Electric Power Industry - Asset Management

From compressors, turbines and generators to the transmission towers and distribution lines that carry the electric current produced, MATCO engineers have the experience and know-how to assess component and structure failures at each aspect of the infrastructure. Our goal as a full service testing lab and field inspection company is to provide a comprehensive one stop shop that our clients can count on to identify areas of concern, inside the plant facility and out.

Field Inspection Services Include:

• Field Inspections of Transmission & Distribution Lines - Above & Below Grade
• Cathodic Protection System Design, Implementation & Trouble Shooting

• Training Seminars

Plant Services Include:

• Condition Assessment of Boilers, Turbines, Generators, High Energy Piping, BOP Equipment
• Remaining Life Predictions
• Failure Analysis

Condition Assessment of Boilers, Turbines, Generators, High Energy Piping, BOP Equipment

Deregulation of the electric utility industry has had several of its intended effects and a few important unintended consequences. Worldwide growth in demand has exacerbated the problems. For example, while there have been unprecedented advances in plant efficiencies, wild swings in fuel prices have led suppliers to try to use fuels in systems not designed for them. Unplanned-for combustion chemistries have changed boiler conditions and maintenance personnel experience unexpected corrosion regimes. There are no simple answers for these challenges. The smart operator increases the level of scrutiny of their systems to avoid unpleasant surprises.

MATCO is well prepared to help in these turbulent times. Our engineers have deep experience in inspection of plant systems and in analysis of the sustainability of the operating conditions for the plant. One of the most common components analyzed at MATCO are turbine blade and nozzle failures. The image below shows a turbine blade that failed while in service.

SEM/EDS analysis indicates the presence of high chlorides in the failed turbine blade.

MATCO engineers collected samples at the plant facility for a detailed laboratory failure analysis. Various problems were observed with the coated hot gas path components; blades and nozzles. The turbine blades exhibited corrosion deposits at the trailing edge on the concave sides; flaking and corrosion build-up along both leading and trailing edges on the concave sides. SEM/EDS analysis indicated a very high chloride content. The turbine blade substrates, at locations where the coating was absent, were found to be deteriorating due to high temperature sulfidation followed by oxidation. The nozzle substrates, at locations where the coating was absent, were found to be deteriorating due to phase transformation at high temperature, the formation of subsurface intermetallic precipitates, and subsequent oxidation of the now unalloyed matrix.

Failures commonly observed due to corrosion or materials related issues include the following for the Electric Power Utility Industry:

A typical preliminary inspection of the boiler section of a mid-sized power plant will take about two days and produce a plan for a more detailed inspection. Preliminary inspection of the turbine section may take a similar period of time. In both cases samples are likely to be taken for analysis in MATCO’s Pittsburgh laboratories.

Common Failure Types:

Failure Analysis of Tube(s) Methodology

Performing a failure analysis of an HRGS tube actually begins prior to sample removal in the form of documentation of the tube and its surrounding environment. An exact description of where the failure occured, date and time of failure, description of start-up, operating information, and how the failure was discovered is valuable information that provides insight into the failure mechanism.

To remove tube sample(s) for analysis the following specific procedures should be used:

1. The tube section should be saw-cut in a manner that will prevent any slag from flowing inside non-failed areas.
2. The sample should be cut approximately 8 to 10 inches above, or on either side, of the failed area if possilbe.
3. Exact location of failed tube(s) should be documented.
4. Failed tubes should be numbered and counted from left to right and inlet to outlet of HRSG.
5. The module, row and number should be noted and marked on tube(s).
6. The tube should be marked as to which end is "up", indicating flow direction.
7. If part of a multi-pass module, the tube sample should be identified as either first, second, third or fourth pass.

Once the sample(s) arrives at MATCO, we typically conduct the following standard procedures.

