Anticorrosive composition

Field of the Invention

The present invention relates to an anticorrosive composition and the use of such a composition for imparting anticorrosive properties to a material, and a material comprising such a composition.

Background of the Invention

Corrosion is the deterioration of a metal as result of a chemical reaction between it and the surrounding environment. Corrosion involves the conversion of the metal to a more chemically stable form, such as oxide, hydroxide or sulfide.

Corrosion of steel occurs in the presence of water and oxygen. Corrosion of steel parts is a major economic problem which often times makes up a major part of the maintenance and renewal costs of steel structures.

A very specific problem is the problem of corrosion under insulation (CUI) which affects steel parts which are thermally isolated by an insulating material. Steel structures are often insulated in order to avoid heat loss. Such a thermal insulation might be desirable for steel structures which are much warmer or colder than their surrounding environment. CUI occurs in particular under insulation for steel structures which undergo cyclic temperature changes like e.g. pipelines in the oil and gas industry. Since corrosion of steel occurs in the presence of water and oxygen, the presence of water in contact with the steel structure is a major factor contributing to corrosion. Since thermal insulation materials surrounding the steel structures in order to avoid heat loss tend to keep water in contact with the steel structure for a longer time than the contact would last without the surrounding insulating material, such insulating materials can contribute to increased corrosion. Steels are in general susceptible to CUI in the temperature range of 0 °C to 175 °C. The most frequently occurring types of CUI are general and pitting corrosion of carbon steel which may occur if wet insulation comes in contact with carbon steel, and external stress corrosion tracking (ESCT) of austenitic stainless steel, which is a specific type of corrosion mainly caused by the action of water-soluble chloride or if the insulation is not meeting the appropriate requirements. Since the corroded surface is mostly hidden by the insulation system and will not be observed until the insulation is removed for inspection or in the event of metal failure leading to incidents, it is very important to control CUI as much as possible.

In order to avoid CUI, the insulated steel structures are often covered by an additional cladding which is to prevent the entering of water. However, experience shows that water often enters via fault or damages in the cladding system or via humid air in structures which undergo cyclic temperature changes. Water may also come into contact with the steel structure internally from non-tight fittings or externally from events like flooding.

In order to avoid CUI, steel structures like pipelines in the oil and gas industries are often protected against corrosion by coating the steel parts with a protective layer, e.g. with other metals like zinc or aluminum. However, such coating layers are never a completely protecting layer and these protective measures can be extremely cost-intensive and might be economically unacceptable for extensive pipeline systems.

In view of the high economic damage caused by corrosion in any form, be it in form of corrosion under isolation or any other form of corrosion, numerous strategies have been developed in order to avoid corrosion. One strategy is to keep water out by imparting water repellence to a material. Another strategy is the reduction of the time of wetness of a material by causing water to quickly vanish from the material after contact. Another strategy is the use of corrosion inhibitors.

While many corrosion inhibitors of different compositions have been proposed in the past, many of these anticorrosive compositions suffer from either lack of effectiveness, and/or come at high prices, and/or are difficult to handle, and/or are harmful for humans and/or environment.

Summary of the Invention

Accordingly, it was the object of the present invention to provide an anticorrosive composition, which is highly effective in inhibiting corrosion, is economically advantageous, easy to handle, and is non-harmful for humans and the environment.

It was a further object of the present invention to provide a use for an anticorrosive composition for imparting anticorrosive properties to a variety of materials, in particular selected from the group consisting mineral wool products, such as a stone wool or glass wool, and other fibrous materials.

It was a further object of the present invention to provide a mineral wool product comprising such an anticorrosive composition.

In accordance with a first aspect of the present invention, there is provided an anticorrosive composition comprising one or more alkali metal silicate components of the formula MezO xSiOz, wherein x is 0.5 to 3.0, one or more alkali metal phosphate components of the formula MezO : nPzOs, wherein n is 0.33 to 1, or hydrates thereof, one or more carboxylic acids with 6-22, such 7-14 carbon atoms, or salts thereof.

