scholarly journals Study of the Structural-Phase State of Pipeline Welded Metal

2021 ◽  
pp. 38-45
Author(s):  
Olena Harashchenko ◽  
Vitaly Dmytryk ◽  
Tetiana Syrenko
Keyword(s):  
Service Life ◽  
Welded Joints ◽  
Structural Changes ◽  
Low Cycle Fatigue ◽  
Structural Phase ◽  
Operating Time ◽  
Relative Content ◽  
Statistical Characteristics ◽  
Metallographic Analysis ◽  
Structural Phase State

The issues of research of structural changes as applied to welded joints of steam pipelines are considered. The results of metallographic analysis of structural changes in the metal of steam pipelines are presented. There was carried out the analysis for a number of samples cut from different sections of the steam line at different operating time under creep and low-cycle fatigue conditions. In the analyzing process of the images of micro sections, the relative content of the structural-phase components and their distribution in the metal were revealed. A comparative analysis of the statistical characteristics of the distribution and the relative content of structural components for different sections of the metal of welded joints with different operating time is carried out. A scientifically substantiated description of structural changes in the metal of various sections of samples of welded joints is given, as well as the possibility of extending the service life of elements of steam pipelines with a degraded structure and the presence of damageability. The most promising, in the opinion of the authors, directions of further research of samples to provide conditions for extending the service life of steam pipelines have been formulated and substantiated.

scholarly journals Structural-&-Phase Condition and the Damageability of the Welded Joints of Steam Pipelines at Thermal Power Plants

2021 ◽  
pp. 56-63
Author(s):  
Vitaly Dmitrik ◽  
Igor Kasyanenko ◽  
Alexandr Krakhmalyov
Keyword(s):  
Service Life ◽  
Welded Joints ◽  
Power Plants ◽  
Low Cycle Fatigue ◽  
Thermal Power ◽  
Economic Effect ◽  
Structural Phase ◽  
Initial Structure ◽  
Thermal Power Plants ◽  
Phase Condition

The authors studied the interrelation between the type of structure and the damage rate of the welded joints of steam pipelines made of the heat-resistant pearlitic steels that were operated for a long time, i.e. more than 270 thousand hours in the conditions of creepage and low-cycle fatigue. The purpose of this research was to establish the interrelation between the structural-&-phase condition of the metal used for welded joints of the elements of steam systems and their damageability rate for the service life of welded joints exceeding 270 thousand hours. During the studies, the methods of optical and electron microscopy were used according to the requirements of the guideline documentation and also the methods that are used for the determination of mechanical properties. The level of their reliability has been substantiated and the residual life has been determined. To impart functional performances to welded joints we used well-known methods that were appropriately emended according to the structural changes of above joints. Such changes condition the conversion of the original structure of welded joints into the ferrite-carbide mixture. The availability of the conversion process of the initial structure on the thermal action zone sections (TAZ) of welded joints has essential distinctions due to a different disposition of metal to its own damageability. On the whole, the welded joints are damaged more intensively in comparison to the basic metal of steam pipelines. The analysis of the structural state of welded joints in the steam pipelines of thermal power plants as for the extension of their service life results in a considerable economic effect. Understanding the fact that the metal deterioration in welded joints adheres mainly to the fragile mechanism we managed to establish the level of their damageability that demands the renewal of damaged welded joints. We believe that the damageability level of welded joints that tots up to 0.25 or 0.35 of the volume of their TAZ section should be considered as critical for the service life exceeding 270 thousand hours. The damaged welded joints should be renewed throughout the time period of 15 to 20 thousand hours as soon as the specified damageability level is attained.

Study of the damage to 12Cr18Ni10Ti steel samples under low cycle fatigue using methods of nondestructive control

2021 ◽  
Vol 87 (5) ◽  
pp. 61-67
Author(s):  
A. A. Khlybov ◽  
Yu. G. Kabaldin ◽  
D. A. Ryabov ◽  
M. S. Anosov ◽  
D. A. Shatagin
Keyword(s):  
Structural Changes ◽  
Residual Life ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Operating Time ◽  
Test Material ◽  
Magnetic Characteristics ◽  
Propagation Time ◽  
Cycle Fatigue ◽  
Number Of Cycles

The possibility of determining the degree of damage to flat samples in the area of low-cycle fatigue at the stage of accumulation of scattered damage before the appearance of a macroscopic crack is demonstrated. Flat samples were tested for cantilever bending at room temperature with a constant loading amplitude until a fatigue crack appeared. Austenitic steel 12Cr18Ni10Ti was used as a test material. The velocity (propagation time) of elastic waves in the material and the coercive force were measured upon testing at intervals of 500 cycles. The zone of damage development was analyzed and value of hardening (based on microhardness measurements) was determined within 15 mm of the developed crack. The analysis of the images of the alloy microstructures in the zone of the most likely crack propagation was performed following different number of cycles at the same point on the sample surface. The structural changes (γ – α transition (formation of martensite deformation)) that occur during cyclic loading, as well as nucleation and development of damage, followed by the formation of fatigue cracks, inevitably lead to changes in the elastic and magnetic properties of the material. At the initial stages of loading, we observed changes in the initial (both acoustic and magnetic) characteristics of the material, which later became stable or changed slightly. When operating time exceeded 80 % of the number of cycles before failure, a significant change in the measured parameters occurred. The obtained dependences of the acoustic and magnetic characteristics of the material provide reliable information about the current damage and can be used in estimating the residual life of the structures made of 12Cr18Ni10Ti steel.

