Piping Piping Inspection and Testing 3

Question 1

What is 'high-frequency guided wave ultrasonic testing (GWUT)' used for in piping inspection?

Accepted Answer

Screening long sections of pipe for corrosion from a single test point, even under insulation or through road crossings

Answer

GWUT sends low-frequency ultrasonic waves along the pipe axis, detecting reflections from corrosion, cracks, and features over distances of tens of meters from a single transducer location.

Question 2

What is the purpose of 'baseline thickness measurements' taken when a new piping system is commissioned?

Accepted Answer

To establish reference values for future corrosion rate calculations and remaining life assessments

Answer

Baseline measurements establish the as-installed thickness so that future measurements can be compared to calculate the actual corrosion rate occurring in service.

Question 3

What is 'erosion corrosion' in piping, and where does it most commonly occur?

Accepted Answer

Accelerated metal loss caused by the combined effect of corrosive fluid and mechanical erosion from flow, most common at bends, tees, and reducers

Answer

Erosion corrosion occurs where turbulent or high-velocity flow removes protective corrosion films and physically erodes the pipe wall, especially at directional changes.

Question 4

According to API 570, how is the 'long-term corrosion rate' different from the 'short-term corrosion rate'?

Accepted Answer

Long-term uses all inspection data back to baseline; short-term uses only the last two inspection readings

Answer

API 570 defines long-term rate using all available thickness data back to baseline, while short-term rate uses only recent measurements; inspection intervals are based on the more conservative of the two.

Question 5

What is the 'minimum required thickness' (t_min) in piping inspection?

Accepted Answer

The calculated minimum acceptable wall thickness based on design pressure, material strength, and applicable code formula

Answer

t_min is calculated using the ASME B31.3 pressure design formula and represents the minimum wall thickness at which the pipe can safely operate at design pressure.

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Piping Piping Inspection and Testing 3