When constraints such as limited outage time or budgets disallow a more comprehensive assessment, even a limited boiler tubing inspection can provide valuable information regarding the overall condition of the boiler and its components. With proper planning and thorough surface preparations, an array of information can be gathered and serve to diagnose and predict imminent failures as well as provide estimates for the remaining useful life of the components. Boiler tube failure mechanisms that may occur individually or collectively include:
- Low-temperature creep cracking
- Long-term overheating
- Dissimilar metal weld failure
- Stress corrosion cracking
- Fatigue
- Graphitization
- Fly ash erosion
- Fireside corrosion
- Short-term overheating
- Sootblower erosion
- Pitting
- Rubbing
- Material flaws
- Welding flaws
The presence of these failure mechanisms can be revealed through a targeted inspection of the tube bundle girth welds. The surface preparations for such an inspection can be as limited as a 4 inch band sandblasted clean to shiny metal on either side of the girth weld. Despite a relatively small area for inspection, the following examinations can be performed to expose adverse conditions:
- Visual Examination
- Of both surface prepared and surrounding areas for obvious defects
- Ultrasonic Phased-Array Scanning
- Provides a full volumetric scan from both sides of weld
- Identifies surface and subsurface defects including cracking, pitting, porosity, lack of fusion, and lack of penetration
- Pinpoints locations of defects to minimize repairs by welding
- Scans dissimilar metal welds providing a more thorough examination than liquid penetrant examinations
- Hardness Determinations
- Determines hardness of material
- Soft material (ductile) may indicate creep
- Hard material (brittle) may indicate graphitization
- Determines the condition of the microstructure
- Metallographic Replications
- Determine the condition of the microstructure to identify creep or graphitization
- Provide remaining useful life estimates for the tubes
- Allow microstructure samples to be taken without removing tube sample
- Ultrasonic Tube Thickness Measurements
- Determine whether internal or external wall loss has occurred as well as severity
- Oxide Scale Measurements
- Estimate the exposure time or temperature history of the tube
- Reveal overheated areas of the boiler and incorrect firing procedures
- Used to estimate the remaining useful life of the tubes
When a row of tube butt welds is inaccessible, most of these examinations can be performed on more accessible portions of the tube bundle providing the same quality information. These measurements, when combined with tube specification data (material, pressure, temperature, etc.), allow for a comprehensive analysis of the condition of a boiler or component in a time and cost-effective manner.
Thielsch Engineering has over 30 years of experience performing condition assessments, engineering analyses, remaining life determinations, failure analyses, nondestructive examinations, and repair services for power generating and industrial plants on a national and international level. Our expert inspectors are qualified to meet the requirements of the American Society for Nondestructive Testing Practice SNT-TC-1A as well additional codes and standards. Thielsch Engineering has extensive laboratory capabilities and state-of-the-art inspection equipment and materials offering a full range of advanced engineering services.
Contact us for further information on how you can maximize your tubing inspections.