Machinery Analysis

Fundamental Tool for Robust Design

Machinery Analysis

Machinery Analysis

Machinery analysis is of utmost importance in various stages of machine life. From design up to performance evaluation, from single components to systems, from machine to foundation, and so on, a strong computational capability is mandatory to manage machinery in all its different aspects. CST has given top priority to this aspect. Nowadays CST has got an extremely wide array of computational tools both proprietary and commercial.

Pulsation and Mechanical vibration analysis

Pulsation and Mechanical vibration analysis

SUCCESSFUL VIBRATION CONTROL ESSENTIAL FOR PLANT RELIABILITY

Machinery vibration is one of the main causes of damage and equipment failures. Reciprocating compressors are particularly exposed to vibration problems due to the alternating motion of reciprocating masses and shaking forces produced by the pulsating flow waves generated in the piping and vessels by the piston movement.

CST EXPERIENCE AND SOLUTION

CST has combined the long-standing experience of its design engineers with advanced and integrated proprietary computational tools, aiming to identify the most efficient and cost-effective solution to any pulsation and vibration problem, both for new units and existing installations.

Our Pulsation and Mechanical Vibration study fully complies with API 618/688. It supports plant designers and end-users from the early stage of a project up to servicing and troubleshooting.

CST has done also field measurements of pressure pulsations in order to validate its calculation methods.

CST EXPERIENCE AND SOLUTION

CST solves and identifies the best solution for the following complex technical challenges:

  • Volume bottle sizing and verification
  • Pressure pulsation effects on the plant system, from cylinder valves up to large non-resonant vessel sufficiently far from the compressor, including piping and vessels of the compressor island
  • Shaking forces and pressure drops
  • Optimization of bracketing type and position
  • Small bore connections
  • Cylinder valve dynamic response
  • Compressor capacity and power consumption
  • Acoustic and mechanical resonances

The CST Pulsation and Mechanical Vibration Study goes far beyond an accurate mathematical calculation but is extended to finding the best solution for the volume of bottles, piping arrangement and support type and position.

SOME EXAMPLES OF CST PULSATION AND MECHANICAL VIBRATION STUDY

HIGH HYPER-COMPRESSOR PIPING VIBRATION
HIGH HYPER-COMPRESSOR PIPING VIBRATION
High piping vibrations on a Hyper-compressor was investigated and cured by strain gage measurement, pulsation analysis, orifices insertion and support modification.
LDPE HIGH PRESSURE COOLER RUPTURES
LDPE HIGH PRESSURE COOLER RUPTURES
Repeated Hyper-compressor interstage cooler dangerous ruptures due to excessive vibrations were cured by FEM study, new support design and reinforced grouting.
MINOR BRANCHES FAILURE
MINOR BRANCHES FAILURE
Several ruptures occurred on an Off-Shore Gas Lift Compressor and were cured with new supports and restriction orifices.
WELDING RUPTURES ON INLET NOZZLE
WELDING RUPTURES ON INLET NOZZLE
Unexpected trips with gas leakages on a HDPE reciprocating compressor were cured with the new supporting structure and restriction orifices.
FLOW INDUCED VIBRATIONS IN A PLANT WITH CENTRIFUGAL COMPRESOR
FLOW INDUCED VIBRATIONS IN A PLANT WITH CENTRIFUGAL COMPRESOR
A difficult high flow induced vibration problem due to a Tee junction was overcome with a cost effective solution by Flow modelling, Piping FEM and the appropriate modifications.
HIGH VIBRATIONS ON A SCREW COMPRESSOR
HIGH VIBRATIONS ON A SCREW COMPRESSOR
High vibration causing continuous compressor shut-downs were solved with an on-site measurement campaign and a pulsation study to eliminate resonance with the first stage passing frequency.
TORSIONAL & LATERAL VIBRATION ANALYSIS

TORSIONAL & LATERAL VIBRATION ANALYSIS

SAFE ROTATING MACHINERY OPERATION REQUIRES SMART ROTOR-DYNAMIC, TORSIONAL & LATERAL VIBRATION ANALYSES

Rotating machinery (compressors, pumps, turbines, etc.) is subject to cyclic forces along the shaft line mainly due to load fluctuations, unbalancing, instability, misalignment etc. The variable conditions of pressure, handled capacity and speed as well as the geometry of some components produce exciting forces and therefore vibrations, torsional and lateral. Vibration can be very harmful for the whole machinery, in particular when one or more harmonics are close to one or more natural frequencies, or the shaft line is in a resonant condition.

