US2318663A

US2318663A - Composition and method for treating boiler water to prevent caustic embrittlement

Info

Publication number: US2318663A
Application number: US381762A
Authority: US
Inventors: Paul G Bird; Evans Wilson; Harmon Carlyle; Salvesen Jorgen Richter
Original assignee: National Aluminate Corp; Marathon Paper Mills Co
Current assignee: ChampionX LLC; Marathon Paper Mills Co
Priority date: 1941-03-04
Filing date: 1941-03-04
Publication date: 1943-05-11
Anticipated expiration: 1960-05-11

Description

' Patented May 11, 1943 COMPOSITION ING B TIC owl AND METHOD FOR 'rnnmrwa'rna TO PREVENT C lnl G. Bird, Western Springs, and Evans,

111., and Carlyle Harmon and Jon-gen tion of Delaware, jointly No Drawing. Applion March 4, 1941, Serial. No. 381,762

13 Claims.

This invention relates to the treatment of boiler water to prevent caustic embrittlement or intergranular attack of steel boiler plates.

The invention consists in the discovery that caustic embrittlement of steel boiler plates can be prevented by adding to the normal boiler water a combination of chemicals consisting of a sufllcient minimum amount of sodium sulphlte, or its equivalent, and a sulphonated organic substance of suitable colloidal character and which has the property of preventing or retarding the oxidation of the sodium sulphite, such as lignin sulphonate.

The exact mechanism taking place in steel boiler plates undergoing caustic embrittlement is not well established. It is known that failure occurs only in plates under great mechanical stress when in contact with caustic soda solution of the order of 20,000 to 40,000 parts per million, together with a small amount of sodium silicate. In order to obtain such a high concentration of caustic it is nwessary that a small leak exist so that the boiler water may escape very slowly. As the water evaporates around such a leak it concentrates and deposits caustic soda, sodium sulphate and other dissolved materials present 11117118 water.

Previous attempts to prevent caustic embrittlement were based on maintaining in the boiler water a certain ratio of sodium sulphate to total alkalinity. The A. S. M. E. code recommends that for boiler pressures up to 150 lbs., one part of sodium sulphate be maintained for each part of total alkalinity, expressed as sodium carbonate present in the water. For pressures from 150 to 250 lbs. the recommended ratio is increased to two parts 01 sodium sulphate for each part of caustic, and for pressures greater than 250 lbs.

the recommended ratio is increased to three parts. It is known that caustic embrittlement takes place even when these recommended ratios are maintained. It was this fact, and the difiiculties encountered in maintaining such ratios that led us to seek a successful solution of the problem of preventing caustic embrittlement.

In general, boiler waters are treated for at'least five different purposes: -(1) To prevent the formation of scale on the heated surfaces; (2) To prevent encrustation or deposition of the material in the feed lines, preheaters, etc.; (3) To prevent the corrosion of the metal; (4) To prevent foaming of the boiler water; (5) To prevent caustic embrittlement or intergranular cracking of the heated surfaces. It frequently happens that a chemical or mechanical treatment may be used for one of these functions without having any efiect whatever on the other objects of the treatment.

The presence of dissolved oxygen in boiler water is responsible for pitting and corrosion and many methods have been proposed for removing this dissolved oxygen. The use of sodium sul'phite for this purpose is well known (see Oxygen removal from boiler water by Sodium Sulphite, by Kobe and Gooding, Industrial 8: Engineering Chemist y. vol. 27, p.331-333, 1935) The following reaction takes place when the oxygen is removed: 2NazSO3+Oz 2NazSO4. In this case the sodium sulphite is readily converted to sodium sulphate by the dissolved oxygen present in the water, but caustic embrittlement is not prevented as the sodium sulphite is converted in its reaction with oxygen;

The use of sulphonic acid salts or waste sulphite liquor products in the treatment of boiler water is also well known (French Patent 619,040, French Patent 581,750) (Protecting steel against intercrystalline attack in aqueous solution, by W. C. Schroeder, A. A. Berk, and R. A. OBrien, A. S. M. E. Transactions for January 1938). However, the use oflignin sulphonate alone does not offer complete protection against caustic embrittlement.

We have discovered that Sulphonated organic material such as sodium lignin sulphonate has the property of inhibiting the oxidation of sodium sulphite in aqueous solution. This is illustrated by the following table:

Table Per cent oxidation of sulphite after Composition of boiler water 5 hours 16 hours 48 hours 1250 ppm 1 NaOH-50 ppm NBzSOa 20.0 52. 4 88. 3 1250 ppm N aOH-50 ppm Na SO 500 ppm Na-lignosulphonate '8. 9 l9. 5 33. 2 625 ppm NaOH-25 ppm NazSOa" 23.0 55. l 86. 2 625 ppm NaOH 25 p m Nn2SOa 250 ppm Na-lignosu phonate 10.6 20.0 30. 6 250 ppm Na0Hl0 ppm NmSOa" 20. 6 5i. (i 85. i 250 ppm NaOH IO ppm NazS O3- 100 ppm Na-lignosulphonate 9. 4 20. 8 35. 4

1 Abbreviation for parts by weight per million parts of water.

expected and efiective results not obtainable by the use of either material alone and that such mixture ofiers complete protection against caustic embrittleme'nt.

