Automating a tube pressurization test sequence requires precise ramp rate control, stable hold phase monitoring, and rapid burst detection. Here is the engineering approach.
The test profile for a proof pressure test consists of three phases: a controlled pressure ramp from ambient to proof pressure (typically 10–30 bar/minute to minimise dynamic effects), a hold phase at proof pressure (typically 10 minutes with tight pressure band monitoring), and a controlled release phase. For burst testing, the ramp continues beyond proof pressure at a specified rate until failure.
The ramp rate control challenge is that Haskel intensifier pumps deliver flow in discrete piston strokes, creating inherent pressure pulsing. The PLC controls ramp rate by modulating the air supply to the Haskel driver — increasing supply pressure increases stroke rate and therefore flow and pressurisation rate. A PID controller on the pressure ramp rate (not the absolute pressure) maintains a smooth, specification-compliant ramp despite the pulsing nature of the Haskel output.
The hold phase monitor applies a tighter criterion: any pressure drop exceeding a defined threshold over a rolling 30-second window constitutes a leak indication and triggers a hold-fail verdict with automatic test abort. For a 414 bar proof hold, a typical leak threshold is 2 bar drop in 30 seconds — equivalent to a small but detectable leak rate through the test connections. Temperature compensation is applied to remove pressure drift from thermal expansion during the hold, isolating leak-driven pressure loss from thermal effects.
Burst detection uses rate of change of pressure: during a burst test ramp, a sudden increase in the rate of pressure decrease — exceeding the normal pulsing amplitude by a factor of 5 or more in a 100ms window — triggers the burst event detection and stamps the burst pressure from the last valid pressure reading before the event. Post-burst, the system automatically closes the supply valve and vents the test chamber through a restricted orifice.
WIKA pressure transducers provide ±0.1% full-scale accuracy with 4–20 mA output, sampled at 100 Hz during ramp and burst phases, and 1 Hz during hold phase. Thermocouple inputs at tube midpoint and ends monitor temperature during thermal-pressure tests and feed the temperature compensation algorithm during hold.
The Neometrix Tube Pressurization Test Setup implements this automation with PLC-based sequence control and optional LabVIEW DAQ integration.
→ https://neometrixgroup.com/products/tube-pressurization-test-setup
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