To avoid resonances and damage to machinery a Torsional and /or Lateral Vibration Analysis is strongly recommended.

CST EXPERIENCE AND SOLUTION

CST developed a proprietary software CSTors to perform very accurate torsional and lateral analysis. CSTors is kept continuously up-to-date to the best of breed available technology. In addition, CST has long-standing experience gained by troubleshooting machines of various types. CST can deliver the most appropriate torsional and lateral vibration analysis to prevent vibrational issues on rotating equipment, both for new and existing units.

CST calculation methodology focuses on:

  • Equivalent shaft calculation by FEM analysis
  • Optimum flywheel and coupling selection
  • Exciting harmonics by CST SW ReciPerf
  • Electric motor air-gap effect evaluation
  • Small bore connections
  • Cylinder valve dynamic response
  • Compressor capacity and power consumption
  • Acoustic and mechanical resonances

CST proprietary software CSTors allows to supply API 618/684 studies with:

  • Modal Analysis to find possible resonances
  • Steady-state & Transient Forced Response Analysis
  • Post process evaluation of torsional shaft stresses and endurance limits and induction motor current pulsations

SOME EXAMPLES OF CST TORSIONAL/LATERAL VIBRATION STUDY

FROM GAS ENGINE TO ELECTRIC MOTOR
FROM GAS ENGINE TO ELECTRIC MOTOR
Change of the driver of a reciprocating compressor required an accurate torsional analysis to assess the proper operation of the new machine train.
IGCC COMPRESSOR START-UP FAILURE
IGCC COMPRESSOR START-UP FAILURE
Impeller destroyed twice at first start-up. Lateral analysis revealed wrong clearance on bearings being the cause. Clearance correction was the solution.
HIGH SPEED ELECTRIC MOTOR WITH SIGNIFICANT VIBRATIONS
HIGH SPEED ELECTRIC MOTOR WITH SIGNIFICANT VIBRATIONS
High vibrations were encountered during the commissioning of a permanent-magnet electric motor detected with the detailed lateral analysis. The rotor had to be re-designed to avoid the first critical speed within the operating range.
COMPUTATIONAL FLUID-DYNAMICS

COMPUTATIONAL FLUID-DYNAMICS

ADVANCED CFD ANALYSIS ALLOWS BETTER PERFORMANCE OF TURBO AND RECIPROCATING COMPRESSORS

3D Model CFD simulation is an essential tool in the design of turbomachinery. It enables the following improved design capabilities:

  • accurate characterization of velocity fields
  • pressure distribution
  • loss sources
  • design and off-design performance verification
  • identification of critical points

CST has access to the most advanced software, hardware and skill to perform 3D Modelling, CFD simulation for the design of new centrifugal compressors and revamping of existing units.CST utilizes 3D Modelling CFD simulation also for designing gas flow path in the cylinders of reciprocating compressors. In this specific field, CST has also developed a parametric computational tool (CylOpt) for the preliminary design of valve-valve pocket area.

SOME EXAMPLES OF CST 3D MODEL CFD SIMULATION

Finite Element ANalysis

Finite Element ANalysis

FEA FOLLOWED BY POST-PROCESSING WITH FATIGUE ANALYSIS ARE MANDATORY FOR SAFE MACHINE OPERATION

FEM analysis (FEA) is a great tool extensively used in Virtual Prototyping enabling design engineers to size and shape every machine component. For components subject to static stresses, it is normally sufficient a good elastic FEM analysis. For components subject to fluctuating stresses, such as those of the reciprocating compressors, it is often necessary to go deeper and make an elastic-plastic FEM analysis followed by a fatigue analysis through a dedicated post-processing software.CST is equipped by the most advanced FEA and fatigue analysis software, it has grown a group of engineers, developed great collaborations with universities specialized in this technology, also producing many scientific articles for international congresses and technical magazines.

