Possibility of High Phosphorus Pig Iron as Sacrificial
Anode
Nisheeth Kr. Prasad, A.S. Pathak, S. Kundu, and K. Mondal
(Submitted November 15, 2017; in revised form May 11, 2018; published online May 30, 2018)
Cathodic protection is an effective method to control the corrosion of underground pipelines and sub-
merged structures. In the present work, high phosphorus containing pig iron was utilized as sacrificial
anode for cathodic protection of underground mild steel plates and the results were compared with that of a
commercially pure magnesium sacrificial anode. Driving potential and current between the galvanically
coupled sacrificial anodes and mild steel plates were continuously monitored in real time for one month.
Microstructure and morphology of the corrosion products formed on the surface of pig iron, magnesium
sacrificial anodes and mild steel plates were observed with the help of optical microscope and scanning
electron microscopy, and phase identification were performed using x-ray diffraction, Raman spectroscopy
and Fourier transform infrared spectroscopy. The distribution of phosphorus in the pig iron matrix and
soluble rust formation on the surface of pig iron under buried condition were critical from the point of
sacrificial effect, indicating the possible scientific reasons for high phosphorous pig iron to be used as
sacrificial anode.
Keywords cathodic protection, potential, sacrificial anode
1. Introduction
The failure of underground pipelines due to corrosive nature
of soil has been a major concern for corrosion engineers. The
dissolved ion contents and sulfate reducing bacteria present in
soil play major role in corrosion of buried pipelines (Ref 1, 2).
The standard methods for the protection of buried pipeline
involve the use of protective coatings and cathodic protection
(CP) (Ref 3). However, coating alone does not serve well for
the long-term corrosion protection of buried pipelines since any
discontinuity on the coating could result in localized aggressive
failure of the pipelines (holiday corrosion). Hence, CP along
with a protective coating enhances the life and ensures long-
term corrosion protection of buried pipelines.
CP is widely used for the protection of underground and
undersea metallic structures, such as oil and water pipelines, oil
drill platforms, hulls of the ships and heat exchangers. It was
first implemented by Sir Humphrey Davy to curb the failure of
copper sheathing on the hulls of British Naval Ships in 1824 as
a result of galvanic effects of dissimilar metals (Ref 4, 5). CP is
based on the principle of supplying electrons to the metal
structure to be protected suppressing the metal dissolution from
the structure to be protected and increasing the cathodic
reaction, which would finally reduce the corrosion of metal
structure to a great extent (Ref 4). There are basically two
methods to achieve cathodic protection to metal structures. One
of the methods involves applying external power supply to the
metal structure to be protected [impressed current cathodic
protection (ICCP)], while the other method protects the metal
structure by galvanic coupling (sacrificial anode cathodic
protection).
Sacrificial anode cathodic protection is regarded to be a cost-
effective method for protection of submerged structures when
the current requirement is small (i.e., below 500 mA), and soil
resistivity is low (< 10,000 X cm) (Ref 6). Moreover, this is a
well-accepted method where availability of electricity is scares.
Magnesium (Mg), zinc (Zn) and aluminum (Al) are the
commonly used sacrificial anodes for cathodic protection of
steel structures. Zn and Al are widely used to protect ships and
harbor structures, whereas Mg-based sacrificial anodes have
highly negative free corrosion potential and therefore dissolve
too vigorously in seawater. Hence, they are restricted to the
protection of underground pipelines (Ref 7, 8).
However, these sacrificial anodes possess few limitations
when they are used for commercial applications. Zn sacrificial
anodes tend to contaminate the local water bodies by
solubilized Zn, which may cause ecological damage and can
also contaminate the food chain if the Zn level in water rises
beyond 5 lg/L (Ref 7). The formation of passive oxide film
on pure and unalloyed Al restricts their use as sacrificial
anodes. Hence, in order to make it suitable for cathodic
protection, they are often alloyed with mercury (Hg), indium
(In), tin (Sn) and titanium (Ti). As a result, these improved
properties also result in environmental concern due to the
presence of alloying elements like indium (Ref 9). Mg anodes
have low current efficiency of about 50%, which could be due
to enhanced corrosion rate of the anode (Ref 10). As a result,
in order to increase the efficiency of magnesium sacrificial
anodes, they are alloyed with Al, Zn and Mn, adding up to
the cost. Adding to this, the absence of any alternative
sacrificial anode in the commercial market bounds the
customer to select among the limited available sacrificial
anodes. Hence, today there is an urge to focus on some
alternative cheaper and easily available materials to be used as
Nisheeth Kr. Prasad and K. Mondal, Department of Materials
Science and Engineering, Indian Institute of Technology Kanpur,
Kanpur, Uttar Pradesh 208016, India; A. S. Pathak and S. Kundu,
Research and Development and Scientific Services, Tata Steel Limited,
Jamshedpur, Jharkhand 831001, India. Contact e-mail:
kallol@iitk.ac.in.
JMEPEG (2018) 27:3335–3349 ÓASM International
https://doi.org/10.1007/s11665-018-3429-0 1059-9495/$19.00
Journal of Materials Engineering and Performance Volume 27(7) July 2018—3335
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