Stainless Steel Straight Pipes Research Articles

Prediction of fatigue crack initiation life in SA312 Type 304LN austenitic stainless steel straight pipes with notch

In the nuclear power plants, stainless steel is widely used for fabrication of various components such as piping and pipe fittings. These piping components are subjected to cyclic loading due to start up and shut down of the nuclear power plants. The application of cyclic loading may lead to initiation of crack at stress raiser locations such as nozzle to piping connection, crown of piping bends etc. of the piping system. Crack initiation can also take place from the flaws which have gone unnoticed during manufacturing. Therefore, prediction of crack initiation life would help in decision making with respect to plant operational life. The primary objective of the present study is to compile various analytical models to predict the crack initiation life of the pipes with notch. Here notch simulates the stress raisers in the piping system. As a part of the study, Coffin-Manson equations have been benchmarked to predict the crack initiation life of pipe with notch. Analytical models proposed by Zheng et al. [1], Singh et al. [2], Yang Dong et al. [25], Masayuki et al. [33] and Liu et al. [3] were compiled to predict the crack initiation life of SA312 Type 304LN stainless steel pipe with notch under fatigue loading. Tensile and low cycle fatigue properties were evaluated for the same lot of SA312 Type 304LN stainless steel as that of pipe test. The predicted crack initiation lives by different models were compared with the experimental results of three pipes under different frequencies and loading conditions. It was observed that the predicted crack initiation life is in very good agreement with experimental results with maximum difference of ±10.0%.

Fatigue crack growth behavior of a 170 mm diameter stainless steel straight pipe subjected to combined torsion and bending load

Fatigue crack growth behavior of a 170 mm diameter stainless steel straight pipe subjected to combined torsion and bending load

Fracture studies on narrow gap welded SA 312 Type 304LN stainless steel straight pipes under quasi-cyclic loading

Fracture studies were carried out on narrow gap welded SA 312 Type 304LN stainless steel straight pipes having circumferential through-wall notch in the weld. Totally six specimens were tested; one specimen was subjected to monotonic loading and the remaining five specimens were subjected to quasi-cyclic loading. Under quasi-cyclic loading, one specimen was tested under incremental displacement-controlled loading and the remaining four specimens were tested constant amplitude load-controlled loading. Based on the load-controlled experimental results, a plot of the cyclic load amplitude versus number of cycles to failure of the specimens was obtained. The experimental results indicate that the piping components subjected to quasi-cyclic loading may fail in very less number of loading cycles even when the load amplitude is sufficiently below the monotonic fracture/collapse load. Crack growth behaviour and cyclic tearing instability in the specimens, which are required for realistic assessment of Leak Before Break applicability, was studied.

One-Step Cleaning-in-Place for Milking Systems and Mathematical Modeling for Deposit Removal from Stainless Steel Pipeline Using Blended Electrolyzed Oxidizing Water

Cleaning-in-place (CIP) is widely used on dairy farms to clean and sanitize the inner surfaces of milking system components after the milking event is completed. Recently, an increasing number of dairy farms are adopting a one-step CIP process, which combines the alkaline wash and acid wash cycles into one wash cycle. This one-step CIP has the advantage of reducing time, energy consumption, and chemical usage. Electrolyzed oxidizing (EO) water is an emerging technology that produces alkaline and acidic EO water by electrolyzing a dilute sodium chloride solution. Previous studies in our lab have shown that by blending the alkaline EO water with the acidic EO water at a certain ratio, the blended solution can be used as a one-step CIP alternative. Therefore, this study was undertaken to evaluate the deposit removal process during a one-step CIP wash cycle using the already optimized blended EO water solution and a stainless steel surface evaluation simulator. Stainless steel straight pipes were used as testing specimens, and the remaining milk deposit mass on the inner surfaces of the specimens was evaluated. A two-term exponential decay kinetic model was developed for the one-step blended EO water wash; the mathematical model comprises an initial fast deposit removal along with a slow deposit removal throughout the entire one-step wash. The proposed models were in agreement with the experimental data, with acceptable root mean square errors (0.08 mg mg-1 m-2) and low percentage error differences (5.16%). The relative light unit (RLU) reading from the adenosine triphosphate (ATP) bioluminescence method was also used as an indirect evaluation method at every time sampling point during the one-step wash cycle. Furthermore, scanning electron microscopy (SEM) was used to understand the residual deposit morphology on the specimen inner surfaces and qualitatively evaluate the cleanliness of the inner surfaces after the one-step wash. On average, 60% reduction of deposit coverage in the viewing area was observed after the blended EO water one-step wash as compared to after the warm water rinse cycle. Moreover, results showed that at the completion of the blended EO water one-step wash, the specimens could be considered clean, as indicated by the RLU cutoff reading for stainless steel material. Therefore, it is concluded that the developed and validated mathematical model for the blended EO water one-step wash could be used for CIP of the simulator.

