Page 201 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

PULP AND PAPER INDUSTRY 179

TABLE 3.12 Corrosion Failure Modes Along with the
Frequency of Occurrence
Failure Mode Average Frequency (%)
Cracking 36
General corrosion 26
Local attack 20
Temperature effects 7
Velocity effects 5
Galvanic, stray current, and “macro cell” 3
Hydrogen effects 2
Biological 0
Total 99

TABLE 3.13 Distribution of Stress Corrosion Cracking of
Different Construction Materials
Material Average Frequency (%)
Stainless steel 61.4
Steel 30.4
Copper alloys 4.3
Nickel alloys 2.8
Titanium 0.7
Tantalum 0.3

Chlorides were involved mainly in the cracking of stainless steels, and caustics and
nitrates were responsible for the cracking of steel. The studies reported that a 50–50
distribution between mechanical and corrosion failures was found to hold good.

3.26 PULP AND PAPER INDUSTRY

The paper-making process consists of various steps from pulp production, pulp pro-
cessing and chemical recovery, pulp bleaching, and stock preparation to paper man-
ufacturing.
Pulp production is done by: (i) mechanical pulping; (ii) semichemical pulping, and
(iii) chemical pulping.

1. Mechanical pulping utilizes steam, pressure, and high temperature to tear the
fibers. Newspaper and paperboards are typical products of the mechanical pulp-
ing process. Mechanical pulping is done in 300 series stainless steel containers
to prevent corrosion.
2. Semichemical pulping involves the use of dilute solutions of sodium sulfite and
sodium carbonate to digest the lignin in the pulp. In addition to this, mechanical
refining is used to separate the fibers.