KR101058965B1 - How to suppress grain boundary corrosion on metal surfaces - Google Patents

Abstract

The present invention is directed toward the use of a reaction product of an alkynediol and a polyalkylene polyamine to inhibit intergranular corrosion of metal surfaces in industrial processing systems caused by spray water mist or condensation.

Description

METHODS FOR INHIBITING INTERGRANULAR CORROSION OF METAL SURFACES}

The present invention relates to the use of the reaction product of alkyindiol and polyalkylene for inhibiting intergranular corrosion of the metal surface in industrial water and process systems where the surface is in contact with sprayed water or condensate.

 The microstructures of metals and alloys consist of crystals separated by grain boundaries. The grain boundary corrosion can be defined as a localized attack along the crystal boundary or a localized attack immediately near the crystal boundary. This precipitation can result in zones of reduced corrosion resistance in the immediate vicinity.

Examples of grain boundary corrosion include increase and decrease of stainless steel or weld corrosion. Chromium-rich crystal boundary precipitates result in local depletion of Cr adjacent to these precipitates, thereby making the region vulnerable to corrosion attack.

Peel corrosion is a specific form of intergranular corrosion. Peeling or flakes appear as a loss of metal in the layer along the crystal boundary along the surface. Peeling from the casting occurs, for example, in less fragments of non-wet structure in which no direct spray water contact occurs. Steel is exposed to a high temperature wet environment where the surface is wetted only by sprayed water mist or condensate. Corrosion spreads rapidly along the steel surface, causing a loss of structural integrity of the secondary support structure.

The mechanism for exfoliation corrosion is related to the presence of chloride in the spray water. Mist (vapor), when used in spray water systems, moves through the vapor chamber and condenses on steel surfaces. Heat and moisture evaporate water from this steel surface, which leaves concentrated chloride ions. This process continues, concentrating more chloride ions until the point at which exfoliation occurs.

Coupon analysis reveals that the corrosion mechanism occurs as follows: chloride ions deposited on the metal surface migrate through the brittle layers of the corrosion product / generated deposits. A temporary iron chloride salt is formed under the deposit. This salt is hygroscopic (absorbs moisture) and produces acid chloride conditions upon hydrolysis. As acidic corrosion proceeds deeper at the metal surface, additional iron oxide corrosion products remain.

As mentioned above, there is a need in the art for techniques and inhibitors to remove exfoliation corrosion present in industrial process systems.

The present invention is a method of inhibiting intergranular corrosion of metal surfaces in contact with sprayed water or condensate in industrial process systems, such as steam and cooling water systems, wherein the reaction products of alkyidadiol and polyalkylene polyamine It relates to a method comprising the step of adding to the spray water in an amount sufficient to inhibit.

The conditions under which the reaction product is formed are disclosed in US Pat. No. 3,211,667, which is incorporated herein by reference in its entirety.

Alkydinadiols and alkenediols which are considered to be effective in the preparation of the reaction products are those containing from 4 to 12 carbon atoms. Preferably, the carbon number of the alkyindadiol is four. An example of an alkyindiol is butydinol.

Polyalkylene polyamine compounds taught to be effective in preparing reaction products are those comprising from 2 to 10 amine groups, preferably from 3 to 7 amine groups. These amine groups may be substituted or unsubstituted, and are each separated by alkylene groups having 1 to 6 carbon atoms, preferably 2 to 4 carbon atoms. Representative polyamines include ethylene diamine, diethylene triamine, pentaethylene hexamine, pentapropylene hexamine, triheptylene diamine, and the like.

The weight ratio of the reactants is such that a complete reaction of each component is obtained, with the weight ratio of amine to diol being 4: 1 to 1: 1, preferably 3: 1. Ionizable copper compounds such as copper acetate are used in this reaction in catalytic amounts.

The reaction product of the present invention may be added to the sprayed water in an amount sufficient to inhibit corrosion of the metal surface. The reaction product may be added to the feed line in an amount of 0.5 to about 500 ppm of water present in the feed line. Preferably, about 1 to 100 ppm, particularly preferably 5 to 10 ppm of water is added.

