Ring Expansion Testing Innovations: Hydraulic Clamping and Strain Measurement Methods

2020 ◽  
Author(s):  
William Walsh ◽  
Sandeep Abotula ◽  
Bharath Konda
Keyword(s):  
Tensile Testing ◽  
Point Contact ◽  
Ring Expansion ◽  
Hydraulic Pressure ◽  
Stress Strain ◽  
Line Pipe ◽  
Pipe Surface ◽  
Expansion Test ◽  
Round Bar ◽  
Dial Indicator

Abstract Ring expansion testing is one of the three accepted methods in API 5L for the measurement of yield strength for line pipe. The other two are flattened-strap tensile testing and round-bar tensile testing. A novel-concept ring expansion test machine has recently been commissioned which uses hydraulic pressure to clamp the top and bottom pressure-reacting plates rather than a traditional bolting arrangement. The benefit of hydraulic clamping is vastly reduced set-up times. This paper describes the design approach and the pitfalls that were overcome in commissioning the ring expansion test unit. Expansion measurements are taken using two different methods: a chain extensometer and an LVDT with a band wrapping the circumference of the pipe. Both approaches are used simultaneously to generate and compare two stress-strain curves for one pressure test. In addition, a 3-Point contact approach is developed to determine the hoop strain during pipe expansion. The 3-point contact approach is an attempt to infer the full hoop expansion behavior by measuring the radius change over a segment of the circumference. The device has two rollers which contact the pipe surface while a dial indicator midway between measures the radius change. As the pipe expands, the rollers maintain contact with the pipe surface while the dial indicator records the change in radius. Tests are performed on HFI, SAWL, and SAWH pipes ranging in outer diameter from 20-inch (508 mm) to 48-inch (1219 mm) and wall thicknesses from 0.375-inch (9.5 mm) to 0.969-inch (24.4 mm). The differences in the stress-strain behavior of these pipe forms are described and related to the residual-stress profiles generated by their respective manufacturing operations. The comparison to flattened-strap and round-bar tensile results are presented in a companion paper. The results of the 3-Point contact approach show that the radius change during early stages of expansion are not uniform around the pipe circumference and different patterns are observed in the HFI, SAWL, and SAWH pipe forms.

Measurement of Mechanical Properties on Line Pipe: Comparison of Different Methodologies

2014 ◽  
Author(s):  
Steven Cooreman ◽  
Dennis Van Hoecke ◽  
Martin Liebeherr ◽  
Philippe Thibaux ◽  
Mary Yamaguti Enderlin
Keyword(s):  
Mechanical Properties ◽  
Yield Strength ◽  
Tensile Tests ◽  
Ring Expansion ◽  
Isotropic Hardening ◽  
Forming Process ◽  
Element Analysis ◽  
Line Pipe ◽  
Expansion Test ◽  
Round Bar

Line pipe manufacturers always have to verify the mechanical properties on pipe to make sure that the pipe meets the requirements specified by the standard and/or customer. This involves measurement of mechanical properties along the hoop direction. The most accurate way to do so is by performing a ring expansion test, which, however, requires dedicated tools. The two other methodologies consist of standard tensile tests on either non-flattened round bar samples or so called ‘flattened tensile samples’. Round bar samples have the disadvantage that only part of the pipe’s wall thickness is considered. Furthermore they can only be used in case of larger OD/t ratios. Tests on flattened samples, on the other hand, require a flattening operation, which induces additional plastic deformation. However, this flattening operation is not standardized. Moreover, it was observed that the mechanical properties — especially the yield strength — resulting from tensile tests on flattened samples largely depend on test parameters such as residual deflection, extensometer position, flattening procedure, etc. Most manufacturers prefer to test flattened samples, because sample preparation is straightforward and cheap. Moreover it only requires a standard tensile bench. An extensive FEA (Finite Element Analysis) study was launched to investigate the influence of those parameters on the measured yield strength. The applied FEA methodology consists of three steps. First the complete pipe forming process is modeled (in a simplified way). Next a pipe sample is flattened. Finally a tensile sample is cut from the flattened pipe sample and loaded in tension. The mechanical material behaviour is described by a combined kinematic-isotropic hardening model, which allows taking into account the Bauschinger effect. The results are also compared to simulations of ring expansion tests and tests on round bar samples. Next a dedicated experimental test campaign was performed to verify the results of FEA. Results of ring expansion tests are compared to results obtained on round bar samples and flattened tensile samples. The results of this study have shown that the applied methodology significantly affects the measured yield strength. Moreover tests on insufficiently flattened samples could considerably underestimate the actual yield strength on pipe. Finally some guidelines are provided to improve the reproducibility of the measured yield strength when using flattened samples.

