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 of Ring Expansion vs Flat Tensile Testing for Determining Linepipe Yield Strength

1996 ◽  
Author(s):  
Wahib E. Saikaly ◽  
William D. Bailey ◽  
Laurie E. Collins
Keyword(s):  
Standard Deviation ◽  
Yield Strength ◽  
Yield Stress ◽  
Tensile Testing ◽  
Accurate Determination ◽  
Tensile Tests ◽  
Ring Expansion ◽  
Tensile Specimen ◽  
Ring Test ◽  
Ring Testing

Ring expansion testing has been compared to conventional tensile testing as a means to evaluate the circumferential yield strength of pipe products. It was found that ring expansion testing provides a more accurate determination of hoop yield stress than tensile testing of flattened pipe samples. In addition, ring testing was found to be more sensitive to the metallurgical condition of the steel. Tests were conducted on ERW and Spiral pipes. Different grades and diameter to thickness (D/t) ratios were evaluated. In comparison to tensile testing on flattened specimens, ring expansion tests gave: a) higher yield strength; and b) reduced standard deviation in test data. The difference in yield strength measured by ring and tensile tests increased with increasing grade and lower D/t. The higher yield strength measured in the ring test is a result of reducing the Bauschinger effect associated with flattening tensile samples. The reduced standard deviation is due to the elimination of flatness and machining variations that occur on a flattened tensile specimen. It was concluded that ring testing provides a true measure of pipe circumferential yield stress.

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.

Quantitative Analysis of Pre-Strain Effect on Mechanical Properties of the Austenitic Stainless Steel

2014 ◽  
Author(s):  
Zhiwei Chen ◽  
Caifu Qian ◽  
Guoyi Yang ◽  
Xiang Li
Keyword(s):  
Experimental Data ◽  
Mechanical Properties ◽  
Tensile Strength ◽  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Yield Strength ◽  
Tensile Testing ◽  
Control Mode ◽  
Strain Effect ◽  
Strain Control

The test of austenitic stainless steel specimens with strain control mode of pre-strain was carried out. The range of pre-strain is 4%, 5%, 6%, 7%, 8%, 9% and 10% on austenitic stainless steel specimens, then tensile testing of these samples was done and their mechanical properties after pre-strain were gotten. The results show that the pre-strain has little effect on tensile strength, and enhances the yield strength more obviously. According to the experimental data, we get a relational expression of S30408 between the value of yield strength and pre-strain. We can obtain several expressions about different kinds of austenitic stainless steel by this way. It is convenient for designers to get the yield strength of austenitic stainless steel after pre-strain by the value of pre-strain and the above expression.

Effects of Aging on the Mechanical Properties of Pipeline Steels

2008 ◽  
Author(s):  
Martin Hukle ◽  
Brian Newbury ◽  
Dan Lillig ◽  
Jonathan Regina ◽  
Agnes Marie Horn
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Uniform Elongation ◽  
Weld Line ◽  
Base Material ◽  
Pipeline System ◽  
Line Pipe ◽  
Pipeline Steels ◽  
Reduction Of Area ◽  
Effects Of Aging

The intelligent design of a given pipeline system intended for operation beyond the elastic limit should incorporate specific features into both the base material (line pipe) and girth weld that enable the affected system to deform safely into the plastic regime within the intended strain demand limits. The current paper focuses on the mechanical properties known to influence the strain capacity of the base material (i.e., line pipe steel independent of the girth weld). Line pipe mechanical properties of interest include: longitudinal yield strength, tensile strength, yield to tensile strength ratio, reduction of area, elongation and uniform elongation. Of particular interest (in consideration of the conventional thermally applied corrosion protection coating systems to be employed), are the longitudinal mechanical properties in the “aged” condition. The present study investigates six (6) different pipeline steels encompassing grades X60 (415 MPa) to X100 (690 MPa), and includes both UOE Submerged Arc Welded - Longitudinal (SAW-L) and seamless (SMLS) forming methods.

scholarly journals A Study on Fiber Laser Welding of High-Manganese Steel for Cryogenic Tanks

Processes ◽  
2020 ◽  
Vol 8 (12) ◽  
pp. 1536
Author(s):  
Jaewoong Kim ◽  
Jisun Kim ◽  
Changmin Pyo
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Yield Strength ◽  
Laser Welding ◽  
Base Material ◽  
Manganese Steel ◽  
High Manganese ◽  
Fiber Laser Welding ◽  
High Manganese Steel ◽  
Welding Part

