chattopadhyay ◽  
B.K. Dutta ◽  
H.S. Kushwaha ◽  
S.C. Mahajan ◽  
A. Kakodkar
Keyword(s):  
Safety Assessment ◽  
Bending Moment ◽  
Limit Load ◽  
Circumferential Crack ◽  
Load Analysis

Fully Plastic Failure Stresses and Allowable Crack Sizes for Circumferentially Surface Cracked Pipes Subjected to Tensile Loading

2021 ◽  
Author(s):  
Kunio Hasegawa ◽  
David Dvorak ◽  
Vratislav Mares ◽  
Bohumir Strnadel ◽  
Yinsheng Li
Keyword(s):  
Experimental Data ◽  
Bending Moment ◽  
Limit Load ◽  
Tensile Loading ◽  
Crack Size ◽  
Plastic Failure ◽  
Circumferential Crack ◽  
Asme Code ◽  
American Society ◽  
Better Than

Abstract Fully plastic failure stresses for circumferentially surface cracked pipes subjected to tensile loading can be estimated by means of limit load criteria based on the net-section stress approach. Limit load criteria of the first type (labelled LLC-1) were derived from the balance of uniaxial forces. Limit load criteria of the second type are given in Section XI of the ASME (American Society of Mechanical Engineering) Code, and were derived from the balance of bending moment and axial force. These are labelled LLC-2. Fully plastic failure stresses estimated by using LLC-1 and LLC-2 were compared. The stresses estimated by LLC-1 are always larger than those estimated by LLC-2. From the literature survey of experimental data, failure stresses obtained by both types of LLC were compared with the experimental data. It can be stated that failure stresses calculated by LLC-1 are better than those calculated by LLC-2 for shallow cracks. On the contrary, for deep cracks, LLC-2 predictions of failure stresses are fairly close to the experimental data. Furthermore, allowable circumferential crack sizes obtained by LLC-1 were compared with the sizes given in Section XI of the ASME Code. The allowable crack sizes obtained by LLC-1 are larger than those obtained by LLC-2. It can be stated that the allowable crack size for tensile stress depends on the condition of constraint of the pipe, and the allowable cracks given in Section XI of the ASME Code are conservative.

Capacity Analysis and Safety Assessment of Polyethylene Pipeline With Local Wall-Thinning Defect

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Weijie Jiang ◽  
Jianping Zhao
Keyword(s):  
Safety Assessment ◽  
Mechanical Performance ◽  
Orthogonal Design ◽  
Bending Moment ◽  
Limit Load ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Assessment Procedure ◽  
Wall Thinning ◽  
Local Wall Thinning

The purpose of this study is to propose a safety assessment procedure for polyethylene (PE) pipe with local wall-thinning defect. A uniaxial tensile test is performed to test the mechanical performance of PE. Then, the constitutive model for PE can be established. The limit load of the PE pipe with local wall-thinning defect can be studied with the method of combining the orthogonal design of experiment and finite element (FE) analysis. Then, the factors of local wall-thinning defect can be analyzed. The results show that the depth of the defect has a great effect on the limit load (internal pressure and bending moment) of PE pipe. The effects that the axial length of the defect and the circumferential length of the defect have on the limit load are not significant. Referring to the safety assessment of metal pipe proposed by GB/T19624-2004, a safety assessment for PE pipe with local wall-thinning defect is revised.

Limit Load Analysis of Elbow with Local Wall Thinning under Combined Loads

2015 ◽  
Vol 750 ◽  
pp. 198-205
Author(s):  
Peng Cui ◽  
Chang Yu Zhou
Keyword(s):  
Safety Assessment ◽  
Bending Moment ◽  
Limit Load ◽  
Orthogonal Experimental Design ◽  
Limit Loads ◽  
Pressure Pipe ◽  
Combined Loads ◽  
Wall Thinning ◽  
Volume Defect ◽  
Local Wall Thinning

The local wall thinning(LWT) is a kind of common volume defect in pressure pipe. The limit loads of elbows with LWT under pressure, bending moment, torque and their combined loads have been studied in detail by orthogonal experimental design and finite element method. The results have shown that the influence of depth and circumferential length of LWT on the limit load is more obvious compared to that of axial length when an elbow is under pressure, bending moment or torque. The change of limit bending moment and torque with the depth of LWT and circumferential length is significant for an elbow under combined bending moment and torque. At last, the safety assessment equations for elbow under combined in-plane closing bending moment and torque were proposed by regression analysis.

