Take a look on some CST Success Stories

PROBLEM

Sudden welding ruptures on minor branches

• high vibrations since the first start-up
• skid design failed to consider alternating forces
• poor support design

SOLUTION

• acoustical study revealed the need for:
  • restriction orifices
  • new support installation

PROBLEM

Unexpected trips for gas leakage

• welding ruptures of the inlet nozzle on piping
• acoustic resonance and poor piping clamping

SOLUTION

• installation of restriction orifices
• stiffening of the existing piping structure
• optimization of clamps disposition

PROBLEM

Forced maintenance every 3 months due to fast wearing of PTFE piston sealing elements

SOLUTION

• high performance PEEK material suggested
• scheduled temperature monitoring program

PROBLEM

Rod packing elements life was <1000 hours

• recurrent rod scratching
• chromium on the rod surface

SOLUTION

• roughening treatment to increase the transfer film capacity
• suggested high performance PEEK material

PROBLEM

Ruptures on cooler and HP piping (every 2-3 months)

• high vibrations (up to 250 mm/s rms)
• modifications to be performed in one week

SOLUTION

• FEM study of the mechanical system to define modifications to existing supports and structure
• foundations reinforced through grouting
• follow-up survey to confirm root cause analysis and resolution

PROBLEM

High vibrations since first start-up

• vibrations above SWRI danger curve in some points
• acoustic analysis verified through strain gage measurements
• both acoustic and mechanical resonances found

SOLUTION

• inserted restriction orifices in key points
• modified supporting structure to shift MNF
• inserted fabric pads between clamps and pipes

SCOPE

User wanted to change driver type from gas engine to electric motor

SOLUTION

• Design of the new train arrangement with:
  • Brake and Starting torque Analysis
  • Torsional Analysis
  • New coupling and flywheel selection
• On site installation and commissioning through Blackstone (CST Canadian partner)

PROBLEM

Extremely fast rings consumption

• rings provided by OEM failed after less than 100 h
• major damages to pistons and liners due to inadequate protection system
• alternate material from OEM’s competitor lasted for 1500 h

SOLUTION

• new lubrication system
• improved cylinder cooling system
• stronger material (PEEK) with optimized dimensions
• new piston desing

PROBLEM

Frequent piping support failure

• inadequate type and position of supports
• piping weight applied on compressor flange
• wood layer between steel supports

SOLUTION

• FEM analysis to find better supports design
• new “spring type” supports
• new antifriction damping layer between steel supports

PROBLEM

Impeller destroyed twice at first Start-up

SOLUTION

• RCA with rotor-dynamic and metallurgical analyses revealed wrong clearance on bearings
• New bearing arrangement defined and installed

PROBLEM

Turbine trip during start-up on both units. Severe damage to the rotors due to rubbing against the stator

SOLUTION

• RCA indicated casing bow (non uniform expansion), resulting from an insufficient thermal insulation of the casing
• Re-calculation of the thickness of the thermal insulation
• Suggested new procedure for turbine warm-up
• Revised seal radial clearance

PROBLEM

After a maintenance stop, Turbine could not start due to high vibrations (both low and high frequency)

SOLUTION

• RCA results: not appropriate bearing clearances and oil inlet design
• Bearings replaced with 4-lobe types (low-frequency vibration)
• Trim balancing (for synchronous vibration)

PROBLEM

Explosion of the Gas Turbine cabinet

SOLUTION

• RCA indicated explosion due to a failure of lube oil trap level control loop and vent line clogged
• Lube oil vent system modified
• Lube oil tank fill-up procedure established

PROBLEM

OEM no longer available. User wanted to extend the operating life of this old unit by upgrading machine monitoring

SOLUTION

• Design and implementation of mechanical modifications to house new sensors
• Supply and installation of a new vibration monitoring cabinet, linked to the plant DCS

PROBLEM

Performance loss (efficiency and flow rate) caused by  increased clearance between impeller and casing due to corrosion

SOLUTION

• Labyrinth seal insertion
• Clearance reduction

PROBLEM

Gas leakage between upper and lower semi-casings

SOLUTION

• RCA indicated a reduction of contact pressure due to corrosion and wrong maintenance
• Static FEA to determine contact pressure distribution
• Increased stud bolts diameter, added new tie rod