According to the second aspect of the present invention, there is provided a use of a composition comprising one or more alkali metal silicate components of the formula MezO xSiOz, wherein x is 0.5 to 3.0, one or more alkali metal phosphate components of the formula MezO : nPzOs, wherein n is 0.33 to 1, or hydrates thereof, one or more carboxylic acids with 6-22, such 7-14 carbon atoms, or salts thereof, for imparting anticorrosive properties to a material, such as a material selected from the group consisting of a mineral wool product, such as stone wool or glass wool, and other fibrous materials.

In accordance with a third aspect of the present invention, there is provided a material, such as a mineral wool product or other fibrous materials, comprising a composition comprising one or more alkali metal silicate components of the formula Me ₂ 0 xSi0 ₂ , wherein x is 0.5 to 3.0, one or more alkali metal phosphate components of the formula Me ₂ 0 : nP ₂ 0s, wherein n is 0.33 to 1, or hydrates thereof, one or more carboxylic acids with 6-22, such 7-14 carbon atoms, or salts thereof.

The present inventors have surprisingly found that by such a composition comprising a metal silicate component as described, a metal phosphate component as described and a carboxylic acid as described, a highly effective anticorrosive composition can be prepared. All the components mentioned are fairly inexpensive, easy to handle, and are not hazardous for humans or the environment. Therefore, the anticorrosive compositions according to the present invention show a unique combination of properties not found in previously known anticorrosive compositions.

Description of the Preferred Embodiments

The present invention is directed to an anticorrosive composition comprising one or more alkali metal silicate components of the formula Me20-xSi02, wherein x is 0.5 to 3.0, one or more alkali metal phosphate components of the formula Me ₂ 0 : hR2q5, wherein n is 0.33 to 1, or hydrates thereof, one or more carboxylic acids with 6-22, such 7-14 carbon atoms, or salts thereof.

In one embodiment, the anticorrosive composition according to the present invention is in form of a mixture of solids.

In one embodiment, the anticorrosive composition according to the present invention is in form of an aqueous solution/ dispersion. Alkali metal silicate component

The present inventors have found that alkali metal silicate components of the formula Me ₂ 0 xSi0 ₂ , wherein x is 0.5 to 4.0, such as wherein x is 0.5 to 3.0, can be used in a very effective anticorrosive composition. These components are inexpensive, easy to handle and harmless for humans and the environment.

In one embodiment, the alkali metal silicate component is a sodium silicate of the formula IS^O xSiChx, with x = 1 or 2, such as Na2Si0 ₃ .

In one embodiment, the alkali metal silicate component is Na^O^Si (sodium orthosilicate), corresponding to Me ₂ 0-xSi0 ₂ , wherein x is 0.5.

It is pointed out that the alkali metal silicate component, such as sodium silicate of the formula IS^O xSiCh _x , with x = 1 or 2, such as Na ₂ Si0 ₃ can hold crystal water.

Alkali metal phosphate component

The present inventors have surprisingly found that alkali metal phosphates of the formula Me ₂ 0 : nP ₂ 0s, wherein n is 0.33 to 1, or hydrates thereof, can be used in a highly effective anticorrosion composition. These alkali metal phosphate components are inexpensive, easy to handle and completely harmless for humans and the environment.

In one embodiment, the alkali metal phosphate component is a sodium phosphate such as Na ₃ P0 ₄ .

Carboxylic acid component

The present inventors have surprisingly found that carboxylic acids with 6-22, such 7-14 carbon atoms, or salts thereof, can be used in a highly effective anticorrosion composition. These carboxylic acid components are inexpensive, easy to handle and completely harmless for humans and the environment.

