Advanced Computer Modelling for Metal-to-Metal Seal in API Flanges
- Harshkumar Patel (University of Oklahoma) | Hari Hariharan (Shell International Exploration & Production Inc.) | Greg Bailey (Shell International Exploration & Production Inc.) | Gonghyun Jung (Shell Global Solutions US Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 24-26 September, Dallas, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2018. Society of Petroleum Engineers
- API Flange, Gasket Sealability, Wellhead Integrity, Leakage Modelling, Metal-to-Metal Seal
- 21 in the last 30 days
- 305 since 2007
- Show more detail
- View rights & permissions
|SPE Member Price:||USD 8.50|
|SPE Non-Member Price:||USD 25.00|
API flanges maintain integrity through metal-to-metal seal between gasket and flange groove, where sealability depends on contact stresses through bolt makeup-load, tension, fluid-pressure, bending moment. Approaches like API-6AF2 have limitations. With increased deep-water operations, there is an urgent need to understand true sealability/leakage. This requires micro-scale examination of seal. Very few FEA in literature model surface conditions. The objective here has been to develop an analytical model to estimate contact stresses and leakage considering surface topography.
This work presents a novel approach for modelling sealability/leakage in metal-to-metal surfaces. It utilizes a contact-mechanics and a fluid-flow model. Deterministic multi-asperity contact-mechanics model provides quantitative estimation of gasket contact stresses, contact gap, and contact area. The leakage model uses contact gap information and correlates it with hydraulic permeability between gasket and groove surfaces and predicts leakage using fluid flow through porous media equations. User inputs are gasket surface topography, size, material properties, operating pressure, and fluid viscosity. The calculations are performed on a small surface domain and results are then scaled-up to obtain contact load/leakage for the entire flange/gasket.
Various types of artificially generated surfaces were considered in the model and a parametric study was conducted. Effects of surface finishing have been explained by visual representation of model outputs such as contact status, load distribution, and leakage path. It was observed that critical contact stress to achieve complete sealability is highly dependent on surface characteristics. For similar surface topography, leakage rates are primarily a function of surface RMS. For the same RMS, it is more difficult to seal a randomly rough surface than a patterned or uniform one. As expected, it is easier to seal a soft gasket than a harder one. Similarly, it becomes progressively difficult to seal larger flanges.
Parametric studies/analysis can help improve understanding of leakage. The models can be used to understand relative magnitude of challenges in sealing gases/liquids at true viscosities. With further refinement and experimental validation, the models could serve as a design tool that could greatly assist in selecting effective seal and improve well process safety. Further, the presented approach can also be applied to develop leakage models for other metal-to-metal seal applications such as tubular connections, expandables, etc.
|File Size||2 MB||Number of Pages||21|
Chang W. R., Etsion, I. I., and Bogy, D. B. 1987. An Elastic-Plastic Model for the Contact of Rough Surfaces. ASME Journal of Tribology: 109(2), 257–263. http://dx.doi.org/10.1115/1.3261348.
Chang, R. T., Fisher, E. A., and Hall, G. 1991. BX Flange Analysis: Significance of Gasket on Load Capability of a Subsea Connection. Presented at Offshore Technology Conference, 6-9 May, Houston, Texas. OTC-6779-MS. http://dx.doi.org/10.4043/6779-MS
Fowler, J. 1995. Sealability of API R, RX, and BX Ring Gaskets. Presented at Offshore Technology Conference, 1-4 May, Houston, Texas. OTC-7908-MS. https://doi.org/10.4043/7908-MS
Greenwood, J. A., and Williamson, J. B. P. 1966. Contact of nominally flat surfaces. Proc. of the Royal Society of London: A(295), 300–319. https://doi.org/10.1098/rspa.1966.0242
Greenwood, J. A., and Tripp, J. H. 1970. The contact of two nominally flat rough surfaces. Proc. of the Institution of Mechanical Engineers: 185(1), 625–634. https://doi.org/10.1243/PIME_PROC_1970_185_069_02
Jeng, Y.-R., and Wang, P.-Y. 2003. An Elliptical Microcontact Model Considering Elastic, Elastoplastic, and Plastic Deformation. Journal of Tribology: 125(2), 232. http://dx.doi.org/10.1115/1.1537744.
Konafi, M. 2016. Surface Generator: Artificial Randomly Rough Surface. Mathworks File Exchange. https://www.mathworks.com/matlabcentral/fileexchange/60817-surface-generator--artificial-randomly-rough-surfaces (accessed on June 10, 2017)
Pasaribu, H., and Schipper, D. 2005. Application of a Deterministic Contact Model to Analyze the Contact of a Rough Surface Against a Flat Layered Surface. Journal of Tribology: 127(2), 451. http://dx.doi.org/10.1115/1.1866163
Persson, B. N. J. 2006. Contact mechanics for randomly rough surfaces. Surface Science Reports: 61(4), 201–227. http://dx.doi.org/10.1016/j.surfrep.2006.04.001.
Zhao, Y., Maietta, D. M., and Chang, L. An Asperity Microcontact Model Incorporating the Transition from Elastic Deformation to Fully Plastic Flow. Journal of Tribology: 122(1), 86. http://dx.doi.org/10.1115/1.555332