Wide Plate Tension Test Research Articles

Combined numerical-experimental framework for strain based design and flaw assessment of girth welds

An increasing number of transmission pipelines have to be installed and operated in harsh conditions, due to the diminishing reserves of exploited fossil fuel sources. Under certain environment related circumstances, longitudinal plastic strains are imposed. When tensile, these may induce failure in girth welds in conjunction with the inevitable presence of weld defects. A large number of factors related to environment, material, geometry and operating conditions influence the tensile strain capacity and, hence, the acceptability of girth weld flaws. Therefore, a project specific development of guidelines in this strain based context is recommended. This paper provides systematic frameworks on (a) how to design pipelines under strain based conditions, and (b) how to assess girth weld flaws that were detected using non destructive testing. Attention is given to several technical and economical aspects related to the selection and qualification of pipe and weld metals, and to the evaluation of flaw acceptability. Both frameworks comprise a combined experimental-numerical approach, collecting project development reports from literature with research carried out at Soete Laboratory. Concretely, four in-house realizations are adopted: the UGent equation for strain capacity, the curved wide plate tension test, the UGent stress-strain equation and a finite element model of full scale pressurized pipe tension testing. The proposed frameworks aim to facilitate in performing thorough and economically justifiable strain based design and assessment processes.

Design of a (mini) wide plate specimen for strain-based weld integrity assessment

Wide plate tension tests are commonly executed to investigate the integrity of defective weldsunder a uniaxial load. The specimen can be flat or curved, depending on the geometry from which it hasbeen extracted (plate or pipe). Despite its usefulness, the design of the (curved) wide plate test is still notstandardized up-to-date. This paper compares two specimen designs with a different length-to-width ratiothrough finite element analysis, using a design-of-experiments approach to account for different influentialfactors. The results reveal significant differences between the interpretation of tests with net sectioncollapse and gross section collapse, promoted by weld strength overmatch. Further, both investigateddesigns tend to provide similar estimates of failure mode, strain capacity and crack driving force. Hence,the shorter specimen is considered an acceptable alternative to the slightly more representative longerspecimen.

Study on Fracture Toughness Evaluation by centre-notched small size specimen for heavy-thick steel plates

In order to evaluate the fracture toughness of steel plates, centre-notched wide plate tension test is usually conducted using 400 mm width specimens. However, a large testing machine and huge expenditures are necessary in the case of 50–90 mm heavy-thick steel plates. In this paper, centre-notched small size tension test is proposed to evaluate the fracture toughness of heavy-thick steel plates by a simplified method. That is, centre-notched small size tension test specimens using the steel plate thickness (70 mm) as the specimen — width were made and employed for the tests, and the test results were evaluated and investigated.

Crack Opening Displacement Characteristics of Welded Joint on Low Temperature Service Steel for LPG Storage Tanks

With a view mainly to safety considerations of LPG storage tanks, V-notch Charpy, three point bending COD and wide plate tension tests were undertaken on four plate materials and thirteen weld metals welded by shielded metal arc, submerged arc and automatic TIG welding processes. In respect of fracture toughness of the weld metals, some correlation was seen between V-notch Charpy absorbed energy and three point bending COD value, both these values being found to be particularly high for Ni free 1.4Mn-Ti-B type weld metal. For the base metal, Ti-added Al-killed steel showed good toughness in the heat-affected zone by both V-notch Charpy and through-thickness notched three point bending COD tests. This latter test applied to specimens with surface notch, however, yielded a low COD value within 400μm of fusion line for all the metals tested and for all values of heat input. Nonetheless, tensile tests using wide plate welded specimens with artificial defects located in the region of lowest toughness proved that, from considerations of fracture mechanics, all the joints possessed ample strength against brittle fracture initiation. It should thus appear that evaluation of welded joints may not always be valid when based on local three-point bending COD test, and that it should be more practical to assess the safety of such welded joints by wide-plate tests.