A thorough study of the reactions taking place between sodium lignosulphonate and the other constituents in the boiler water such as sodium carbonate, sodium hydroxide, sodium phosphate, sodium chloride, sodium sulphate, etc., indicates that lignin sulphonate releases small quantities of sodium sulphite under such condition and thereby lessens somewhat the dispersibility of the lignin sulphonate. However, for normal boiler operations the amount of sodium sulphite thus released is not sufiicient to fully prevent caustic embrittlement. We have discovered that the addition of a predetermined quantity of sodium sulphite and sodium lignin sulphonate t the boiler water effectively prevents caustic embrit tlement, as illustrated in the following examples:

Example 1.--Standard boiler test water containing 500 P. P. M. of sodium hydroxide, 50 P. P. M. of sodium silicate, to which was added 200 P. P. M. of sodium lignin sulphonate, was

placed in a Schroeder test bomb (Association of American Railroads Circular No. D. V. 989, entitled Intercrystalline Cracks in Locomotive Boilers by W. C. Schroeder, A. A. Berk and R. A. OBrien), and the solution maintained at a temperature corresponding to 250 lbs. gauge pressure.

The solution was in contact with a piece of highly stressed S. A. E. 1020 boiler plate of inch thickness. After days one plate was cracked through 22% of, its thickness, the second plate through 25% of its thickness and the third through of its thickness.

Example 2.--A similar test was made using a boiler water containing 500 P. P. M. of sodium hydroxide, 50 P. P. M. of sodium silicate, and 10 P. P. M. of sodium sulphite. The plate was cracked through 100% at the end of the 30-day period. Similar tests with the sodium sulphite increased from 10 up to 200 P. P. M. showed 63% cracking. Thus, apparently no practical amount of sodium sulphite alone is satisfactory.

Example 3.Four similar tests were made using a boiler water containing 500 P. P. M. of

sodium hydroxide, P. P. M. of sodium silicate,

and 200 P. P. M. of sodium lignin sulphonate, to which 10 P. P. M. of sodium sulphite was added. After '30 days in the test block the steel sample showed no sign of cracking whatever. Similar tests with increased amounts of sodium sulphite also showed complete protection. Since the water used in these tests contained approximately 8 P. P. M. of dissolved oxygen there was enough oxygen present to react with 63 P. P. M. of sodium sulphite to convert *it to sodium sulphate. Such oxidation was prevented by the presence of the sulphonate organic matter, such as sodium lignin sulphonate, which inhibited oxidation of sodium sulphite.

Example 4.A similar test was made usinga boiler water containing 500 P. P. M. sodium hydroxide, 50 P. P. M. sodium silicate, 500 P. P. M. sodium chloride, and 1500 P. P. M. sodium sulphate. The 1020 steel sample was cracked through 61% of its thickness in 30 days.

Example 5.-A similar test was made with the same solution as Example 4 with the addition of 200 P. P. M. of lignin sulphonate. The plate cracked through 58% of its thickness in 30 days. Example 6.A similar test was made using the same solution as in Example 4 but with the addition of 90 P. P. M. of lignin sulphonate and 10 P. P. M. of sodium sulphite. The plate showed no cracking whatever in 30 days.

We have found that the addition of about 10 to 50 parts by weight of a sulphite such as sodium sulphite, or its equivalent, and 50 to 300 parts by weight of a colloidal sulphonated organic compound selected from. the group consisting of lignin sulphonate, and sulphite cellulose liquors, such as sodium lignin sulphonate, per million parts of boiler water is an effective concentration for preventing caustic embrittlement under normal boiler operations. We prefer to regulate the amount present in the boiler water by adding known amounts of the constituents to the feed water or directly to the boiler, taking into consideration the number of times the feed water is concentrated in the boiler, this being determined by means well known to those proficient in the art of boiler water treatment. For example, by means of the chloride ratios, per cent blowndown, etc.

Since the exact nature of the reaction causing embrittlement is not known it cannot be said with certainty how a small quantity of sulphite and lignin sulphonate can stop such reaction. In addition to the lignin sulphonate preventing the oxidation of the sulphite, the sulphite may in turn act to maintain the colloidal dispersion of the lignin sulphonate so that it can form a protective coating for the steel, and thus protect it from the action of the concentrated alkali. Another possibility is that the sulphite, or the lignin sulphonatemay affect the nature of the oxide film present on the stressed steel plate and thus prevent the concentrated caustic from attacking the intergranular structure.

While the specific example have referred to sodium sulphite we do not wish to be limited to sodium alone. The active ingredient is the sulphite ion which may be supplied by adding any suitable compound, such, for example, as alkali or alkaline earth sulphites, or bisulphite or other materials that after addition to hotalkaline boiler water will yield sulphite ions.

