JPS5912752B2 - metal corrosion inhibitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an anticorrosive agent for metals that come into contact with water, and particularly to an anticorrosive agent for metals in closed circulating water systems and open circulating water systems with a small amount of blowout.

One way to prevent corrosion of metals that come into contact with ice water is to add corrosion inhibitors to the water. Conventionally, inorganic substances such as dichromates, chromates, nitrites, and phosphates, as well as various amines, have been added. Organic substances such as , carboxylic acid salts, mercaptans, alcohols, and imidazoles are used as anticorrosive agents. Among these anticorrosive agents, inorganic chromates and nitrites are inexpensive and exhibit remarkable anticorrosion effects, but are toxic.
Phosphate also promotes the growth of algae that causes slime problems. Furthermore, inorganic anticorrosive agents require complicated system pH adjustment in order to provide an effective anticorrosive effect, and sometimes promote local corrosion such as pitting corrosion, which may lead to major accidents. Under these circumstances, corrosion inhibitors made of organic substances, especially carboxylic acid salts, are attracting attention, but they do not have an excellent anticorrosion effect in high-temperature systems, and have little effect at temperatures exceeding 50°C, and are more likely to cause pitting corrosion. Therefore, there is a need for an economical anticorrosive agent that is stable against temperature changes.

The present invention provides an alkali metal salt or alkanolamine salt of phthalic acid (hereinafter referred to as phthalate) and an alkali metal salt or alkanolamine salt (hereinafter referred to as phthalate) of benzoic acid or salicylic acid, which were provided in view of the above-mentioned current situation. , other aromatic carboxylates) as an active ingredient.

Although phthalates are already known anticorrosive agents, it has been found that when used in combination with other aromatic car90phonates, a stable and excellent anticorrosion effect can be achieved even at high temperatures. Examples of phthalates include orthophthalates, metaphthalates, and terephthalates, with orthophthalates being particularly preferred.
Other aromatic carphonic acids used in combination with phthalates are one or more of benzoates and salicylates. Phthalates or other aromatic carboxylates include alkali metal salts such as sodium salts, potassium salts, monoethanolamine salts, diethanolamine salts,
Alkanolamine salts such as triethanolamine salts can be used. The compounding ratio of the drug of the present invention is usually a weight ratio of phthalate to other aromatic carboxylate of 1:9 to 9.
:1, particularly preferably 4 to 4:1.

35 The amount of the metal corrosion inhibitor of the present invention added is usually 500% to water.
It is more than p concave, preferably more than 1000 pμm.

The metal corrosion inhibitor of the present invention has a stable corrosion prevention effect in an aqueous system from low to high temperatures, and is thought to form a passive film or a chelate film on the metal surface. This film protects the metal by suppressing the diffusion of dissolved oxygen from the aqueous phase to the metal surface. Next, the present invention will be explained by examples.

Example 1 A mixture of sodium phthalate and sodium benzoate or sodium salicylate was dissolved in Yokohama city water, and a mild steel test piece (SS-41, surface area 31 crA) was placed in this solution.
A corrosion protection test was conducted by immersing the sample in a sealed container at 45±2° C. for 120 hours.

The results are shown in Table 1. For comparison, the case where each drug was added alone and the case where no drug was added are also shown. As can be seen from this table, when other aromatic carboxylic acids are blended with phthalate, excellent anticorrosion effects are exhibited.

Example 2 A mixture of 1:1 triethanolamine salt of phthalic acid and triethanolamine salt of benzoic acid was added to Yokohama city water at 2000 ppm, and a mild steel test piece (SS-41. 31ct!i) was immersed and left at each temperature for 14 days to perform a corrosion protection test.

The results are shown in Table 2. From this table, it was found that the metal anticorrosive agent of the present invention exhibits a stable anticorrosive effect from low to high temperatures.

Claims (1)

[Claims] 1. A metal anticorrosive agent containing as active ingredients an alkali metal salt or alkanolamine salt of phthalic acid and an alkali metal salt or alkanolamine salt of benzoic acid or salicylic acid.