Mathematical modeling and cycle time reduction of deposit removal from stainless steel pipeline during cleaning-in-place of milking system with electrolyzed oxidizing water

The safety of raw milk largely depends on using a clean milking system during the milk production. The milking system cleaning process widely used on dairy farms is a highly automated process called cleaning-in-place (CIP), which comprises of four cycles: i) warm water rinse; ii) alkaline wash; iii) acid wash; and iv) sanitizing rinse before the next milking event. Electrolyzed oxidizing (EO) water is an emerging technology, which consists of acidic and alkaline solutions by the electrodialysis of dilute sodium chloride solution. Previous studies in our lab showed that EO water can be an alternative for milking system CIP. Despite the progress made to enhance the CIP performance and evaluate alternative CIPs, the mechanisms behind the cleaning processes were still largely unclear. Therefore, this study was undertaken to evaluate the deposit removal rate during the EO water CIP process using a stainless steel surface evaluation simulator. Deposit removal data from the simulator formed the basis for developing mathematical models to describe the deposit removal process during the CIP process with EO water. Stainless steel straight pipe specimens were placed at the end of undisturbed entrance length along the simulator pipeline. The mass of milk deposits on the inner surfaces of the specimens were measured using a high precision balance after the initial soiling, and then after certain time durations within the warm water rinse, alkaline wash, and acid wash cycles. A unified first order deposit removal rate model dependent on nth power of remaining deposit mass was used for all three cycles. ATP bioluminescence method was also used as a validation approach at the end of each CIP cycle. Experimental results showed that the milk deposit on the inner surfaces of the specimens was removed rapidly by the warm water rinse within 10 s of rinse time. For the alkaline and acid wash cycles, the co-existence of a fast deposit removal at the beginning of the wash cycle and a slow deposit removal throughout the entire wash cycle was inferred. The proposed models matched the experimental data with small root mean square errors (0.23 mg/[(mg) (m2)] and 0.07 mg/[(mg) (m2)] for the upstream and downstream locations, respectively) and satisfactory percent error differences (3.67% and 0.93% for the upstream and downstream locations, respectively). Based on the experimental data and the proposed models, the time duration of the CIP process was shortened by 55% (10 s warm water rinse, 3 min alkaline wash and 6 min acid wash) and validated, which yielded an average deposit of 0.28 mg/[(mg) (m2)] at the end of the CIP as compared with that of 0.29 mg/[(mg) (m2)] at the end of the original CIP, to achieve a satisfactory CIP performance for the simulator.

