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CORROSION MONITORING IN PAPER MACHINEWHITE WATERS

Angela Wensley & Harry Dykstra

Bacon Donaldson Consulting Engineers

12271 Horseshoe Way

Richmond, BC, Canada

V7A 4V4

Alicja Augustyn

Avenor Inc.

2001 Neebing Avenue

Thunder Bay, ON, Canada

P7E 6S3

ABSTRACT

A year-long program of white water corrosion monitoring was

initiated at the Avenor Thunder Bay mill after rapid corrosion ofbronze couch rolls was observed. The program consisted of

weekly chemical analysis of white waters from three paper

machines, in conjunction with suction roll bronze (85Cu-5Pb-

5Sn-5Zn) corrosion rate monitoring by the linear polarization

resistance (LPR) method. using corrosion probes installed in

white water piping. White water corrosivity was found to be

related to the thiosulfate concentration. As the thiosulfate

concentration often exceeded 20 ppm, it was necessary to

employ corrosion inhibitors to protect the bronze rolls.

Keywords: corrosion testing, paper machines. suction

rolls. white water

INTRODUCTION

The newsprint machines in the Avenor mill in Thunder Bay,

Ontario, have a number of suction rolls made from centrifugally

cast 1N bronze alloy (nominally 85% Cu, 5% Pb, 5% Sn, 5%

Zn), an alloy more noteworthy for its good casting properties

than for its corrosion resistance1-7

.

The suction roll shells at the Thunder Bay mill are experiencing

corrosion of both the outside and inside surfaces (manifested by

the appearance of black streaks on the surfaces), and

enlargement of the suction hole bores. It has been necessary toapply a corrosion inhibitor to showers on both the inside and

outside of the bronze suction shells, although this is an

expensive process and the need for continual application has

been questioned.

water corrosion monitoring program was initiated for three

paper machine white water systems at the Thunder Bay mill.

The program duration was one year. In that time period:

1. White waters were sampled on a weekly basis for chemical

analysis of inorganic species, including thiosulfate and

chlorides.

2. Six corrosion probes were installed in white water systems

for instantaneous corrosion rate monitoring of 85-5-5-5

bronze by the linear polarization resistance (LPR) method.

3. The LPR results were verified by weight loss

measurements on the bronze electrodes, which were

removed and replaced every 3-6 months.

4. The bronze electrodes were also examined by scanning

electron microscopy ( S E M) a n d X - ra y e n e r g y

spectroscopy (XES) after exposure in white water systems.

EXPERIMENTAL

The white water corrosion monitoring program involved both

mill personnel and consultants. White water analysis, corrosion

probe installation, and LPR corrosion rate monitoring were

performed by Avenor personnel; data analysis, and microscopy

were performed at the Bacon Donaldson laboratory.

Monitoring Locations

Two locations on three paper machines (PMs 3,4. and 5) were

selected for corrosion monitoring by simultaneous white water

sampling and LPR corrosion rate measurements. The locations

were selected for accessibility for installation of the corrosionprobes and of nearby valves for white water sampling. The

locations selected also had high flow velocities (mostly in pipes

ahead of pumps), which prevented buildup of slimy deposits

around the probe electrodes.

The six monitoring locations were:

1. PM3 inlet of pump from wire pit overflow to saveall.

2. PM3 white water silo.

3. PM4 inlet of pump from wire pit overflow to saveall.

4. PM4 inlet of seal pit pump.

5. PM5 white water silo.

6. Inlet to rich white water chest.

To obtain a better understanding of the causes and control of

corrosion of bronze suction roll shells, a comprehensive white

1997 Engineering & Papermakers Conference /48

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