UT Technique | References

Hydrogen Damage in Boiler Tubes

Hydrogen damage in boiler tubes is caused by a corrosive reaction between steam and steel, shown below:

Fe + H₂O = Fe₃O₄ + H₂

The hydrogen that is released reacts with carbides to decarburize the steel and forms methane gas at the grain boundaries. Hydrogen damage results in wall loss due to corrosion and decreases the strength in the material attacked by hydrogen. Figure 2 shows a boiler tube attacked by hydrogen damage. Hydrogen damage in boiler tubes is localized and requires careful scanning to detect this damage.

Hydrogen damage occurs in waterwall tubes when the pH level drops below the normal level. The damage usually occurs in areas of high heat flux and flow disturbances. These include circumferential welds, tubes opposite burners, and tube bends.

Figure 1. Boiler tube scanning to detect Hydrogen Damage in boilers. Marked locations indicate hydrogen damage detected by ultrasonic testing. Hydrogen damage in boiler tubes is very localized. Inspection at Webster Plant, Houston Lighting and Power, 1991.
 

Technique

Inspection for hydrogen damage in boiler tubes is accomplished in a two step procedure (1, 2). The first step is locating areas with ID surface corrosion by using an ultrasonic scanning method. Since hydrogen damage is highly localized one hundred percent scanning is necessary to detect any instance of damage.

The second step is to determine whether the corrosion was a result of hydrogen attack or some other mechanism. Ultrasonic velocity measurements are taken in the material under the corroded area. A loss of ultrasonic velocity is an indication of hydrogen damage. This velocity loss is measured by a pitch catch method. This technique led to US Patent, 4,890,496

A client gave the following comment after a boiler inspection:
"Anmol Birring conducted inspection to detect hydrogen damage in the nose cone of the boiler. After the inspection,  tube samples were removed for verification. Damage was positively identified where ultrasonic test found damage.  No damage was detected where the inspection result was negative. The inspection reliably detected the damage." - Plant Manager, Montana Power, Bozeman, 1989.

Figure 1: Hydrogen attack (a) The dark area on the Boiler Tube ID represents hydrogen damage. (b) Hydrogen Attack in the 18 mm thick pipe sample from a failure in a Refinery.

Field Testing - Fossil Fired Power Plants

NDE Associates, Inc. personnel have performed boiler tube inspections for the following clients:

• Reliant Energy (now Center Point), Deep Water Plant, Houston, Texas
• Reliant Energy (now Center Point), Sam Bertron Plant, Houston, Texas
• Houston Lighting and Power Company, Webster Plant, Houston, Texas
• Southern California Edison, Los Angeles, California
• Public Service of California, Boulder, Colorado
• Montana Power, Bozeman, Montana
• Los Angeles Department of Water and Power, Los Angeles, California
   

References

1. A. S. Birring, et al. "Method and Means for Detection of Hydrogen Attack by Ultrasonic Wave Velocity Measurements" US Patent, 4,890,496, January 2, 1990
2. A. S. Birring, et.al. "Detection of Hydrogen Damage", Materials Evaluation, March 1989

"Anmol Birring conducted inspection to detect hydrogen damage in the nose cone of the boiler. After the inspection,  tube samples were removed for verification. Damage was positively identified where ultrasonic test found damage.  No damage was detected where the inspection result was negative. The inspection reliably detected the damage." - Plant Manager, Montana Power, Bozeman, 1989.

Microcracks and decarburization by Hydrogen Attack

NDE Associates, Inc.
515 Tristar Drive
Webster, TX 77598
Phone: 281-488-8944    Fax: 281-488-8485