Water, acid service

All cooling water treatment programs, whether designed in-house or via a water treatment service company, continue to focus on the minimization of hard water crystalline scales and sludges in the system as a major criteria for success. Program techniques employed are either pretreatment processes, such as lime-soda softening or ion exchange, the use of sulfuric acid or polymer-based chemicals that operate in an alkaline environment, or combinations of some or all of these processes. 

Hydrofluoric acid causes two types of corrosion, direct corrosion, in which iron fluoride is formed, and stress corrosion, in which the metal cracks. Electrolytic corrosion can also take place when the acid becomes diluted with water and two dissimilar metals or carbon are used. Because of the possibility of stress corrosion, all vessels in acid service must be stress-relieved. Monel is also subject to stress corrosion and must be stress-relieved. Care must be taken in stress-relieving Monel that sulfur or sulfur compounds do not come in contact with the Monel either before or during the heat treatment. 

Possibly the most widely used sulfonated copolymers, used both as dispersants in boiler treatment and as cooling water additives, are composed of acrylic acid and 2-acrylamido-2-methylpropane sulfonic acid (AA-PSA). Since the 1980s, water-treatment service companies from the smallest to the largest have phosphate-based cooling water programs incorporating AA-PSA polymers. 

Properties Dk. low-vise, liq. sol. in org. soivs. and oils insol. in water acid no. 160-230 7-30% unsaponifiables MCRS High Purity Naphthenic Acid [Merichem Chems. Refinery Services]... 

Properties Gardner 3 min. color high sol. in hydrocarbons and oils low sol. in water acid no. 220-310 3 max.% unsaponifiables MCRS Refined Naphthenic Acid [Merichem Chems. Refinery Services] Chem. Descrip. Naphthenic acid CAS 1338-24-5 EINECS/ELINCS 215-662-8 Uses Chem. and surfactant intermediate (derivs. used in paint and ink driers, lubricant/fuel additives, heat/UV stabilizers, cutting oils, and also wood preservatives, corrosion inhibitors, emulsifiers, defoamers, tire cord adhesives) prod, of metal soaps... 

Excellent resistance to strong mineral acids and water. Most popular lining for water storage tanks used in water immersion service (potable and marine) and beverage processing. 

The sodium and potassium silicates are available as two-component systems filler and binder with the setting agent in the filler. Sodium and potassium silicates are referred to as soluble silicates because of their solubility in water. This prevents their use in many dilute acid services while they are not affected by strong concentrated acids. This disadvantage becomes an advantage for formulating single component powder systems. All that is required is the addition of water at the time of use. The fillers of these materials are pure silica. 

Type 430 stainless is resistant to chloride stress corrosion cracking and elevated sulfide attack. Applications are found in nitric acid services, water and food processing, automobile trim, heat exchangers in petroleum and chemical processing industries, reboilers for desulfurized naphtha, heat exchangers in sour-water strippers and hydrogen plant efluent coolers. The compatibility of type 430 stainless steel with selected corrodents is provided in Table 7.4, which is taken from Reference [1]. 

S. Arrington and G. Bradley, "Service Water System Cleaning with Ammoniated Citric Acid," paper presented at Corrosion 87-NACE, No. 387, San Francisco, Calif., 1987. 

Clostridia frequently are found where sulfate-reducing bacteria are present, often in high numbers inside tubercles. A typical microbiological analysis of tubercular material removed from a troubled service water system main is given in Table 6.4. Clostridia counts above 10 /g of material are high enough to cause concern. When acid producers... 

In-service issues. As mentioned previously, many early service failures of bonded structure were due to adherend surface treatments that were unstable in long-term exposure to water. A majority of these problems were resolved by the adoption of surface treatments such as chromic and phosphoric acid anodize for aluminum details. The remaining few were alleviated by the adoption of phosphoric acid anodized honeycomb core and foaming adhesives resistant to water passage. Other service durability issues such as the cracking of brittle potting compound used to seal honeycomb sandwich assemblies, and subsequent delamination, have been minor in scope. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reactions Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Polymerization is accelerated by heat and exposure to oxygen, as well as the presence of contamination such as iron rust. Iron surfaces should be treated with an appropriate reducing agent such as sodium nitrate, before being placed into isoprene service Inhibitor of Polymerization Tertiary butyl catechol (0.06 %). Di-n-butylamine, phenyl-beta-naphthylamine andphenyl-alpha-naphthylamine are also recommended. 

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