Process piping
API 570: piping inspection, explained
API 570 is the American Petroleum Institute's in-service inspection code for metallic and FRP piping systems and their pressure-relieving devices. It covers inspection, repair, alteration and rerating of piping that has been placed in service, and it assumes the system was designed and built to ASME B31.3 or another recognized code. It does not cover new construction, and it excludes classes of piping the scope section lists, so class assignment and the exclusion list are the starting point of any program.
What the standard requires
Piping classification
Every circuit is assigned a class based on the consequence of a failure, with the highest-consequence services in Class 1. Class sets the maximum inspection interval and how much of the system needs thickness coverage.
Circuits and CMLs
Piping is broken into circuits of similar service, material and corrosion behavior, and each circuit carries condition monitoring locations chosen where damage is most likely. CML selection has to be justified and revisited when the process changes.
Corrosion rate and remaining life
Long-term and short-term rates are computed per CML from thickness readings over time, and the one that yields the shorter life governs. Remaining life is measured thickness minus required minimum, divided by that rate.
Inspection intervals
Thickness measurement and external inspection intervals may not exceed half the remaining life or the maximum the code sets for the class, whichever is less, unless a documented RBI assessment supports a different interval.
Injection points and dead legs
Injection points, dead legs and soil-to-air interfaces are treated as their own circuits or special-emphasis locations with closer CML spacing and more frequent examination, because they corrode faster than the surrounding line.
Inspector qualification and records
An authorized piping inspector under API 570 certification accepts the inspection. The owner-user keeps permanent records covering design data, class, circuit maps, thickness history, corrosion rates, repairs and rerating.
What the record must carry
- Circuit identification, piping class, material, service and design conditions
- CML locations with the reason each was chosen
- Every thickness reading with date, method, gauge and technician
- Required minimum thickness with the ASME B31.3 formula behind it
- Long-term rate, short-term rate, and the governing value per CML
- Remaining life and next thickness measurement date per circuit
- Injection point, dead leg and CUI special-emphasis flags
- Repairs, alterations and the authorized inspector's acceptance
How intelliSPEC handles it
In intelliINTEGRITY a piping circuit's tMin routes to ASME B31.3 and comes back with the code and formula, and the corrosion summary computes short-term, long-term and maximum rate with the maximum governing and remaining life as thickness minus tMin over rate. The API 570 interval is capped at half remaining life, and CML points carry 64 fields so an injection point or dead leg keeps its special-emphasis status with the reading. UT readings arrive through intelliNDT from DeFelsko, Elcometer and Evident gauges over Bluetooth, and the CUI wizard family in intelliINSPECT covers the visual and insulation-removal work API 570 expects on susceptible circuits.
Answers
API 570 questions
What is a piping circuit under API 570?
A circuit is a section of piping with similar service, material and expected corrosion behavior that is inspected and evaluated as one unit. Grouping this way lets a corrosion rate from a few CMLs be applied across the circuit. When the process or metallurgy changes mid-run, the circuit boundary should change with it.
How are API 570 inspection intervals set?
The interval is the lesser of half the remaining life or the maximum the code sets for the piping class. Class 1 carries the shortest maximum, Class 3 the longest. A documented RBI assessment can justify a different interval, and remaining life is recomputed after each thickness survey.
Why do injection points and dead legs get special treatment?
Local conditions at an injection point, and stagnant fluid in a dead leg, produce corrosion rates far higher than the rest of the circuit. API 570 asks for them to be identified, given closer CML coverage, and examined more often. Treating them as ordinary CMLs is one of the most common findings in a program review.
What qualifications does an API 570 inspection need?
The inspection has to be accepted by an authorized piping inspector holding API 570 certification or an equivalent the jurisdiction recognizes. Examiners taking readings, including UT technicians, work under that inspector's direction and their qualifications belong in the record.