Sealability of Stationary Metal-to-Metal Seals

Murtagian, Gregorio; Fanelli, Victor; Villasante, Jose ́ A.; Johnson, Daniel; Ernst, Hugo A.

doi:10.1115/1.1715103

Cited by 70 publications

(61 citation statements)

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“…In the field of the metal-to-metal seals of a premium threaded connection, several sealability studies have been conducted by fundamental laboratory tests [2][3][4]. Based on these test results, experimental criteria were proposed for designing their products.…”

Section: Introductionmentioning

confidence: 99%

Influence of Grease on High-Pressure Gas Tightness by Metal-to-Metal Seals of Premium Threaded Connections

2016

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A premium threaded connection for oil country tubular goods (OCTG) has a metal-to-metal seal portion to ensure its gas tightness under high pressure and high temperature. The metal surfaces are coated with grease and then integrated by rotary sliding. Despite several studies, the gas tightness mechanism of the metal-to-metal seal has not yet been clarified. In this study, as the first step to clarify the mechanism, we evaluated how grease affects the gas tightness by fundamental tests considering rotary sliding and grease degradation due to high temperature. Our results showed that grease is mandatory for the gas tightness of the metal-to-metal seals and the gas tightness is affected by both types of base oils and solid additives of grease. The seals coated with the grease composed of mineral oil had better gas tightness than those coated with that composed of plant oil, even after degradation due to high temperature. In addition, grease containing soft metal particles had better gas tightness than grease containing hard inorganic particles because the extended soft metal particles adhering to the rough parts of the seal surfaces reduced the size of the leakage paths.

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Section: Introductionmentioning

confidence: 99%

Influence of Grease on High-Pressure Gas Tightness by Metal-to-Metal Seals of Premium Threaded Connections

2016

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“…Next to that, a selection of commercially available, environmentally acceptable [30] thread compounds were tested, designated with YD in Table 2. The base oil was used to assess the influence of the thickener and the additives on the sealing performance [31].…”

Section: Lubricantsmentioning

confidence: 99%

On the Sealability of Metal-to-Metal Seals with Application to Premium Casing Connections

Ernens

Pérez-Ràfols

Hoecke³

et al. 2019

Day 1 Tue, March 05, 2019

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Metal-to-metal seals are used in connections of casing in oil and gas wells. This paper describes the mechanisms of sealing of metal-to-metal seals as investigated using an experimental set-up and a sealability model. Experiments were conducted for a variety of thread compounds and applied pin/box surface coatings. The results were used to validate a numerical model for sealability. The stochastic model couples a contact mechanics model with a flow model and takes the influence of all the surface topography features into account. Once validated, the model was used together with the experimental results to explain the sealing mechanisms of metal-to-metal seals. The sealing configuration is a face seal with an R=80 mm round-off radius pressing against a flat. The face seal specimens were manufactured from P110 tubing. The used test set-up is designed for investigating only the metal-to-metal seal of the connection. The set-up can carry out rotary sliding under constant load to simulate surface evolution during make-up and subsequently perform a leakage test. The sealing limit is determined by applying 700 bar fluid pressure and then gradually reducing the normal force until leakage is observed. The data is subsequently used to validate a previously published model. The results indicate a strong dependence of the type of thread compound used on the onset of leakage. The thread compound affects the amount of wear and thus changes the surface topography of the interacting surfaces. It is shown that the sealability model is capable to predict the onset of leakage within the experimental accuracy. The model shows further that certain surface topographical features improve the sealing performance. Namely, a turned against a flat surface topography leads to highly localized contact areas, which in turn yields the best sealing performance. The combination of experimental data with the validated model leads to much deeper insights for the sealing mechanisms than what could be obtained using either on their own.