Use of acoustic emission and ultrasonic techniques for monitoring crack initiation/growth during ratcheting studies on 304LN stainless steel straight pipe

This paper describes the use of acoustic emission (AE) and ultrasonic techniques for monitoring crack initiation/growth during ratcheting studies on a straight pipe made of 304LN austenitic stainless steel under reversed four point bending. Generation of higher AE activity and AE events with higher peak amplitudes accompanied by AE cluster formation in a localized region between 826 and 845 cycles revealed the initiation of crack during the ratcheting test. Ultrasonic examination by using multiple skip technique conducted periodically at regular intervals of 25 cycles confirmed the formation of the crack only after 1000 cycles. Final rupture of the pipe occurred by through-thickness cracks after 1203 and 1225 cycles at two locations. In the range of cycles where the cracks grew, AE increased with the accumulated cycles, indicating good correlation between crack growth and AE. Acoustic emission was correlated with ballooning. While the ballooning rate decreases with cycles, count rate for different sensors increase. This has been attributed to the superposition of the generation of AE due to crack growth which increases continuously to that generated by circumferential change in strain. The superior sensitivity and reliability of acoustic emission for early detection of fatigue cracks during ratcheting test in pipe specimen is demonstrated.

Ratcheting failure of pressurised straight pipes and elbows under reversed bending

Ratcheting studies were carried out on Type 304LN stainless steel straight pipes and elbows subjected to steady internal pressure and cyclic bending load. The internal pressure for all the straight pipes was 35 MPa and in the case of elbows the internal pressure was varied for different elbows, ranging from 27.6 MPa to 39.2 MPa. Cyclic bending load was applied on the specimens by subjecting them to different levels of load-line displacement. The specimens have undergone significant ratchet swelling (ballooning), ovalization and consequent thinning of the cross-section during ratcheting. The straight pipes failed either by occurrence of through-wall crack accompanied by simultaneous ballooning, or bursting with simultaneous ballooning. All the elbows failed by occurrence of through-wall crack accompanied by simultaneous ballooning. Ratcheting behaviour of straight pipes and elbows were compared and it was generally inferred that ratcheting was more pronounced in straight pipes than in elbows.

Cyclic Fracture, FCG and Ratcheting Studies on Type 304LN Stainless Steel Straight Pipes and Elbows

Abstract With an objective of understanding the cyclic fracture, fatigue crack growth and ratcheting behaviour of Type 304LN stainless steel piping components used in primary heat transport system of nuclear power plants, subjected to various operational, loading and environmental conditions, experimental studies were carried out on totally 36 straight pipes and eight elbows. The pipe dimensions were in two categories: 170 mm OD and 15 mm thickness or 324 mm OD and 25 mm thickness. These studies on actual size piping components of power plants have resulted in very valuable fatigue behaviour related data, which would form important inputs in assuring safety and damage tolerant design of power plants. An overview of the studies is presented in this paper.

Dependence of charge transfer phenomena during solid–air two-phase flow on particle disperser

An experimental investigation of the tribo-electrification of particles has been conducted during solid-air two-phase turbulent flow. The current induced in a metal plate by the impact of polymethylmethacrylate (PMMA) particles in a high-speed air flow was measured for two different plate materials. The results indicated that the contact potential difference between the particles and a stainless steel plate was positive, while for a nickel plate it was negative. These results agreed with theoretical contact charge transfer even if not only the particle size but also the kind of metal plate was changed. The specific charge of the PMMA particles during solid-air two-phase flow using an ejector, a stainless steel branch pipe, and a stainless steel straight pipe was measured using a Faraday cage. Although the charge was negative in the ejector, the particles had a positive specific charge at the outlet of the branch pipe, and this positive charge increased in the straight pipe. The charge decay along the flow direction could be reproduced by the charging and relaxation theory. However, the proportional coefficients in the theory changed with the particle size and air velocity. Therefore, an unexpected charge transfer occurred between the ejector and the branch pipe, which could not be explained solely by the contact potential difference. In the ejector, an electrical current in air might have been produced by self-discharge of particles with excess charge between the nickel diffuser in the ejector and the stainless steel nozzle or the stainless steel pipe due to a reversal in the contact potential difference between the PMMA and the stainless steel. The sign of the current depended on the particle size, possibly because the position where the particles impacted depended on their size. When dual coaxial glass pipes were used as a particle disperser, the specific charge of the PMMA particles became more positive along the particle flow direction due to the contact potential difference between the PMMA and the stainless steel. Furthermore, the current in air using the dual coaxial glass pipes was less than that using the ejector.

