Cracked deaerators and tired feedwater pumps quietly erode capacity, efficiency, and safety. Plants that inspect on schedule and maintain aggressively are avoiding catastrophic failures and seven‑figure losses.
The deaerator—designed to strip dissolved oxygen and carbon dioxide from HRSG (heat recovery steam generator) feedwater to prevent corrosion—is failing too often, too quietly. One industry study found 41% of inspected units had general cracking, typically in weld seams and nozzle connections (TÜV SÜD). In Alaska, a combined‑cycle plant discovered flow‑accelerated corrosion (FAC—wall thinning driven by high‑velocity, low‑protective‑film flow) had eaten roughly 33% of a deaerator wall in just 11 months, triggering emergency replacement (Power Magazine).
Damage like this doesn’t just cost steel. TÜV SÜD tallied ~$27.7 million in lost generation tied to cracked deaerators across surveyed sites—about $1.32 million per site (TÜV SÜD).
Downstream, high‑pressure feedwater pumps—the heart of the steam cycle—carry their own risk. If a pump fails the boiler can’t fire, and a boiler feed pump on a 500 MW unit can draw on the order of 10 MW of motor power, so even small efficiency losses are costly (ResearchGate). “A feedwater pump failing results in a large capacity reduction or full shutdown…presenting an opportunity loss and safety issue” (MDPI).
Deaerator internal inspection schedule
Industry guidelines (NACE SP0590‑2015) call for an intensive inspection 1–2 years after start‑up, then periodic inspections based on findings (TÜV SÜD). If weld cracks were repaired, re‑inspect every year; for non‑weld defects, every 1–2 years; if clear, every 3–5 years (TÜV SÜD).
Plants that followed this cadence uncovered problems early. One site began detailed inspections in 2005 under NACE SP0590; within two years, technicians found significant wall loss and weld cracking, and by 2007–08 FAC had consumed about one‑third of the shell thickness (Power Magazine; Power Magazine). Periodic inspections of deaerators are integral to safely running both boiler feed pump systems (Power Magazine).
Deaerator inspection methods and checkpoints
Crews remove internal trays, spargers, and baffles for full access, then apply non‑destructive testing (NDT) tools: ultrasonic thickness (UT) scans measure wall loss on shell, nozzle necks, and floor; magnetic particle or dye‑penetrant tests (surface crack detection) target welds and attachments; pit‑depth surveys quantify localized attack (Power Magazine).
Inspect and clean internals—trays, spargers, level probes, overflows—and replace worn insulation and gaskets. Verify vent valves, pressure gauges, and level controls are operational and calibrated. Test that the deaerator achieves design venting pressure (approximately saturation temperature) so dissolved oxygen levels stay ≤0.005 mg/L (Power Magazine).
The payoff is immediate: visual exams and magnetic particle inspection (MPI) have revealed LP‑steam nozzle cracks and FAC thinning on tank roofs at real plants, enabling repairs during planned outages (Power Magazine; Power Magazine).
Oxygen ingress control and chemistry
High oxygen or low outlet pressure signals trouble. At one site, routine testing tied elevated deaerator oxygen (~100 ppb versus a goal of <10 ppb) to steam‑turbine leaks; annual steam‑jet pump and turbine leak tests and tightened pump seals cut air in‑leakage, restoring performance (Power Magazine).
Risk, cost, and replacement decisions
Undetected damage escalates quickly. The same Alaska case saw the LP deaerator eventually abandoned—overcapacity had become a factor—nearly crippling feedwater flow (Power Magazine). FAC in the deaerator was also linked to repeated failures of all HP feed pump impellers and economizer tubes (Power Magazine). Installing a deflector and, later, new vessels helped avoid uncontrolled pit propagation (Power Magazine; Power Magazine).
The economics are stark. TÜV SÜD estimates that modest inspection and fixes (~€4,000 per site) can avert ~$1.32 million in losses (TÜV SÜD).
High‑pressure feedwater pump maintenance plan
High‑pressure feedwater pumps (HPFWPs—multi‑stage pumps that deliver treated water into the HRSG at 100–650 psi or higher) demand everyday discipline and periodic deep work. Daily or shift checks track bearing oil level and temperature, vibration/amperage, and leaks; operators also verify normal pressure and flow readings and listen for abnormal noise (MDPI).
Lubrication and cooling follow OEM intervals with regular lube‑oil sampling (debris flags bearing wear). Alignment is re‑checked with laser tools after outages or thermal events; coupling balance and fasteners are verified because misalignment and imbalance lead to bearing and seal failure (ResearchGate).
Filters matter: clean or replace suction filters and strainers to avoid cavitation; many sites specify a robust suction strainer to protect the pump. Mechanical seals are inspected for leakage and packing glands adjusted where present (ResearchGate).
Condition monitoring underpins reliability. Quarterly vibration analysis with accelerometers and FFT (frequency analysis) highlights imbalance, misalignment, and bearing defects before breakdown. Annually or bi‑annually, a site performance test compares operating head and flow to the OEM curve; any 5–10% drop triggers inspection—one guide specifically recommends “annual or bi‑annual performance testing” for critical pumps (Engineer News Network).
Overhauls are scheduled every few years, typically during major outages. Teardowns inspect impellers, wear rings, diffuser vanes for erosion/cavitation; bearings, seals, and O‑rings are replaced per the OEM master parts list (ResearchGate).
Pump performance gains and analytics
A comprehensive maintenance cycle can move the needle. One high‑pressure boiler feed pump flowed ~8% more at operating conditions after maintenance; the study also reported a 23–29% “performance improvement ratio” under ideal valve settings—bringing the pump nearer to its design efficiency (ResearchGate; ResearchGate). On a 10 MW motor, an 8% flow improvement translates roughly to 0.8 MW saved at full load—about 7 GWh per year (ResearchGate).
Plants are also pushing into predictive maintenance. SCADA data trends—slow drifts in current, flow, or vibration—are being analyzed with machine learning to forecast gearbox or alignment faults; programs increasingly act when conditions warrant rather than by calendar. Vendors and maintainers often recommend spare rotating assemblies or exchangeable modules to minimize downtime when service is due (ResearchGate; MDPI).
Operational takeaway
Regular internal inspection of deaerators—welds, ferrous surfaces, trays, and nozzles—prevents corrosion‑related failures that degrade boilers or trigger outages (TÜV SÜD; Power Magazine). Preventive maintenance on high‑pressure feedwater pumps—daily basics, periodic performance testing, and scheduled overhauls—keeps flow and head on spec and avoids unplanned trips. The benefits are measurable: restored pump capacity (~8% in one documented case) and avoided multi‑million‑dollar losses on the deaerator side (ResearchGate; TÜV SÜD).