We prefer to employ as the sulphonated organic material, sodium lignin sulphonate but other sulphonated compounds such as magnesium or calcium ligninsulphonate or concentrated pa-' per mill waste sulphite liquors may be used.

From the chemical nature of-quebracho, cutch and from the claims made by other investigators regarding the protection against caustic embrittlement offered by these materials it might be reasoned that they would react in a similar manner with bisulphite. However, our investigation indicates that quebracho actually accel erated the oxidation of bisulphite in aqueous so,- lution and that cutch has little or no action on the oxidation.

Our invention can be conveniently practiced by first preparing suitable boiler water treating compositions containing the usual caustic alkalinity producing compounds. such as caustic and changes of our specific embodiments can be steam boilers which comprises adding to the normal feed water containing caustic alkalinity producing compounds 9. mixture of a sulphite selected from the group consisting of alkali and alkaline earth metal sulphites and a colloidal sulphonated organic compound selected from the group consisting of alkali and alkaline earth lignin sulphonates and sulphite cellulose liquors in sumcient-proportions to inhibit caustic embrittlement and thereafter introducing the water in a boiler.

2. The method of preventing caustic embrittlement in a steam boiler which comprises adding to the normal feed water containing caustic alkalinity producing compounds a mixture of a sulphite selected from the group consisting of alkali and alkaline earth metal sulphites and a lignin sulphonate selected from the group consisting of alkali and alkaline earth metal lignin sulphonates in suflicient proportions to inhibit 7. A composition for treating boiler water to prevent caustic embrittlement comprising an inorganic sulphite selected from the group consisting of alkali and alkaline earth metal sulphites, a iignosulphonate selected from the group consisting of alkali and alkaline earth metal lignin sulphonates and a caustic alkalinity producing compound for normal boiler operation in suitable proportions when dissolved in boiler water consisting of alkali and alkaline earth metal lig-' operation of said steam boiler and thereafter introducing the water in a boiler. I

3. The method of preventing caustic embrittlernent in steam boilers which comprises adding to the normal feed water containing caustic alkalinity producing compounds a mixture of sodium sulphite and sodium lignin sulphonate in sufilcient proportions to inhibit caustic embrittlement and thereafter introducing the water in a boiler.

4. The method of treating boiler water used in steam boilers which comprises adding to the normal feed water a mixture of a sulphite selected iromthe group consisting of a and alkaline earth metal sulphites and a lignin sulphonate selected from the group consisting of alkali and alkaline earth metal lignin sulphonates in sumcient proportions to prevent caustic embrittlement.

5. A method of treating boiler water used in steam boilers which comprises adding to the normal feed water a mixture of a sulphite selected from the group consisting of alkali and alkaline earth metal sulphites and a lignin sulphonate selected from the group consisting of alkali and alkaline earth metal lignin sulphonates in sufficient proportions to result in -a concentration water to prevent causticembrittlement duringbciler operations.

to yield in solution about 10 to 50 parts by weight of sulphite and about 50 to 300 parts by weight of lignosulphonat per million parts of water.

8. A composition for treating boiler water to prevent caustic embrittlement comprising an inorganic sulphite selected from the group consisting of alkali and alkaline earth metal sulphites and a lignosulphonate selected from the group nin sulphonates in suitable proportions to yield in solution 10 to 50 parts by weight of sulphite and 50 to 300 parts by weight of lignosulphonate per million parts of water. p

9. A composition for treating boiler water to prevent caustic embrittlement comprising sodium sulphite and a sodium lignosulphonate in suitable proportions to yield in solution 10 to 50 parts by weight of sulphite and 50 to 300 parts by weight of lignosulphonate per million parts of water.

10. A composition for treating boiler water to prevent caustic embrittlement comprising an inorganic sulphite selected from the group consisting of alkali and alkaline earth metal sulphites and a colloidal suphonated organic compound selected from the group consisting of alkali and alkaline earth lignin sulphonates and sulphite cellulose liquors in suitable proportions to yield in solution 10 to 50 parts by weight of sulphite and 50 to 300 parts by weight of a colloidal sulphonated organic compound per million parts of water.

11. A process ,of inhibiting oxidation of an aqueous solution of sodium sulphite which comprises the step of adding to the solution small amounts of lignin sulphonate selected from the group consisting of alkali and alkaline earth metal lignin sulphonates.

12. A composition comprising sodium sulphite inhibited against oxidation by the presence of lignin sulphonate selected fromthe group consisting of alkali and alkaline earth metal lignin sulphonates.

. 1-3. A composition comprising a sodium sulphite inhibited against oxidation by the presence of a colloidal sulphonated organic compound selected from the group consisting of alkali and alkaline earth lignin sulphonates and sulphite cellulose liquors.

'PAUL G. BIRD.

WILSON EVANS.

CARLYLE ON.

JGRGEN RICHTER SALVESEN.