Method for evaluating hydrochloric acid and corrosion inhibitor used for cleaning, and working liquid thereof

Abstract

The invention relates to a method for evaluating hydrochloric acid and a corrosion inhibitor which are used for cleaning, and a working liquid thereof. The working liquid contains 5.0%(m / V) of hydrochloric acid, 0-0.50% (V / V) of a hydrochloric acid corrosion inhibitor, 0-300mg / L of Fe<3+>, and the balance water. The method has the advantages of no need of a large device, simple operation, short time consumption, and realization of accurate site simulation, allows the quality, the oxidizability and the corrosion to an iron matrix of industrial hydrochloric acid used at the site to be accurately reflected through adopting analytically pure hydrochloric acid and the industrial hydrochloric acid used for site cleaning to carry out parallel tests, and allows the quality of chemical cleaning to be ensured and the running safety of a unit to be guaranteed through timely replacing unqualified industrial hydrochloric acid causing the high corrosion rate of a test piece.

Description

technical field [0001] The invention relates to an evaluation method of hydrochloric acid and a corrosion inhibitor for cleaning and a working solution thereof. Background technique [0002] Hydrochloric acid is a commonly used acid in the metal cleaning industry. Most of the chlorides produced by the reaction of hydrochloric acid and metals have good water solubility, but both hydrochloric acid and halides have a corrosive effect on metals. For example, the following reactions often occur in the hydrochloric acid cleaning of boilers: [0003] (1) Rolling of the carbon steel surface of the new boiler (Fe 3 o 4 ) will undergo the following dissolution reaction: [0004] Fe 3 o 4 +8HCl=2FeCl 3 +FeCl 2 +4H 2 o [0005] 2FeCl 3 +Fe=3FeCl 2 [0006] (2) Iron oxide scale (Fe 2 o 3 ) will undergo the following dissolution reaction: [0007] Fe 2 o 3 +6HCl=2FeCl 3 +3H 2 o [0008] 2FeCl 3 +Fe=3FeCl 2 [0009] (3) Hydrochloric acid will also react with the iro...

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Problems solved by technology

But these two kinds of tests all have drawbacks, and the related test equipment that dynamic test needs is more, complicated operation, time-consuming is long and not suitable for on-site test; Static test adopts chemical pure hydrochloric acid to test, but the quality of chemical pure hydrochloric acid is far better than Industrial hydrochloric acid for on-site chemical cleaning, and Fe is not added to the pickling solution 3+ , is not consistent with the actual situation on site, and cannot fully reflect the effect of on-site hydrochloric acid cleaning to inhibit corrosion

[0013] At the same time, hydrochloric acid is a volatile acid. When used above 40°C, hydrogen chloride gas will volatilize from the hydrochloric acid solution, which will affect the use effect.

The quality of commercially available industrial hydrochloric acid varies. Some hydrochloric acid suppliers deliberately reduce the quality of industrial hydrochloric acid for various reasons, especially by-product acid mixed with more strong oxidizing acids to pretend to be industrial synthetic hydrochloric acid, which will cause iron in the cleaning process. The corrosion rate doubles, seriously affecting the safe operation of the unit, and there is no effective test method to evaluate the quality of hydrochloric acid for cleaning

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