Shaiful Rizam Shamsudin

AISI type 316L stainless steel was used
as a heat exchanger tube material in an
inter-cooler column. After less than a year
of operation, severe corrosion failures occurred
and a transverse opening leakage
was observed on one of the heat exchanger
tubes. The failed tube was carefully analyzed
using various metallurgical laboratory
equipments. The root cause of the tube
leakage was believed due to the presence
of horizontal micro and macro pores as a
hydrogen gas entrapment during casting of
the parent ingot. The overlapped and gaping
pores formed notch on the shell side of
the tube surface, and it increasingly evident
when the use of a high-energy water-jet and
metal brush as cleaning procedure results
in an establishment of pitting type localaction
corrosion cells penetrated the tube
wall. As a result, corrosive fluid in the tube
side dissolved into the cooling water, accelerating
the corrosion process.

Magnesium is among the anode material usually applied in cathodic protection in soil application. The corrosion behaviour of Mg anode was studied to understand corrosion behaviour of the Mg anode. The electrochemical polarisation test on the Mg ingot, ascast Mg (99.9 wt% Mg, 0.1wt% Mn) and pure Mg (99.7wt% Mg, 0.2wt% Mn, 0.01wt% Si and 0.047 wt% Fe) were done using potentiostat Gamry G 300. These test were done
to obtained polarisation curve and open circuit potential (OCP). The value of open circuit potential of for as cast Mg, Mg ingot and pure Mg are -1.679 V vs. SCE, -1.546 V vs. SCE and -1.709 V vs. SCE respectively. The corrosion rate exhibits the significantly
different between Mg anodes. The highest corrosion rate achieved by As-cast Mg anode (25.78 um/year). The corrosion current density of the As-cast Mg revealed the highest
value (1.02 A/cm2) compared to Mg ingot and pure Mg. The research found that the different of electrochemical properties were believed resulted by different of alloying elements and processes among these Mg anodes.