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chemical composition of aqueous environments and type of mechanical loading on

the resistance of steels of pipeline systems and their welded joints to corrosion-

mechanical fracture and also to development of methods for predicting their

corrosion fatigue durability, as well as application of inhibitor protection during

cavitation in aqueous environments.

The main factors of reduction of corrosion fatigue durability of the carbon

steel under cavitation and cyclic loading, and their combined action has been

established. It has been found that the combined action of cavitation and cyclic

loads reduces the corrosion fatigue limit of the 35 steel in tap water by 2.4 times,

and the limited durability for loads close to the fatigue limit – by an order of

magnitude due to increased corrosion. Preliminary cavitation (amplitude 45 μm) of

the 35 steel in tap water for 180 min reduces in only 1.3 times its corrosion fatigue

durability in tap water.

The effectiveness of inhibitor protection of the 30ХГСНА steel against

corrosion cavitation damage in tap water by iodide salts of alkyl-substituted

ammonium and quinoline, which depends on the intensity of cavitation loading,

has been established. For the first time, it was revealed that a triethylammonium

iodide inhibitor provides protection degree of 90–97% depending on the cavitation

loading (the amplitude of the magnetostrictor is 10–45 μm). A triethylammonium

iodide inhibitor has been proposed to protect steels against corrosion cavitation

damage in tap water.

An ambiguous effect of applications of low concentrations (0.005 N) of

anions in 0.01 N NaHCO 3 solution, which is the basis of the model soil

environment NS4, on the corrosion resistance of the 17Г1С steel has been

revealed: nitrate ions enhance local corrosion, phosphate and carbonate ions – on

the contrary, inhibit general and local corrosion. Chloride ions intensify general

and local corrosion of steel, especially in carbonate-bicarbonate solution.

It has been found that sensitivity of the 17Г1С steel to corrosion-static fracture
in 0.01 N NaHCO 3 solution increases with increasing cathodic polarization (from -0.7

-
to -1.1 V), does not depend on the intensity of local corrosion (the presence of Cl