SOME EXAMPLES OF FEM ANALYSIS

RECIPROCATING COMPRESSOR:CONROD FEA
RECIPROCATING COMPRESSOR:CONROD FEA
The tie-bolts of connecting rods and their relevant contact areas with shank are the most stressed points of reciprocating compressor and engines. A normal FEA is not sufficient to accurately design these parts. CST designs these components within an elastic-plastic stress analysis, which results are then post-processed for evaluation of the fatigue safety coefficient.
RECIPROCATING COMPRESSOR: FEA OF THE PISTON ROD TO CROSSHEAD CONNECTION
RECIPROCATING COMPRESSOR: FEA OF THE PISTON ROD TO CROSSHEAD CONNECTION
The connection between piston rod and crosshead is one of the most stressed points of reciprocating compressors. CST designs this threaded connection by the aid of an elastic-plastic stress analysis whose results are post-processed for evaluation of the fatigue safety coefficient.
CENTRIFUGAL COMPRESSOR:TOXIC GAS LEAKAGE PROBLEM SOLVED WITH FEA OF CASING
CENTRIFUGAL COMPRESSOR:TOXIC GAS LEAKAGE PROBLEM SOLVED WITH FEA OF CASING
A lack of contact pressure between the two halves of the horizontally split compressor caused serious problems of toxic gas leakage. An accurate FEA allowed the restoration of an adequate contact pressure in the critical zones, guarenteeing the complete avoidance of dangerous leakages solving the problem experienced by the customer.
RECIP THERMO-DYNAMIC PERFORMANCE ANALYSIS

RECIP THERMO-DYNAMIC PERFORMANCE ANALYSIS

GAS MIXTURE AND COMPRESSOR SIMULATIONARE ESSENTIAL FOR MACHINE DESIGN AND DIAGNOSTICS

One of the most significant development of CST is its Software for Thermodynamic performance analysis of reciprocating compressors, the ReciPerf. This software can deal with a very large number of operational cases in terms of cylinder types and settings, suction temperature from cryogenic to high temperature, discharge pressure up to the very high values for LDPE, capacity control from step through reverse flow, type of gas with a large number of state equations available in the associated CSThermo software. Because of these features, the ReciPerf is not a generic selection software but is a very precise scientific tool to determine the performance of any given compressor and can be utilized both for design of new compressors and diagnostics of the operating ones. The ReciPerf calculates all the aspects of the compression evaluating with great precision all the mechanical and thermodynamic parameters.

CST solves and identifies the best solution for the following complex technical challenges:

  • All loads (gas, inertia, combined) at every crank along the cylinder line (piston rod, Xhead to piston rod connection, Xhead pin, crankpin, main bearings)
  • Polar diagram of loads on all bearings
  • Data for torsional analysis
  • Data for flywheel selection

CST, by means of its thermo-dynamic software, can support its customers in all the circumstances where a precise evaluation of the thermodynamic performance of the compressor is needed for design, diagnostics & troubleshooting, RCA, plant performance assessment, a.s.o.

DYNAMIC SYSTEM SIMULATION

DYNAMIC SYSTEM SIMULATION

SERVICES TO EVALUATE SYSTEM TRANSIENT CONDITIONS

Dynamic system analysis is fundamental to study and optimize the overall behavior of an industrial plant. Centrifugal compressor trains are generally exposed to risk of surge and require adequate protection through dedicated control systems. These one shall be designed to meet normal operating - as well as transient - conditions. Possible process plant modifications may be identified by the outcomes of the analysis. To this purpose CST performs full plant dynamic simulation studies focusing on key risk areas: compressors, drivers, piping system, control valves, and control system.

PACKAGE STRUCTURAL DESIGN

PACKAGE STRUCTURAL DESIGN

SERVICES TO ADDRESS PACKAGE STRUCTURAL INTEGRITY

Process compressors, both reciprocating and centrifugal, are supplied in a packaged configuration, whenever their size allows it. Machine preassembling with its accessories on one or more skids, depending on the size is the preferred arrangement solution. Compressor packaging requires a deep analysis of some special aspects, some of them being in conflict each other, create a real challenge. Pulsation/vibration control, safe lifting, transportation, machinery alignment and ergonomics for maintainability.