The Effect of Sample Flattening on Yield Strength Measurement in Line Pipe

2010 ◽  
Author(s):  
Dave G. Crone ◽  
Laurie E. Collins ◽  
Yankui Bian ◽  
Paul Weber
Keyword(s):  
Tensile Strength ◽  
Yield Strength ◽  
Tensile Testing ◽  
Measurement Techniques ◽  
Base Material ◽  
Ring Expansion ◽  
Tensile Specimen ◽  
Forming Process ◽  
Line Pipe ◽  
Ongoing Research

Tensile testing is a key part of the qualification process of Line Pipe. When qualifying pipe products various items are considered when tensile testing; Yield Strength (YS), Ultimate Tensile Strength (UTS), Percent Elongation (%EL), and the Yield Strength to Tensile Strength Ratio (Y/T) are all important. Of these, the YS is the most critical and yet the most sensitive to both preparation and measurement techniques. During the pipe forming process, the base material is plastically formed into a curved shape, and then welded into the final product. The Transverse to Pipe Axis (TPA) tensile specimen removed for testing is curved and must be flattened prior to testing. The flattening process is varied in many facilities and the standards to which testing is conducted are not specific enough to ensure uniformity of procedures. ASTM acknowledges flattening processes and the degree of flatness “may affect test results”, though no guidance is given. This paper will provide an overview of ongoing research efforts, concerning the measurement of the Yield Strength of TPA tensile specimens and its relationship to curvature and flattening methods, prior to testing. By comparing flattened strap tests, to round bar and ring expansion tests, it is shown that the flattened strap test provides a conservative estimate of the actual YS of the pipe.

Comparison Between Yield Strength Results Obtained From Methods Using Both Flattened and Non-Flattened Specimens

2020 ◽  
Author(s):  
Pratham Nayyar ◽  
Dimitris Dimopoulos ◽  
William Walsh
Keyword(s):  
Yield Strength ◽  
Large Diameter ◽  
Longitudinal Direction ◽  
Ring Expansion ◽  
Test Methods ◽  
Production Test ◽  
Pipe Axis ◽  
Line Pipe ◽  
Expansion Test ◽  
Weld Properties

Abstract Tensile properties of API 5L large diameter pipes are typically determined with the use of full thickness flattened strap samples extracted in the transverse direction with respect to the longitudinal pipe axis (TPA) [1, 2, 3, 4]. It has been well established that the process of sample flattening has a significant influence on determination of the yield strength of the pipe [5, 6]. The flattening process is sensitive to a number of variables such as method of flattening, equipment used, number/sequence of strokes, and operators conducting the flattening. As a result, issues with repeatability are frequently encountered and despite several efforts, the industry lacks any type of official standard for universal use. Historically, the industry has been focused on ensuring that the actual strength of pipes was safely higher than the specified minimum. Recently, there has been interest to also establish an upper limit on pipe strength particularly in the longitudinal direction with respect to the pipe axis (LPA) in order to avoid under matching between pipe and girth weld properties. These new requirements create the need for enhanced process control to minimize the variation due to flattening. Samples obtained from longitudinally welded (SAWL) and helically welded (SAWH) seam Grade X70M line pipe of various nominal wall thickness to diameter (t/D) ratios were flattened using different procedures, measured for curvature, and tensile tested, all in controlled laboratory environments with minimized repeatability variation. Special attention was given to the definition and measurement of different types of curvatures observed through the range of different t/D ratios and effort was made to assess criteria for curvature measurement prior to testing. Additionally, non-flattened specimens were tensile tested using round bar and full ring expansion test methods, and a comparison between the results obtained from both flattened and non-flattened specimen methods was made. The sample transverse yield strength results confirmed the expected variation between samples flattened by different methods. In addition, a much greater variation was observed when comparing the yield strength results between flattened and non-flattened samples. Considerations of extending the use of non-flattened specimens as a production test and benefits or limitations associated with such practice are discussed.