In one embodiment, the carboxylic acid component is a dicarboxylic acid component of the formula H0 ₂ C(CH ₂ ) _n C0 ₂ H, whereby preferably n is 2 - 20, in particular 4 - 10, such as n = 8. In one embodiment, the carboxylic acid component is in form of a soap, such as e.g. sodium stearate.

Weight proportion of the components

In principle, the components of the anticorrosive composition of the present invention can be used in any weight proportions.

In one embodiment, the weight proportion of the alkali metal silicate component, alkali metal phosphate component, and carboxylic acid component is 60 - 96 weight parts, such as 70 - 93 weight parts, such as 75 - 90 weight parts alkali metal silicate component, 1 - 25 weight parts, such as 2 - 20 weight parts, such as 3 - 15 weight parts alkali metal phosphate component, and 1 - 20 weight parts, such as 2 - 15 weight parts, such as 5 - 12 weight parts carboxylic acid component, based on the total weight of alkali metal silicate component, alkali metal phosphate component and carboxylic acid component.

In one embodiment, the composition is an aqueous solution/dispersion and comprises 4 - 30 gram/litre, such as 6 - 20 gram/litre, such as 8 - 14 gram/litre alkali metal silicate component, 0.1 - 5 gram/litre, such as 1 - 3.5 gram/litre, such as 2 - 2 gram/litre alkali metal phosphate component, and 0.1 - 10 gram/litre, such as 0.2 - 5 gram/litre, such as 0.3 - 1.5 gram/litre carboxylic acid component, based on the total volume of the aqueous solution/dispersion.

In another embodiment, the composition is an aqueous solution/dispersion and comprises

100-500 g/l such as 150-300 g/l NazSiCb; 2-50 g/l such as 10-20g/l sebacic acid; 20-80 g/l such as 30-60g/l NasPO

Further components

The anticorrosive composition according to the present invention can comprise further components which can further improve the properties of the composition. In one embodiment, the composition further comprises a hydrophobic agent comprising at least one silicone compound, such as silicone resin, such as a reactive silicone resin, such as a reactive silicone resin chosen from the group of polyalkylethoxysiloxane, polymethylethoxysiloxane, polyphenylethoxysiloxane, polyphenylsiloxane, polyphenyl methylsiloxane.

In one embodiment, the composition according to the present invention comprises a hydrophobic agent comprising polymethylethoxysiloxane in an amount of 30 to 60 percent by weight, and octyltriethoxysilane in an amount of 1 to 5 percent by weight, based on the total weight of the hydrophobic agent, an emulsifier and optionally trace amounts of ethanol.

In one embodiment, the composition according to the present invention comprises one or more alkali stable water dispersible surfactants.

In the framework of the present invention, surface active compounds are to be understood as compounds which lower the surface tension between two liquids, between a gas and a liquid, or between a liquid and a solid.

In another embodiment, the composition according to the present invention comprises one or more alkali stable water soluble surfactants.

In one embodiment, the composition according to the present invention comprises a surface-active compound selected from the list of soaps, surfactants, such as an alkali stable water dispersible surfactant, such as an alkali stable water soluble surfactant, such as an emulsifying surfactant.

In one embodiment, the composition according to the present invention comprises

100-500 g/l such as 150-300 g/l NazSiCb 2-50 g/l such as 10-20g/l sebacic acid 20-80 g/l such as 30-60g/l NasPO 0.1-100 g/l surface-active compound, such as 0.05-50 g/l alkali stable surfactant and optional 0.1-100 g/l emulsifying co-surfactant.

In one embodiment, the composition according to the present invention comprises at least one siliconate compound, such as an organically modified water glass, such as alkalimetal organosiliconate, such as potassium methyl siliconate.

In one embodiment, the composition according to the present invention is an aqueous solution/dispersion and comprises 0.01- 20 gram/litre, such as 0.05- 15 gram/litre, such as 0.1-10 gram/litre silicone compound.

In one embodiment, the composition further comprises one or more water-miscible organic solvents.

In one embodiment, the water-miscible organic solvent is an alcohol, such as isopropanol.

