AC-corrosion on cathodically protected pipelines:
A description of the involved processes, the risk assessment and a new normative approach
SGK Swiss Society for Corrosion Protection, Switzerland
The first damages on cathodically protected pipelines occurred in 1988. The subsequent research of the past 28 years has resulted in a conclusive understanding of the involved processes. The most recent results are completing this picture. This updated model allows for the design of mitigation measures that go beyond the decrease of the induced acvoltage. The depth of the ac-corrosion attack and the associated critical coating defect size in combination with the soil resistivity were identified as key parameters with respect to damages on pipelines. The corresponding model concepts are discussed and their validation presented. Moreover, the consequences on the threshold values in ISO 18086 as well as the effect of time variation of ac-and dc-interference are addressed. Furthermore the approach in the new German Standard GW 28-B1 is presented.
Keywords: ac-corrosion, corrosion rate, cathodic protection, model
2018, Vol. 61, nr 8, pp. 204-212
Modeling the process of electrochemical corrosion in the inter-pipe space
SPZP CORRPOL, Gdańsk
The presence of the water between casing line and main line is being doubtful among one of the biggest group of cathodic protection technology utilizers – high pressure gas pipelines operators. There are numerous questions related to the issue such as: “is there a real corrosion treat in case of flooding the space between the casing line and gas line?”, “how big and how deep corrosion defects are to be expected?”, “is there a possibility of perforation?”, “how much time does it take to seriously damage the gas line?” and of course: “is there any way to prevent gas line corrosion damage in case of flooding the space between the casing?”. An attempt to answer some of the questions and to dispel cathodic protection utilizers doubts was taken in the paper. A simple theoretical model that allows to calculate maximal depth of corrosion defects and estimate the rate of corrosion loss was presented. In the further part of the paper limits of the model used was discussed. Factors that can increase or decrease corrosion rate in soil and soil electrolyte were described and their impact was discussed.
Keywords: isolation defect, corrosion in isolation defects, corrosion in the inter-pipe space
2018, Vol. 61, nr 8, pp. 213-217
High rate dischargeability of hydride electrode modified with magnetron sputtered MCrFeCoNi (M = V or Mn) coatings
Politechnika Częstochowska, Wydział Inżynierii Produkcji i Technologii Materiałów, Katedra Chemii
High rate dischargeability (HRD) of surface modified LaNi4.5Co0.5 powder composite hydride electrodes has been studied. Two kinds of multicomponent thin coatings of MCrFeCoNi composition (M = V or Mn) have been deposited on LaNi4.5Co0.5 material powder fraction of 20 - 50 μm using magnetron sputtering method. The galvanostatic charge/ discharge technique has been applied at some discharge rates (in the range of 1C to 5C) to determine the HRD behavior. The improvement in HRD parameter has been observed for both of the examined coatings.
Keywords: Hydrogen storage, discharge capacity, active powder modification, high rate dischargeability
2018, Vol. 61, nr 8, pp. 218-221
CORROSION PROTECTION IN PRACTICE
Atypical unidirectional drainage bond
Operator Gazociągów Przesyłowych GAZ-SYSTEM S.A. Oddział w Gdańsku
The paper presents atypical unidirectional drainage bond where there is no cable connection between the pipeline and rails. Before, the protection of this pipeline against stray currents was also atypical. It consisted of using a completely tight insulation coating in the critical points; it worked as long as the coating was really hermetic. The causes for loss of tightness are truly suprising.
Keywords: pipeline, coating, coating discontinuity, cathodic protection, stray currents, unidirectional drainage bond, heat – shrinkable wrap-around sleeves
2018, Vol. 61, nr 8, pp. 222-224