US3600125A - Method of utilizing piperidine as a condensate corrosion inhibitor - Google Patents

Abstract

A METHOD OF AND DOSAGE CONCENTRATION FOR INHIBITING CO2 AND O2 CORROSION IN BOILER STEAM CONDENSATE SYSTEMS COMPRISING ADDING PIPERIDINE IN CONDENSATE CONCENTRATIONS OF FROM ABOUT 1.0 TO 10.0 P.P.M. TO ACHIEVE A PH OF ABOUT 8.8 TO 9.5 THIS METHOD PROVIDES ADEQUATE LPROTECTION ESPECIALLY FOR THE FERROUS METAL PIPES NORMALLY UTILIZED IN CONDENSATE SYSTEMS AND UTILIZES A REAGENT WITH A FAVORABLE DISTRIBUTION RATIO BETWEEN VAPOR AND INITIALLY FORMED CONDENSATE.

Description

Patented Aug. 17, 1971 3,600,125 METHOD OF UTILIZING PIPERIDINE AS A CONDENSATE CORROSION INHIBITOR Kenneth G. Phillips, River Forest, Ill., assignor to Nalco Chemical Company, Chicago, 111. N Drawing. Filed May 16, 1969, Ser. No. 825,395

Int. Cl. C23f 11/04, 11/08 US. Cl. 212.7 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a novel treating compound which is useful in inhibiting corrosion in return steam condensate lines. More particularly, the subject invention is directed to a member of a group of cyclic saturated imines known as pentamethyleneimine or piperidine.

It is well known that steam lines and steam condensate lines are subject to corrosion which is very diflicult to control. This corrosion is apparently due, to a large extent, to carbon dioxide and oxygen in the boiler-steamcondensate system. Carryover from the boiler water can also increase the corrosion. The problem of corrosion of the internal surfaces of steam condensate return lines has been recognized for many years. Generally, the difficulties that have been experienced are pitting, grooving and ultimate deterioration of sections of the condensate return system and the plugging of constrictions in the system with the insoluble products of corrosion. To evaluate properly the actual cost of return line corrosion, it is necessary not only to consider the loss in terms of labor, curtailed production and the cost of the material destroyed, but also to weight effects in terms of inefficient operation of fouled equipment.

Experimental studies by various investigators indicate that dissolved carbon dioxide and oxygen are responsible for practically all the corrosion in the condensate lines. The various expedients that have been devised for combating this attack are as follows:

1) The use of corrosion resistant alloys, which is generally prohibitive from a cost standpoint.

(2) Minimizing the amount of carbon dioxide and oxygen in the condensate either by venting or pretreatment of the boiler feedwater.

(3) Chemical treatment of the condensate.

It has been found that a readily volatile alkaline base compound may be utilized for the treatment of steam condensate return systems and examples of prior art treatments of such systems are found in 2,582,138 Lane et al., 2,956,889 Denman, 3,029,125 Hummel, 3,378,581 Hummel.

Additionally, the use of other imines such as hex-amethyleneimine as a corrosion inhibitor but in a strongly acid medium has been described and taught in 3,091,591 Hackerman et al., but the problem of the dosage concentration and monitoring of the pH level in a restricted alkaline range is not suggested by this teaching. Furthermore, the favorable qualities of piperidine in the concentration utilized imparting thermal stability,

high pH producing ability, and favorable distribution ratio in the initially formed condensate all militate for novelty in the present development.

Pursuant to the present invention, it has been found that corrosion in the steam and condensate return systems may be lowered or substantially mitigated by treating such systems with a dosage or corrosion inhibiting amount of piperidine. This material is effective when added either to the boiler feedwater, to the steam lines, or to the condensate return lines, but due to the economics and wastage in the other methods, it is preferred to add the treatment to the steam condensate line since it is this part of the system where corrosive attack is the severest and the smallest amounts of the treatment are the most effective. The amount of piperidine added should be at least 1.0 part per million (ppm) of the corrosion inhibiting chemical by weight of the steam of steam condensate, preferably 1.0-10.0 p.p.m., and even more preferably 1.04.0 ppm. The dosage Will, of course, vary depending upon the conditions of the system and other variable factors; hence, dosages as high as 50 p.p.m. may be necessary under extraordinary corrosion conditions.

The employment of the corrosion inhibiting chemicals in accordance with this invention is applicable to the generation of steam at various temperatures and pressures. Good results can be obtained where steam is generated under atmospheric conditions, subatmospherie conditions or superatmospheric conditions. In most cases, steam is generated at pressures from atmospheric up to 1500 pounds per square inch or more and the corresponding temperatures.