In one embodiment, the composition according to the present invention comprises:

5 - 60 g/l, such as 25-45 g/l NazSiCb

0.5 - 5 g/l, such as 1.5 - 3.5 g/l sebacic acid

2 - 15 g/l, such as 4 - 10 g/l NasPO^

50 - 500 ml/l, such as 150 - 350 ml/l isopropyl alcohol.

In one embodiment, the composition further comprises one or more surfactants.

In one embodiment, the composition according to the present invention comprises: 100-500 g/l such as 150-300 g/l Na ₂ SI0 ₃

2-50 g/l such as 10-20g/l sebacic acid

20-80 g/l such as 30-60g/l NasPO^ 0.05-50 g/l alkali stable surfactant 0,1-100 g/l emulsifying co-surfactant

Use of the Composition

The present invention is also directed to the use of the composition described above for imparting anticorrosive properties to a material. There is no principal limitation to the materials on which the composition can be used for imparting anticorrosive properties.

In one embodiment, the present invention is directed to the use of the anticorrosive composition described above for imparting anticorrosive properties to a product selected from the group consisting of a mineral wool product, such as stone wool or glass wool, and other fibrous materials.

In one embodiment, the present invention is directed to the use of an anticorrosive composition described above for imparting anticorrosive properties to an insulation product selected from the group of a mineral wool insulation product, such as stone wool or glass wool insulation product, and an insulation product made from other fibrous materials.

In one embodiment, the use of the anticorrosive composition is such that the composition is dispersed in the product, such as a mineral wool product, such as a mineral wool insulation product or the other fibrous materials, such as the aerogel insulation product.

In one embodiment, this dispersion is such that dispersion takes place on a surface layer, such as a surface layer having a thickness of 0.5 to 10 cm, of the mineral wool product, such as mineral wool insulation product, or other fibrous materials, such as aerogel insulation product.

In one embodiment, the use is such that the product is selected from a pipe section, a roof product, a facade product, a mat, a wired mat. Product

The present invention is also directed to a material, which has been treated by the anticorrosive composition described above.

In one embodiment, the product is a mineral wool product.

In one embodiment, the product is an aerogel.

In one embodiment, the product is a mineral wool product or other fibrous materials with improved anticorrosion properties, in particular improved anticorrosion under insulation properties.

The present invention is further illustrated by the following examples:

In order to test the performance of the anticorrosive composition according to the present invention, the CUI performance of stone wool pipe sections of the commercially available Prorox PS960 with the anticorrosive composition according to the present invention has been compared with the anticorrosive performance of a standard stone wool pipe section Prorox PS960 without the anticorrosive composition according to the present invention.

Test setup and test conditions

The test setup in general follows ASTM G189-07, but with the following modifications:

• PTFE spacers between samples have been replaced by special silicone O-rings

• Clamping of the test equipment and coupons is achieved using a spring compression system to counter for thermal expansion of the system

• Ring formed test coupons are 14.3 mm wide compared to the width in ASTM G189-07 of 6.35 mm None of the modifications can be considered a relaxation compared to the test method and apparatus described in ASTM G189-07.

Equipment

The following simulation equipment is used: a) Ring shaped test coupons made from carbon steel pipe, ASTM A106 Grade B, with a width of 14.3mm and diameter of 60 mm, polished to a 600 grit finish. b) O-rings for sealing and separation. c) Pipe insulation, 0160 ex., 060 inside with and without corrosion inhibitor. d) Aluminium pipe jackets. e) Specially designed test rig consisting of two end pieces, between which test rings are mounted. f) Threaded rods mounted with coil springs to tighten the arrangement. The coil springs ensure that thermal extensions can be absorbed. g) Julabo Corio heating/cooling bath with circulation as well as pipe and hose connections. The bath is programmable according to the time / temperature control. h) Liquid circulating non-corrosive heating medium that can run at 60 ° and 150 ° C. Thermocouples measuring the temperature on the pipe surface under the insulation. i) Control computer. j) Data logger for logging temperature during test. k) Test liquid delivery system / metering pumps with controllers.

