Akzo-3039 Akzo-3034 Acid Corrosion English Importante Stimolazione

Products for the petroleum industry

Acid corrosion inhibitors for oilfi eld stimulation

Fig. 1 Schematic illustration of acid corrosion of carbon steel.

1. Acid corrosionAcid corrosion is the corrosion of materials in acidic environments. Many metallic materials are susceptible to acid corrosion. One of the most widely used industrial materials, carbon steel, suffers serious acid corrosion. Corrosion protection, such as the use of corrosion inhibitors, is often required for the use of carbon steel in acidic media.

The mechanism of acid corrosion is straightforward.

In the case of carbon steel, the iron will react with hydrogen ions to form iron ions and hydrogen gas (Fig. 1). The reaction is shown below.

Fe + 2H+ Fe++ + H2During the process steel is essentially dissolved away. Weight loss, therefore, is a good measure of the severity of the acid corrosion.

The corrosion rate of materials in acid is dependent on parameters such as concentration of pH of the acidity solution, temperature and the use

of corrosion inhibitors. As acid concentration increases, the corrosion rate goes up correspondingly. At a constant acid concentration, the corrosion react increases exponentially with rising temperatures The presence of an acid corrosion inhibitor will have a profound effect on the corrosion rate. The addition of 0.1 to 2.0% of acid corrosion inhibitors can reduce the corrosion rate up to 95%.

AKZO-3039 AKZO-3034 Acid Corrosion ENGLISH.indd 1 6/6/11 4:48 PM

2. Armohib acid corrosion inhibitors from AkzoNobel Armohib is the trade name for corrosion inhibitors developed by AkzoNobel. These aliphatic nitrogen inhibitors effectively retard acid corrosion during oil well acidizing operations, pickling and acid cleaning. AkzoNobel carries two types of acid corrosion inhibitors: Armohib CI-28 and Armohib CI-31. They are specially formulated to inhibit corrosion of different acids as listed in Table 1.

Table 1. Application of Armohib corrosion inhibitors in different acids.

Armohib CI-28 Hydrochloric Hydrochloric-Hydro uoric acid mixtures

Armohib CI-31 Sulfuric Sulfamic Citric Phosphoric

Fig. 2 Schematic illustration of acid corrosion inhibition by Armohib corrosion inhibitors.

Although the exact mechanism of nitrogen corrosion inhibitors is not fully understood, it is generally agreed that the positive hydrophilic nitrogen headgroup absorbs on the metal surface and the aliphatic chains form a hydrophobic fi lm, which block the attack of hydrogen ions (Fig. 2). Higher coverage of the surface with the impervious fi lm leads to higher acid corrosion inhibition.

2.1 General properties of Armohib CI-28 and Armohib CI-31The typical properties of Armohib corrosion inhibitors are listed in Table 2. These inhibitors are easy to use in the fi eld. They are available in liquid form and are soluble in acid. They are non-staining to metal surfaces and do not precipitate

when standing for a prolonged period of time.

The application of these inhibitors provides low-cost, dependable protection over a wide range of temperatures, since only a small quantity of Armohib inhibitor mixed with the acids will deliver the desired cleaning effect, while retarding the acid attack on metals. For example, 0.25% Armohib CI-28 in 15% hydrochloric acid at 200F leads to less than 0.022 lb/ft2/day corrosion

rate of mild steel. In another example, 0.06% Armohib CI-31 in 15% sulfuric acid at 200F leads to less than 0.027 lb/ft2/day corrosion rate of mild steel.

Table 2. Typical properties of Armohib corrosion inhibitors.

Armohib Specifi c Pounds per gallons Appearance at 25C Pour point F Flash point F Cloud point F gravity at 25C

28 0.925 7.69 Amber Liquid 52 90

31 1.042 8.66 Amber Liquid 24 340 28

2.2 Applications of Armohib CI-28 and Armohib CI-31There are three major applications for Armohib inhibitors: oil well acidizing, acid pickling and plant cleaning.

Fig. 3 Corrosion data of mild steel in

hydrochloric acid with Armohib CI-28.

MILD STEEL INHYDROCHLORIC ACID

WITH Armohib CI-28 6 HOURS AT 200F

Cor

rosi

on r

ate

Ib/f

t2/d

ia

Percent inhibitor concentration based on total solution

2.2.1 Oil well acidizingIn the fracturing and acidizing of compact oil formations, various concentrations of hydrochloric acid are used to dissolve the undesirable carbonate deposits of scales, which interfere with the passage of oil, in tubing or in the formation itself.