Microstructure and Microhardness Changes of 30CrMnSiA Steel Modified Surface Layers by Electrolyte-Plasma Processing

2013 ◽  
Vol 423-426 ◽  
pp. 824-827 ◽  
Author(s):  
Mazhyn Skakov ◽  
Erlan Batyrbekov ◽  
Laila Zhurerova ◽  
Michael Scheffler
Keyword(s):  
Arc Discharge ◽  
Structural Phase ◽  
Optical Microscope ◽  
Mechanical Tests ◽  
Metallographic Analysis ◽  
Surface Layers ◽  
Iron Carbides ◽  
Structural Phase State ◽  
Processing Modes ◽  
Modified Surface

This work is devoted to research of 30CrMnSiA steel structurally modified surface layers and study of electrolyte-plasma treatment parameters influence on changing peculiarities of structural-phase state and also the increase of constructional 30CrMnSi steel operating ability. The chosen technology leads to the formation of stable ferrite-pearlite structures in 30CrMnSi steel surface layers, provides high mechanical properties. As for the basic experimental methods of research in the work we used metallographic analysis applying optical microscope «NEOPHOT-21» and «AXIOPHOT-2», Х-ray analysis on the diffractometer ХPertPRO in monochromatic CuKα-radiation, mechanical tests for microhardness on PMT-3М installation. It is established that microstructure of 30CrMnSi steel modified layers samples while different processing modes, consists of α - phase, iron carbides. Using technology of structural steels electrolytic-plasma cementation under arc discharge terms in the electrolyte, we get diffusive surface layer with increased microhardness parameters and wear resistance providing good operating ability for details often subjected to wear.

scholarly journals Features of damage to welded joints of steam pipes made of steel 12X1M1F and 15X1MF

2021 ◽  
pp. 73
Author(s):  
Tatyana Syrenko ◽  
Mykola Ivanchenko
Keyword(s):  
Welded Joints ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Practical Experience ◽  
Phase Changes ◽  
Practical Significance ◽  
Metallographic Analysis ◽  
Variable Stresses ◽  
Start Ups

A significant number of heat and power equipment, including welded connections of steam pipelines made of 15x1m1f and 12x1mf Steels, have now reached the design service life. Their practical experience is about 200,000 hours at an estimated temperature of 545°C, and the park resource according to regulatory documentation is 250,000 hours. Note that aging welded joints are operated in conditions of start-ups and stops, which have become more frequent, which contributes to an increase in the intensity of their damage. In this connection, the question arose about the possibility of their operation longer than the estimated period in the new conditions. Goal. The goal is study of the features of damage to welded elements of steam pipelines operating in conditions of creep and low cycle fatigue. Methodology. The study of samples from existing damaged steam pipelines was carried out by the method of structural analysis, based on the consideration of the processes of structural and phase changes occurring in the areas of welded joints and conclusions were drawn regarding their resistance to destruction during operation. Results. The mechanisms of crack formation, their causes and the main provisions of metallographic analysis on the study of damaged welded joints operating under creep conditions and representing a certain number of types of cracks are presented. Such cracks are cold-breaking cracks, which are brittle cracks at moderate temperatures (up to 100–150 0C) during hydraulic tests and start-ups; long-term ductility failure cracks, which are brittle cracks caused by the failure of long-term ductility creep temperatures and rated stresses below permissible; cracks on exhausted areas, which are cracks when operating in the range of creep temperatures and rated stresses above permissible and fatigue cracks, which are cracks caused by the action of variable stresses with an amplitude greater than permissible values.  Scientific novelty and practical significance. It is established that the mechanism of aging of long-term operated welded joints of steam pipelines is associated with structural transformations that cause the appearance of cracks in the welded joints.

Structural changes in the metal of welded joints of long-term operating steam pipelines

2020 ◽  
Vol 2020 (2) ◽  
pp. 24-28
Author(s):  
V.V. Dmytryk ◽  
◽  
. A.V. Glushko ◽  
S.P. Iglin ◽  
◽  
...  
Keyword(s):  
Welded Joints ◽  
Structural Changes ◽  
Operating Steam

Viability of turbine blade material with a long service life

2019 ◽  
pp. 28-35
Author(s):  
O. B. Berdnik ◽  
I. N. Tsareva ◽  
M. K. Chegurov
Keyword(s):  
Heat Treatment ◽  
Service Life ◽  
Yield Strength ◽  
Mechanical Characteristics ◽  
Operating Time ◽  
Structural Features ◽  
Operating Conditions ◽  
Standard Methods ◽  
Experimental Values ◽  
Plasticity Coefficient

This article deals with structural features and characteristic changes that affect the mechanical characteristics after different service life in real conditions using the example of the blades of the 4th stage of turbine GTE-45-3 with an operating time of 13,000 to 100,000 hours. To study the change in the state of the material under different operating conditions, determine the degree of influence of heat treatment on the regeneration of the microstructure, and restore the mechanical characteristics of the alloy after different periods of operation, non-standard methods were used: relaxation tests on miniature samples to determine the physical yield strength and microplasticity limit and quantitative evaluation of the plasticity coefficient of the material from experimental values of hardness, which allow us to identify the changes occurring in the microvolumes of the material and predict the performance of the product as a whole.

Influence of composition on the structural-phase state, electrophysical and magnetotransport properties of alloy thin films based on Co and Cu

Vacuum ◽  
2021 ◽  
Vol 187 ◽  
pp. 110141
Author(s):  
I.O. Shpetnyi ◽  
I.Yu Protsenko ◽  
S.I. Vorobiov ◽  
V.I. Grebinaha ◽  
L. Satrapinskyy ◽  
...  
Keyword(s):  
Thin Films ◽  
Phase State ◽  
Structural Phase ◽  
Structural Phase State
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