The reaction product of the present invention is included in the solvent or fed to the feed line in net form. Preferably, the reaction product is added to an aqueous solvent, for example water. This reaction product can be added to the sprayed water together with other suitable components such as antifoaming agents, corrosion inhibitors and the like. Typically, the temperature of the spray water in the system to be treated is about 110 to 180 degrees Fahrenheit.

The following data demonstrates unexpected results in the use of the present invention. The following examples are illustrative of the invention and are not intended to limit the scope of the invention.

In order to suppress the corrosion mechanism occurring on the metal surface, a film material was added which separates the surface from water and chloride. The addition of 2-butyne-1, 4-diol-polyethylenepolyamine (Product A) significantly reduced the corrosion rate of steel (see Tables 1 and 2). In all tests, a coupon tree was constructed to place various corrosion coupons in the spray chamber. This solution was injected into the feed line to the casting spray furnace. The material was distributed through the spray chamber.

Iron levels in the deposits were greatly reduced.

The results show that the chloride concentrations are similar in both untreated (5%) and treated (6%), while the other components are significantly different. The iron level of untreated cotton is 88%; Peel levels are also significant. In terms of treatment, the iron level was only 23% and no delamination occurred. The calcium content of the treated cotton was 52%, which meant that corrosion was suppressed.

In a further test, the corrosion coupon was immersed in Product A and placed after the untreated coupon in both treated and untreated strands. In the untreated strands, the soaked coupons were hardly corroded while the untreated coupons were peeled off. In the treated strands, there was a significant improvement in corrosion control over coupons.

In another test of the present invention, another coupon tree was constructed. Coupons tested included mild steel, stainless steel, copper and coated mild steel.

After 8 days as a start-up check, a single set of mild steel coupons was removed. Coupon results are shown in Table 3 below. Coupons from strand 2 showed delamination, while coupons from strand 1 only showed a general corrosion mechanism.

As further shown in Table 4 below, the corrosion rate on the corrosion coupon tree was significantly reduced in strand 1 into which product A was injected. Product A was supplied at 15 ppm through the system. Mild steel corrosion rate was reduced by about 50 to 80% at most locations. As noted above, coupons from strand 2 exhibited delamination, while coupons from strand 1 exhibited only general corrosion mechanisms (not peeled).

Note that the remaining coupons are not all stainless steel or coated coupons, and no serious corrosion was found in any of these coupons. In addition, the treatment of the present invention did not adversely affect the impact nozzle performance of the spray water system.

While the invention has been described with reference to specific embodiments, many other forms or modifications of the invention will be apparent to those skilled in the art. It is to be understood that the appended claims and the invention generally include the above obvious forms and modifications without departing from the spirit and scope of the invention.

Claims (15)

Adding a reaction product of alkynediol and polyalkylene polyamine to the sprayed water, A method of inhibiting intergranular corrosion of a metal surface in an industrial process system where the metal surface is in contact with sprayed water. The method of claim 1, The intergranular corrosion is exfoliative corrosion. delete The method of claim 2, Peeling corrosion occurs on metal surfaces wetted by sprayed water mist or condensate. The method of claim 1, Alkaindiol comprises an alkane group having 4 to 12 carbon atoms. delete The method of claim 1, Wherein the polyalkylene polyamine comprises 2 to 10 amine groups, wherein the amine groups are each separated from each other by alkylene groups having 1 to 6 carbon atoms. delete The method of claim 1, The reaction product is added to the sprayed water in an amount of 0.5 to 500 ppm of the sprayed water. The method of claim 1, The temperature of the spray water is from 110 to 180 ° F. The method of claim 1, The reaction product is included in the aqueous solvent and added to the spray water. delete The method of claim 9, The reaction product is added to the sprayed water in an amount of 1 to 100 ppm of the sprayed water. The method of claim 13, The reaction product is added to the sprayed water in an amount of 5 to 10 ppm of the sprayed water. delete