Recently, elevation of steam conditions and construction of coal-fired boilers have been in progress in thermal power plants, employing new boiler materials, while automation and robotization for welding have rapidly been advancing in boiler fabrrcation works in response to demands for improvements of welding quality and its cost curtailment under shortage of skilled workers in Japan.
This paper presents the current situation and technical problems of welding technology for new high-strength materials which have already begun to be used for the boiler components of the highest service temperature in boiler structures and discusses the present situation and expected future course of automation and robotization for welding in fabrication processes of boilers.

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Much attention has recently been paid to laser surface cladding techniques as approach in controlling the composition and structure of the base metal surface. In this study, experiments on laser surface cladding whth wire feeder were carried out for the outer surface of boiler piping to prevent hot corrosion. The results indicated that 1) width and thickness of single pass clad depend strongly on laser irradiation speed, 2) dilution of clad depends strongly on irradiation speed and wire feed speed and increased with increasing laser irradiation speed, 3) enlarging the width of single pass bead due to laser beam oscillator shortened the time of making the cladding on outer surface of piping, 3) by using laser surface cladding technique with wire feeder, sound clad was foumed on entirely outer surface of long piping with the length of 5m and the outside diameter of 38.1mm.

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When boilers are constructed for business and private use, Electric Utilities Industry Law shall be applied. In that law, the technical standards regarding thermal power equipments for power generation and regarding weld of structures in electric power plant are specified on the work to be constructed in order to generate electricity.
These tecnical standards specify duty of the electric utility business and the owner of private electric work that is to maintain the electric work in order to meet these standards. These standards ate, also, quoted as standard for approving work plan and the acceptance or rejection judging standard for the inspection prior to actasl use.
Inspection of boilers is made acorrding to these standards. Now we will introduce outline of nondestructive tests of boiler which are specified in these standards.

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Some of the Japanese fossil power plants have been operating more than 200 thousand hours, and several kinds of damage was observed. So the assessment of residual life of these aged components has became important increasingly. In order to improve the accuracy of residual life prediction, several new techniques have been developed. In this paper, recent three kinds of techniques in IHI are introduced as follows. —For the creep-fatigue damage in header tube stub, Y-piece of main steam pipe and pipe stub, the assessment method based on the behavior of small cracks was developed. —For the creep damage in early stage of life, which could not be detected before, the assessment method based on the change of carbides components was developed. —For the assessment of creep damage in tube, the creep rupture tests of sampled pieces have performed until now. The alternative non-destructive method based on the creep deformation was proposed to reduce the assessment cost and to improve the accuracy.

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The factors that govern the life of boiler components include creep, creep-fatigue, fatigue and corrosion. Among them creep and creep-fatigue are important and dominant failure mechanisms for high temperature components, and various researches and development in creep life assessment have been extensively carried out. Presently the creep damage detecting method and life assessment technique based on physical properties have not yet been completely established, however the metallographic techniques have become available and widely used for the detection fo creep damages and life assessment. This paper reviews recent progress and status in various life assessment methodologies including nondestructive metallographic evaluation, physical evaluation, creep modeling and destructive evaluation as well as the practical experiences with creep damages and materials degradations.

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The number of the thermal power plants that have been operated more than 100, 000 hours is increasing and 60-70% of them have already been operated beyond the design life.
In order to operate these old plants efficiently, it is necessary to assure the reliability of its components and to repair the parts where damage is accumulated. Accordingly, the life evaluation technique will be playing a big role in performing the life assessment and extension.
One of the damages leading to failure of components is a creep damage. The creep damage does not always occur in the components of 2.25Cr-1Mo steel, because several low alloy steels are used in area to coincide with temperature. Accordingly, in order to evaluate the remaining life of each components, it is necessary to prepare the data about various materials.
This paper introduces non-destructive creep damage detecting methods and the results of investigation whether the methods can be applied to any low alloy steel or not. And also the method of improved extrapolation in the creep rapture test is described.

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An improvement of the creep-fatigue evaluation method for the tube-header welding parts of the electric power generation boiler operated frequently start-stop operating condition is strongly required.
In this paper, firstly, specimen-based evaluation method was established through the creep-fatigue test using acutual welding simulated, acutual size specimens and the theoretical analysis about those specimens. Secondarily, the computer code, that compute stress history under alternative temperature and strain conditions imaged actual boiler operation, and presume creep-fatigue life using same analysis method for the tested specimens was developed.
This computer code was applied to analyze the cracked tube welding of actual boiler. consequently, it was showed very good agreement between the predicted life by this code and the actual life. So, it was proved that this computer code was very successful.

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Water-wall tubes have been taken out of some different power boiler plants that have seen each an accumulated service life of 75000-210000h, involving 110-1200 start-and-shop operations, and their states of corrosion fatigue damage were examined. The damage was assessed in terms of the corrosion pits and cracks found on the inside surfaces of the tubes near by welded attachments. As the causes of the damages, thermal fatigue loading, stress concentration and environmental conditions had been considered. However, the mechanism and causes have not been fully understood.
In the present study, we have taken an approach to make the calculation for crack depth based on a corrosion fatigue model. The model is characterized as combined cycles (a-b-c-d-c-d-c-d…) in the followings.
a. Growth of corrosion pit
b. Initiation of fatigue crack at critical pit-size
c. Corrosion under normal operation
d. Growth of fatigue crack at a start-and-stop operation
The life has been calculated as a function of operation time, number of start-and-stop cycles and applied stress in the operation-histories of actual plants. The results have been compared with depths of actual corrosion pits or fatigue cracks which had been acquired in the field survey of several boiler units. These results are summarized with a plan and a result of laboratory corrosion-fatigue study, in this paper.

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Since a number of power boilers, currently being operated in Japan, were constructed before 1975, accidents due to the deterioration tend to increase in these days. In order to achieve safety operation of these boilers, it is essential to know the degree of deterioration at each part of boiler by executing suitable examination and by repairing/replacing the damaged parts before accidents would happen.
In this paper, the method of deterioration diagnosis are to be introduced, and new knowledge which were obtained from actual diagnosis results especially for superheater tubes is also to be presented.
1. Long term operation of superheater tubes will cause the following phenomena.
(1) Accumulating of steam oxidation scale deposit inside tubes,
(2) Softening of hardness with changing of micro-structure.
2. The steam oxidation scale continuously thickens during boiler operation and accelerates the consumption of creep life of superheater tubes.
3. There is correlation between degree of creep damage and thickness of steam oxidation scale.

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This paper provides a comprehensive review of the current status on the inspection and regulation systems in the safety-managemental aspects of boilers and pressure vessels in China. After the nineteen-seventies when a lot of serious and large-scale accidents due to the explosions or fracture of boilers and pressure vessels had happened with the growth of economics and modern industries, the Chinese government strongly suggested to enforce the safety regulation for boilers and pressure vessels. As the result of it, the present safety management and inspection systems for boiler and pressure vessel in China have been established, and these played important roles for the resolution of accident problems.
In this review, the governmental and local administration system and scheme for inspections and safety performance of boiler and pressure vessel, and their related rules and regulations, the non-destructive testing personnel certification system including the NDT qualification bodies and also the specification of boiler and pressure vessel in China are described.

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