Amine Pump Trip – Root Cause Analysis

At an onshore gas terminal (OGT) On 14-04-2015, at around 22:40 Hrs, heavy rain with the wind was witnessed and later at around 23:06 Lean amine charge pump, 11-P-103A which was running normal suddenly tripped on Axial Displacement High High (11-VAHH 3111A, 1 out of 2 logic).

At the substation, the Rotor lock alarm appeared and the start delay timer got activated for 3000 sec. Immediately at 23:16 hrs, Pump-B (11-P-103B) was started, but it was tripped on overload, and the start delay timer got activated for 3000 sec at the substation.

Later Pump-B start delay timer was reset and it was again started @ 23:55 hrs, and the plant was stabilized. The event caused a production loss of 1 hour.

Amine Pump Trip

A team is formed to identify and perform root cause analysis for the following incidents:

  1. Sudden tripping of running Pump-A and going to rotor lockout condition
  2. Tripping of standby Pump-B on overload while starting
  3. Delay in Second Cold starting of HT motor of the Pump      
Equipment information                               Failure information
Unit: Gas Sweetening Unit (GSU) Train-1                          Date of Failure: 14/Apr/2015
Service: Lean Amine Service                          Time of Failure: 23:06
Equip. Tag No.: 11-P-103 A LA Charge PumpFailure Category: Operation upset
Equip. Tag No.: 11-P-103 A LA Charge PumpFailure Impacts: Production Loss
Equip. Criticality: Critical                             
Amine Pump Trip - Root Cause Analysis

Probable Causes

  1. Actual and true vibration of the shaft in Pump-A
  2. Malfunctioning of vibration probes in Pump-A (11-VAHH 3111A)
  3. In case of Pump-B overload trip is due to sudden higher opening of pump discharge manual valve or recycle valve FCV-1609 or amine feed valve FCV-1201 (to the absorber) while starting of the pump

Observations

Following are the observations after performing relevant mechanical, electrical, and instrumentation checks on Pump-A:

  • Pump decoupled and mechanical checks (shaft free rotation, shaft integrity etc) performed and all parameters are found OK
  • Pump AOP ran and found OK
  • Pump Electrical Motor was found OK
  • No loose connections were observed in the Vibration Probe loop
  • Rain water droplets found on the joint of Vibration Probe cable and Extension cable but not inside the cable joint
  • Blackish foreign paste type material observed on the tip of Vibration probe

Following are the observations on Pump-B:

  • On 15/04/2015 Pump-B started and observed all parameters are normal.  However a peak flow of 250 M3/Hr was recorded while starting the pump and this caused the overload tripping of the pump

Root Cause Analysis

  • Pump-A: From the observations above, it is concluded that this is a case of malfunctioning of Axial Displacement Vibration Probe (11-VAHH 3111A) which caused tripping of the Amine Pump-A
  • Pump-B: From the observations above, it is concluded that the Pump-B tripped on over load due to sudden  and full opening of discharge valve and full open condition of the Recycle Control valve.

Recommendations

Following are the recommendations to avoid Amine Pumps tripping due to

  1. malfunctioning of Vibration Probes
  2. motor overloading during start up
EquipmentDepartmentRecommendationsRemarks
11-P-103 A/BOperationsRevision/modification of existing SOP for Amine Pumps operationTo avoid overload tripping of the motor during start-up
11-P-103 A/BInstrumentationInstall rain protection casing tube on the Vibration Probes cable loops and seal it with Silicone SealantTo prevent water ingress into the system during rains and leading to malfunction of probes
11-P-103 A/BInstrumentationSMP for Periodic cleaning of the Vibration Probes (as Blackish foreign paste-type material observed on the tip of Vibration probe),  Periodic checking of Vibration Probe linearity function,  Periodic checking of Digital Output Relay function and replacement if required.i) To avoid the accumulation of foreign & dirt material into the probes and leading to malfunction of probes

ii)  Preventive and proactive measure
11-P-103 A/BInstrumentation3 sec Time delay to trip may be considered in consultation with OEM with necessary MOCTo avoid spurious tripping
11-P-103 A/BElectricalThermal lockout settings to be reviewed and Relay vendor may be communicated for resolutionTo ensure early availability of the pump motor for startup
11-P-103 A/BElectricalActivation of Start delay timer: The maximum number of Hot / Cold Successive starts data of  Motor to be obtained from OEM (BHEL) and accordingly parameterization to be done in consultation with Relay VendorTo ensure early availability of the pump motor for startup
11-P-103 BElectricalLocked Rotor Alarm: Review of relay settingsThe points to be considered during Relay co-ordination study for optimum settings as per the current operation of motors
11-P-103 BMechanicalCheck  pump rotor and bearings healthinessTo avoid  Locked Rotor Alarm

Documents and Reports

  1. DCS sequence of events
  2. DCS Trends

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Amine Pump Trip - Root Cause Analysis

 
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