L) Silicone sealant. m) Insulation for heating pipes between heaters and installation.

A schematic of the test setup can be seen in figure 1 and a picture of the test setup can be seen in figure 2.

Test conditions

Two separate tests were conducted. The Conditions during the test were as follows: Test 1: a) Cyclic testing with the following temperature conditions, see also figure 3 for graphical representation of the test cycle. Total water injection per test cycle is 85 ml and total injection of 1785 ml for the entire test of 21 days b) Test duration 21 cycles (21 days) c) Test solution is deionized water d) Test solution enters through the top of the insulation via two feed tubes placed 42.9 mm apart, see figure 1 and 2 e) The insulation is drained via a centred hole in the bottom of the insulation, see figure 1 f) 6 identical ring formed test coupons made from carbon steel pipe, ASTM A106 Grade B, with a width of 14.3mm and diameter of 60 mm, polished to a 600 grit finish g) The Insulation material is sealed to the test pipe using silicone, creating a 25 cm long annulus. The insulation is secured tightly to the pipe surface using stainless steel wire. The outer aluminium jacket is secured around the insulation using hose clamps and sealed longitudinally and to the flange ends using silicone. Test 2:

Test conditions identical to test 1, but with a higher volume of water injected per test cycle. Total water injection per test cycle is 119 ml and total injection of 2499 ml for the entire test of 21 days

Anticorrosive composition tested

Two different concentrations of the anticorrosive composition were used in the two tests and were applied to the stone wool insulation with different techniques, however resulting in the same concentration of anticorrosive composition per cubic centimetre of treated pipe insulation.

Test 1:

To apply the anticorrosive composition to a 500mm long pipe insulation, with inner diameter of 60mm, a total of 0,851 iters of the anticorrosive composition mixture is needed, in order to treat the inner layer of the pipe insulation with a depth of 10mm. The anticorrosive composition according to the present invention tested was as follows:

33,75 g/l NazSiCb + 2,25 g/l sebacic acid + 6,75 g/l NasPO^ + 250 ml/l Isopropyl alcohol and 750 ml/l demineralized water

The corrosion inhibitor has been applied to the test specimen by mixing in a plastic container of 1L size 0,75 litres of demineralized water and then mix in the following chemicals in the order listed below:

1. 33,75 g of sodium silicate NazSiCb and let dissolve under stirring/shaking

2. 2,25 g of sebacic acid, and let dissolve under stirring or shaking

3. 6,75 g trisodium phosphate NasPO^ and let dissolve In the end 0,25L IPA is to be used with each 0,75L mixture.

The solution is then sprayed on the inner side of the pipe insulation, first the IPA and then the anticorrosive mixture to ensure that at the inner layer of the insulation product is fully impregnated with a depth of around 10mm, and then dry it.

The insulation sample, now treated with the anticorrosive composition is then tested for CUI performance as per above described test 1.

Test 2:

To apply the anticorrosive composition to a 500mm long pipe insulation, with inner diameter of 60mm, a total of 0,13 liters of the anticorrosive composition mixture is needed, in order to treat the inner layer of the pipe insulation with a depth of 10mm. The anticorrosive composition according to the present invention tested was as follows:

220 g/l Na2Si03 + 14,67 g/l sebacic acid + 44 g/l NasPO +10 g/l emusifying co- surfactant+ 4 g/l alkali stable surfactant

All chemicals dissolved in demineralized water in the above order balanced to 1 litre.

The solution is then sprayed on the inner side of the pipe insulation and the inner layer of the insulation product is fully impregnated with a depth of around 10mm, and then dried.

The insulation sample now treated with the anticorrosive composition is then tested for CUI performance as per above described test 2.