CST EXPERIENCE AND SOLUTION

CST compressor package design carefully considers all aspects above through a dedicated study of piping support, skid structure, lifting devices, mode shapes, a.s.o.

The supporting skid is of paramount importance for a good package performance in the field. Skid optimization is therefore one fundamental step within CST’s package design process.

The best weight/stiffness compromise is done by a combination of the following tools:

  • Concrete filling: it is possible to optimize the mechanical response of the skid by filling selected empty spaces of the skid with concrete. Putting concrete into the skid increases the mass and the stiffness.
  • Beam reinforcements: Thanks to the dynamic structure analysis, it is possible to identify the best position to apply reinforcement beams to increase the stiffness of the structure and avoid dangerous resonance frequencies.
  • Foundation block and bolts: it is also possible to improve the vibratory behavior of a skid through an accurate definition of foundation bolts position and foundation block design.
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Pipe Stress Analysis

Pipe Stress Analysis

SERVICES TO ADDRESS PIPE THERMAL STRESSES

To avoid too high stresses on piping and excessive thrusts on its connections to the machinery it is necessary to perform a deep thermal and flexibility stress analysis of the piping system. This analysis allows to verify the adequacy of the position and constraint type of supports. This study defines also if any expansion joint would be required to reduce the stiffness of system and keep the thermal thrust within acceptable limit.

Often, requirements for piping flexibility to avoid excessive thermal stresses or forces/moments on the flanges connecting to the machines are clashing with piping vibration containment solutions which need stiffer piping structure. This is particularly true for reciprocating compressors that are subject to excitations of cyclic forces (pulsations and inertia forces). Therefore, making a sound analysis requires the knowledge about both disciplines.CST know-how, coupled with its computational capabilities and field experience, makes available the multidisciplinary approach to assure a flawless design of the piping systems associated to machinery design.

FOUNDATION DESIGN & DYNAMIC ANALYSIS

FOUNDATION DESIGN & DYNAMIC ANALYSIS

CST SERVICES TO ADDRESS
RECIPROCATING COMPRESSOR FOUNDATION BLOCK DESIGN

Any compressor, driver and their accessories are solidly mounted on a foundation block to avoid harmful vibrations and misalignment that could damage compressor components and equipment nearby. The foundation block interacts between the soil and the machine, and it must be designed to take into account requirements of both elements. Particular care needs to be taken for reciprocating compressors foundation block design due to the forces and moments coming from reciprocating and rotating masses movement transmitted to the foundation block. Dangerous mechanical resonances between the natural frequencies of foundation block and compressor excitations can only be avoided by an accurate mechanical analysis.

CST EXPERIENCE AND SOLUTION

CST coupled the long-standing experience of its design engineers with advanced and integrated computing tools. CST can define the most appropriate solution for a correct foundation system design for both rotating and reciprocating machines, new or existing units.

In the event of any issues the end-user faces on existing machinery, CST, together with its partner Blackstone Industrial, can help by providing a wide portfolio of services for foundations and vibration problems:

  • Visual inspection of foundation block, primarily the area of contact between the foundation block and the compressor casing or crankcase to check its integrity and evaluate any possible crack
  • Field measurements and machine vibration analysis to detect potential dangerous situations
  • Finite element analysis to evaluate the foundation system behavior in order to reinforce weak areas
  • Reduction of excitations (shaking and inertia forces), whenever possible
  • Elimination of resonances by changing vibration modes.

Review of foundation block:

Check of any possible change in soil properties (e.g. water level) with consequent review of foundation block and anchor-bolts design, providing the necessary foundation repair.

For information on CST activities, email to:

FILIPPO CINELLI at filippo.cinelli@cstfirenze.com

LUCIA MATTESINI at lucia.mattesini@cstfirenze.com

GIULIA TOSI at giulia.tosi@cstfirenze.com

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