Multi-Tier Tensile Strain Models for Strain-Based Design: Part 3 — Model Evaluation Against Experimental Data

2012 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang ◽  
David Horsley ◽  
Steve Nanney
Keyword(s):  
Experimental Data ◽  
Test Data ◽  
Wall Thickness ◽  
Model Evaluation ◽  
Tensile Strain ◽  
Full Scale ◽  
Weld Strength ◽  
Model Predictions ◽  
Girth Welds ◽  
Level 2

This is the third paper in a three-paper series related to the development of tensile strain models. The fundamental basis [1] and formulation [2] of the models are presented in two companion papers. This paper covers the evaluation of the models against large-scale experimental data which include a total of 24 full-scale pipe tests with and without internal pressure [3,4] and 30 curved wide plate (CWP) tests [5,6]. The 24 full-scale pipe specimens are nominally X65 grade (12.75″ OD and 12.7-mm wall thickness) and made by two manufacturers. The actual yield strength of the two pipes differs by approximately 14 ksi. The girth welds are made with three welding procedures, creating three weld strength levels. The full-scale test program are designed to evaluate the effects of internal pressure, weld strength mismatch, pipe strength, pipe Y/T ratio, flaw location, flaw size, and toughness. The 30 CWP specimens are from 36″ OD and 19.1 mm wall thickness X100 pipes. The girth welds are made with two welding procedures, creating two slightly different weld strength mismatch levels. The CWP test specimens expand the range of material grade and wall thickness for the model evaluation. The model evaluation demonstrates that the overall correlations between the experimental test data and model predations are similar when the model predictions are made with Level 2 and 3 procedures and various toughness options. The Level 2 procedure with Charpy energy option and Level 3b provide the best overall one-to-one correlation between the test data and model prediction. The Level 3b shows greater scatter than Level 2 with the Charpy energy option. The most significant contributor to the TSC variations and the difference between the measured and predicted TSCs is the strength variation in the pipes. A small variation in the strength can lead to a large variation of the measured remote strain even when the flaw behavior is essentially the same. For the 24 full-scale pipe tests, a strength variation of 1 ksi in the pipes would explain the large variations of the measured TSC in comparison to the model predictions. The TSC models produce consistent results that capture the overall trend of the test data.

Curved-Wide Plate Testing of X100 Girth Welds

2014 ◽  
Author(s):  
Timothy S. Weeks ◽  
J. David McColskey ◽  
Mark D. Richards ◽  
Yong-Yi Wang ◽  
Marie Quintana
Keyword(s):  
Test Data ◽  
Tensile Strain ◽  
Considerable Effort ◽  
Future Paper ◽  
Model Predictions ◽  
Post Test ◽  
Consensus Standard ◽  
Girth Welds ◽  
Welded Pipe

Curved-wide plate (CWP) tests are frequently used for assessing the quality of pipeline girth welds. Despite a large number of CWP tests having been conducted at great expense over many decades, an industry consensus standard remains unavailable. Considerable effort at several research institutions is focused on the standardization of test protocols. It is widely recognized that comparing results from CWP tests from different institutions is difficult without accounting for all the possible parametric differences. This paper presents the procedural details recently used in testing X100 girth welds. The protocols cover (1) specimen design and dimensions, (2) instrumentation plan and data acquisition, (3) specimen fabrication and preparation, (4) preparing and executing the tests, (5) processing of raw test data and (6) post-test metallurgical examination. The evaluation of specimen deformation, flaw growth, and comparison of test data with model predictions will be presented in a future paper. Selected CWP test data from this program were evaluated and compared to tensile strain models of the girth welded pipe in a recent paper [1].

