Boiler Tube Inspection System
The field trials of boiler tube inspection with MsS system were conducted at an operating plant in Texas. The MsS guided-wave
testing was conducted on horizontal reheater tubes in one of the boilers at the plant. The outer diameter of the tube was 2-1/8 inches.
The overall horizontal length of the reheater tube was approximately 40 feet. Each tube line was made of five different materials
(SA-210 A-1, SA-213 T-11, SA-213 T-22, SA-213 T-9, and SA-213 TP-304H), with thicknesses ranging from 0.148 to 0.300 inch. Each line also
contained three U-bends and two or more 90° bends.
The MsS instrument was set up outside the boiler near a manway on the 7th floor of the unit, and the MsS coils installed on the tubes to be
tested were connected to the instrument via a 100-foot-long system cable. Both 128-kHz torsional-mode wave and 128-kHz longitudinal-mode wave
were used in this trial.
The longitudinal-mode probe and test data are shown in the below figure. In the figures, "W" indicates a signal from a weld and "S" from a vertical
spacer between the tubes in adjacent rows. The locations of 90° and U-bends in the reheater tube network are indicated in the plot.
Based on the findings from these field trials, we conclude the following:
- The long-range guided-wave inspection technique has potential for comprehensive inspection of reheater boiler tube networks in the field
- The achievable inspection range in one direction was approximately 30 feet for both 128-kHz T-waves and 128-kHz L-waves
- All tube networks could be inspected with proper tooling from the accessible side of the tube bank without requiring scaffolding and tube removal
- Vertical spacers increased background noise level and, thus degraded inspection capability. The degradation was greater for the L waves than for the T waves
- Except for tight U-bends, other 90° bends and U-bends in the tube networks did not show any observable negative influence on wave propagation.
Tight U-bends (bend radius estimated to be three tube diameters or less) appeared to impair wave propagation and, thus, prevented inspection of the area
- The entire length of the tube network between the inlet and outlet headers could be examined from two to three test locations, depending on the number
of tight U-bends in the network.