JPS60149970A - Detection of deterioration and damage of high temperature pressure resistant member - Google Patents

Abstract

PURPOSE:To accurately detect the deterioration and creep damage of a material during the use of a high temp. pressure resistant member, by collecting a part of the outer surface of the high temp. pressure resistant member in a range not less than a predetermined thickness so as to include the surface thereof and observing the cross-sectional area or ground surface of the collected specimen by a microscope. CONSTITUTION:With due regard to such a fact that the damage generation place due to the creep of a high temp. pressure resistant member used for a long time is present in the surface layer of said pressure resistant member, this method is constituted so that a small piece having a thickness corresponding to the excessive wall thickness part of the high temp. pressure resistance member is collected from said pressure resistance member to as to include the surface thereof and inspected by a microscope. By this method, the damage state of this member can be detected in an extremely accurate manner without exerting substantially any destruction upon the high temp. pressure resistant member. Furthermore, in the microscopic observation of the small piece used in this method, not only voids due to creep but also the distribution state and form of precipitates can be accurately grasped and the element analysis of the precipitates and a matrix is enabled. Further, by observing the small piece from each part of the member, information relating to the deterioration and damage of the material can be accumulated and statistically processed and, as a result, the max. damage degree of the whole of the member can be also known.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for non-destructively detecting material deterioration and creep damage in high-temperature pressure-resistant members that have been used at high temperatures for long periods of time.

(Summary of conventional products and their drawbacks) In boilers and high-temperature equipment of various plants, pressure-resistant materials that are used at high temperatures for long periods of time may change in material quality due to the stress or heating that is applied to the materials during use, and may change depending on the usage conditions. Material life is consumed.

In general, even if a small stress below the yield point is applied to a member, it will deform at high temperatures and eventually break. These phenomena are called creep deformation and creep rupture, but even though there is almost no deformation in parts that have been used for a long time, vacancies are generated at grain boundaries and these grow into cracks. It may also be destroyed.

Even when this type of deformation is not involved, it is a type of creep damage, and in fact, this kind of damage often occurs in materials that have been used for a long time.

In this case, the vacancies that occur at the grain boundaries are called creep vacancies, and even when a small stress that does not apparently cause creep deformation is applied, the vacancies that occur at the grain boundaries are caused by the formation of precipitates in the metal structure. As cracks form and grow, they occur at grain boundaries and grow into cracks. When creep vacancies are generated,
It is thought that most of the time is consumed before creep failure occurs, and it is necessary to replace it with a new material.

Furthermore, recently, many power generation plants have been operated for a long time of 100,000 hours or more, and their maintenance management has become an important issue. In other words, in the current design standards, each pressure-resistant part is designed based on the creep rupture strength of 100,000 hours, and a safety factor is expected, but after 100,000 hours of use, the remaining life is It is difficult to estimate. Therefore, in general, materials are often replaced only after damage or an accident occurs, which requires a great deal of effort and expense in handling the accident and purchasing new materials.

In addition, recently, non-destructive detection of damage and repair or material replacement has been considered, but it is still unreliable and has not yet been put to practical use. It is.

Therefore, it is difficult to accurately detect damage using conventional methods such as those described above, and even if it is estimated that there is still enough life to avoid accidents, it is difficult to detect new damage from a safety point of view. We are in a situation where we have no choice but to replace the material.

(Aim and Motive of the Invention) 'The purpose of the present invention is to accurately detect material deterioration and creep damage during use of high-temperature and pressure-resistant members, and to detect the occurrence of damage to high-temperature and pressure-resistant members that have been used for a long time. This was done by examining the behavior in detail.

(Structure and novel points of interest of the present invention) The present invention collects a part of the outer surface of a high-temperature and pressure-resistant member, including the surface within a range not less than the required design thickness of the member, and collects a cross-section of the sample or a polished surface. The gist of this study is to observe them using a microscope.

Here, the novel point of the present invention is to focus on the fact that damage occurs due to creep in high-temperature and pressure-resistant members that have been used for long periods of time, and that the damage occurs in the surface layer. The point is to take a sample of the sample and examine it under a microscope.

In terms of design, the portion corresponding to excess thickness may vary depending on the dimensions of the member, but it is sufficient that it includes approximately α2fi, where creep damage can be best detected.

(Application Field) The present invention can be applied to detecting material deterioration and creep damage in high-temperature and pressure-resistant members of thermal power plants and the like that have been used for long periods of time.

(Specific example of the present invention) A portion of a 5US316H steel pipe that had been used as steam piping for approximately 170,000 hours under conditions of an internal pressure of 300 kg/'cm2 and a temperature of 620°C was cut out, and its cross section was observed under a microscope. As a result, crystal grains were observed. A large number of precipitates were observed at the boundaries and within the grains, and at the same time, vacancies, which appeared to be caused by creep, were observed along the precipitates at the grain boundaries. A detailed observation of the distribution of pores in the cross section of the tube revealed that they were concentrated on the outer surface of the tube and in the depth range of about Q, 2gm to about 2gm, and that they were distributed even deeper. It was found that the density was low.

Therefore, in addition to the test tube mentioned above, only the surface layer of the tube used under the same conditions was deepened to a depth of approximately 2 m. As a result of comparing, it was within the range of sufficient extra meat. ), small pieces (3 bombs x 5 ran
X 2 arm) was collected. Next, this small piece was buried in resin, polished so that its cross section could be observed, and then lightly corroded using picric acid, and its structure was observed using a scanning electron microscope.

As a result, it was confirmed that there were pores along coarse precipitates at grain boundaries in the cross section of the small piece.

(Effects of the Present Invention) Therefore, it can be seen that according to the method of the present invention, the damaged state of the pressure-resistant member can be detected very accurately by simply collecting a small piece of excess thickness from the surface of the pressure-resistant member. In addition, microscopic observation of small pieces used in the method of the present invention makes it possible to accurately grasp not only the pores caused by creep but also the distribution and morphology of precipitates, as well as elemental analysis of the precipitates and matrix. . Additionally, with this method, by sampling and observing many small pieces from each part of the component, it is possible to accumulate and statistically process information regarding material deterioration and damage, which also makes it possible to determine the maximum degree of damage to the entire component. .

Among the sub-agents: 1) Akira Sub-agent Ryo Hagi Hara -

Claims (1)

[Claims] A high-temperature method characterized by sampling a part of the outer surface layer of a high-temperature pressure-resistant member, including the surface, to the extent that the thickness is not less than the required design thickness of the member, and observing the cross section or polished surface of the sample using a microscope. Method for detecting deterioration and damage of pressure-resistant components.