The predominant technique for inspecting HRSGs is visual. Visual inspection is performed at nearly every opportunity. Generally, a visual exam encompasses a walkdown of the interior to view accessible components within the gas path as well as the adjoining accessible compartments. These are located above and below the gas path on horizontal gas path (HGP) units and at the sides on vertical gas path (VGP) units. These compartments contain interconnecting piping such as jumpers, risers, drains and vents. The walkdown should also include drum internals and the HRSG casing with supporting structures. The external power piping on the unit and piping supports might be added given sufficient time. Deaerator tanks and condensers are also subject to opportunistic visual inspection and periodic nondestructive inspection as required by insurers.
Visual inspection is an effective method to identify certain types of HRSG component damage including: failed pressure parts (even if the specific tube/header is relatively inaccessible – leaking water can usually be spotted), leaking or failed drains, damage to structural components and supports such as duct burner runners, gas baffles, casing liner plates, insulation, penetration seals and expansion joints. In addition, sophisticated visual instruments provide enhanced inspection of interior surfaces via borescopes, videoscopes and a variety of special purpose optical instruments such as laser profilometers. These tools provide effective means to identify corrosion, cracking and related damage to tubes, headers, attemperator spray liners and flow nozzles, riser piping to drums and feeders.
The following areas should be included in the HRSG Visual Inspection scope:
- Gas Path
- Steam/Water Side
- Drums & Tanks
Figure 1: Typical LP Drum appearance