The Limit Load and Safety Assessment of Pressure Pipe With an External Pit Defect at High Temperature

2011 ◽  
Author(s):  
Bo Wang ◽  
Changyu Zhou ◽  
Xiaohua He ◽  
Jilin Xue
Keyword(s):  
High Temperature ◽  
Safety Assessment ◽  
Relative Length ◽  
Bending Moment ◽  
Limit Load ◽  
Relative Depth ◽  
Strain Criterion ◽  
Limit Loads ◽  
Pressure Pipe ◽  
Strain Data

Local pit is the common volume defect in high temperature pressure pipe which is widely used in the fields of electric plant, nuclear power station, petrochemical plant and so on. In this paper finite element analysis code ABAQUS was used to simulate limit load of high temperature pressure pipe with an external pit defect which is in service for 105 hours. Four-point bending loading model was applied to calculate the limit load of the pipe. There are three dimensionless factors: relative depth, relative gradient and relative length which characterized the shape of an external pit defect. Orthogonal test of three factors at four different levels was carried out to analyze the sequence of the influence of these three parameters. In present paper when the maximum principal strain reaches 2%, the corresponding load is selected as the limit load. According to this strain criterion and isochronous stress strain data of P91 steel, limit load of high temperature pressure pipe with an external pit was determined by using ABAQUS. Firstly, isochronous stress strain data was generated and was inputted into ABAQUS as equivalent elastic-plastic constitutive relation. Then, sustained load versus cumulative strain curves at high temperature during service was obtained after the simulation. At last, limit loads of high temperature pipe during service time was determined based on 2% total strain criterion. In order to obtain the safety assessment curve of high temperature pipe, five types of limit loads for pressure pipe with an external pit were needed: ultimate limit bending moment, limit internal pressure, limit bending moments at the pressure of 0.25PL,0.5PL and 0.75PL individually. 16 sets of data formed 16 groups of curves which expressed the relationship between the ratio of limit pressure and the ratio of limit bending moment for defective pipe and non-defective pipe. Based on the calculation results of limit load for pipe with 16 kinds of defects, a set of limit load formulae were established through multiple nonlinear regression of relative depth, relative gradient and relative length. So the equations of limit load and safety assessment for pressure pipe with an external pit under combined loading of pressure and bending moment were obtained. The results could provide a reference for safety assessment of high temperature creep pressure pipe with local pit defect.

Reliability Calculation of Welded Pressure Pipe with Circumferential Crack Based on 3-D Elastic-Plastic SFEM

2008 ◽  
Vol 575-578 ◽  
pp. 639-642
Author(s):  
Bo Lin He ◽  
Ying Xia Yu ◽  
Li Xing Huo ◽  
Yu Feng Zhang
Keyword(s):  
Surface Crack ◽  
Safety Assessment ◽  
Crack Depth ◽  
Three Dimensional ◽  
Bending Moment ◽  
Mean Value ◽  
Pressure Pipe ◽  
Circumferential Crack ◽  
The Mean ◽  
Welded Pipe

In this paper, the reliability of welded pressure pipe with circumferential surface crack was calculated by using three dimensional stochastic finite element method. This method has overcome the shortcomings of conservative results in safety assessment with deterministic fracture mechanics method. The calculation of reliability was based on three dimensional elastic-plastic stochastic finite element program which was developed by ourselves. The effects of variables such as fracture toughness, bending moment and the depth of the circumferential surface crack on the structure reliability were also discussed. The calculation results indicate that the crack depth has great effect on the reliability of the welded pipe. When the mean value of the crack depth is changed from 3mm to 7mm, the failure probability of the welded pipe will change from 10-8 to 10-2. The bending moment also has great effect on the reliability of the welded pipe. When the mean value of moment is changed from10000 N.m to 15000 N.m, the failure probability of the welded pipe increases dramatically for the same circumferential crack depth. Irrespective of the changing of moment, the pipe has higher reliability if the crack depth is less than 5mm(a/t<0.5, t is the thickness of the pipe). The method has put forward a new way for safety assessment of welded pipe with circumferential surface crack.

