TECHNICAL PAPERS

During centrifugal compressors life, End Users often experience performance reduction as well as component deterioration/malfunction or even have to meet new operating conditions. Whenever possible, it is fundamental to prevent a useless, costly, and time-consuming machine replacement. This paper describes two cases of old centrifugal compressor refurbishment by leveraging new technologies injection. See how new technologies have created cost effective opportunities to bring old compressors to new life.

Pressure pulsations are one of the main issues in reciprocating compressors applications. They cangenerate high pulsation induced shaking forces leading to high vibrations on compression plant elements such as piping, dampers, coolers, smallbranches and shaking forces, which can even lead to fatigue failures. In addition, pulsations can affectthe reliability and life of compressor valves. For this reason, pressure pulsation prediction accordingto API 618 standard is a fundamental step in reciprocating compressor plant design.

Evaluate the pros and cons of different recovery systems for reducing leakages from natural gas compression and storage stations.

In 2015, CST supported Blackstone for the replacemente of an engine driver with an electric motor with variable frequency drive (VFD) on a Dresser-Rand 5RDS-4 (Southwest Industries - Ingersoll Rand) reciprocating compressor. The machine was a four-stage reciprocating compressor with five cylinders that had been operational since 1954 in boil-off service in a natural gas plant located in Tulsa, Oklahoma.

If operators want their lubricated reciprocating compressors to run properly and reliably, then two issues should be avoided: poor lubrication and over lubrication. Poor lubrication with consequent premature wear of piston rings and wear bands, and over lubrication which leads to process gas contamination, impaired machine performance and higher operating costs. The article describes the completely customized lubrication system designed by CST, aimed at overcoming the drawbacks of the lubrication mechanisms currently available on the market.

Among the most widespread lubrication systems on the market two types are most commonly used, the “pump to point” and “divider block” types, but further solutions can be developed according to the specific application and customized to fit the user’s requirements. This paper describes the solution applied to a critical application: retrofitting of the cylinder lubrication system of five hydrogen make-up reciprocating compressors operating in the ENI Refinery in Taranto.

In a tubular reactor polyethylene plant, high piping vibrations were present on the Hypercompressor piping from the first machine start-up. Despite immediate analysis and small modifications to a few pipe supports, some areas continued to be subject to this phenomenon, potentially leading to ruptures, welding failures and hazardous gas leakages.

CST is a HT design and maintenance engineering company, established by a group of experienced engineers to support OEMs, Packagers, Main Contractors and End Users in designing, assembling and servicing of compression equipment.

Una delle principali cause di rotture e di conseguenti fermate inaspettate negli impianti industriali sono le vibrazioni dei vari macchinari e tubazioni.
I compressori alternativi sono, per loro natura, particolarmente inclini a questo tipo di problematiche, pertanto una particolare attenzione deve essere posta in fase di design della macchina e del layout delle tubazioni per prevenire il presentarsi di questi inconvenienti.

From service engineering provider to full scope design, engineering and execution of complete compressor systems. The article retraces the history of CST, from its origin, when the company was initially composed of just four people and worked as a service engineering provider mainly to Nuovo Pignone (now GE Oil & Gas) for reciprocating compressors, to today, when, in the span of 15 years, CST has transformed into an international player for critical machine applications in the Oil & Gas and other industrial sectors. 

Le vibrazioni sono una delle principali e più diffuse cause di danno e di guasto sulle macchine rotanti. I compressori alternativi in particolare sono spesso affetti da problemi di vibrazione, dal momento che queste sono un inevitabile effetto del moto alternato e delle pulsazioni di pressione che tali macchine generano.
Durante l’ingegneria di dettaglio vengono solitamente prese misure tecniche preventive per evitare alti livelli vibratori, generati dalle così dette shaking forces: ad esempio design appropriato delle fondazioni, sistemi di bilanciamento delle forze, polmoni smorzatori, orifici e adeguati supporti per le tubazioni. Nonostante questo, ci sono molti casi in cui i problemi di vibrazione si presentano già dal primo avviamento della macchina nell’impianto.

Reciprocating compressors generate considerable torque variations that cause torsional vibrations into the drive train that, if excessive, could bring to the failure of the components of the train. If the rotor has a superimposed torsional vibration over the steady rotation, the flux linkages, produced by the induction motor, start to oscillate.

Machinery vibration is one of the main causes of damage and failures in industrial plants, and reciprocating compressors are particularly subject to vibration-related phenomena as alternating forces and pressure pulsations are inherent in their design. Vibration problems may also arise after a machine is installed and is set in operation due to inadequate attention to interaction between the compressor and plant as a whole during the design stage. This paper will examine a case that occurred in a polyethylene plant located in Ragusa, Italy, where high vibration issues resulted in broken pipes and welding failures.

In natural gas vehicle refueling stations, the reciprocating compressor is the key element in defining both the refueling process efficiency and the operating costs of the whole station. Great attention is therefore devoted at increasing both the performance and reliability of the machine. The valve-retainer is a component that plays a key role in determining the compressor performance, by introducing significant pressure losses, which affect the suction and discharge phases. However, the valve-retainer is essential for the proper orientation of the valve during the compressor operation and guarantees a simple and reliable design of the machine.

Gli idrocarburi sono trattati ogni giorno dall’ industria di processo e, nelle fasi di compressione, i trafilamenti di gas sono eventi sempre presenti e purtroppo dannosi sia dal punto di vista della produzione sia per l’impatto ambientale. Il monitoraggio continuo delle fughe e la manutenzione predittiva possono rappresentare una soluzione efficace sotto diversi punti di vista.

Al fine di ammortizzare al meglio i costi di acquisto e gestione delle macchine e degli impianti il loro ciclo di vita si sta sempre più allungando. Cresce anche la necessità realizzare prodotti sempre più flessibili, al passo con le possibili variazioni dei parametri operativi, alla tecnologia e alle richieste sempre più esigenti dei clienti; affinché questo possa essere possibile è necessario quanto meno un legame saldo e continuo tra progettista e operatore. Purtroppo il legame tra le due figure, in particolare tra progettista e manutentore, tradizionalmente non è mai stato molto stretto: il primo spesso legato alla teoria e con pochi riscontri diretti dal campo, il secondo impegnato per lo più direttamente in campo a cercare di tenere efficienti e funzionali le macchine. Un ruolo importante può essere svolto dal docente dei corsi di formazione il cui lavoro non può essere limitato a trasmettere informazioni e conoscenza, ma dovrebbe anche avere la funzione di rendere possibile un agile ed efficace scambio di informazioni tra il campo e l’ufficio tecnico.

The fluid handled by reciprocating compressors has to be strictly limited to gas and, under no circumstances, can there be a liquid fraction ingestion, as this event can cause the famous “liquid hammer effect” that can generate catastrophic failures. A study was conducted to evaluate the quantitative effects of the ingestion of a liquid slug into a reciprocatingcompressor cylinder with the goal of calculating the pressure distribution on the piston during such an event.

The crosshead to piston rod threaded connection is one of the most critical parts of the whole reciprocating compressor. Traditionally, this critical connection is dimensioned by the classic method of the “Load/Deformation diagram” or “triangle of elasticity’s” to evaluate mean and fluctuating stresses on the thread and then the relevant safety factor with the specific Smith fatigue diagram.

Special reciprocating compressors are required to reach the very high pressures necessary to feed the reactors used in LDPE plants. The working conditions of the compressors are determined by the reactor operating pressures and are considered for evaluation of the loads, torsional, pulsation and vibration conditions.