Effects of Post-Tightening on the Residual Bolt Force and the Sealing Performance of Flanged Connections With PTFE Gaskets (Long Term Effects at Room Temperature)

2011 ◽  
Author(s):  
Taiki Hagiri ◽  
Takashi Kobayashi ◽  
Kengou Nishiura ◽  
Kazuaki Uchiyama
Keyword(s):  
Room Temperature ◽  
Test Results ◽  
Long Term Effects ◽  
Viscoelastic Characteristic ◽  
Sealing Performance ◽  
Nominal Size ◽  
Gasket Material

It is known that bolt forces reduce significantly after tightening bolted flanged connections in which expanded PTFE gaskets are used. Bolts are often post-tightened in practice after a while to compensate for the reduction of bolt forces. The viscoelastic characteristic of expanded PTFE gaskets is the main cause for the phenomenon. However, the long term effects of the post-tightening on the residual bolt forces and the sealing performance of flanged connections have not been clarified yet. In this study, two sets of flanged connections (2 inch in nominal size), in which PTFE gaskets were used, were prepared and tightened. One of the flanges was post-tightened after a designated time. The reduction of bolt forces and the change in the sealing performance were measured for about two months. The results were compared with those of flanges without post-tightening. Based on the test results, the effectiveness of post-tightening was discussed from the viewpoint of the residual bolt force and the sealing performance. It has been clarified that the effectiveness of post-tightening depends on gasket material and that post-tightening is effective for expanded PTFE gaskets.

The Residual Bolt Force and the Sealing Performance of Flanged Connections With Expanded PTFE Gaskets (Based on Test Results for One Year)

2012 ◽  
Author(s):  
Takashi Kobayashi ◽  
Taiki Hagiri ◽  
Kengou Nishiura ◽  
Masaaki Hiratsuka ◽  
Katsutoyo Itoi
Keyword(s):  
Thermal Expansion ◽  
Room Temperature ◽  
Early Stage ◽  
Thermal Characteristic ◽  
Temperature Dependency ◽  
Test Results ◽  
Viscoelastic Characteristic ◽  
Sealing Performance ◽  
One Year

It is known that bolt forces reduce significantly after tightening bolted flanged connections in which expanded PTFE gaskets are used. Bolts are often post-tightened in practice after initial tightening to compensate for the reduction of bolt forces. The viscoelastic characteristic of expanded PTFE gaskets is thought to be the main cause for the phenomenon. Some gasket users are not confident whether the bolt forces remain above a minimum required gasket load until next maintenance. However, the long term characteristics of the residual bolt forces and the sealing performance of flanged connections have not been clarified yet. In this study, using flanged connections with expanded PTFE gaskets, the reduction of bolt forces and the change in the sealing performance were measured at room temperature for one year. Based on the test results, the residual bolt force and the sealing performance were studied. It was clarified that bolt forces converges to a certain level at early stage within almost 1000 hours. After that, the bolt forces were significantly affected by the ambient temperature change. This is because the thermal expansion of PTFE material is high and also the thermal characteristic of PTFE material has a temperature dependency. It was confirmed that although the bolt force reduced significantly at early stage, it is maintained in long-term. The sealing performance was improved due to the increased compression of gasket.

Challenges to Overcome and Scaffolding to Build on

2019 ◽  
Vol 9 (3) ◽  
pp. 50-67
Author(s):  
Hao Yang ◽  
Zhiqiang Ma
Keyword(s):  
Teacher Perceptions ◽  
Flipped Classroom ◽  
Public University ◽  
Test Results ◽  
Learning Behavior ◽  
Long Term Effects ◽  
Exploratory Case Study ◽  
Flipped Classrooms

While current research on the flipped classroom generally focuses on test results and (or) student/teacher perceptions as a measurement of its pedagogical efficacy, students' adaptation to it and the essential conditions for its application are rarely explored. This exploratory case study aims to rectify this by examining how university students adapted to flipped classrooms implemented in a public university in East China. The findings suggest that while the flipped model is impeded by entrenched polarity between students in terms of their learning dispositions and academic competence, students do develop a prototype of theories of learning, a sense of better self through learning from their peers and an awareness of the importance of intrinsic motivation. A gradualist approach is thus proposed for implementing flipped classrooms, which requires longitudinal studies accordingly to understand its long-term effects on learning behavior hitherto left unexplored.

scholarly journals Indicators of COVID-19 status in a cohort study of university staff and post-graduate research students, including results from home antibody testing