Analysis and Experiments on the Plastic Limit Load of Elbows under Combined Pressure and In-Plane Closing Bending Moment

2013 ◽  
Vol 774-776 ◽  
pp. 1090-1097 ◽  
Author(s):  
Zhi Xiang Duan ◽  
Kun Shi
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Safety Assessment ◽  
Bending Moment ◽  
Limit Load ◽  
Experimental Results ◽  
Plastic Limit ◽  
Element Analysis ◽  
Limit Pressure ◽  
Plastic Limit Load

This paper discusses the plastic limit load of elbows without defects and with local thinned area (LTA) in the extrados under combined pressure and in-plane closing bending moment. Finite element analysis (FEA) and experiments have been used. The results of FEA show that, for the elbows without defects, when the ratio of pressure to the limit pressure (P/PL) is smaller than 0.469, the limit moment of elbows increases with the increasing pressure; when the ratio (P/PL) is bigger than 0.469, the limit moment of elbow decreases with the increasing pressure. For the elbows with LTA, the FEA results show that with different LTA the variation of the limit load of elbows to the pressure is different. Perhaps, the limit moment of elbows always decreases with the increasing pressure. It is also likely that the limit moment of elbows increases with the increasing pressure and then decreases with the increasing pressure. The results of FEA are consistent with the experimental results. By fitting the results of FEA, the safety assessment figure for elbows under combined pressure and in-plane closing bending moment is drawn.

Limit Load Analysis of Pipe Bend With Extrados Wall Thinning

2014 ◽  
Author(s):  
TaeRyong Kim ◽  
ChangKyun Oh
Keyword(s):  
Internal Pressure ◽  
Bending Moment ◽  
Limit Load ◽  
Plastic Limit ◽  
Pipe Bend ◽  
Limit Loads ◽  
Wall Thinning ◽  
Piping Systems ◽  
Load Analysis ◽  
The Difference

Since pipe bend has a characteristic that extrados becomes thinner and intrados thicker after fabrication process, it can be expected to be vulnerable to extrados wall thinning due to corrosion or erosion during its operation. In this paper, limit loads of pipe bend with the thinning are computed under the loading conditions of internal pressure and bending moment. Several case studies with varying geometries and wall thinning shapes are presented. The difference in the limit loads behavior between pipe bend and welded elbow is also reviewed. The calculated plastic limit loads of pipe bend are compared with other research results for the welded elbow. The results show that pipe bend can be applied to safety-related piping systems as far as the internal pressure and bending moment only are considered.

J-Integral Analysis of Surface Cracks in Round Bars under Bending Moments

2011 ◽  
Vol 52-54 ◽  
pp. 43-48 ◽  
Author(s):  
Al Emran Ismail ◽  
Ahmad Kamal Ariffin ◽  
Shahrum Abdullah ◽  
Mariyam Jameelah Ghazali ◽  
Ruslizam Daud
Keyword(s):  
Finite Element ◽  
Crack Depth ◽  
Crack Tip ◽  
Bending Moment ◽  
Limit Load ◽  
Fe Model ◽  
Surface Cracks ◽  
Element Analysis ◽  
Reference Stress ◽  
Proposed Model

This paper presents a non-linear numerical investigation of surface cracks in round bars under bending moment by using ANSYS finite element analysis (FEA). Due to the symmetrical analysis, only quarter finite element (FE) model was constructed and special attention was given at the crack tip of the cracks. The surface cracks were characterized by the dimensionless crack aspect ratio, a/b = 0.6, 0.8, 1.0 and 1.2, while the dimensionless relative crack depth, a/D = 0.1, 0.2 and 0.3. The square-root singularity of stresses and strains was modeled by shifting the mid-point nodes to the quarter-point locations close to the crack tip. The proposed model was validated with the existing model before any further analysis. The elastic-plastic analysis under remotely applied bending moment was assumed to follow the Ramberg-Osgood relation with n = 5 and 10. J values were determined for all positions along the crack front and then, the limit load was predicted using the J values obtained from FEA through the reference stress method.

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