Power plants increasingly “cycle” to meet market conditions. That’s especially true of many newer combined cycle plants that were designed for continuous operation. Cycling operation creates a host of issues from thermal fatigue failure to freeze protection. Preservation of boilers and heat recovery steam generators (HRSGs) during shutdown and cycling operation generates much discussion. Since most of these plants were designed for base-load and continuous operation, their designs don’t include the equipment one might include for a plant designed for cycling operation.

“Concrete sewer structures and pipes are corroded by sulphuric acid which destroys the cement binder and ultimately results in corrosion of the reinforcing steel. Sulphuric acid is produced in sewers by a complex chain of microbiological and gas/liquid solubility stages which occur as the sewage travels through the sewerage system. These bacteria can create levels of sulphuric acid concentrations as high as 7%. This acid diffuses into the concrete structure, destroys the cement gel binder, and forming soft and soluble gypsum (calcium sulphate hydrate)”.

The degradation problem of naphtha arises since hydrocarbon acts as an excellent food source for a wide variety of microorganisms. Microbial activity leads to unacceptable level of turbidity, corrosion of pipeline and souring of stored product.

T. S. Raoa, Corresponding Author Contact Information, E-mail The Corresponding Author, T. N. Sairamb, B. Viswanathanb and K. V. K. Nair; Corrosion Science, Volume 42, Issue 8, 1 August 2000, Pages 1417-1431
Microbiologically influenced corrosion of carbon steel has been investigated. Carbon steel coupons were exposed online in the cooling water system of a nuclear test reactor to assess the microbial growth on the coupons and the corrosion phenomena. Iron bacteria, sulphate reducing bacteria (SRB) and culturable aerobic heterotrophic bacteria (CAHB) were monitored both on the coupons and in the cooling water.

Chromex
Cerakote Chromex coatings were designed as an alternative to chrome plating for high temperature applications. It provides a highly polished "chrome-like" finish that resists high heat oxidation while protecting the metal substrate. These ceramic coatings provide thermal stability along with flexibility, excellent adhesion, and superior resistance to corrosion. Chromex coatings provide protection up to 1100ºF. Sustained temperatures above 1200°F may oxidize the coating and reduce some performance properties. Extensive testing with Chromex coatings has shown no loss of weight or deterioration of carbon steel after 100 hours at 1000°F.

Microbial growth in fuel tanks and fuel systems can result in rapid and severe corrosion. For example occasional problems occur in aircraft wing tanks due to the growth of moulds and also yeasts and bacteria which produce organic acids and also stimulate corrosion by creating oxygen gradients which enhance electrochemical corrosion cells. In steel tanks, growth of Sulphate Reducing Bacteria in water and sludge in the bottoms of tanks can cause pitting corrosion.

SPC Ardmona has implemented hydro-optic disinfection (HOD) technology at its Shepparton processing plant, reducing potential corrosion of machinery affected by chlorine.

The most common use of plastics in solar collectors and dryers is as a transparent cover allowing incident radiation to pass through and impinge on an absorber surface, or on the commodity being dried. Used in this way, plastics must be able to withstand elevated temperatures, which is high levels of insolation, high humidities, wind loading and the effects of heavy rain over long periods of time. Low cost, low density, and good optical properties make some plastics very suitable for use in solar collectors and dryers. Stemming from its convenience as a building material, black polythene also finds use as an absorber material. However its shiny surface, a characteristic of the manufacturing process, is not conducive to high absorption efficiency.

 The UV protective coatings, prepared by the Sol-Gel method, are based on organic UV absorber molecules in modified silica matrices (ormosil) and are capable to reduce drastically the UV light reaching the substrate that needs to be protected, and hence its photodegradation upon prolonged exposition to UV sources.

For high quality, high performance products of Brass and other decorative metals, the range has been developed and upgraded from traditional formulations manufactured by Llewellyn Ryland, and brought into the Indestructible portfolio in 1996. Extensive development has seen the range expanded and improved, taking into account new raw materials and practices and the changing requirements of the Environmental Protection Act and the need to reduce the use and emission of Volatile Organic compounds.

MIC processes at metal surfaces are associated with microorganisms, or the products of their metabolic activities including enzymes, exopolymers, organic and inorganic acids, as well as volatile compounds such as ammonia or hydrogen sulfide. These can affect cathodic and/or anodic reactions, thus altering electrochemistry at the biofilm/metal interface.

Corrosion, including microbially influenced corrosion (MIC), negatively impacts the integrity, safety, and reliability of natural gas pipeline or metal operations throughout the world. Cost-effective MIC management requires the early detection of MIC problems, which can only be achieved by routine monitoring of the physical, chemical, and biological characteristics of pipeline systems.

Reduced Chemical Use and Toxicity in Produced Water Systems

In pipelines and storage vessels, many unexpected failures can be traced to sustained, localized pitting corrosion. Bacteria can catalyze this pitting by setting up a localized corrosion cell and producing organic acids that pit the metal and remove reactants from the surface. Detecting such pitting is often difficult because standard corrosion probes can only measure generalized corrosion, not the localized corrosion that can drill holes into metal. The development of an inexpensive probe to identify conditions under which sustained localized pitting can occur would allow companies to target their mitigation efforts rather than treating an entire system with chemical corrosion inhibitors and biocides. This detector research is coupled with the use of simulated pipeline test loops to evaluate new treatment methods that involve non-toxic chemicals and less-frequent applications.

TWI has dedicated laboratories for electrochemical and direct exposure small scale tests, larger facilities for testing specimens under load in sweet conditions, seawater (including CP), plus laboratories for H2S sour service testing. Evaluation of materials corrosion behaviour is undertaken by relevant techniques covering rapid electrochemical testing and longer term direct exposure tests in simulated environments. Testing is in accordance with internationally recognised standards or developed by our experts in conjunction with client requirements as part of our corrosion services.