As the environmental regulations on ship emissions by the International Maritime Organization (IMO) become stricter, the demand for a ship powered by liquefied natural gas (LNG) is rapidly increasing worldwide. Compared to other materials, high-manganese steel has the advantages of superior impact toughness at cryogenic temperatures, a low thermal expansion coefficient, and a low-cost base material and welding rod. However, there is a limitation that the mechanical properties of a filler material are worse than those of a base material that has excellent mechanical properties. To solve these shortcomings, a basic study was performed to apply fiber laser welding with little welding deformation and no filler material to high-manganese steel. The relationship between laser welding parameters and penetration shapes was confirmed through cross-section observation and analysis by performing a bead on plate (BOP) test by changing laser power and welding speed, which are the main parameters of laser welding. In addition, the welding performance was evaluated through mechanical property tests (yield strength, tensile strength, hardness, cryogenic impact strength) of a welding part after performing the high-manganese steel laser butt welding experiment. As a result, it was confirmed that the yield strength of a high-manganese steel laser welding part was 97.5% of that of a base metal, and its tensile strength was 93.5% of that of a base metal.

Influence of Solution Treatment on Atomic Diffusion and Mechanical Properties of AZ80 Magnesium Alloy

2012 ◽  
Vol 479-481 ◽  
pp. 27-30
Author(s):  
Ju Mei Zhang ◽  
Zhi Hu Wang ◽  
Wan Chang Sun ◽  
Li Bin Niu
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Magnesium Alloy ◽  
Yield Strength ◽  
Grain Boundaries ◽  
Tensile Testing ◽  
Solution Treatment ◽  
Solution Time ◽  
Atomic Diffusion ◽  
Az80 Magnesium Alloy

The atomic diffusion and mechanical properties of as-cast AZ80 magnesium alloy after solution treatment at different time were studied by OM,SEM,EDS as well as tensile testing. The results show that the coarse β-Mg17Al12 phase distributed along the grain boundaries as net microstructure is almost dissolved after solution treatment, and the content of Al that in the α-Mg matrix is well distributed with the solution time prolonged. Because of the β-Mg17Al12 phase reducing and granulating, the function of precipitates phase strengthening was depressed and the hardness (HB) of alloy dropped obviously. However, the tensile strength(σb ) and elongation(δ) enhanced remarkably and the yield strength (σ0.2) decreased slightly.

The Effect of Pre-Strain and Strain Aging on Properties of X100 Line Pipe

2013 ◽  
Vol 690-693 ◽  
pp. 2270-2274
Author(s):  
Qiu Rong Ma ◽  
Hong Da Chen ◽  
Yan Hua Li ◽  
He Li
Keyword(s):  
Tensile Strength ◽  
Impact Toughness ◽  
Yield Strength ◽  
Tensile Properties ◽  
Aging Temperature ◽  
Strain Aging ◽  
Longitudinal Direction ◽  
Line Pipe ◽  
Toughness Test ◽  
The Impact

Tensile and impact toughness test on X100 line pipe with different pre-strain at different aging temperature were conducted to study the effect of pre-strain and aging temperature on properties of X100 line pipe. The result shows that yield strength and tensile strength of X100 line pipe would increase significantly with the introduction of pre-strain, while the impact toughness would decrease significantly. Effect of strain aging on tensile properties of X100 line pipe are more significantly. The yield strength, and tensile strength would increase significantly with the introduction of strain aging both transversal and longitudinal direction.

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.

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.

Tensile Properties and Microstructure of Butt Weld of Q235A Steel Made by Wet Welding Process

2011 ◽  
Vol 337 ◽  
pp. 448-451 ◽  
Author(s):  
Hong Tao Zhang ◽  
Wen Jie Jiang ◽  
Ji Cai Feng ◽  
Shi Sheng Zhong
Keyword(s):  
Tensile Strength ◽  
Tensile Test ◽  
Tensile Properties ◽  
Base Material ◽  
Welding Process ◽  
Tensile Specimen ◽  
Cored Wire ◽  
Butt Weld ◽  
Welding Processes ◽  
Rolled Plates

The effect of underwater wet welding processes with flux-cored wire on tensile properties and microstructure of Q235A steel was studied. Rolled plates of 8 mm thickness have been used as the base material for preparing single pass butt welded joints. OM and SEM were used to analyze the microstructure of the joint and the fractography of the tensile specimen. Tensile test showed that the fracure was occured at base metal and tensile strength could reach 415Mpa.

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