Results

Upon conclusion of the 21 test cycles, specimens have been washed with DI water and a nylon brush, rinsed with ethanol and dried to remove loose corrosion products and insulation from the surface, before the first weighing. Following this, corrosion products have been removed from the test specimens by immersion in inhibited 16 wt % hydrochloric as per DS/EN ISO 8407. Following rinsing the test specimens were weighed again.

After removal of corrosion products, the extent of localised corrosion was estimated (if relevant), as well as measurement of pitting depth (if relevant).

The results are summarised in table 1 (test 1 with Prorox PS960 with corrosion inhibitor), table 2 (test 1 with Prorox PS960) and table 3 (test 2 with Prorox PS960 with corrosion inhibitor, and higher water injection during test)

Photos from test 1 of test coupons tested with Prorox PS960 with corrosion inhibitor prior to and after removal of deposits and corrosion products can be seen in figures 4 to 7.

Photos from test 1 of test coupons tested with Prorox PS960 prior to and after removal of deposits and corrosion products can be seen in figures 8 to 12.

Photos from test 2 of test coupons tested with Prorox PS960 with corrosion inhibitor prior to and after removal of deposits and corrosion products can be seen in figures 13 to 20.

Test 1 Prorox PS960 with corrosion inhibitor

Regarding the results from testing with Prorox PS960 with corrosion inhibitor, there is an error in the weight result from test coupon A-21-1, as some of the original mill scale from the unexposed side of the coupon was removed during cleaning, thus resulting in an erroneous weight loss result. The coupon was upon inspection free from corrosion, and only one very shallow small pit-like attack was observed using 10X magnification.

On test coupon A21-6 one small diameter pit was detected.

Due to the very few, small and shallow localised attacks observed on the tested coupons and the inherent uncertainties and measurement error associated with determining the area of affected surface, calculation of localised corrosion rate has not been performed as this would give misleading results.

During the 21 cycles of testing water draining from the test were measured to be slightly alkaline (app. pH 8-10).

Table 1 Prorox PS960 with corrosion inhibitor, measurement data from test coupons

Prorox PS960

The corrosion attacks observed on the test coupons as result of the test although localised in nature due to the wetting properties of the insulation material and the metal surface do not give rise to pronounced pitting corrosion, instead the corrosion is observed to be general in appearance upon removal of the corrosion products, see figure 12.

During the 21 cycles of testing water draining from the test were measured to go from slightly alkaline (app. pH 8) to slightly acidic (app. pH 6). Table 2 Prorox PS960, measurement data from test coupons

Test 2 Prorox PS960 with corrosion inhibitor

The test where conducted in duplicate with a 40% higher water injection volume than in test 1.

The coupons were upon inspection free from corrosion and only small areas with shallow localised corrosion was observed upon inspection under 10-50X magnification. The total area of these the localised corrosion attacks was less than 0,5% of total exposed sample area.

Due to the very few, small and shallow localised attacks observed on the tested coupons and the inherent uncertainties and measurement error associated with determining the area of affected surface, calculation of localised corrosion rate in table 3 has not been performed as this would give misleading results. The calculated average annual uniform corrosion rate, based on all twelve test coupons and on the 21 test cycles, is 2.22 pm/year. During the 21 cycles of testing water draining from the test A&B were measured to be slightly alkaline (app. pH 8-10).

Table 3 Prorox PS960 WR-Tech with corrosion inhibitor, measurement data from test coupons

Conclusion

The modified ASTM G189-7 test schedule was carried out successfully testing stone wool insulation material with and without treatment with corrosion inhibiting compounds using no spacers to the pipe substrate. The stone wool insulation material impregnated with corrosion inhibiting compounds results in markedly lower corrosion rate on the pipe specimens compared to tests performed with the standard stone wool pipe insulation material. The calculated annual uniform corrosion rate, based on the 21 test cycles, is in average approximately fourteen times lower on the test substrates using the anticorrosive insulation material.