Development of a FAD-Based Girth Weld ECA Procedure: Part II — Experimental Verification

2002 ◽  
Author(s):  
Yong-Yi Wang ◽  
David Rudland ◽  
David Horsley
Keyword(s):  
Experimental Verification ◽  
Companion Paper ◽  
Full Scale ◽  
Weld Strength ◽  
Pipe Surface ◽  
Experimental Database ◽  
Plate Test ◽  
Wide Range ◽  
Girth Welds ◽  
Almost All

An ECA procedure specifically tailored to pipeline girth welds is developed under a PRCI (Pipeline Research Council International) funded project. This procedure of FAD (Failure Assessment Diagram) format incorporates some of the most recent developments in crack driving force, plastic collapse, and effects of weld strength mismatch match. The theoretical framework of this procedure is given in a companion paper. This paper focuses on the experimental verification of the procedure. Some particular issues related to girth weld ECA are discussed first. The experimental database includes both full-scale and wide plate test results. Most of the full-scale data are from pipes of API Grade X70 (483 MPa); a few were X65 (448 MPa) and X60 (414 MPa) grades. The diameter of the pipes ranged from 20 inch (508 mm) to 42 inch (1067 mm). The wide plate test data are taken from a PRCI project performed at the University of Gent. The plates were cut from an X60 36-inch OD 11.6-mm pipe. Surface-breaking defects were artificially introduced from the root side of the girth welds. The plates were loaded to failure in tension after the defects were fatigue pre-cracked. The girth welds had a range of yield stress levels ranging from 20% undermatching to 24% overmatching. In almost all the cases, the newly developed procedure proved conservative as compared to the experimental data. The comparison with the wide plate tests was particularly interesting with its wide range of weld strength mismatch levels. It was demonstrated that the inclusion of the weld strength mismatch in the new procedure improves the consistency and the accuracy of the predictions. It also showed that non-conservative predictions might result if the undermatching welds are not properly accounted for.

Effects of Biaxial Loading on the Tensile Strain Capacity of Girth Welds With Weld Strength Undermatching and HAZ Softening

2020 ◽  
Author(s):  
Banglin Liu ◽  
Yong-Yi Wang ◽  
Xiaotong Chen ◽  
David Warman
Keyword(s):  
Internal Pressure ◽  
Tensile Strain ◽  
Biaxial Loading ◽  
Reduction Factor ◽  
Pressure Level ◽  
Weld Strength ◽  
Strain Capacity ◽  
Weld Region ◽  
Girth Welds ◽  
Tensile Strain Capacity

Abstract The ability to accurately estimate the tensile strain capacity (TSC) of a girth weld is critical to performing strain-based assessment (SBA). A wide range of geometry, material, and loading factors can affect the TSC of a girth weld. Among the influencing factors, an increase in the internal pressure level has been shown to have a detrimental effect on the TSC. The overall influence of internal pressure is usually quantified by a TSC reduction factor, defined as the ratio of the TSC at zero pressure to the lowest TSC typically attained at pressure factors around 0.5–0.6. Here the pressure factor is defined as the ratio of the nominal hoop stress induced by pressure to the yield strength (YS) of the pipe material. A number of numeric and experiment studies have reported a TSC reduction factor of 1.5–2.5. These studies generally focused on strain-based designed pipelines with evenmatching or overmatching welds, minimum heat affected zone (HAZ) softening, and a surface breaking flaw at the weld centerline or the fusion boundary. This paper examines the effects of pipe internal pressure on the TSC of girth welds under the premise of weld strength undermatching and HAZ softening. The interaction of biaxial loading and the local stress concentration at the girth weld region was quantified using full-pipe finite element analysis (FEA). The relationship between TSC and the internal pressure level was obtained under several combinations of weld strength mismatch and HAZ softening. Results from the FEA show that the effects of the internal pressure on the TSC are highly sensitive to the material attributes in the girth weld region. Under less favorable weld strength undermatching and HAZ softening conditions, the traditionally assumed reduction factor or 1.5–2.5 may not be applicable. Further, the location of tensile failure is found to depend on both the weld material attributes and the internal pressure. It is possible for the failure location to shift from pipe body at zero internal pressure to the girth weld at elevated internal pressure levels. The implications of the results for both girth weld qualification and integrity assessment are discussed.

