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|FLUVIAL AND MARINE POLLUTION AND CORROSION|
IN INFRASTRUCTURE INSTALLATIONS
B. VALDEZ * M. SCHORR * and A. ELIEZER **
*Red Nacional de Corrosión, Instituto de Ingeniería, Universidad Autónoma de Baja California, México
* * Sami Shamoon Engineering College, Corrosion Research Center, Israel
ABSTRACT: There is a worldwide, concern today about the influence of pollutants on the environment including water, and about the durability of the engineering materials and the deterioration of the infrastructure. Corrosion control in natural and industrial environments contributes to the protection and preservation of the environment quality. The Kishon is one of Israel’s largest, most important and complex rivers, which empties into the Kishon Port on the Mediterranean Sea coast. During 1997 – 2000, pollution of the river by acidic industrial effluents and by chemical and biological decomposition of organic compounds has caused corrosion damage in fishing boats, cruiser ships, and port installations such as the steel floating dock and the port steel retaining walls. River water quality analyses indicated that water reached pHs in the range 2 to 4, the sulphide concentration was 1 to 4 mg/l, the Fe ions content 1 to 3 mg/l and total N, covering NH3 and NO3-, was about 30 mg/l. Nutrients from sewage and agricultural runoff increased the extent of steel corrosion.
Keywords: Kishon River, pollution, corrosion, steel
The environment quality has been established as a central discipline in modern science, engineering and technology. It is already being linked to the crucial problems of climate change and global warming.
The deterioration of seashore-based structures requires a modern approach to get a quantitative assessment and to estimate a given level of safety performance. Loss of structural element thickness and loss of integrity through pitting corrosion may be particularly critical where protective measures such as paint coatings or cathodic protection are ineffective. Reliable corrosion protection measures in form of coatings, tapes or linings to sustain long service life underwater, at tidal and splash zones have to be carefully controlled.
Ports are the central link between maritime and terrestrial transportation that advance the economy of a nation. Their structures, installations and equipment are built of suitable construction materials: steel and concrete, nonetheless they undergo process of corrosion and deterioration, therefore they should be protected applying anti-corrosion technology.
2. CORROSION IN KISHON PORT AND RIVER
The Kishon port is located on the coast of the Mediterranean Sea, near the city and port of Haifa; both on the Haifa Bay, in the north of Israel. The Kishon port includes docks for fishing and general cargo ships, a marine harbor for yachts and rowing 3boats, and a shipyard for the construction and repair of naval vessels. The port installations are built of two basic construction materials: steel and reinforced concrete. Due to their limited resistance to marine and fluvial corrosion, they are protected by paint, coating and cathodic protection as necessary. Fishing boats, patrol launches and civil yachts are constructed from reinforced plastics and aluminum alloys.
The Kishon River is flanked by industrials plants, sewage treating facilities and agricultural fields that contribute industrial waste effluents and pollutants containing organic matter and nutrients (1) from the synthetic and organic fertilizers dispersed on the fields. The Kishon River is one of Israel’s largest, most important and complex rivers, it empties into the port and then into the Haifa Bay (Figure 1). It crosses agricultural fields, a vast industrial area and sometimes drains non-treated municipal waste, collecting the effluents generated by these activities. The river is polluted with chemically active, corrosive and toxic substances (2). Several years ago corrosion had been accelerated due to an increase in pollutants discharge, damaging the fishing ships and port installations.
Figure 1. Kishon River and port on the Mediterranean Sea
1. Kishon river, 2.Kishon port, 3.Haifa port, 4. Haifa Bay
2.1. Environmental pollution and corrosion
The quality of the river water that flows into the port depends on its physical, chemical, biological and thermal characteristics. Biological and chemical processes convert the matter into toxic and corrosive substances (3,4). The concentration range in a typical polluted river and the Kishon, crossing an industrial region is presented in Table 1.
Table 1.Concentration of pollutants in river water containing industrial, agricultural and municipal wastes
According to the water acidity, expressed by its pH, river corrosion happens by two different mechanisms: Reaction of steel with dissolved oxygen (DO) producing hydrated iron-oxide (rust) in water at pH 6 to 8. In polluted, acidic water, pH<5, steel reacts with hydrogen ion (H+) forming a dissolved, ionized iron salt with evolution of hydrogen gas.
