Stainless Steel Elbows Research Articles

Creep ratchetting tests and analysis of a pressurized elbow at 593°C subjected to cyclic bending

This paper presents the results of an inelastic analysis of a type 304 stainless steel elbow subjected to alternating in-plane closing and opening bending moments and internally pressurized to 2.76 MPa (400 lb/ 2). The elbow diameter was 406 mm (16 in) with a wall thickness of approximately 12.5 mm (0.5 in). The purpose of the analysis was to validate the use of an inelastic finite element program (MARC) for the prediction of plastic and creep behavior of LMFBR components at elevated temperature (593°C). The approach used was to compare the analysis results with detailed measurements of strain and deformation obtained from a test elbow subjected to the same cyclic bending and internal pressure. The results confirmed the ability of the MARC program to reproduce, in detail, the complex elevated temperature inelastic response history which occurred in the test. In particular, the analysis confirmed test results which indicated that creep ratchetting of the elbow would occur only with respect tooccurred in the test. In particular, the analysis confirmed test results local hoop strains at mid-elbow under conditions of reversed cyclic loading and internal pressure. The analysis was apparently conservative in predicting significantly more ratchetting than was observed in the test. The analysis also confirmed that cyclic elbow ovalization was stable, i.e., did not show any progressive ovalization (ratchetting).

In-plane bending test of a piping elbow

This paper presents some experimental results of cyclic tests at room temperature in the elastic/inelastic regimes of an AISI 304 stainless steel elbow, which was subjected to in-plane closing and opening bending. The purpose of the work is the analysis of fittings subjected to a specific history of load/deflection in order to verify the correct prediction of the strain/stress state by means of stress intensification factors with the help of standards or elaboration by computer codes. A comparison with numerical data, from a large intensive computer analysis, is not the subject of this paper.standards or elaboration by computer codes. A comparison with numerical dat The experimental activities reported here have been performed in the framework of a research program supported by the Italian Electricity Board (ENEL-CRTN).

Experimental study of behavior and functional capability of ferritic steel elbows and austenitic stainless steel thin-walled elbows

This paper presents the results of two series of tests performed on 90° large-radius elbows. A first series of 10 tests was conducted on TU 42 C (equivalent to ASME SA 106 grade B) ferritic steel elbows with an outside diameter-to-wall thickness ratio of 6·7. A second series of 15 tests was conducted on Z2 CN 18-10 (equivalent to ASME TP 304 L) austenitic stainless steel elbows with an outside diameter-to-wall thickness ratio of 90. These elbows were subjected to in-plane (opening and closing) and out-of-plane bending moments. Changes in elbow angular deflection and ovalization of the mid-section were recorded as a function of applied moment. Measurements were made well into the plastic region. Influence of pressure, temperature and cyclic loading was also studied. The tests supplied extensive data on the behaviour of thin-walled austenitic stainless steel elbows when subjected to large displacements, including ability of the elbow to carry the flow under high loadings. Analysis in accordance with the requirements of the RCC-M 1 was also performed to quantify flow area reduction at stress limits allowed by these rules, in addition to the displacement amplitude margin allowed by the level D service limit criteria with respect to the experimental limit moment. A criteria is proposed which aims to limit secondary stresses under faulted conditions.

The Southwell Method for Predicting Plastic Buckling Loads for Elbows

The Southwell method for the prediction of buckling loads is applied to results obtained from tests of two 16-in-dia Type 304 stainless steel elbows loaded by an in-plane closing bending moment M. The basis of the method is discussed, and it is shown that proper application of the method requires that the nonlinear component of the deformation, δnl, be used in the Southwell plot. Predicted buckling loads determined from four experimental M-δnl curves for each test are found to be consistent and accurate, with an average value that is only slightly above the experimental plastic buckling load. The major conclusion of this paper is that the Southwell method based on δnl is valid for elbows loaded by an in-plane closing bending moment, and for a certain broader class of elastic or plastic nonlinear buckling (geometric collapse) problems for imperfection-insensitive structures. Consequently, tests and analyses of such structures need not be carried out to buckling to determine buckling loads. Practical advantages of such nonbuckling tests and analyses are discussed.

Comparison of ICEPEL Predictions With Single-Elbow Flexible Piping System Experiment

The ICEPEL Code for coupled hydrodynamic-structural response analysis of piping systems is used to analyze an experiment on the response of flexible piping systems to internal pressure pulses. The piping system consisted of two flexible Nickel-200 pipes connected in series through a 90-deg thick-walled stainless steel elbow. A tailored pressure pulse generated by a calibrated pulse gun is stabilized in a long thick-walled stainless steel pipe leading to the flexible piping system which ended with a heavy blind flange. The analytical results of pressure and circumferential strain histories are discussed and compared against the experimental data obtained by SRI International.

Low Cycle Fatigue of Nuclear Pipe Components

This paper presents the results of low-cycle fatigue testing and analysis of 26 piping components and butt-welded sections. The test specimens were fabricated from Type-304 stainless steel and carbon steel, materials which are typically used in the primary piping of light water nuclear reactors. Components included 6-in. elbows, tees, and girth butt-welded straight sections. Fatigue testing consisted of subjecting the specimens to deflection-controlled cyclic bending with the objective of simulating system thermal expansion type loading. Tests were conducted at room temperature and 550 deg F, with specimens at room temperature subjected to 1050 psi constant internal hydraulic pressure in addition to cyclic bending. In two tests at room temperature, however, stainless steel elbows were subjected to combined simultaneous cyclic internal pressure and cyclic bending. Predictions of the fatigue life of each of the specimens tested have been made according to the procedures specified in NB-3650 of Section III[1] in order to assess the code design margin. For the purpose of the assessment, predicted fatigue life is compared to actual fatigue life which is defined as the number of fatigue cycles producing complete through-wall crack growth (leakage). Results of this assessment show that the present code fatigue rules are adequately conservative.