1.How does zinc layer thickness affect deep sea service life?
Conventional hot-dip galvanized layer: Without additional protection, if directly exposed to the deep sea full immersion area, the zinc layer may be completely corroded within 8-15 years. For example, in the seaside or chemical corrosion environment, the life of a 100-micron zinc layer is about 8-15 years, while the deep sea has higher salinity and more complex microbial corrosion, which may further shorten the life.
Thick zinc layer: If heavy anti-corrosion galvanizing is used, combined with outer layer isolation protection, the life of the zinc layer can be extended to more than 30 years. For example, the galvanized steel wire of a deep-sea photovoltaic composite cable is isolated from seawater in the seabed mud area due to the outer layer protection, and the corrosion rate is reduced by more than 50%, and the life span exceeds 30 years
2.What are the characteristics of the deep sea environment?
The slowing effect of low temperature and high pressure: Low temperature in the deep sea will reduce the electrochemical corrosion rate, while high pressure may inhibit microbial activity, thereby slowing down local corrosion. For example, the corrosion degree of the seabed mud area is lighter than that of the fully immersed area.
The accelerating effect of high salinity and microorganisms: The deep sea water has high salinity and strong conductivity, which will accelerate the electrochemical corrosion of zinc; at the same time, microorganisms such as sulfate-reducing bacteria will produce hydrogen sulfide through metabolism, causing sulfidation corrosion, which may shorten the life of the zinc layer by 30%-50%
3.What is the key role of additional protective measures?
Physical isolation: The outer layer of PP rope, asphalt or plastic coating can block direct contact with seawater and significantly extend the service life. For example, the life of galvanized steel wire in photovoltaic composite cable doubles from 17 years to more than 30 years due to the outer layer protection.
Cathodic protection: If combined with sacrificial anode or impressed current cathodic protection, the life of galvanized steel can be further extended by 50%-100%. For example, deep-sea oil and gas pipelines often use a combination of "galvanizing + cathodic protection", with a life of more than 50 years
4.What is the life range of bare galvanized steel without additional protection?
Fully immersed area (below 1000 meters):
Zinc layer 50 microns: life span is about 5-8 years (high salinity, active microorganisms).
Zinc layer 100 microns: life span is about 8-12 years (low temperature delays corrosion, but microorganisms still exist).
Seabed mud area (below 2000 meters):
Zinc layer 50 microns: life span is about 8-10 years (low oxygen content, less corrosion).
Zinc layer 100 microns: life span is about 12-15 years (microbial corrosion is relatively weak).
5.What are the key factors that affect life expectancy?
Zinc layer thickness: directly determines the initial corrosion tolerance (each micron of zinc layer can resist about 0.1-0.2 years of corrosion).
Type of deep sea area: corrosion intensity in full immersion area > tidal area > seabed mud area.
Protection system: whether there is coating, cathodic protection, etc., affects the multiple changes of corrosion rate.