Remaining life from the corrosion rate
Corrosion rate from two wall thickness surveys and the remaining life to the retirement thickness; the longest interval to the next inspection.
CR = (t_prev − t_act) / ΔτRL = (t_act − t_req) / CRΔτ_insp ≤ RL / 2The rate is taken as constant (linear extrapolation, as in API 570). At pitted locations use the minimum thickness and the rate of the deepest pits. The inspection interval is not more than half the remaining life nor the limit for the piping class (API 570: 5 years for class 1, 10 years for classes 2 and 3). If no thinning is seen, take the rate from similar service.
Source: API 570, section 7 (corrosion rate and remaining life); API 510 for vessels
Inputs
You can change a field's unit: the value is converted to the formula's units automatically.
Or the initial (nominal) one for the long-term rate.
The lowest ultrasonic reading at this location.
The pressure design thickness without the corrosion allowance (t_p in the wall thickness calculator) or by the retirement criteria.
Unit converter for this formulaLength · Time
- m1
- cm100
- mm1,000
- km0.001
- ft3.28084
- in39.3701
- 1/32 in1,259.84
- 1/64 in2,519.69
- mile0.000621371
- CR — Corrosion rate–mm/yr
- Δτ_insp — Longest interval to the next inspection–
More in Corrosion protection
Mean protective current from the surface area, the current density and the coating breakdown factor, and the net mass of galvanic anodes for the design life — per DNV-RP-B401; the number of anodes.
Average general corrosion rate from the mass loss of a corrosion coupon over the exposure time, in mm/yr and mpy; the corrosivity rating per NACE SP0775.
Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.