Investigation of the Stress-Strain Behaviour of Large-Diameter X100 Linepipe in View of Strain-Based Design Requirements

2008 ◽  
Author(s):  
Andreas Liessem ◽  
Jens Schro¨der ◽  
Martin Pant ◽  
Gerhard Knauf ◽  
Steffen Zimmermann ◽  
...  
Keyword(s):  
Circumferential Stress ◽  
Ring Expansion ◽  
Ground Movement ◽  
Pipe Material ◽  
Stress Strain ◽  
Line Pipe ◽  
Cold Forming ◽  
Strain Capacity ◽  
Strain Behaviour ◽  
Experimental Step

The use of high strength steels is considered as the best economical option to transport large gas volumes under high pressure from remote areas to the market. Exploration of new energy resources located in areas of complex ground and ambient climate imposes strict requirements on pipeline material and design. One of the major research issues in such areas is differential ground movement, which may be associated with large longitudinal straining in addition to plastic circumferential elongation. Hence, common design principles need thorough re-consideration, notably with respect to strain hardening properties of both base metal and girth welds. The present paper addresses several characteristics of axial and circumferential stress-strain behaviour as it is encountered in high-grade UOE line pipe. Two delivery states are taken into account, namely the “as expanded” as well as the “as coated” state. In a first experimental step, the effect of thermal cycle of the anti-corrosion coating process on stress-strain behaviour is simulated subjecting pipe material to temperatures in the range of 180° up to 250° C. In a second experimental step, stress-strain behaviour in both axial and transverse direction is mapped along the pipe production process in order to assess when and to what extent plastic strain capacity is lost during cold forming. The experimental work is complemented by instrumented ring expansion tests and instrumented burst tests. In a third future step, stress-strain information measured in both directions will be analyzed using a theoretical model based on Hill’s plasticity in order to clarify in which way circumferential stress-strain behaviour may impose constraints on strain capacity of axial direction. Within the scope of this paper, first and foremost, underlying principles are outlined and discussed and indications with respect to modelling implications given. Based upon these three sequential investigatory steps, it will be possible to draw conclusions with respect to stress-strain behaviour of parent material and the pipe forming process and to show that unfavourable effects triggered by coating do not show within the structure while they might do in material tests.

Nonlinear Harmonic Monitoring of Gouged Dents in Pipeline Specimens Under Cyclic Loading

2006 ◽  
Author(s):  
Alfred E. Crouch ◽  
G. Graham Chell
Keyword(s):  
Cyclic Loading ◽  
Signal Strength ◽  
Hazardous Materials ◽  
Line Pipe ◽  
Pipe Surface ◽  
Depth Data ◽  
Southwest Research Institute ◽  
The Us ◽  
Pressure Changes ◽  
Research Institute

The only in-line inspection technology commercially available for quantitative evaluation of gouged dents is the geometry pig which cannot discriminate between gouged and smooth dents and has no sensitivity to re-rounded dents. Southwest Research Institute® (SwRI®), has been funded by the US Pipeline and Hazardous Materials Safety Administration (PHMSA) and the Gas Research Institute (GRI) through the Pipeline Research Council International (PRCI), to determine the capability of the nonlinear harmonic (NLH) method to characterize the severity of gouged dents, including those that have been re-rounded by internal pressure. This paper describes the NLH method and presents a summary of results from previous work involving burst tests of gouged dents in 24” pipe as a precursor to the current work that involves experiments with four pressure chambers made from 12-inch line pipe under cyclic pressure changes. In each case, internal scanner hardware, driven from outside the pipe, deployed NLH probes against the pipe inner surface, the gouges being on the outer surface. Analysis of the mapped NLH signals on the inner pipe surface revealed residual strain patterns in the pipe and the strain anomalies produced by gouging. The strain anomalies clearly indicated the presence of the gouges on the outside surface, even when they had re-rounded. The signal maps also indicated the length and width of the gouges whereas the signal strength indicated the residual depth. Data are presented showing that the NLH method is capable of ranking the severity of pipeline gouged dents and their propensity for failure under cyclic loading.

