The Situation
A critical issue arose for a customer with a Bently Nevada Supporting Services Agreement (SSA). The customer faced an urgent problem with an LP Gas Compressor. This unit, crucial for increasing sour pressure gas from 0.5 bar to 15 bar, was experiencing critically high vibrations. Without a standby unit, any downtime would result in a 40% loss of NGL production. The plant's total capacity was 1500 Tons/day.
The compressor train in question included two centrifugal compressors driven by an asynchronous motor through a speed-increasing gearbox.
The Challenges
On March 18, 2021, high vibration was detected on the HP compressor's Non-Drive End (NDE) bearing. The situation worsened the following day, causing the unit to trip. This vibration was unprecedented since the machine was commissioned.
The vibration levels at the NDE bearing peaked at 445 µm pp, significantly above the alarm level of 60 µm pp and the trip level of 75 µm pp. Given the machine's critical role, the urgency to restore it quickly was paramount. The customer called for Bently Nevada’s remote support.
Immediate Action
Bently Nevada promptly provided remote assistance, analyzing the System 1 archive data sent by the customer. This data revealed signs of rubbing, likely at the HP NDE seal and bearing. The customer’s machinery datasheet initially indicated a liquid film seal type. However, it was later confirmed that the compressors had been upgraded to dry gas seals (DGS) a few years ago.
The extreme vibration and slow roll were caused by a change in rotor dynamics due to severe rubbing, which led to a thermal bow. Bently Nevada recommended an inspection of the HP NDE DGS and bearing.
The Solution
Following Bently Nevada’s recommendations, the customer inspected the compressor and found 2-3 mm of scoring on the rotor at the DGS throttle ring, as well as rubbing marks on the NDE bearing pads. The root cause analysis revealed foreign material ingress, specifically piping scales from liquid carryover. This had caused rubbing at the DGS throttle ring and secondary rubbing at the bearing. Additionally, a seal-gas supply alarm was in bypass due to a malfunction, which might have detected the issue earlier.
The Impact
Thanks to Bently Nevada’s swift intervention, the customer avoided costly unplanned downtime. The accurate diagnosis and timely inspection allowed for quick corrective action. The compressor was restored to normal operation with vibration levels returning to acceptable limits.
Without this support, the customer might have faced extended startup trials, potentially leading to further failures and additional downtime. The estimated loss was at least three days of NGL production, totaling 600 Tons.
Bently Nevada’s expertise in machinery diagnostics and their 24/7 remote support played a crucial role. Their prompt and effective intervention not only saved significant production but also reinforced their commitment to delivering unmatched customer value through long-term partnerships.
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