Corrosion Behavior of X80 Pipe Steel under HVDC Interference in Sandy Soil

Runzhi Qin,Xiuyun Wang,Yi Lu,Yanxia Du,Zitao Jiang,Anqing Fu

doi:10.3390/met8100809

Abstract

With the development of high voltage direct current (HVDC) systems, some pipelines have been badly interfered. The corrosion mechanism of pipelines has not been clearly clarified. In this work, laboratory experiments were designed to study the corrosion behavior of X80 steel under HVDC interference in sandy soil. The corrosion rates were related to the change in direct current (DC) density, which experienced three stages in the interference process. As soon as high DC interference voltage was applied to the working electrode, the current density increased sharply to a peak value in a few seconds. It then decreased rapidly to a steady value over dozens of seconds. Finally, it remained steady for the remaining time. With the measurement of local soil properties, the change in DC density was attributed to the local soil temperature increment, the water content decrement, and the substantial growth in the soil spread resistance. Moreover, the parameters contribute to the corrosion reaction during the interference process. The corrosion products were characterized at different times of interference via Raman spectroscopy. Lepidocrocite was produced under high DC density and then transformed to hematite under low DC density. Based on the above, the corrosion model during HVDC interference is proposed.

Highlights

High voltage direct current (HVDC) technology has been widely used for bulk power transmission at long distances
The DC density climbed to a peak sharply in 3 s after the application of interference and the peak value was 315 A·m−2
When the X80 coupons were under 50, 100, 200, and 300 V of HVDC interference in the sandy soil, the corrosion rates were 5.59, 11.90, 16.56, and 18.00 mm·year−1, respectively

Summary

Introduction

High voltage direct current (HVDC) technology has been widely used for bulk power transmission at long distances. More HVDC systems were constructed in Europe, North America, and many other regions and countries. HVDC systems develop fast in China because of the advantage of great power, low electrical loss, easy tower configuration, and low construction cost. There are more than 30 systems in construction and operation [1,2,3,4,5,6]. There are mainly two configurations of HVC systems: bipolar and monopolar. The bipolar configuration is a normal state and the monopolar configuration is usually used in failure or maintenance. When working in a monopolar configuration, a pair of ground electrodes together with the soil is employed as a conductor. A large amount of direct current (DC)

Methods

Results

Discussion

Conclusion