2020 ◽  
Author(s):  
Katrina A. S. Davis ◽  
Ewan Carr ◽  
Daniel Leightley ◽  
Valentina Vitiello ◽  
Gabriella Bergin-Cartwright ◽  
...  
Keyword(s):  
Cohort Studies ◽  
Antibody Test ◽  
Self Report ◽  
Test Results ◽  
Long Term Effects ◽  
Antibody Testing ◽  
Postgraduate Students ◽  
Research Students ◽  
Core Symptoms

AbstractBackgroundCohort studies of people with a history of COVID-19 infection and controls will be essential to understand the epidemiology of long-term effects. However, clinical diagnosis requires resources that are frequently restricted to the severely ill. Cohort studies may have to rely on surrogate indicators of COVID-19 illness. We describe the prevalence and overlap of five potential indicators: self-reported suspicion, self-reported core symptoms, symptom algorithm, self-reported routine test results, and home antibody testing.MethodsAn occupational cohort of staff and postgraduate students at a large London university who participated in surveys and antibody testing. Self-report items cover March to June 2020 and antibody test results from ‘lateral flow’ IgG/IgM antibody test cassettes sent to participants in June 2020.ResultsValid antibody test results were returned for 1882 participants. Of the COVID-19 indicators, the highest prevalence was core symptoms (770 participants positive, 41%), followed by participant suspicion of infection (n=509, 27%), a symptom algorithm (n=297, 16%), study antibody positive test (n=124, 6.6%) and self-report of a positive external test (n=39, 2.1%). Study antibody positive result was rare in people who had no suspicion they had experienced COVID-19 (n=4, 0.7%) or did not experience core symptoms (n=10, 1.6%). When study antibody test results were compared with earlier external antibody results in those who had reported them, the study antibody results agreed in 88% cases (kappa= 0.636), with a lower proportion testing positive on this occasion (proportion with antibodies detected 15% in study test vs 24% in external testing).DiscussionOur results demonstrate that there is some agreement between different COVID indicators, but that they a more complete story when used together. Antibody testing may provide greater certainty and be one of the only ways to detect asymptomatic cases, but is likely to under-ascertain due to weak antibody responses to mild infection, which wane over time. Cohort studies will need to review how they deal with different and sometimes conflicting indicators of COVID-19 illness in order to study the long-term outcomes of COVID-19 infection and related impacts.What is already known on this subject?Research into the effects of COVID-19 in the community is needed to respond to the pandemic. Objective testing has not been widely available and accuracy may not be high when carried out in retrospect. Many cohort studies are considering how best to measure COVID-19 infection status.What this study adds?Antibody testing is feasible, but it is possible that sensitivity may be poor. Each indicator included added different aspects to the ascertainment of COVID-19 exposure. Using combinations of self-reported and objectively measured variables, it may be possible to tailor COVID-19 indicators to the situation.

An Estimation of Long-Term Sealing Performance for Bolted Pipe Flange Connections With Spiral Wound Gaskets Under Elevated Temperature

2020 ◽  
Author(s):  
Koji Sato ◽  
Toshiyuki Sawa
Keyword(s):  
Elevated Temperature ◽  
Heat Conduction Problem ◽  
Estimation Method ◽  
Transient State ◽  
Sealing Performance ◽  
Nominal Size ◽  
Calculation Results ◽  
Flexible Graphite ◽  
Spiral Wound

Abstract SWGs (Spiral Wound Gaskets) are well known as a most used gasket type in bolted pipe flange connections all over the world. Recently, the connections with SWGs have been used under more severe conditions such as higher temperature and pressure, and in addition, the connections have been used in the more long-term application. Thus, it is necessary for plant owners (gasket users) to know the long-term characteristics of the connections with SWGs from a standpoint of integrity in the connections. In this study, the objective is to establish a long-term estimation method of sealing performance for bolted pipe flange connections with SWGs under elevated temperature. The long-term characteristics of pipe flange connections with SWGs are estimated using FEM calculations in which the fundamental mechanical characteristics of SWGs such as compression property under changed temperature is considered, thermal expansion behavior, creep relaxation and sealing performance are taken into considerations. For verification of FEM calculations, the experiments are carried out for the pipe flange connections with SWGs of which the nominal size is ASME class 300 2inch under elevated temperature and internal pressure. The gasket used is chosen as SWG with flexible graphite filler. The change in axial bolt forces and an amount of leakage are measured and the measured results are fairly coincided with the FEM calculation results. In addition, the contact gasket stress in the connection with SWG is shown in 72 months. The FEM calculations are performed as heat conduction problem in transient state.

