Flow accelerated corrosion doesn't announce itself. A carbon steel elbow can lose most of its wall thickness while looking completely normal from the outside, because FAC eats metal from the inside of the pipe where flow turbulence strips away the protective oxide layer faster than it can reform. The only way to know a component is thinning is to measure it, rank it against the components most likely to fail, and measure it again. Sign up to track UT thickness readings, thinning rates, and risk ranking for every susceptible component in your fleet.
Why It Matters
FAC has caused some of the industry's most serious piping failures, and in every case the thinning had been progressing for years before anyone measured it. A single elbow rupture on high-energy piping can injure personnel and force weeks of forced outage. A structured inspection program catches the same thinning while it's still a scheduled repair.
Where FAC Concentrates Its Damage
Elbows & Bends
Flow separation on the outer radius creates turbulence that strips the protective oxide layer fastest at these points
Tees & Reducers
Any geometry change that disrupts smooth flow becomes a thinning site, especially downstream of the transition
Orifices & Control Valves
High velocity through a restriction is one of the strongest predictors of accelerated wall loss just downstream
Feedwater Heater Drains
Two-phase flow in drain piping combines high turbulence with elevated temperature, a known high-risk combination
Running A Susceptibility Assessment
Map The Piping System By Metallurgy And Flow
Carbon steel lines carrying wet or two-phase steam at velocity are flagged first, since chrome content and flow regime drive susceptibility more than any other factor
Rank Components By Geometry And Operating Conditions
Elbows, tees, and reducers score higher than straight runs, and the ranking shifts further with temperature, pH, and oxygen level from the chemistry program
Take Baseline UT Thickness Readings
Grid readings at each high-risk location establish the starting wall thickness that every future inspection gets compared against
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Calculate Thinning Rate And Set Re-Inspection Intervals
Comparing two or more readings over time gives a wear rate in mils per year, which sets how soon that component needs to be checked again
Turn UT Readings Into A Real Risk Ranking
Oxmaint logs every UT thickness reading, calculates thinning rate automatically, and ranks components by risk across your entire fleet. Sign up for a free trial to bring FAC tracking to your units, or book a demo to see it configured for your piping systems.
Ranking Components By FAC Risk
| Risk Factor |
Low Risk Condition |
High Risk Condition |
| Metallurgy |
Chrome-molybdenum alloy steel |
Plain carbon steel with no chrome content |
| Flow Regime |
Straight run, single-phase, low velocity |
Elbow or tee with two-phase, high velocity flow |
| Temperature |
Below roughly 300°F or above 500°F |
Within the 300 to 480°F peak FAC range |
| Cycle Chemistry |
Oxygenated or well-controlled AVT(O) |
Low pH or reducing chemistry with oxygen drift |
The Inspection Lifecycle For A Susceptible Component
Baseline UT
Starting wall thickness
Repeat Reading
Thinning rate calculated
Interval Set
Re-inspect before minimum
Repair Or Replace
Scheduled, not forced
Each cycle through this loop tightens the thinning rate estimate. A component tracked this way gets replaced on a planned outage, well before the wall reaches the minimum thickness a code calculation requires.
The Payoff
A FAC program that ranks components correctly and re-measures them on schedule turns an unpredictable failure mode into a routine capital planning line item. Skipping the ranking step means every component gets treated the same, which wastes inspection time on low-risk piping while the highest-risk elbow goes unchecked.
Frequently Asked Questions
Q
Why can't visual inspection catch FAC before it's serious?
FAC removes metal from the inside surface of the pipe and leaves the outside diameter completely unchanged, so a visual walkdown shows nothing unusual right up until the wall fails. Ultrasonic thickness measurement is the only reliable way to see the thinning while it's still developing.
Q
How often should high-risk components be re-inspected?
There's no single interval that fits every component. The interval is calculated from the measured thinning rate and the margin remaining to minimum allowable thickness, so a fast-thinning elbow gets checked far more often than a slow-thinning straight run on the same line.
Q
Does upgrading to chrome alloy piping eliminate FAC risk?
Chrome-molybdenum alloys are far more resistant to FAC than plain carbon steel and are the standard replacement material at known high-wear locations, but they don't make inspection unnecessary. Chemistry excursions and unusual flow conditions can still cause measurable wear over the long service life of these components.
Rank Every Component Before The Next Outage
Oxmaint tracks UT readings, thinning rates, and risk ranking for every susceptible component across your fleet, so the highest-risk elbow is never the one that gets missed. Sign up for a free trial to bring FAC tracking to your units, or book a demo to see it configured for your piping systems.
