Boiler Tube and Boiler Drum Analysis (Boiler/Economizer/HRSG)

Fossil fired boilers of all sizes continue to experience boiler tube failures and if the boiler tube root cause and scope of damage is not identified repairs will be incomplete and worse a dangerous condition may exist. AIS Metallurgical Testing has a decade of experience with boiler tube failures including steam drums and water drums (mud drums) as well as boiler headers and economizer tubes.

A boiler tube failure is typically a warning sign of other problems in the boiler waterside or boiler fireside. Therefore, the boiler tube evaluation in itself can possibly be incomplete with the cause(s) being something else but manifesting at the boiler tube. You should examine all aspects of boiler that lead up to the time of the boiler tube failure to resolve the cause(s). AIS can assist you by using our field experienced staff to find the root cause.

AIS boiler tube analysis will complete boiler tube (Boiler/Economizer/HRSG) metallurgy, deposit weight analysis, boiler tube erosion, boiler tube external corrosion, water side and steam side corrosion, boiler overheating of tubes, tube sheet, steam drum and water drum (mud drum) including headers and economizer tubes. Specifically, our laboratory can perform, based on a level of afforded effort on, the following:

Why did the failure occur (Failure Mode)- Very Broad

Failure mode distinguishes the mechanisms of the boiler tube failure. AIS would use metallography to determine cause of failure for instance identify corrosion and may not be limited to metallography, but may include boiler tube scale or deposit analysis with microstructure evaluation and chemical analysis with physical properties.

Changes in Microstructural Analysis – Very Cost Effective

You know something happened but the metal appears okay. You have no assurances about the boiler tube’s or boiler part’s condition. Evaluating the microstructure can expose boiler metal deterioration. As a minimum, AIS Metallurgical Testing will use optical microscopes on your boiler tube specimen including hardness and dimensional measurements.

Scale and Deposit Analysis with Deposit Weight Measurements -

Watersides scaling/deposits and fireside scaling/deposits on boiler tubes decrease heat transfer and sometimes overheat the boiler tube or establish a localized corrosion cell. When unscheduled shutdowns and higher-than normal costs are experienced, then a Scale and Deposit Analysis with Deposit Weight Measurements provides information about the steps you should take to solve and correct the problem including cleaning with a chemical wash, acid cleaning or alkaline cleaning.

Boiler Tubes and Drums Condition Assessment / Remaining Life Estimation

In conjunction with a boiler pressure integrity useful life study, AIS Metallurgical Testing Laboratory can provide information on your boiler tube’s future reliability.

When shipping samples include the following where applicable to begin developing a baseline of information:

Short description of location of sample and ensure there is 1-foot of tube length of additional tube material at both ends of the tube and seal the ends with paper and tap to preserve the tube evidence.
Boiler/Economizer/HRSG Manufacturer
Boiler/Economizer/HRSG Year Built
Fuel Burned in Furnace
Boiler/Economizer/HRSG Size in any of the following (MW, pounds per hour, BHP, MMBtu/hr)
Type of Boiler/Economizer/HRSG (Use a combination - WT, FTSM, Package, D-Type, Forced Circulation,…)
Boiler/Economizer/HRSG Operating Pressure
Superheater pressure and temperature outlet
Reheater pressure and temperature outlet
Last Chemical/Wash Cleaning: Date & Solvent(s) if Used

Case Studies (A few from the files)

Independent Power Producer – Small Utility Station – Biomass with Light Refuse Supplement

Superheater Tube Failure: High-temperature Oxidation: The unit had an unscheduled shutdown with penalties. The superheater tube experienced rupture when the tube wall thinned from localized high-temperature oxidation where the outside boiler tube surface temperature relative to the oxidation limit of the tube material was elevated. In this case the fireside ash corrosion characteristics is dependent on temperature including fuel and boiler design. Damage occurs when particular ash constituents which are corrosive when molten on the superheater tube surfaces.

Institution – Hot Water Heating Fire Tube Rear Tube Sheet – Fuel Oil

Low water condition occurred in the fire tube scotch marine boiler requiring a retube. The rear tube sheet appeared visually acceptable and was initially considered safe. However, the rear tube sheet was found to have experience a reduction in strength and microstructure changes consistent with moderate to long term localized elevated temperatures in the ASME carbon steel that was specified when built decades ago.

Institution – High-Temperature Hot -Water Tube Generator (Boiler) – Fuel Oil and Gas Fired

The boiler had been experiencing unexpected costly shutdowns during the heating season. A macro examination was afforded of a tight bend (hair-pin) radius tubes that were failing. These tubes were failing from corrosion from the watersides. The corrosion pattern found were isolated pitting corrosion from the following sources when AIS assisted the heating plant staff and found the corrosion products (iron-oxides) originated from the heating loop off site including entrainment of atmospheric air when drained (poor lay-up) and under treated fresh domestic water for dissolved O2 (oxygen) and CO2 (carbon-dioxide).

Microscopy

Even the best experts do not have eyes that can see the minute detail that a microscope can identify. When used in conjunction with field and other laboratory techniques microscopy can bring value to better decision making.

Introduction to Metallurgy

Metallurgical Tutorial: This is an introductory metallurgy tutorial on metals to give people a basic metallurgical understanding of metals and steel. This tutorial even covers galvanic corrosion of steel.

Click here to learn more!