Piperidine has the following formula:

on fun zs It was found from the experimental data that the piperidine appeared to collect preferentially in the initially formed condensate so that it acted to neutralize the freshly carried over CO and apparently acid in a similar fashion as a few other reagents such as morpholine in this connection. Thus, a good distribution ratio for the reagent indicated that the greatest portion of the reagent settles in the water phase of the initially formed condensate providing corrosion protection rapidly at the liquid/metal interface.

In the operation of an on stream boiler system for steam condensate return, it has been found that a reagent should be utilized in dosage concentrations sufficient to impart or raise the pH level of the slightly acid initial condensate to the alkaline range and preferably to a pH of about 8.8-9.5. A pH level above 9.5 is not deleterious to the system, but efiiciency and cost consideration make it an unpreferred modus of operation. A pH value below about 8.8 begins to subject the sys tem to corrosion damage principally from the carryover CO and defeats the mission of the corrosion inhibitor reagent employed. In on stream boiler usage, the present system preferably contemplates incremental addition of reagent to permit monitoring and maintaining of the pH within the desired alkaline bracket. It is to be noted that the present reagent also has favorable stability characteristics in this setting, which unlike many other nitrogen base compounds permits utilization in the severe heat and acid conditions without breakdown of the reagent.

It has also been found that the narrow range of a pH of about 8.8-9.2 is optimum in this connection of steam condensate return systems. Thus, a monitoring system employing the reagent at this pH is one which will operate at the greatest efficiency.

Example 1 P.p.m. P 200-250 NaCl 1400-1600 D.S. 2600-3200 P 40-60 80;, 40-60 A Milton-Roy mini-pump was set up so that the treatment solution could be injected directly into the feedwater line at a point near the feedwater storage tank and input to boiler feed pump.

Live Steam was throttled from a take-01f line and passed through an Inconel steam sampling coil where it was condensed and cooled to 4050 F. at a rate of 100-300 ml. per minute.

The cooled condensate was passed continuously through 0.1 cell constant pencil type conductivity cell which was connected to a Bailey conductivity recorder using 24 hour round charts with a range of 0-50 micro mhos.

After passing through the conductivity cell, the condensate entered the pH flow cell which consisted of a polyethylene cup (3 dia. x 3 /2" deep) into which standard laboratory pH electrodes were immersed. Condensate entered near the bottom of the cup and overfiowed near the top. Measurement of the pH was by a Beckman Zeromatic pH meter which was connected to a 24 hour round chart Foxboro pH recorder. The open pH flow cell was kept shielded from dust by a paper covering.

Samples of condensate were collected daily to be analyzed for copper, iron, ammonia, and amine content.

Treatment chemicals.-In preparing the amine solutions used as treatment, piperidine was utilized from commercial sources. The diluted treatment solutions were fed from a 2 gallon calibrated glass bottle.

Results.Data indicated that about 1.5 p.p.m. of piperidine produced a 9.0 condensate pH.

In other tests giving similar results when the plant boilers were operating with a steady load and about 25% makeup, about 1.0 to 4.0 p.p.m. of piperidine, based on total steam flow, was needed to give a condensate pH of 8.8-9.0.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of inhibiting the corrosion of steam condensate lines caused by C0 and O in the steam condensate which comprises adding to the condensate in said lines a small but effective amount of piperidine to raise the condensate pH level to a range of about 8.8 to 9.5.

2. The method of claim 1 wherein the pH level is raised to a range of about 8.8 to 9.2.

3. The method of claim 1 wherein the pH of said condensate is maintained and monitored at about a pH of 8.8 to 9.5 by addition of incremental amounts of piperidine while said steam condensate line is on stream.

4. The method of claim 3 wherein the condensate system is maintained and monitored at a pH of about 8.8 to 9.2.

References Cited UNITED STATES PATENTS OTHER REFERENCES Rosenfeld, I.L., et al.: Corrosion, July 1964; vol. 20, No. 7, pp. 222t to 234t.

Hackhs Chemical Dictionary, Third Edition, 1944; p. 662 relied on.

Sperry, S. M.: Combustion, November 1955; vol. 27, No. 5, pp. -67 and 71 relied on.

MORRIS O. WOLK, Primary Examiner B. S. RICHMAN, Assistant Examiner U.S. Cl. X.R. 2l2.5