The Case of the Stubborn LACT Station

THE MYSTERY

A purchaser and transporter of crude oil products contacted ACES with a challenge relating to one of their LACT stations. A LACT unit (Lease Account Custody Transfer) is the critical control system in an oil pumping station, which measures and regulates the flow of petroleum products being transferred from place to place and from owner to owner.

The customer wanted to set one of the pumps to transfer 450 barrels of oil per hour, but the HMI was limited to a range of 500-850 bbl/h.

THE CLUES

The ACES’ CSI (Control Systems Inspector) investigated and found that when the pump was put on automatic the PID wasn’t working correctly. The PID (proportional-integral-derivative control algorithm) is a programming loop that adjusts the equipment to output at a given quantity and velocity. In this case, the PID was swinging wildly so the CSI adjusted some of the parameters, which helped some, but there was still the issue of the limited bbl/h range.

After examining the PLC code, the CSI couldn’t uncover the bounds for the setpoint. He finally discovered that the value was being limited by the HMI input field itself. The CSI looked into the HMI software to adjust the range, and found that the customer had an unusual setup: there was no physical HMI, only a webserver which displayed an HMI on the user’s laptop. The software was so old that it wasn’t even compatible with Windows 7.

THE PERP

After the ACES’ CSI backed up the HMI webserver software he contacted tech support who recommended that the CSI upgrade the software, but once he’d done that there were multiple errors, inconsistencies and even a 404 Not Found error. Obviously the upgrade wasn’t going to be compatible.

At one point the CSI looked at the files for the HMI itself to try to figure out what was going on, he noticed that the file for the main HMI screen was in lowercase, and in the address browser bar it was in uppercase. So the program was looking for the file, but it was case sensitive. He logged on to the HMI and revised the file name manually to uppercase so the program could recognize the file.

THE SOLUTION

The CSI was able to successfully restore the original software, and used a virtual machine to run it on his laptop. Then he was able to reprogram it and adjust the range so the flow set point could be set to 450 bbl/h.

The oil transfer pump took off at a consistent flow rate of 450 bbl/h and the oil has been streaming smoothly ever since.

CASE CLOSED

Have you had issues with a stubborn LACT Station? Leave us a comment below about The Case of the Stubborn LACT Station.