Framework for Key Influences on Tensile Strain Capacity of Flawed Girth Welds

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Stijn Hertelé ◽  
Rudi Denys ◽  
Anthony Horn ◽  
Koen Van Minnebruggen ◽  
Wim De Waele
Keyword(s):  
Tensile Strain ◽  
Influence Factor ◽  
Weld Strength ◽  
Strain Capacity ◽  
Strain Behavior ◽  
Weld Geometry ◽  
Girth Welds ◽  
Tearing Resistance ◽  
Tensile Strain Capacity ◽  
Element Study

A key influence factor in the strain-based assessment of pipeline girth weld flaws is weld strength mismatch. Recent research has led to a framework for tensile strain capacity as a function of weld flow stress (FS) overmatch. This framework is built around three parameters: the strain capacity of an evenmatching weldment, the sensitivity of strain capacity to weld FS overmatch, and the strain capacity at gross section collapse (GSC). A parametric finite element study of curved wide plate (CWP) tests has been performed to identify the influence of various characteristics on each of these three parameters. This paper focuses on flaw depth, tearing resistance of the weld, stress–strain behavior of the base metal, and weld geometry. Influences of these characteristics are mostly found to be limited to one or two of the three framework parameters. A preliminary structure is proposed for equations that further develop the strain capacity framework.

Fatigue Design Data Derived From Full Scale Tests on 6”OD Pipe Girth Welds

2007 ◽  
Author(s):  
Per J. Haagensen ◽  
Hans Olav Knagenhjelm ◽  
Oddvin O̸rjasæter
Keyword(s):  
Fatigue Test ◽  
Test Data ◽  
Local Stress ◽  
Fracture Initiation ◽  
Full Scale ◽  
Published Data ◽  
High Quality ◽  
Design Data ◽  
Failure Initiation ◽  
Girth Welds

A literature survey of high quality girth welds intended for pipelines risers was carried out and the results are compared with full scale resonance fatigue test data on 6” pipes. The samples were made from 168.3×9.9mm (OD×WT) seamless pipes, each having two welds. Axial misalignments (hi-lo’s) and lack of penetration (LOP) defects were introduced in the test pipes to study the effects on the mean minus 2 stand, deviation design S-N curve that was calculated. Post failure examination of the welds was performed to determine the type and size of defects in the failure initiation area. Fracture mechanics calculations were carried out to determine the effect of defects on fatigue life. The test results were compared with published data on 6” pipes with high quality welds. The scatter in the fatigue test data was reduced when comparisons were based on the local stress at the point of fracture initiation. The implications for design rules of the findings in this work are discussed.

Remaining Collapse Capacity of Corroded Pipelines

2011 ◽  
Author(s):  
Qishi Chen ◽  
Mark Marley ◽  
Joe Zhou
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Wall Thickness ◽  
Numerical Models ◽  
Substantial Reduction ◽  
Assessment Method ◽  
Full Scale ◽  
Finite Element Models ◽  
Pipe Material ◽  
Corrosion Defects

It is known that, for given pipe material and diameter, collapse capacity of a plain pipe subjected to external pressure is proportional to the second or third power of wall thickness. In lieu of sophisticated numerical models and experimental data, conservative approaches such as those in which thickness losses at corrosion defects are extended to the entire circumference have been adopted in practices to assess the collapse resistance of corroded pipes. This reduced wall thickness is then used in the design equation of plain pipe to predict remaining collapse capacity. Such conservative assumptions result in substantial reduction of collapse capacity for pipelines with localized corrosion defects. During the course of a multiple-year PRCI research project, results of full-scale collapse tests and three-dimensional finite element analysis demonstrated that the reduction of collapse capacity was less than 10% for defects with a depth of 50% wall thickness, an axial length of one diameter and a circumferential width of half a diameter. These findings illustrated that the actual collapse capacity of corroded pipes is significantly higher than that estimated according to the conservative assumptions. This paper presents the development of a reliability-based, practical assessment method that allows remaining collapse capacity of corroded pipelines be determined based on defect size data obtained from in-line inspections. Work involved included characterization of corrosion defects, full-scale collapse tests, validation of finite element models using experimental data, analysis of parametric cases using finite element models, development of empirical equation based on experimental and numerical results, and calibration of partial safety factors which addressed the uncertainties associated with model error, load variation, and sizing inaccuracy of corrosion defects. Practical implications of the proposed assessment method were evaluated based on selected examples.