極低温用４０％Ｎｉ系溶接金属に関する研究 ＩＩ 突合せ溶接継手の静的引張強さ

The 40 % Ni type weld metal is undermatching for 9 % Ni steel with regard to static tensile strength. In this case, the tensile strength of welded joints is influenced remarkably by strength of weld metal and base metal, and by the welding conditions such as heat input, groove shape and so on. Welded joint performance tests were carried out, in this report, to investigate the static tensile strength of MIG welded joints of 9 % Ni steel with 40 %Ni type weld metal. Main experimental results are summerized as follows:(1) The transverse tensile strength of welded joints increases with decreasing relative thickness (average width of weld metal/plate thickness). Therefore, it is beneficial, both for increasing strength and for improving efficiency, to narrow the groove as far as possible according to the plate thickness.(2) The transverse tensile strength of welded joints decreases with increasing welding heat input; but, in case of vertical position, it is possible to obtain 66.8 kg/mm2 (95 Ksi) or more within heat input of 35 KJ/cm.(3) It may be considered that, in case of multi-pass weld metal, the strength of intermediate pass weld metal has increased due to the precipitation hardening caused by the fine carbides of molybdenum and chromium.(4) It was confirmed by center-notched wide plate tension test that the weld metal and fusion zone possess a satisfactory cryogenic fracture toughness as all the fracture occurred in a high-stress ductile manner with fracture stress equal to the cryogenic strength of the 40 % Ni type weld metal.

厚板80kg/mm<SUB>2</SUB>高張力鋼溶接部の脆性破壊発生特性(第3報)

Effects of residual stress and repair welding on the brittle fracture initiation in weld fusion line of the manual arc welded joints for 80kg/mm2 high strength steel were investigated using the wide plate tension test specimen with an angular distortion and a surface notch. And the results were analyzed by application of the fracture mechanics. The main results are summarized as follow:(1) The maximum residual stress of T-shaped welded joints is about 50kg/mm2 in the direction of weld line. That of repair weld zone is about 35kg/mm2 in the direction of right angle with weld line and is about 50kg/mm2 in the direction of weld line.(2) The brittle fracture strength of the T-shaped welded wide plate specimen with a surface notch, is lower than that of the transversely welded W(1) specimen. The test results with the specimen in which residual stress is superimposed can be adjusted quantitatively by taking stress intensity factor KR of Eq. (4) into consideration. The fracture toughness obtained by the above procedure agrees with that of a transversely welded W(1) specimen without residual stress.(3) The fracture toughness of the repair welded wide plate specimen almost equals to the minimum values of stress relieved welded joints when the notch tip is heated to the temperature range, 300-550°C, in repair welding. Therefore, the fracture stress of the repair welded joints is extremely lowered if defects remain in the fusion line. But it is as high as the fracture stress of the transversely welded W(1) joints as welded, when the maximum temperature of notch tip is below 250°C in repair welding.(4) It is important that the maximum heat temperature of fusion line is below 250°C in repair welding. Removal ofhydrogen by heating is effective, but its temperature should be below 250°C.(5) We calculated relation between fracture stress and crack length of T-shaped welded joint and repair weld zone for welded structure.

Consistency of Critical COD and a Proposed Method of ρ+c Determination

The three-point bending COD test with clip gauge technique is a promising method of determining the toughness of structural steels in terms of the modern concept of fracture mechanics. The consistency of the critical COD value has been demonstrated by many investigators. The present authors supplement here some information in this aspect of problem, viz, the effect of notch acuity, the thickness insensitivity, comparison between small sized bending test and deeply notched wide plate tension test, and so on.A simple method of converting the critical COD to the value of ρ+c is experimentally established. It is supported by the fact that the critical COD divided by the yield strength is proportional to the fifth power of the absolute temperature. As an example of practical application, the welded-and-notched wide plate tension test is successfully analysed by the ρ+c concept. The ρ+c value used in the analysis is one converted from the critical COD value measured by simple testing.

Gas Metal Arc Welding of 9% Nickel Steel Using Ferritic Filler Metal Used for Building LNG Transport Tanker

An investigation has been carried out to realize commercial application of welding of 9% Ni steel using ferritic filler metal having chemical composition similar to that of base steel, which was developed by the authors.The weldments having excellent notch impact properties and superior strength were obtained by gas metal arc welding.And the brittle fracture initiation characteristics before general yielding of the weldment was surveyed both experimentally by three kinds of the large scale type tests such as Welded Wide Plate Tension Tests, W-I Type Notched and Welded Wide Plate Tension Test and Deep Notch Test and theoretically based on the fracture mechanics.The safety to brittle fracture before general yielding was confirmed especially at LNG temperature.