Boiler tube failures continue to be the leading cause of costly down time. Diagnosis of the root cause is critical to determining appropriate corrective action. Our metallurgical laboratory is dedicated to providing you with a comprehensive inspection and metallurgical assessment, from initial diagnosis in the field to a metallurgical analysis in our own laboratory facilities.
To complement the assessment, we issue a thorough report on the inspection findings, including color photographs and all metallurgical and testing results. Full-time metallurgical personnel staff our laboratory, with expertise in essentially all ASTM designation tubing and pipe products used in most boilers. This includes not only carbon and low alloy steels, but also more exotic stainless steels and other metal alloys. We provide services for all OEM steam generating, fuel burning and other ancillary equipment, including environmental systems and equipment.
- Metallurgical Analysis
- Failure Analysis
- Replication Analysis
- Remaining Creep life
A metallurgical analysis of tube samples from each unit component is recommended at least every 5 years to provide a critical check of boiler condition; this allows you to address potential concerns before they grow into unmanageable problems.
Conducting assessments of boiler tube microstructure can reveal deterioration resulting from corrosion, cracking, thermal aging, or mechanical deformation. Accurate tubing assessment provides important data for determining your boiler’s overall condition as part of remaining life assessment. Tube samples are also analyzed for metallurgical and manufacturing defects and internal and external surface discontinuities. Using optical and electron microscopes, we evaluate tube sections and hardness and dimensional measurements are also made to further assess the tube’s condition. A complete metallurgical assessment of a component includes: visual inspection, dimensional measurements, micro structural assessment, hardness measurements, and chemical analysis of internal and/or external depositions, remaining creep life (as appropriate) and deposit weight density calculations (as appropriate).
Our Metallurgical Laboratory specializes in forensic failure analysis of metallurgical components. By performing a comprehensive failure analysis, we can identify the root causes of failures, discover metallurgical problems, and make recommendations to prevent future reoccurrences. Using the most advanced analytical equipment and techniques, test results are interpreted and recommendations are made by our licensed professional engineers registered in the discipline of metallurgical engineering. We can provide failure analysis of tube samples, headers, casing, pulverizers, burners, grate clips, and many more components.
A failure analysis includes a full metallurgical analysis, as well as a description of the failure mode, and recommendations inspection of similar components, replacement/repair, and changes to operating conditions.
Some of the more common failure mechanisms in boiler components include:
- Corrosion Fatigue
- CorrosionFireside corrosion
— Hydrogen damage
— Acid phosphate corrosion
— Caustic gouging
— Acid dew point corrosion
— Liquid ash corrosion
— Stress corrosion cracking
- Over temperature conditions (including spheroidization and graphitization)
- Material defects
- Weld defects
- Stress overload
- Operational Issues
Metallurgical replication is a non-destructive technique that is suitable for components that are too large, expensive, or time-consuming to replace – such as headers and high energy piping. Our skilled personnel perform a replication at your site. A small area of the surface of a component (roughly 2” sq. in) is ground and polished to a 1 micron finish and etched, revealing the microstructure. A piece of plastic is then placed on the etched surface, capturing the microstructure. The replication is then sent back to the Metallurgical Laboratory for analysis. Replication provides the same level of micro structural detail as a sample sent to the Laboratory. Replication is commonly performed at the heat-affected-zone (HAZ) of welds, an area particularly susceptible to creep damage.
Remaining Creep Life
Creep is defined as the time-dependent plastic deformation of a material under stress and at elevated temperatures. It is a common problem for steam tubes, particularly in units with extended service time. The four primary factors in predicting remaining creep life are time in service, metal temperature, stress, and material dependant properties. The metal temperature can be estimated from the thickness of the internal oxide/scale of a tube. Estimate of the stress is based on the tube dimensions and the operating pressure of the unit.
Remaining creep life calculations are performed on all superheater and Reheater tube samples received in the Metallurgical Laboratory; readings can also be taken in the field with Ultrasonics. In this way, hundreds of the tubes can be analyzed for RCL, creating a map of a component or unit. Based on the results of the RCL calculations, recommendations can be made about the components, including changes in the operating conditions, tube replacement, or material upgrades.