Failures at Elevated Temperatures

The principal mechanisms of failure of high temperature components include creep, fatigue, creep-fatigue and thermal fatigue. In heavy section components, although cracks may initiate and grow by these mechanisms, ultimate failure may occur at low temperatures during startup-shutdown transients. Hence, fracture toughness is also a key consideration. Considerable advances have been made both with respect to crack initiation and crack growth by the above mechanisms. Applying laboratory data to predict component life has often been thwarted by inability to simulate actual stresses, strain cycles, section size effects, environmental effects and long term degradation effects. This paper will provide a broad perspective on the failure mechanisms and illustrate a few of the typical ones in boilers.

Failure Modes and Mechanisms in Electronic Packages, 1998

Fuel cell faults, transient or permanent, could be generally classified into electrical and chemical in nature. Depending on their severity, these faults may lead to a reduction in performance and, in advanced stages, may even destroy the cell. Failures that occur can be divided into three types: 1. Permanent faults (irreversible faults) 2. Transient faults (reversible faults) 3. External faults 4.2 Permanent Faults (Irreversible Faults) This type of faults is permanent and, if continued, will lead to permanent damage to the fuel cell. The cell's performance and efficiency will degrade when such a fault occurs. The possible solution in this case is to replace the damaged fuel cell. 4.2.1 Membrane Degradation Degradation of membranes is one of the most common faults that affect PEM fuel cell performance, efficiency and lifetime. This type of faults takes place over time such that the system's evolution is looking for new equilibrium points. In this case, the diffusion constants of the system change as well as pressure gradients between the two electrodes. Temperature, humidification and chemical attack cause changes in the characteristics of membrane and mechanical degradation. The chemical attack is caused by radicals initiating membrane degradation, because of their

The physics of failure (POF) is an approach to designing reliable products to avoid failure, based on the knowledge of root cause failure mechanisms. It is based on failure reliability technology that studies the failure regularities from the failure reasons and failure mechanisms of the products. A clear understanding of the physics-of-failure is necessary in applications that afford little opportunity for testing. The purpose of this paper is to present POF as a reliability analysis or science which studies failure mechanisms.

2008

Protective paintwork is an important item in construction and maintenance operations in industrial plants. A properly selected and applied coating system will reduce the rate of corrosion and therefore the costs associated with corrosion. In industrial plants, coating failures may occur if incorrect coating material is used or the materials are poorly applied. Coating failures may appear during application, during drying/curing, or after a certain period of service life. There are many reasons why coatings fail and it requires a lot of experience to find the exact cause. In this paper, case studies of coating failures that were experienced in industrial plants will be presented showing how the varied causes of failure were established as well as the remedial actions that were undertaken. The goal is to demonstrate how to specify the most cost effective coating systems and application procedure for various requirements in plants.

2011

In today's competitive world, the basis of many maintenance decisions is their associated risk and this parameter is directly related to occurrence and severity of failures. In this paper, the relationship between the two parameters has been investigated for which, reliability functions has been used. The results imply that this relationship is not compatible with the traditional diagram used in risk analysis approaches such as Failure Modes and Effects Analysis (FMEA) and respectively, decision making based on existing approaches might be risky.

1.0-INTRODUCTION 1.1 In today's competitive market scenario power utilities are under tremendous pressure to cut down their maintenance costs as they form a significant portion of the operation costs. This has led the utilities to adopt condition-based maintenance of the equipments rather than usual preventive maintenance being carried out at a fixed interval of time. Maintenance intervals are normally fixed on the basis of type of equipment and sometimes on the equipment history. However, tests or measurements are also carried out to assess the condition of the equipment. 2.0 TYPES OF MAINTENANCE Different types of maintenance being done on equipment are: i) Breakdown maintenance ii) Preventive maintenance iii) Condition based monitoring iv) Reliability centered maintenance i) Breakdown Maintenance As the name implies the maintenance is carried out when the equipment fails. This type of maintenance may be appropriate for low value items. However for costly substation equipments, it is not desirable to wait till the breakdown of the equipment, as this cost more to the utility as well as the availability and reliability of power gets affected. The revenue loss due to non-availability of the system shall be much more than the cost of the failed equipment. Therefore identifying the defect before failure, is more appropriate to plan repair / replacement. ii) Preventive Maintenance The preventive maintenance of equipment is being mostly adopted by almost all the utilities. In this type of maintenance, the equipments are inspected at a predetermined period. The frequency determined based on the past experience and also guidance from the manufacturer of the equipment. This type of maintenance would require specific period of shutdown. Maintenance procedure, periodicity of maintenance and formats for maintaining records for various types of sub-station equipments have been discussed separately in detail in a separate section. iii) Condition Based Monitoring This type of maintenance technique is adopted to assess the condition of the equipment. The condition of the equipment is assessed based on different condition monitoring tests. Some of the tests are done on on-line and some are done on off-line. However, this type of maintenance would need sophisticated testing equipments and skills for analyzing the test results. iv) Reliability Centered Maintenance This is the recent technique being adopted in maintenance philosophy. The basic objectives of reliability-centered maintenance are:-Maintenance should keep the equipment at desired level of performance-Optimizing / minimizing the maintenance / shutdown period so as to enhance the availability of the equipment.-Deferring / avoiding the replacement of components and major/minor overhauls till it is absolutely necessary. 1 Reliability centered maintenance policy is based on the life cycle cost concept and the decision for replacement of the equipment is taken based on techno-economic considerations. From the view point of RCM our objective should be to devise a system, which does not need periodic maintenance and at the same time predict in advance possible failures/problems of the equipment. To meet this aim we have to develop equipment which require either no or very little maintenance and on the other hand the concept of condition based maintenance should be implemented. Realization of this objective will result in enhancing availability, reliability and reduction in manpower for maintenance purposes. 3.0 FAILURES OF EQUIPMENTS 3.1 Failure of any equipment should taken up seriously. Detailed analysis of each failure should be done which will help in reduction/stopping of repeated failures of same nature. It is general experience that in spite of doing regular maintenance, failure of the equipment can't be totally eliminated. Number of EHV equipment failures have been reported practically by all the utilities and some of them have been quite serious resulting in consequential damage to the adjoining equipment. Circuit breakers operating on high pressure when they fail, they explode like a bomb resulting in scattering of insulator pieces to a larger distance and damage to the adjoining equipment. Similar situation have also been faced with the failure of surge arrestors and current transformers. Some of the typical failures of equipment and the remedial measures adopted have been discussed in a separate section. 4.0 NEED FOR CONDITION BASED ASSESSMENT OF EHV EQUIPEMNT 4.1 In the present competitive environment, all utilities are making efforts to reduce the O&M expenditure. This puts lot of pressure on the utilities to minimize the outage period due to failure of equipment. This necessitates adopting of condition based monitoring as the Need of the Hour. This has necessitated all the power utilities to introduce condition based monitoring for EHV class equipment so that actual condition of the equipment and its residual life could determined. Modern techniques are available for condition based monitoring and the concept of residual life assessment is picking up world wide.

Failures of electronic devices, in general, can be catastrophic or noncatastrophic. Catastrophic failures render the device totally nonfunctional, while noncatastrophic failures result in an electrically operating device that shows parametric degradation and limited performance.