KROHNE ALTOSONIC V12 – Velocity Path Mismatch

Category: Custody Transfer · Ultrasonic Flowmeter · Natural Gas

Plant / Application

Gas transmission station – fiscal metering skid (custody transfer)

Problem Statement

ALTOSONIC V12 flowmeter started reporting velocity path mismatch alarms and unstable flow readings, raising concerns about custody transfer accuracy.

Observed Symptoms

• Velocity deviation between multiple ultrasonic paths
• Intermittent diagnostic alarms
• Increased uncertainty in reported flow rate
• No obvious electronics or communication faults

Initial (Incorrect) Assumptions

• Suspected ultrasonic transducer failure
• Considered electronics or signal processing fault
• Planned meter recalibration

Root Cause Analysis

Detailed investigation showed that the issue was not related to the meter itself. The actual causes were:

• Flow profile distortion due to upstream piping modification
• Insufficient straight pipe length after a recently added valve
• Swirl and asymmetrical velocity distribution across the meter body

Corrective Actions Taken

• Reviewed installation against KROHNE straight-run requirements
• Removed upstream flow disturbance (control valve repositioned)
• Installed flow conditioner upstream of ALTOSONIC V12
• Verified diagnostics and velocity symmetry after modification

Result After Correction

• Velocity paths returned to balanced condition
• All diagnostic alarms cleared
• Stable and repeatable flow readings restored
• Meter accepted again for custody transfer service

Lessons Learned

• Ultrasonic meters are highly sensitive to flow profile distortion
• Most ALTOSONIC V12 alarms indicate installation issues, not meter failure
• Diagnostics should be trusted before recalibration or replacement
• Custody transfer meters demand strict adherence to piping standards

Golden Field Rule

When a custody transfer ultrasonic meter shows path mismatch, always inspect flow profile and upstream piping before suspecting electronics or calibration.