1. Visual examination of tube(s), including comprehensive photographic documentation of failed areas.
2. Light microscopy to examine tube sample morphology and to determine mode of fracture. A macroscopic examination of the surface of the selected areas begins this stage of analysis, followed by a microscopic examination. A close examination using a stereo microscope at a magnification of 50x or less may reveal additional details. An examination of failed and non-failed samples may reveal that all of the failed samples exhibit similar or varying morphology. Magnifications ranging from 50x to 1000x can be used to examine the cross sections of failed tube samples for microstructural defects and alterations, as well as for observation of corrosion products if present. Metallographic techniques are used to determine if an over-temperature condition has existed.
3. Scanning electron microscopy (SEM) is also used to examine morphology of the tube fracture surface and to determine fracture mode. SEMs have a large depth of field allowing a large amount of the sample to be in focus at one time, a helpful feature on rough surfaces. The SEM produces images of fine features at high resolution.
4. Energy dispersive x-ray spectroscopic (EDS) analysis to determine elemental composition in the area of the tube failure and to identify possible elemental contaminants contributing to the failure. EDS systems excite characteristic x-rays to identify the elemental composition of the sample.
5. Auger electron spectroscopic (AES) analysis may be used to look for elemental segregation at fracture surfaces and to identify corrosion products. AES is used to determine the elemental composition and can provide elemental depth profiles through sputtering. This information can then be used to solve problems associated with surface appearance, cleanliness and chemical bonding.
6. Analysis of all data collected in items 1-5, above, allows determination of the mechanism and mode of failure, and identification of root cause of failure of the tube(s).
7. An illustrated formal report documents the results of the investigation including analysis of data, identification of the cause(s) of failure, conclusions, and recommendations.

*For the most part, the above failure analysis protocol can be used to assess failed turbine blades and other boiler components as well.

A condensed example of a boiler inspection and analyses that led to helpful changes for MATCO’s client is provided in the following Case History.

Case History: Metallurgical Examination of Two Failed Partition Wall Tubes

During the inspection of the boilers at a plant of a major mid-Atlantic-region electricity supplier two tubes were found to have failed. The tubes had been in service for approximately 100,000 hours with service conditions of 850 degrees Fahrenheit and 1900 psi. We were requested to determine the cause of failure. A classic thorough metallographic boiler tube failure analysis was called for to determine what conditions the pipes had actually experienced.

Chemical analysis showed that both failed tubes conformed to the chemical requirements of ASME SA 213 grade T2 chromium-molybdenum alloy steel. One of the tubes was swollen, two were cracked. The mating fracture surfaces exhibited a slanted profile characteristic of a tensile shear mode of fracture. A few transverse cracks were observed in the partition wall sections. Metallographic examination showed that the cracks had wedge-shaped profiles typical of thermal fatigue.

Typical appearance of crack in partition wall tube.

Differences in microstructures on opposite sides of two of the tubes indicated that the failed side of the tube had experienced temperatures in the range of 1250 – 1320 degrees Fahrenheit which had produced the observed spherodized microstructures. In one tube, the fracture occurred in the heat affected zone (HAZ) of the weld between the tube and the partition wall. Localized plastic deformation and elongation of the microstructure was observed immediately adjacent to the fracture.

Comparison of “normal” and elongated grain structure. Elongation takes place during plastic deformation of the metal during overheating events. Both samples etched.

The conclusion is that two of the tubes failed as a result of short term overheating which occurred preferentially on the failed sides of the tubes. The primary causes of overheating are flow interruption or the loss of coolant from an upstream failure. Overheating also produced graphitization of the partition wall adjacent to one of the tubes and thermal fatigue cracking of the partition wall sections between the tubes. Thermal fatigue is caused by the variation in stress caused by fluctuating temperatures.

These analyses helped the client to trouble-shoot his operations and avoid this type of failure in the future.

Major corporations that rely on MATCO's expertise include US Airways, General Electric, Siemens, Westinghouse, Southern California Edison, Allegheny Energy, ABB Power, NY Power and many more.

MATCO's Professional Engineers, NACE Certified Ph.D. Scientists, and engineers work closely with clients to identify critical materials issues, determine life expectancy, extend asset life, increase network reliability and manage risks.

Our team includes NACE Certified Corrosion / Cathodic Protection/ Materials Selection/ Design / Coating Specialists and Technicians (*) and other materials experts including:

Dr. M. Zee *                        Mr. Geoff Rhodes *

Dr. Don Gibbon                   Mr. Kevin Groll *

Dr. George Bayer                Ms. Debra Riley *

Mr. Marty Latona                 Mr. Ed Larkin.

Mr. Walter Gretz, P.E.         Dr. Huiping Xu *