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“…In letteratura sono reperibili studi recenti sulle condizioni di perdita di flange senza guarnizione, tuttavia non esiste un modello di tenuta che descriva il fenomeno in funzione dei parametri macroscopici geometrici. I principali risultati riportati in letteratura sono:  la planarità della superficie ha un ruolo significativo, la tolleranza di planarità deve essere molto stretta al fine di evitare perdite locali di contatto che producono un canale di perdita preferenziale [1];  in modo analogo, anche se ad un livello di scala differente, la rugosità deve essere minima per sfavorire perdite dovute ad un contatto non completo fra le superfici della flangia [2];  l'orientamento dei solchi di rugosità deve essere non allineato con l'eventuale verso del flusso di perdita, quindi possibilmente ortogonale ad esso [3];  l'irregolarità della superficie e la rugosità vengono in buona parte compensate con l'introduzione del sigillante (tipicamente siliconico) [4,5].…”

Section: Introduzioneunclassified

Modello di tenuta della flangia bullonata, senza guarnizione, mediante l’analogia della meccanica della frattura di una fessura parzialmente aperta

Beghini

Bertini

Santus

et al. 2010

Frattura Ed Integrità Strutturale

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RIASSUNTO. I compressori centrifughi di elevate dimensioni non permettono l'utilizzo di guarnizioni deformabili, per cui le due metà della flangia di connessione sono forzate mediante bullonatura e la tenuta è affidata al contatto completo delle due superfici. La previsione della pressione di perdita è un aspetto di progetto di notevole interesse per questa tecnologia. L'azione della pressione interna sollecita la separazione delle superfici della flangia, che invece è contrastata dall'azione di serraggio dei bulloni. Il presente lavoro propone un modello per prevedere la condizione di perdita, basato sulla meccanica della frattura. Dato che le due superfici della flangia sono semplicemente a contatto, esse costituiscono una vera e propria fessura parzialmente aperta. Come ben noto il fattore di intensificazione di una fessura parzialmente aperta è nullo. Imponendo che le due superfici siano parzialmente separate ad una distanza fino al bordo del foro del bullone (che offre un canale di fuoriuscita per il fluido in pressione), e imponendo la condizione di fattore di intensificazione nullo, è possibile determinare la pressione di perdita, analiticamente, mediante la tecnica delle "weight functions" (o "funzioni peso"). Il presente lavoro riporta una positiva validazione del modello proposto mediante sia simulazione numerica sia risultati sperimentali in piena scala e in scala ridotta. Il modello analitico proposto offre uno strumento di progetto di immediata implementazione per comparare diverse geometrie di flangia bullonata.ABSTRACT. The use of a gasket made in soft material is not recommended for large size centrifugal compressor case flanges. The two case halves are assembled with bolted flanges and the leakage is prevented by the "metalto-metal" contact of the flange surfaces. The prediction of the leakage condition is an important engineering challenge for this technology. A new model to predict the leakage condition, based on Fracture Mechanics, is here presented. The partially open flange surfaces interface can be regarded as a partially open crack. The Stress Intensity Factor of a partially open crack is zero, since the flange surfaces can not transfer tensile traction, being just in contact (not "glue" or "welded"). The extension of the open zone, i.e. the crack length, can be obtained imposing the zero Stress Intensity Factor condition. The leakage is expected as the flange surface open front reaches the bolt hole, that produces a way out path for the internal pressurized fluid. By means of the weight functions analytical technique, the leakage pressure can be calculated. The proposed model was then successfully validated by means of both numerical simulations and full scale and small scale experimental tests. The proposed analytical model can be used to compare different flange geometries and then it is a useful design tool. PAROLE CHIAVE. Tenuta. Flangia bullonata. Meccanica della frattura. Fessura parzialmente aperta.

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Sealability of Stationary Metal-to-Metal Seals

Cited by 70 publications

References 0 publications

Influence of Grease on High-Pressure Gas Tightness by Metal-to-Metal Seals of Premium Threaded Connections

Influence of Grease on High-Pressure Gas Tightness by Metal-to-Metal Seals of Premium Threaded Connections

On the Sealability of Metal-to-Metal Seals with Application to Premium Casing Connections

Modello di tenuta della flangia bullonata, senza guarnizione, mediante l’analogia della meccanica della frattura di una fessura parzialmente aperta

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