Tribo-electrification of particles under sudden change of fluid flow in the junction between branch pipe and straight pipe

An experimental investigation of the tribo-electrification of glass beads fed by an ejector has been conducted by measuring both the current generated at the pipe wall and the specific-charge measured by a Faraday cage under sudden change of fluid flow in the junction between a stainless-steel branch pipe and a stainless-steel straight pipe. In measuring a current per unit mass, for Dp,50⩾206μm at the branch pipe section the current has a positive value as expected by the contact potential difference between glass beads and stainless-steel. On the other hand, for Dp,50⩽105μm at the branch and straight pipe section, the current has a negative value couldn’t be explained solely by the contact potential difference. In measuring a specific-charge by the Faraday cage, the specific-charge has a negative highest value at the ejector. The negative specific-charge decreases along the particle flow direction. Therefore, an “unusual” charge-transfer, which couldn’t be explained solely by the contact potential difference, was confirmed also by the Faraday cage. Although the charge-transfer between the beads and the inclined stainless plate with high impact speed has been examined, the sign of the current is positive for all data. It was found that the “unusual” charge-transfer in this study couldn’t be caused by the high speed impaction. An negative current in air by using a stainless steel needle detected at the ejector for Dp,50=51μm while an positive current in air detected at the branch and straight pipe. The reason is suggested that the ion balance in the air does not keep between the ejector and the branch pipe due to both the adsorption of some negative ions on the pipe wall and the decrement of negative charge of particles. Therefore the “unusual” charge-transfer consists of not only the ionization caused by the self-discharge but also an adsorption of ions on the inner wall of the pipe.

Fatigue ratcheting studies on TP304 LN stainless steel straight pipes

‘Fatigue Ratcheting’ is a phenomenon which leads to reduction in fatigue life of a structural component by loss of ductility due to cycle-by-cycle accumulation of plastic strain. One real-life example of a situation with fatigue ratcheting possibility is piping of power plants subjected to internal pressure (primary load) and cyclic bending (secondary load). Fatigue ratcheting studies were carried out on TP304 LN stainless steel straight pipes of 168 mm outer diameter subjected to steady internal pressure and four point cyclic bending. The length and average thickness of the pipes were 2800 mm and 15 mm respectively. The thickness was reduced to 12 mm in the gauge length portion of 200 mm at the centre of the pipe. Post-yield two element rosette strain gauges were mounted at various locations within the gauge length to measure the longitudinal and circumferential strains. The pipes were filled with water and pressurized; the pressure was maintained at 35 MPa till the first through-thickness crack was observed. Cyclic bending load was applied on the pipes by subjecting them to different levels of load-line displacements. Number of cycles corresponding to through-thickness crack/s and final failure of the component were recorded. During the tests, load, load-line displacement and deflections at three locations were continuously monitored. Local bulging, ovalization and consequent thinning of the pipe cross-section were observed due to fatigue ratcheting. These ratcheting studies on pressurized piping components of power plants give valuable inputs necessary for designing the components and assuring the integrity of pressure boundary under design basis loads such as loads arising during an earthquake event.

Crack Initiation and Growth Behavior on SUS304 Steel Piping Components During Cyclic Thermal Transient Strains

A series of thermal transient fatigue tests on five SUS304 stainless steel straight pipe models with circumferential weld joints and a nozzle model were performed to study the general behavior of crack initiation and growth including crack locations, directions and densities under respective loading conditions. The crack initiation sequence at different parts of models corresponded well with the result of analytical prediction using the finite element method. The potential margin on the allowable number of thermal transient cycles according to the ASME CODE CASE N-47 and the Elevated Temperature Structural Design Guide developed by the Power Reactor and Nuclear Fuel Development Corporation was evaluated, and the result showed a considerable safety margin compared with the data on initiation of cracks of 1 mm in depth at all parts of pipe models including circumferential weldings, notches, and other structural discontinuities.