A Preliminary Strain-Based Design Criterion for Pipeline Girth Welds

2002 ◽  
Author(s):  
Yong-Yi Wang ◽  
David Rudland ◽  
Rudi Denys ◽  
David Horsley
Keyword(s):  
Strain Hardening ◽  
Design Criterion ◽  
Defect Size ◽  
Applied Strain ◽  
Full Scale ◽  
Weld Strength ◽  
Factors Affecting ◽  
Strain Capacity ◽  
Girth Welds ◽  
Strain Hardening Rate

The strain capacity of girth welds containing surface-breaking welding defects is examined through numerical analysis and experimental verification under a PRCI (Pipeline Research Council International) funded project. Some important insights on the various factors affecting the girth weld strain capacity are generated. The defect size is identified as one of the most important factors in determining strain capacity of a girth weld. Other factors, such as the strain hardening rate of the pipe and weld metals, weld strength mismatch, fracture toughness, and weld cap height, can play a significant role if the defect size is within certain limits. It is discovered that the girth weld response to the remotely applied strain may be characterized by a three-region diagram. For a given set of defect size and weld strength mismatch conditions, the crack driving force may be bounded, unbounded, or gradually changing, with respect to the remotely applied strain. A set of parametric equations is developed that allow the computation of allowable strains with the input of defect depth, defect length, CTOD toughness, and weld strength mismatch. The comparison of the developed strain criteria with full-scale bend tests and tensile-loaded CWPs (curved wide plates) shows the criteria are almost always conservative if lower bound CTOD toughness for a given set of welds is used. However, the criteria can significantly underpredict strain capacity of girth welds with short defects. Although defect length correction factors were added to the strain criteria based on the comparison of axisymmetric finite element (FE) results and full-scale bend test results, a more thorough investigation of the effects of defect length on strain capacity is needed. Future investigation that incorporates the finite length defects is expected to greatly reduce the underprediction. The influence of other factors, such as strain hardening rate, should be further quantified.

Framework for Key Influences on Tensile Strain Capacity of Flawed Girth Welds

2013 ◽  
Author(s):  
Stijn Hertelé ◽  
Rudi Denys ◽  
Anthony Horn ◽  
Koen Van Minnebruggen ◽  
Wim De Waele
Keyword(s):  
Flow Stress ◽  
Tensile Strain ◽  
Influence Factor ◽  
Weld Strength ◽  
Strain Capacity ◽  
Weld Geometry ◽  
Strain Behaviour ◽  
Girth Welds ◽  
Tearing Resistance ◽  
Tensile Strain Capacity

A key influence factor in the strain-based assessment of pipeline girth weld flaws is weld strength mismatch. Recent research has led to a framework for tensile strain capacity as a function of weld flow stress overmatch. This framework is built around three parameters: the strain capacity of an evenmatching weldment, the sensitivity of strain capacity to weld flow stress overmatch and the strain capacity at gross section collapse. A parametric finite element study of curved wide plate tests has been performed to identify the influence of various characteristics on each of these three parameters. This paper focuses on flaw depth, tearing resistance of the weld, stress-strain behaviour of the base metal, and weld geometry. Influences of these characteristics are mostly found to be limited to one or two of the three framework parameters. A preliminary structure is proposed for equations that further develop the strain capacity framework.

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