scholarly journals Length Scale and Aging Effect on the Mechanical Properties of a 63Sn-37Pb Solder Alloy

2000 ◽  
Author(s):  
T. Jesse Lim ◽  
Wei-Yang Lu
Keyword(s):  
Ultimate Strength ◽  
Tensile Testing ◽  
Failure Strain ◽  
Aging Effect ◽  
Uniaxial Tensile ◽  
Strain Response ◽  
Stress Strain ◽  
Uniaxial Tensile Testing ◽  
Aging Conditions ◽  
Strain Responses

Abstract In this work, uniaxial tensile testing of a 63Sn-37Pb alloy with different specimen sizes and aging conditions had been carried out. Although the stress-strain responses of different specimen sizes and aging conditions differs, the ultimate strength of the specimens with 16 hours, 100°C aging are similar for the sizes tested. The specimens with 25 days, 100°C aging have different stress-strain response with different sizes, and have a lower ultimate strength and higher failure strain compared to 16 hours, 100°C aging specimens.

Introduction to Tensile Testing

2004 ◽  
pp. 1-12
Keyword(s):  
Plastic Deformation ◽  
Data Analysis ◽  
Uniaxial Tension ◽  
Tensile Testing ◽  
Tensile Tests ◽  
True Stress ◽  
Stress Strain ◽  
Engineering Applications ◽  
Test Methodology ◽  
Ultrasonic Techniques

Abstract Tensile tests are performed for several reasons. The results of tensile tests are used in selecting materials for engineering applications. Tensile properties often are used to predict the behavior of a material under forms of loading other than uniaxial tension. Elastic properties also may be of interest, but special techniques must be used to measure these properties during tensile testing, and more accurate measurements can be made by ultrasonic techniques. This chapter provides a brief overview of some of the more important topics associated with tensile testing. These include tensile specimens and test machines; stress-strain curves, including discussions of elastic versus plastic deformation, yield points, and ductility; true stress and strain; and test methodology and data analysis.

Standardization of Flattening Procedure of Transverse to Pipe Axis Strap Tensile Samples

2018 ◽  
Author(s):  
M. Rashid ◽  
S. Chen ◽  
L. E. Collins
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Tensile Testing ◽  
Standard Procedure ◽  
Large Diameter ◽  
Spring Back ◽  
Pipe Axis ◽  
Element Analysis ◽  
Line Pipe ◽  
Experimental Approaches

Tensile testing on large diameter line pipe is generally done using strap samples obtained in the transverse to pipe axis (TPA) orientation of a pipe. The strap samples are then flattened and machined prior to testing. Although the standardized tensile testing is well documented, the variability in the reported TPA tensile properties of the same material tested within a lab or at different labs has always been an issue. Recent work conducted at EVRAZ NA research lab has identified flattening as the main source of the variability in reported yield strength (YS) values for line pipe. The lack of a standard procedure for flattening TPA strap samples is a major obstacle to obtaining consistent results. Therefore, the main objective of this current study was to establish a standardized flattening procedure for TPA strap samples. Both finite element analysis (FEA) and experimental approaches were adopted. Various flattening methods and fixtures were studied. Extensive flattening experiments were conducted on TPA samples from different line pipe products. Results showed that the spring back after flattening in a TPA sample is different for pipes with different gauge and grades. It was established that consistent flattening can be achieved using appropriate fixtures for differerent ranges of tubular products defined by grade, diameter and gauges. Evaluation of the flattening fixture designs and experimental results are discussed in this paper.

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