Different types of corrosion occur depending on the equipment geometry, concentration of corrodents, water motion, etc. Erosion-corrosion in ship propellers is a particular type of corrosion generated by the synergetic action of electrochemical corrosion and mechanical erosion (Figure 2).
The installations affected by corrosion are the port steel sheet pilings of the wharf retaining wall and the shipyard steel floating dock. The steel wall losses thickness until perforation of the plate eventually occurs. Corrosion is accelerated by the impact of waves, which break the fragile rust layer, and then the corroded plates must be repaired or replaced to protect the wharf. The floating dock underwent corrosion resulting in numerous cavities and perforations in the dock floor and the seawater ballast chambers (5,6).
Figure 2. Erosion-corrosion of an aluminum ship propeller
2.2. River corrosion monitoring
Corrosion monitoring techniques are applied for measuring the corrosivity of the port and river water. Real-time corrosion measurements are performed in situ with probes. Laboratory corrosion tests simulate, as closely as possible the river conditions. By these methods that include chemical analyses waters are periodically monitored to determine their composition, level of pollution and corrosion activity (7).
River water quality analyses have been conducted by the Kishon River Authority. Eleven stations, from the river source up to discharge into the port and the bay (Figure 3) are an integral part of port and river monitoring. Water degree of corrosiveness was determined by installing steel corrosion coupons near the port wharf. Corrosion was evaluated by observing the type and intensity of the surface attack comparing with non-exposed coupons.
Underwater inspections by a driver have revealed that corrosion is widespread throughout the port in the retaining wall buttressing the docks. Many sheets are riddled with holes of 30 to 50 cm diameter.
Corrosion laboratory tests performed in sea and river water at neutral and acidic pH, obtained by addition of HCl solution, simulated natural conditions and followed test procedures recommended in ASTM standard G 31. Corrosion rates increased with acidity elevation (pH decreases) and with the intensity of water motion.
2.3. Corrosion factors and processes
Various corrosive agents and processes occur in river water and seawater contaminated by natural and anthropogenic pollutants (8). Harbors adjacent to large cities suffer from depressed oxygen (DO) levels because of biological and chemical oxygen demand. Corrosion of active metals e.g. steel depends on DO concentration. The water O2 and CO2 content affect its pH and both enhance steel corrosion. Hydrogen sulphide and sulphides (S2-) originate from the degradation of organic matter containing sulphur. H2S attacks steel (9,10).
Fe + H2S FeS + H2 (1)
Iron sulphide is not stable in acidic water. It is converted again into H2S promoting further corrosion.
FeS + 2 H+ Fe+2 + H2S (2)
Heavy metals compounds such as FeCl3, an acidic salt, accelerate corrosion by acidic hydrolysis, forming HCl.
FeCl3 + 3 H2O Fe(OH)3 + 3 HCl (3)
The values of four corrosion factors, measured in the river monitoring stations are presented in Figure 4. The largest acidity and its corresponding corrosion rates appear at the stations 5 to 8 in the industrial region. Electrical conductivity increases at the station 11, near the discharge of the river into the bay due to penetration of seawater. At the stations 5 to 8, water having high pollution level has a depleted DO level.
Figure 3. Monitoring stations in Kishon river showing values of pH, dissolved
oxygen, electricalconductivity and temperature.
Kishon, a typical polluted port, is located near a city and a hydrological basin, with a river flowing into the port and then into the Haifa Bay on the Mediterranean Sea. The region enterprises around the river discharge industrial, agricultural and municipal effluents loaded with pollutants, including toxic and corrosive substances.
Environmental organizations in collaboration with port authorities need to develop and implement regulations covering the prevention, protection and monitoring of corrosion and others modes of deterioration in polluted ports.
The Kishon River Authority has implemented several actions to rehabilitate the river such as dredging and cleaning its bed, remediating the soil around the river, developing its landscape and establishing an environment monitoring system. Full ecological rehabilitation will be achieved at 2010 (11).
The authors wish to thank the Kishon River Authority, Haifa, for the supply of detailed information on the Kishon river and port pollution, and the Corrosion Laboratory, Israel Institute of Metals, Technion-Israel Institute of Technology, Haifa for carrying out laboratory corrosion tests.
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