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Pressure Boundary Inspection Quick Guide

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Effective HRSG inspections focus on damage mechanisms that could affect each of the specific components; not all components are susceptible to all damage types.  Focusing an inspection only on components affected at other plants (scope defined by “industry experience”) has in some instances resulted in wasted resources or ineffective utilization of resources.  This is because high-risk locations for some mechanisms (for example, FAC) vary from plant to plant.  Blind inspections that do not consider plant specific conditions often yield sub-optimal results. The table below shows is a quick summary guide to the damage mechanisms affecting pressure parts and the most likely locations where one might look first for that type of damage, if time is limited and/or in the absence of any clear indication that this damage might have occurred in any particular area of the HRSG.  Once the pressure boundary is breached then water and steam will leak out.  If the leak is large enough, it will be detected by excessive makeup water consumption and/or by noting steam or water exiting the casing during operation. During an internal inspection, the location of leaks and the pressure boundary breach are typically identified by the presence of water traces or staining on the inside of the unit.  Nevertheless, it is important to note that the source of most staining or discoloration is not pressure boundary leaks.  Other common sources include: rainwater or vented steam/water leakage from roof, water leaks during testing and tube exposure to elements during construction

Damage Type
Usually Found In
Occasionally Found In
Best Location to First Inspect
1
Corrosion Fatigue
Economizers, Evaporators, Preheaters
Superheaters, Reheaters
P-No. 101 through P-No. 103
2
Creep or Creep Fatigue
Superheaters, Reheaters,
P-No. 101 through P-No. 103
3
Graphitization
Superheaters, reheaters
P-No. 101 through P-No. 103
4
Deposition & Underdeposit Corrosion
Evaporators
P-No. 101 through P-No. 103
5
Erosive Wear and FAC
Economizers,FW Heaters (FAC); LP Evaporator Tubes (FAC and EW); LP and IP Drum Internals (FAC or EW)
LP & IP Evaporators (FAC or EW)
P-No. 101 through P-No. 103
6
External Corrosion and Oxidation
FW Preheaters, LP Economizers
Superheaters, Reheaters,
P-No. 101 through P-No. 103
7
Acid Dewpoint Corrosion
FW Preheaters, or LP Economizers
P-No. 101 through P-No. 103
8
Fatigue
Superheaters, Reheaters
Economizers, FW Preheaters
P-No. 101 through P-No. 103
9
Pitting
Drums, Economizers, FW Heaters, Drain Lines
Evaporators, Superheaters, Reheaters, Vents
P-No. 101 through P-No. 103
10
Stress Corrosion Cracking
Economizers, FW Heaters
Superheaters, Reheaters, Evaporators
P-No. 101 through P-No. 103
11
Thermal Overstress
HP Superheater, Reheater
P-No. 101 through P-No. 103
12
Tensile Overload
HP Superheater, Reheater
P-No. 101 through P-No. 103
13
Thermal Quench
HP Superheater, Reheater
P-No. 101 through P-No. 103
14
Wear
All tubes
P-No. 101 through P-No. 103
15
Weld & Fabrication Defects
All areas
P-No. 101 through P-No. 103
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