Effect of Post-Weld Heat Treatment Conditions on Mechanical Properties, Microstructures and Nonductile Fracture Behavior of SA508 Gr.1a Thick Weldments

This study analyzes the effects of post-weld heat treatment (PWHT) on the mechanical properties and microstructures of SA-508 Gr.1a welds and proposes a new PWHT exemption criterion based on nonductile fracture evaluation considering welding residual stress. The welding coupons were prepared with submerged-arc welding, gas-tungsten arc welding, and shielded-metal arc welding, using ferritic steel, SA-508 Gr.1a. The microstructure of the heat-affected zone (HAZ) was analyzed using optical microscopy, electron-back-scatter diffraction and Vickers hardness testing. The mechanical properties of the welds were evaluated by uniaxial tensile test, transverse side bend test, Charpy V-notch impact test and side bend test. Bainite and ferrite structures formed mainly in the HAZ, and the grain size became coarser with proximity to the surface and fusion line. The mechanical properties did not depend strongly on PWHT, weldment thickness or welding techniques, and they satisfied the welding procedure qualification test specified in the ASME Boiler & Pressure Vessel code. Welding residual stresses were considered in assessing structural integrity using nonductile fracture evaluation. A margin of safety against nonductile fracture with residual stress was calculated for Korean Standard Nuclear Power Plant steam-generator welds, using its design parameters and operating conditions, and this safety margin is suggested as an acceptance criterion for residual stress for exemption from PWHT. Graphic abstract

Four Point Bend Test of 5LPP – Concrete Coated Pipe

The objective of this paper is to present a 4-point bend test of 5LPP (Five Layer Polypropylene) concrete coated pipe. This is the first of its kind of bend test for a complex coating combination of 5LPP and concrete layers. The bend tests have been carried out to simulate S-Lay installation loading conditions to assess the coating integrity of the pipeline during installation. This paper reports the test arrangements including instrumentation, load schedule, test procedure and the challenges involved. Finally, the preliminary results and conclusions of the tests are documented. Two separate full scale four-point bend tests are carried out to study the behavior of the 5LPP concrete coated pipe. The purpose of the first test is to understand the complex behavior of the 5LPP/CWC coated test pipe and validate previously made industry standard assumptions regarding the calculated coated joint stiffness. The purpose of the second test is to observe the coating integrity of the test joint and slippage behavior due to the simulated installation conditions (overbend and sagbend bending moments and/or corresponding curvatures). The nonlinear moment-curvature for the concrete coated pipe is estimated based on an analytical approach taking into consideration plane bending theory and slippage behavior of the coating layers. The moment-curvature is used to prepare the load schedule for the tests. The test string consists of a test joint (40ft) welded to half joints at the ends. The bend test is performed using industry established full scale 4-point bend test arrangements. A global finite element model is used to simulate the tests using the analytical moment-curvature of the concrete coated pipe. The stiffness of the test pipe is calculated using the first bend test and compared against the analytical stiffness. The second test is carried out by applying loads corresponding to an estimated maximum overbend bending moment and then the test string is unloaded and rebent in opposite direction by applying loads corresponding to an estimated maximum sagbend bending moment. The results of the second test are documented at each load step and the integrity of the coating is measured against specified concrete coating damage criteria for tension as well as compression. Finally, field observations from the actual installation operation are compared against the bend test results. Conclusions are presented to address various aspects of concrete coated pipe for S-Lay installations.

Idiopathic scoliosis and associated factors among school children: a school-based screening in Ethiopia

Background Early detection of scoliosis is a preface to prevent progression. In resource-constrained countries like Ethiopia, there is a need for a cost-effective reliable solution for screening. The surprising fact is that there is neither idiopathic scoliosis screening nor reporting of data from Ethiopia. This study aimed to identify the magnitude, associated factors of scoliosis among school children by using non-invasive and less expensive scoliometer Smartphone app and Adams forward bending test. Methods A school-based cross-sectional survey was carried out from March to June 2019 at seven primary schools. Children were screened by using physical examination (Adams forward bend test) and scoligauge iPhone app. Univariate and multivariable binary logistic regression model analysis was used to identify factors associated with idiopathic scoliosis. Results A total of 1905 children aged between 5 and 16 years were screened, 3.3 % (95 % CI 2.5–4.1) of them were found positive using the scoligauge HD and among them only 1.8 % were identified positive for Adam’s forward bend test. The associated factors of idiopathic scoliosis identified by multivariate analysis were; spinal pain (AOR 4.1, 95 % CI 2.42, 6.89), student sitting on stool: (AOR, 7.03; 95 % CI, 1.52, 32.5), sitting on the bench with a backrest (AOR 4.12; 95 %CI, 1.12, 15.14) and sitting on the bench without backrest: (AOR 4.56; 95 % CI 1.20, 17.34). Conclusions The magnitude of idiopathic scoliosis was relatively low in study setup. More attention is needed towards sitting furniture designs and for children reporting spinal pain.There is a reasonable level of recommendation to advocate that large school-based scoliosis screening was able to detect scoliosis among school children.

Correlation Of Printed Circuit Board Properties To Pad-Crater Defects Under Monotonic Spherical Bend

The restriction of lead in solder has caused a change in base materials used to make electronics—the result of which has been a new failure mode known as pad-crater. The susceptibility of six commercially available printed circuit board (PCB) laminates to pad-crater by spherical bend test was determined. The correlation of PCB laminate tensile properties, Vicker’s hardness (VH) of the resin, and weave dimensions showed an inverse relation between susceptibility to pad-crater and VH. Spherical bend testing of pure G10 laminate showed the orthotropic nature of laminates must be accounted for when modeling spherical bend. Comparison of bare PCB spherical bend test results showed the warp and weft direction have different strain responses for some materials. Comparison of strain energy of printed circuit board assemblies and bare PCB subjected to spherical bend showed the additional stiffness added by the ball grid array is almost identical for PCB laminates with different tensile properties.

Correlation Of Printed Circuit Board Properties To Pad-Crater Defects Under Monotonic Spherical Bend

The restriction of lead in solder has caused a change in base materials used to make electronics—the result of which has been a new failure mode known as pad-crater. The susceptibility of six commercially available printed circuit board (PCB) laminates to pad-crater by spherical bend test was determined. The correlation of PCB laminate tensile properties, Vicker’s hardness (VH) of the resin, and weave dimensions showed an inverse relation between susceptibility to pad-crater and VH. Spherical bend testing of pure G10 laminate showed the orthotropic nature of laminates must be accounted for when modeling spherical bend. Comparison of bare PCB spherical bend test results showed the warp and weft direction have different strain responses for some materials. Comparison of strain energy of printed circuit board assemblies and bare PCB subjected to spherical bend showed the additional stiffness added by the ball grid array is almost identical for PCB laminates with different tensile properties.