A major issue in the chemical industry is the control of corrosion and security of chemical processing system and other equipments and preventing corrosive effects of the various commercially significant acids and bases  that are developed and used by the chemical processing plants.

Environmental security is of extreme significance to the processing units. Unanticipated corrosion issues that result into the emission of chemicals cannot be tolerated. The causes of unwanted corrosive damages from the process and environmental factors are discussed.

Corrosive influences of Process and Environmental factors

The chemical processing units made from the same component have different experiences due to corrosion. A steel pipe lasts for several years in a specific service, whilst same pipeline may damage within a couple of weeks of months.

Plant Conditions:

 An aspect that is often ignored is the surrounding media. For instance, the device tubing in a new system, constructed at an existing chemical plant in West Virginia was comprised of copper. The damages of heat exchangers have been noticed due to ammonia. Cooling tower water got contaminated with some magnitude of ammonia when the ammonia plant was constructed. Heat exchanger tubes in the big air compressor stress damaged in cold worked areas subsequent to its configuration from a building where the lab agents involved ammonia hydroxide and nitric acid.

Quenching Water

The magnitude of water utilized to cool shell and tube heat exchangers can change seasonally specifically if the water is received from river that discharges into a bay. Stainless steel type 304 condensers quenched the shell side with river water that changed the chloride concentration from below 50 ppm to 2000 ppm. The stainless steel tubes were damaged by external pitting.

Steam

The corrosive characteristics of the steam that will be utilized in a plant are slightly considered, specifically if the steam will be supplied by public utility or power plant that offers good boiler water treatment, it will resist condensate corrosion.

 The iron filings and dilute hydrochloric acid are agitated with organic nitro compound that is reduced to amine  by hydrogen release, here Monel 400 plate was chosen on the base of lab tests and general experience with units by using filter presses without stream return. In the caustic chlorine unit, steel piping sent saturated alkaline brine at ambient temperature were damaged by crevice corrosion and pitting but alloy 400 offered reliable service.

Seasonal temperature variations

 A five pass Monel 400 alloy was used in heat exchanger to vaporize concentrated hydrofluoric acid. Extreme corrosion occurred in the ending pass. Monel 400 shell and tube heat exchanger had offered adequate performance in organic acids oil for above five years.

Contaminants

A main cause of unwanted corrosive damages is the availability of nominal magnitudes of contaminants in the chemical media. Developers of sulphuric acid offer services to reclaim used acids as a service to the users who find difficulty in disposing the acid in an environmentally acceptable way.

A Monel 400 petrochemical plant extraction unit dealing with 40 – 65 sulfuric acid and alcohol at 30 – 40oC had offered supreme service for more than a decade. In a similar case, Monel 400 isomerization reactor was made on the basis of lab corrosion analyses and plant analyses with corrosion coupons in the various areas in the glass lined isomerizer.

Chemical cleaning is performed to measure the general corrosion rate in pounds per square foot per day. A widely higher corrosion rate is tolerable during the chemical cleaning than permitted in an application. Monel alloy 400 type served excellently in the contaminated media by offering the nominal need of chemical cleaning.

Localized corrosion

Localized corrosion mainly includes pitting attack and stress corrosion cracking. Sulfides exist in the different types of refinery deposits and H2S gas may be emitted when sulfides interact with hydrogen sulfides. Corrosion issues with sulfides and H2S are decreased by reducing the acid content and temperature. Sulfide stringers available in free machining steels have increased sensitivity towards corrosion while acid cleaning. Use of super metal 400 is recommended in this media. 

It is found that in any most of the corrosive media, Monel alloy 400 offered desired service.