The lines and tubing must be protected during this operation, from corrosive attack by the acid, by the high temperatures and pressures, and by the potential for a "sour" environment resulting from the high hydrogen sulfi de and carbon dioxide

contents. Armohib CI-28 used at a concentration of 0.25%, based on the total hydrochloric acid solution, is highly recommended for this purpose (see Fig. 3). It provides effective protection at temperatures in excess of 230F (110C), for at least six hours.


2.2.2 Acid picklingPickling is the removal of oxide scales formed during metal working operations by mineral acids. Hydrochloric, phosphoric and sulfuric acids are commonly used. These scales must be removed without undue acid attack on the base metal surface.

Armohib CI-28: Hydrochloric acid is used for pickling very high carbon alloy steels and for wire pickling. Hydrogen embrittlement is a major problem during the pickling of mild steel wire. The addition of Armohib CI-28 to the hydrochloric acid eliminates or reduces embrittlement. The use of Armohib CI-28 as an inhibitor, in hydrochloric acid pickling of steel, has no adverse effect on the quality of the metal in subsequent hot dip galvanizing.

Armohib CI-31: Phosphoric acid is used in the surface preparation of structural steel to remove mill scale, rust and contaminants, prior to protective surface coating. Phosphoric acid is of particular value in pickling operations where the scale film is thin, or if the film is a hydrate oxide of iron. Sulfuric acid is used extensively in metal cleaning because of its low cost. In the absence of inhibitor, up to 80% of the acid may be wasted in dissolving metal under the scale. The use of Armohib CI-31 as an inhibitor, regulates the scale dissolution reactions and minimizes the amount of surface material that is dissolved.

2.2.3 Plant cleaningInhibited acids are used extensively in plant cleaning; both in pre-commissioning and periodic planned service cleaning. In all applications, the use of a corrosion inhibitor is necessary to maximize the cleaning effect, while minimizing any unwanted corrosion.

Hydrochloric acid is the acid most often used for plant cleaning, although sulfamic, sulfuric, citric and phosphoric acids are also used. The appropriate Armohib CI-28 or CI-31 product will serve the corrosion inhibiting needs of any of the acid applications.

Armohib CI-28 is used to create efficiently inhibited hydrochloric solutions for hydrochloric applications for steels such as admiralty, carbon steels, cast iron, copper and its alloys such as monel, brass, bronze, cupro-nickel and chrome-molybdenum.

Sulfamic acid is often used as an alternative to hydrochloric acid. Sulfamic acid, inhibited with Armohib CI-31, is used to clean deposits from 300 and 400 series stainless steels, and occasional cleaning of aluminum and its alloys.

Armohib corrosion inhibitors may be added to either dilute or concentrated acid solutions. Never dilute the Armohib concentrates with water, as they will separate.

Dilute acid solutions: To obtain the inhibitor concentrations listed in Table 3, add approximately the indicated amounts of inhibitors to each 100 gallons of dilute acid solution.

For instructions on handling and storage, please consult the MSDS sheets for these products.

Table 3. Preparing desired dosage of Armohib corrosion inhibitors

Concentration % total solution .01 .025 .05 .075 .10 .125 .15 .20 .25

Fluid ounces per 100 1.5 3.75 7.5 11.25 15.0 18.75 22.5 30.0 37.5 gallons of total solution

2.3 Applying Armohib CI-28 and Armohib CI-31

Handling and storage


Customer serviceFor additional information, samples or assistance please contact your local sales representative or AkzoNobel's customer service department at:

Brazil & South AmericaAkzoNobel Ltda Diviso Quimica Rodovia AkzoNobel 707 Bairro So Roque da Chave Itupeva SP Brasil 13.295-000 Tel: +55.11.4591.8939 Email: [email protected]

US, Canada & MexicoAkzoNobel Surface Chemistry LLC 525 W. Van Buren Street Chicago IL 60607-3823 (800) 906-9977 (312) 544-7000 Email: [email protected]

Asia-PacficoAkzoNobel Surface Chemistry Pte Ltd 41 Science Park Road Singapore Science Park II #03-03 The Gemini Singapore 117610 Tel: + 55 6773 8488 Email: [email protected]

Europe, Africa & Middle EastAkzoNobel Surface Chemistry AB Stenunge All 3 SE-444 85 Stenungsund Sweden Tel: + 46 303 8500 Email: [email protected]

www.akzonobel.com/surface

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Akzo-3039 Akzo-3034 Acid Corrosion English Importante Stimolazione