Endurance Limit of the Structural Elements of Offshore Stationary Platforms Considering Accumulated Damage


Annotation:

Offshore fixed platforms built in the 1960s–1970s, and sometimes even in the 1940s, are in operation worldwide. The operation of oil and gas hydraulic structures is carried out in the difficult marine conditions.

Throughout the entire period of operation, the offshore oil and gas platforms are exposed to the effect of loads (from wind, waves, seismic, ice, from the bulk of vessels and others). Corrosion, temperature, vibrational and other effects, which also affect the change in the values of amplitudes of the alternating stresses, should be taken into account. The combined action of the loads and effects leads to the occurrence of the alternating stresses in the structural elements of the offshore platforms that cause fatigue damage. Gradually developing from the microdefects, these damages grow into a main crack, which can lead to the destruction of the offshore platform. Therefore, study of the fatigue processes occurring in the elements of offshore platforms is an important and urgent task. The main characteristic, which is a measure of the fatigue damage, is the endurance limit. The comparative analysis of various methods for determining the endurance limit in relation to the elements of the offshore platform with accumulated damage is provided in the article. National and foreign regulatory documents, experimental and theoretical methods for determining endurance limits were analyzed. As a result, it was found that all the values of the endurance limit lie in the same area both in terms of the cycle base (the range of values is about 108 cycles), and in the value of the endurance limit itself (from 14 to 31.25 MPa for steel grade ВСт3Сп5 and from 14 to 41, 5 MPa for 09Г2С steel). The values obtained by Henry's method are identical to the results obtained by the experimental method.

The results of the analysis make it possible to clarify the value of the residual life of platform elements with accumulated damage.

References:
  1. On industrial safety of hazardous production facilities: Federal Law of July 21, 1997 № 116-FZ. Moscow: ZAO NTTs PB, 2020. 56 p. (In Russ.).
  2. On the approval of the Requirements for the registration of the objects in the state register of hazardous production facilities and maintaining the state register of hazardous production facilities (as amended on April 9, 2018): Rostechnadzor order dated November 25, 2016 № 495. Available at: http://docs.cntd.ru/document/420385055 (accessed: May 10, 2020). (In Russ.).
  3. Rules for conducting industrial safety expertise: Federal rules and regulations in the field of industrial safety. Ser. 26. Iss. 12. Moscow: ZAO NTTs PB, 2020. 28 p. (In Russ.).
  4. API Recommended Practice 2A-WSD. Planning, Designing, and Constructing Fixed Offshore Platforms—Working Stress Design. Available at: https://www.api.org/~/media/files/publications/whats%20new/2a-wsd_e22%20pa.pdf (accessed: May 10, 2020).
  5. DNVGL-RP—C203. Fatigue design of offshore steel structures. Available at: https://www.dnvgl.com/oilgas/download/dnvgl-rp-c203-fatigue-design-of-offshore-steel-structures.html (accessed: May 10, 2020).
  6. ND 2-020201—015. Rules for classification, construction and equipment of the floating drilling units and fixed offshore platforms. Russian Maritime Register of Shipping. Available at: https://files.stroyinf.ru/Index2/1/4293738/4293738165.htm (accessed: May 10, 2020). (In Russ.).
  7. Starokon I. Methods for solving the problems of extending the resource of offshore stationary platforms: case study. Available at: https://iopscience.iop.org/article/10.1088/1742-6596/1399/5/055087/pdf (accessed: May 10, 2020). DOI: 10.1088/1742-6596/1399/5/055087
  8. Starokon I. Comparative analysis of the fatigue characteristics of repaired compounds of the «T» and «K» types of fixed offshore platforms. Available at: https://iopscience.iop.org/article/10.1088/1742-6596/1515/4/042030/pdf (accessed: May 10, 2020). DOI: 10.1088/1742-6596/1515/4/042030
  9. Starokon I. Determination of the endurance limit of structural elements of fixed offshore platforms with accumulated damage based on experimental studies. Available at: https://iopscience.iop.org/article/10.1088/1742-6596/1515/4/042034/pdf (accessed: May 10, 2020). DOI: 10.1088/1742-6596/1515/4/042034
  10. GOST 25.504—82. Strength calculation and testing. Methods of fatigue strength behaviour calculation (with Amendment № 1). Available at: http://docs.cntd.ru/document/1200012858 (accessed: May 10, 2020). (In Russ.).
  11. Negoda E.N. Fatigue of the welded joints of large diameter pipes. Vestnik inzhenernoy shkoly DVFU = The Far Eastern Federal University: School of Engineering Bulletin. 2015. № 4 (25). pp. 62–74. (In Russ.).
  12. Fillipov V.Yu., Shchurin K.V., Rassokha V.I. Influence of the instability of the fatigue resistance factors on the durability of the  transportation facilities welded assemblies. Vestnik Orenburgskogo gosudarstvennogo universiteta = Vestnik Orenburg State University. 2003. № 2. pp. 140–144. (In Russ.).
  13. Efimenko L.A. Methodological fundamentals of the evaluation of the weldability of structural materials using oil and gas pipes as an example. Welding International. 2015. Vol. 28. Iss. 9. pp. 727–731.
  14. Efimenko L.A., Kapustin O.E., Gusev V.M., Merkulova A.O., Nikiforov N.I. Evaluation of Structural and Phase Composition and Corrosion Resistance Properties of Coatings Made by Laser Surfacing. Part 1. Chemical and Petroleum Engineering. 2014. Vol. 50. Iss. 5–6. pp. 402–411.
DOI: 10.24000/0409-2961-2020-9-7-12
Year: 2020
Issue num: September
Keywords : offshore stationary platforms damage accumulation endurance limit experimental study
Authors:
  • Starokon I.V.
    Starokon I.V.
    Cand. Sci. (Eng.), Assoc. Prof., Head of the Department, starokon79@mail.ru FGAOU VO «RGU of Oil and Gas (NIU) named after I.M. Gubkin», Moscow, Russia