Space-exposed seed experiment developed for students

1992 ◽  
Vol 50 (1) ◽  
pp. 860-861
Author(s):  
Donna Leeper ◽  
Kelvin Bridgers ◽  
Ernest C. Hammond
Keyword(s):  
The United States ◽  
Test Results ◽  
Long Term Effects ◽  
The Earth ◽  
Long Duration ◽  
Foreign Countries ◽  
Abundant Supply ◽  
Germination And Growth ◽  
To Receive

The SEEDS project was flown in orbit aboard the Long Duration Exposure (LDEF) for nearly six years. During this time in space, the tomato seeds received an enormously abundant supply of cosmic radiation. Upon the return of the LDEF to earth, the SEEDS project was distributed throughout the United States and 30 foreign countries for analysis. The purpose of the experiment was to determine the long term effects of cosmic rays on living tissue. At Morgan, the analysis performed varied from germination and growth rates to electron microscopy and x ray analysis.In analyzing the seeds under the electron microscope, usual observations were performed on the nutritional and epidermic layers of the seed. These layers appeared to be more porous in the space-exposed seeds than in the Earth-based control seeds. This unusual characteristic may explain the increase in the space seeds’ growth pattern. (Several test results show that the space-exposed seeds germinate sooner than the Earth-based seeds. Also, the space exposed seeds are growing at a faster rate.) The porous nutritional region may allow the the seeds to receive necessary nutrients and liquids more readily. Thus, enabling the plant to grow at a much faster rate.

Practical Evaluation of PTFE Thermal Behavior Using the Hot Blowout Thermal Cycling Test

2012 ◽  
Author(s):  
Anita R. Bausman ◽  
A. Fitzgerald (Jerry) Waterland
Keyword(s):  
Thermal Cycling ◽  
Compressive Load ◽  
Temperature Limit ◽  
Cycling Performance ◽  
Current Status ◽  
Test Results ◽  
Sealing Performance ◽  
Practical Evaluation ◽  
Bolted Flange

Differential thermal expansion between polytetrafluoroethylene (PTFE) gasket materials and metallic flange/bolt systems, combined with thermally influenced creep relaxation characteristics of all PTFEs, creates limitations in the ability of some PTFE gasket materials to provide long term, reliable sealing performance in process or thermal cycling applications. ASTM F-36 gasket recovery data is sometimes used to assess a gasket’s thermal cycling capabilities; however, it is a poor means of establishing suitability for cycling performance as it is a short duration, ambient temperature test that measures recovery, or springback, of the gasket after the compressive load has been completely released. In order to provide a direct qualification of thermal cycling performance and capabilities, the Hot Blowout Thermal Cycling (HOBTC) test was developed under the guidance of the PVRC (Pressure Vessel Research Council)Bolted Flange Connection Committee as part of the 1995 PTFE Gasket Protocol. The HOBTC test results provide a practically applicable temperature limit under which the tested material, typically a PTFE, can operate safely. In addition, test data reported graphically provide additional insight about the long term behavior of the PTFE material. This paper reviews the current status of the HOBTC test, in the process of being made into an ASTM standard, and practical application of test results to achieve reliable gasket performance.

A Determination Method of Bolt Preload for Bolted Pipe Flange Connections With Metal Gaskets Under Internal Pressure

2015 ◽  
Author(s):  
Koji Kondo ◽  
Toshiyuki Sawa
Keyword(s):  
Internal Pressure ◽  
Room Temperature ◽  
Bolted Joints ◽  
Test Results ◽  
Bolt Preload ◽  
Sealing Performance ◽  
Bolted Flange ◽  
The Given ◽  
Outside Diameter ◽  
Better Than

FEM calculations and leakage experiments are carried out for bolted flanged connections with metal flat gaskets. It is found that the sealing performance of bolted flanged connections with raised face metal gaskets under internal pressure is improved significantly when the contact gasket stress reaches the gasket yield stress. In our FEM calculations it is demonstrated that the contact gasket stress at the outside diameter is bigger than that at the inside diameter due to the flange rotation. It is also found from the leakage test results and the FEM calculations that the sealing performance of the bolted flange connections with metal flat gasket is better than that of the metal gasket in platen device tests,. In addition, the contact stress in the joints with RTJ (ring type joint) gasket is examined and 4 stress peaks on the oval type and 8 peaks on the octagonal type are found. From the obtained results, a method for determining the bolt preloads in the bolted joints using flat metal gaskets and RTJ gaskets under internal pressure is proposed taking account the given allowable leak rate. Finally, the leak rates for bolted flanged connections tightened under internal pressure are compared with the experimental results. The new method can be proposed for determining the bolt preload for bolted flange connections with metal gaskets under internal pressure at room temperature.

