Relationship between cathodic protection current and limit diffusion current as an additional criteria of cathodic protection
The influence of the temperature and oxygen concentration in NS4 solution on the electrochemical characteristics of X70 steel for pipelines and the relationship of cathodic protection current density to limiting diffusion current density, in the normalized DSTU 4219 range of protective polarization potentials from -0.75 V to -1.05 V (сh.s.е.) were investigated. It has been established that with increasing of the temperature from 20 to 80 °C, the corrosion activity of X70 steel increases, which is confirmed by more negative values of corrosion potential and an increasing of the corrosion rate, and indicates on the prevailing effect of temperature on the corrosion process compared to the effect of oxygen concentration. In the temperature range considered, the limiting diffusion current has a maximum value at 40 °C and decreases with increasing of temperature, correlating with a decreasing of the oxygen concentration. Under conditions of free oxygen access to the NS4 solution in the normalized DSTU 4219 range of protective polarization potentials, the ratio of cathodic protection to limiting diffusion current varies from 0.4 to 1.3 at temperatures (20-40) oС, at temperatures (60-80) oC the ratio is less than 1. Under conditions of limited oxygen access, the ratio increases from 1.1 to 4.7. Using calculated and experimental results, it was shown that, at various values of relationship , conditions for excessive hydrogen evolution can be created, which represents a threat to the safe operation of the pipeline over time. Data on the ratio values should be taken into account when analyzing the protection state of pipelines.
KeYin YaoYang & Y.Frank Chen 2018, Permeability of coal tar enamel coating to cathodic protection current on pipelines. Construction and Building Materials. Vol. 192, 20. pp. 20-27.
Y. Frank Cheng. Stress Corrosion Cracking of Pipelines. Hoboken: John Willey&Sons Publishing. 2013. 257 р.
DSTU 4219-2003. Steel main pipelines. General requirements for corrosion protection. Nat. standard of Ukraine. View. offic. [Valid from 2003-12-01]. Kiev: State Consumer Standard of Ukraine. 2003. 68 p. (in Ukrainian) http://ik-izol.com/wp-content/uploads/2014/12/dstu-4219-2003.pdf
GOST R 51164-98 Truboprovody stal'nye magistral'nye. [Steel main pipelines. General requirements for corrosion protection]. [Valid from 1999-07-01]. Ed IPK Izdatel'stvo standartov. Moscow, 1998. 42 p. (in Russian)
GOST 9.602-2005 Edinaya sistema zashchity ot korrozii i stareniya. Sooruzheniya podzemnye. Obshchie trebovaniya k zashchite ot korrozii [Unified system of protection against corrosion and aging treatment. Underground facilities. General requirements for corrosion protection]. Standartinform Moscow, 2006. 59p. (in Russian)
GOST 9.602-2016 Edinaya sistema zashchity ot korrozii i stareniya. Sooruzheniya podzemnye. Obshchie trebovaniya k zashchite ot korrozii [Unified system of protection against corrosion and aging treatment. Underground facilities. General requirements for corrosion protection] [Valid from 2017-06-01]. Standartinform. Moscow, 2016. 93 p. (in Russian)
DSTU B V.2.5-29:2006 Inzhenerne obladnannia budynkiv i sporud. Zovnishni merezhi ta sporudy. Systema hazopostachannia. Hazoprovody pidzemni stalevi. Zahalni vymohy do zakhystu vid korozii [Engineering equipment of buildings and structures. External networks and structures. Gas supply system. Gas pipelines underground steel. General requirements for corrosion protection]. Nats. standart Ukrainy. [Valid from 2007-06-01]. Minbud Ukrainy. Kyiv, 2006. 130 p. (in Ukrainian)
DSTU EN 12954:2016 Zakhyst katodnyi pidzemnykh ta pidvodnykh metalevykh sporud. Osnovni pryntsypy ta vykorystannia dlia truboprovodiv [Protection of cathodic underground and underwater metal structures. Basic principles and uses for pipelines] (EN 12954:2001, IDT). (in Ukrainian)
EN 12954:2001 Cathodic protection of buried or immersed metallic structures – General principles and application for pipeline (2001).
NACE SP0169-2007 (formerly RP0169) Parts incorporated in pipeline safety regulations Control of External Corrosion on Underground or Submerged Metallic Piping Systems
Tkachenko, VN 2004, Elektrokhimicheskaya zashchita truboprovodnykh setey [Electrochemical protection of pipeline networks]. Stroyizdat. Moscow.320 p. (in Russian)
Nguyen Dang, D, Lanarde, L, Jeannin, M, Sabot, R & Refait Ph 2015, Influence of soil moisture on the residual corrosion rates of buried carbon steel structures under cathodic protection. Electrochimica Acta. Vol. 176, pp. 1410-1419.
Barbalat, M.Lanarde, L. Caron, D. Meyer, M. Vittonato, J.Castillon, F.Fontaine S., Refait Ph. 2012, Electrochemical study of the corrosion rate of carbon steel in soil: Evolution with time and determination of residual corrosion rates under cathodic protection. Corrosion Science. V. 55. pp. 246-253.
Edited by RONALD L. BIANCHETTI 2001. Peabody’s Control of pipeline corrosion. NACE International The Corrosion Society. 1440 South Creek Drive, Houston, Texas. p. 347.
Khizhnyakov, VI 2013. O kontroliruyushchey roli plotnosti toka katodnoy zashchity pri obrazovanii korrozionnykh i stress-korrozionnykh defektov na vneshney poverkhnosti magistral'nykh gazonefteprovodov [Role of current density in oil and gas trunk pipeline cathodic protection for monitoring corrosion and stress-corro-sion defects]. Tambov University Reports. Series: Natural and Technical Sciences Vil.18, vyp. 5.
pp. 2248-2252. (in Ukrainian)
Khizhnyakov, VI, Kudashkin, YuA, Khizhnyakov, MV & Zhilin, AV 2011, Korrozionnoe rastreskivanie napryazhenno-deformirovannykh truboprovodov pri transporte nefti i gaza [Corrosion cracking of stress-strain pipelines during oil and gas transport] Izvestiya TGU [News of TSU].Vol. 319, no. 3. pp. 84-89. (in Russian) http://earchive.tpu.ru/handle/11683/3908
Khizhnyakov, VI. 2008.Vliyanie rezhimov katodnoy zashchity na stepen' podavleniya korrozii i na navodorozhivanie stali 17GS. [The effect of cathodic protection modes on the degree of corrosion suppression and on hydrogen hydrogenation of 17GS steel] All-Russian Conference on Physical Chemistry and Nanotechnology "NIFHI-90"/ Moscow. pp. 178-179. (in Russian)
Khizhnyakov VI 2010. Razvitie nauchnykh osnov, razrabotka i realizatsiya novykh kriteriev effektivnosti elektrokhimicheskoy zashchity truboprovodov ot korrozii. [Development of scientific foundations, development and implementation of new criteria for the effectiveness of electrochemical protection of pipelines against corrosion]. Diss. ... doctor. tech. sciences: 05.17.03. Tomsk, 2010.357 p. (in Russian)
Semiokhin, IA 2001, Fizicheskaya khimiya [Physical Chemistry]. Ed MGU. 272 p.
Zhuk, NP 1976, Kurs teorii korrozii i zashchity metallov [The course of the theory of corrosion and metal protection]. Metallurgiya. Moscow. 472 p. (in Russian)
Szklarska-Smialowska, KZ, Xia, Z & Rebak, RB 1994, Technical note: stress corrosion cracking of Х-52 carbon steel in dilute aqueous solutions. Corrosion. Vol. 50. no. 5. pp. 334-338.