PROBLEM

Performance improvement through upgrading of an old unit which has at present:

• High vibration levels upon certain process conditions
• Missed production targets due to high absorbed power
• High bearing temperature on gearbox

SOLUTION

• Site survey, gathering data from personnel & DCS
• Action list including upgrade on seals, balancing drum and gearbox bearings
• Study possible efficiency increase to improve plant productivity

PROBLEM

Δp on a temporary strainer quickly rose to ~1.3 bar

• Customer could not stop production before scheduled maintenance

SOLUTION

• Finite element analysis and a buckling analysis
• Maximum sustainable pressure drop ~ 4 bar

PROBLEM

Catastrophic failure of stirrer supporting bearing caused heavy damage to the reactor wall

SOLUTION

• RCA revealed too little elasticity in bearing clamping system
• New clamping system developed

PROBLEM

Old PtP lubrication system with recurrent issues

• Faulty sight glasses
• Unstable lubrication (dry run occurred)
• High oil consumption

SOLUTION

• 5 units retrofitted with CST PLS-100 (full redundant + continuous monitoring)
• Reduced oil consumption recovered the investment in less than one year

PROBLEM

Unexpected compressor shutdown

• Cross-head pin failure
• Crank-mechanism lubrication oil polluted by metal particles
• Delivery valves failures (cracked guard)

SOLUTION

Root Cause Analysis based on:

• Visual and metallographic inspection
• Stress and fatigue simulation by means of FEM Analysis assessed sudden overpressure caused by liquid slug ingestion

PROBLEM

Knocking sound from cylinder head

• Piston-to-rod connection found loosened

SOLUTION

• Trend analysis to highlight possible overpressures
• Visual inspection and measurements revealed an “out of tolerance” dimension of rod to piston connection
• FEM Analysis carried out on mating areas confirmed a tightening fault during assembly

PROBLEM

Foundation corruption

• Cracks on the foundation walls
• Inefficient stiffeners
• High vibrations

SOLUTION

Complete turn-key project

1. Excitation reduction adopting a different crankshaft design. Engineering completed with:
   • Dynamic analysis for unbalanced forces and couples
   • Acoustic analysis for pulsations
2. Foundation re-engineered
3. Old Foundation demolition and refurbishment

SCOPE

• Fretting phenomena on the back side of connecting rod bearings and conrod body
• Big end casted aluminum bearing failure

SOLUTION

• RCA to assess the cause of the failure and confirm the fretting phenomena by FEM simulations
• Big end bearing, studs and body reverse engineering and redesign to optimize contact pressure and avoid relative movement between bearing and big end

SCOPE

• Determine the source of piping vibrations
• Apply effective modifications to reduce them below the recommended values

SOLUTION

• Identification of a source of flow induced vibrations in a Tee junction
• Flow modelling to characterize the source of vibrations and the pulsation phenomenon
• Piping FEM modelling to determine mechanical natural frequencies
• Multiple solutions identified to find the best compromise between vibration reduction and cost of modifications

SCOPE

• Determine the source of 1st stage side vibrations, causing continuous alarms and machine blocks
• Apply effective modifications to reduce them below the recommended values

SOLUTION

• On site vibration detection
• Data analysis found a dominant frequency that characterizes the totality of plant components - 1st stage Pocket Pass Frequency
• Countermeasures design focusing on the pipe affected by resonance phenomena
• Torsional analysis of the screw compressor train

PROBLEM

• The compressor ran at 80-90% capacity most of the time
• The exceeding capacity is recycled to the compressor inlet and compression energy is wasted

SOLUTION

• “Flux-to-Flow” system designed and installed on 1st stage
• Compressor thermodynamic and torsional behaviour verified for reliable and safe operation

PROBLEM

Recurrent high vibration on a variable speed compressor

SOLUTION

• RCA revealed correlation between rotation speed and MNF
• Speed variation limited to safe range

PROBLEM

Two cylinder-distance piece tie-rods found broken

• High cylinder vibrations
• High pin load caused by suction pressure higher than design

SOLUTION

• 2nd stage cylinder bore diameter modified
• High-resistance rolled thread tie-rods
• Volume bottles size increased

PROBLEM

Increasing vibration trend suggested machine stop and inspection: resilient element found heavily damaged

SOLUTION

Major compressor failure prevented by substituting resilient element