scholarly journals Expression of SSTR2a, but not of SSTRs 1, 3, or 5 in Somatotroph Adenomas Assessed by Monoclonal Antibodies Was Reduced by Octreotide and Correlated With the Acute and Long-Term Effects of Octreotide

2013 ◽  
Vol 98 (11) ◽  
pp. E1730-E1739 ◽  
Author(s):  
Olivera Casar-Borota ◽  
Ansgar Heck ◽  
Stefan Schulz ◽  
Jahn Marthin Nesland ◽  
Jon Ramm-Pettersen ◽  
...  
Keyword(s):  
Monoclonal Antibodies ◽  
Medical Treatment ◽  
Somatostatin Receptors ◽  
Immunohistochemical Analysis ◽  
Test Dose ◽  
Test Results ◽  
Long Term Effects ◽  
Pretreated Group ◽  
Octreotide Treatment

Context: Reduced expression of somatostatin receptors (SSTRs) in somatotroph adenomas and their potential down-regulation after medical treatment may explain the unsatisfactory response to octreotide in particular acromegalic patients. The expression of SSTRs other than SSTR2a has not been studied in large, unselected cohorts using novel rabbit monoclonal antibodies. Objective: We aimed to determine the expression of SSTRs 1, 2a, 3, and 5 in somatotroph adenomas, to correlate expression with clinical characteristics and the response to octreotide, and to ascertain whether preoperative octreotide treatment affected SSTR expression. Design, Setting, Patients: The study included 78 adenomas from patients operated on consecutively during 2000 to 2010. After exclusion of 13 patients, immunohistochemical analysis with rabbit monoclonal antibodies against SSTRs 1, 2a, 3, and 5 (clones UMB-7, -1, -5, and -4) was performed on 65 adenomas. Intervention: Twenty-eight patients received preoperative octreotide, and 37 patients were operated on without pretreatment. Twenty-six patients were randomized to direct surgery (n = 13) or to octreotide pretreatment (n = 13). Main Outcome Measure: SSTR expression was evaluated using a 12-grade scoring system. The responses to the octreotide test dose (GH reduction) and to 6 months of octreotide (IGF-I reduction) were measured. Results: The majority of adenomas showed membranous expression of SSTRs 2a and 5. SSTR2a expression was reduced in the pretreated group and correlated with the acute octreotide test results and the effect of octreotide treatment. In a linear regression model with SSTR2a expression as the determinant, the correlation with the acute test response improved after adjustment for medical pretreatment. Conclusion: Rabbit monoclonal antibodies are reliable markers of SSTRs in somatotroph adenomas. SSTR2a expression correlated with the response to octreotide and was reduced after octreotide treatment, indicating the need for adjustment when SSTR2a expression is correlated with baseline characteristics. Evaluation of SSTR subtypes may be an important aspect of improving the medical treatment for acromegaly.

scholarly journals Immediate and Long-Term Effects of “Learning By Teaching” on Knowledge of Cognition

2017 ◽  
Vol 6 (4) ◽  
pp. 1 ◽  
Author(s):  
Mary Gutman
Keyword(s):  
Procedural Knowledge ◽  
Test Results ◽  
Long Term Effects ◽  
Face To Face ◽  
Learning By Teaching ◽  
Dependent Variables ◽  
Post Test ◽  
Dual Perspective ◽  
Practical Implications

Learning By Teaching (LBT) programs for pre-service teachers in two different environments (technological and face-to-face) were compared using 100 pre-service teachers as subjects. Both programs were based on the IMPROVE instructional method which provides explicit metacognitive steps for LBT with a dual perspective (2P): that of the teacher and that of the learner. The dependent variables Knowledge of Cognition (KC) in learning and in teaching were tested for their immediate and long-term effects in a Technology-Based System group (TBS+2P), and in a Face-to-Face group (F2F+2P). Post-test results of KC have indicated that the TBS+2P group had shown a higher level of conditional and procedural knowledge of teaching. The TBS+2P group has also performed better in measures of long-term effects of declarative knowledge in teaching. Both theoretical and practical implications of this study are discussed.

Sign in / Sign up

Export Citation Format

Share Document