Iron debris

Economizers are not usually designed to generate steam, and any deposits found in them therefore are not likely to be a result of carbonic acid corrosion or contamination from steam. Rather, the transport and buildup of corrosion debris within an economizer tends to originate from corrosion processes occurring either in the economizer itself or in some upstream part of the pre-boiler system. Economizer deposits typically develop in the presence of oxygen and possess a high iron content. 

Apart from the oxygen corrosion that results in HW and LP steam heating systems where water losses occur as a result of leaking pump mechanical seals, excess BD, faulty steam traps, and other sources, a subsequent effect is the development of fouling. This effect stems from the production of corrosion debris and (high iron content) sludge that eventually settle out in the boiler. This corrosion debris, sludge, and other foulants must be periodically removed from the boiler by BD, which merely adds to the water loss, and the cycle perpetuates. 

Because of the duty requirements of these systems, pipework layouts are often tortuous and may contain stagnant areas where localized corrosion may develop or sludge may accumulate. The breakdown of glycols may also contribute to the development of foulants and corrosion debris. It is therefore good practice to incorporate both general dispersants (say, a 4,000-5,000 MW polyacrylate) and iron dispersants (say, a terpolymer) in the inhibitor formulations. 

The transport of pre-boiler corrosion debris to the boiler section includes the oxides of iron, copper, nickel, zinc, and chromium and results from the corrosion of pre-heaters and condensers, and the like. Specifically, equipment components variously fabricated from admiralty brass, aluminum brass, cupronickels, and stainless steels are most affected. 

Localized pre-boiler scale and corrosion debris deposits. Combination of New phosphate, iron, copper, and silica deposition Old re-deposited debris Transport of Fe, Cu, Ni, Zn, Cr oxides to HP boiler section, leading to deposition, fouling, and possible tube failures Transport of minerals and debris including malachite, ammonium carbamate, basic ferric ammonium carbonate Precipitation in FW line of phosphates, iron, and silicates... 

Iron Oxide and Other Corrosion Debris Deposition... 

Where particulate matter (in the form of corrosion products of iron oxide) is present in returning condensate, it often contains copper, nickel, and zinc oxides as well. This debris can initiate foaming (through steam bubble nucleation mechanisms) leading to carryover. It certainly contributes to boiler surface deposits, and the Cu usually also leads to copper-induced corrosion of steel. 

Internal treatment-related problems may take the form of organic material present in deposits of iron oxide corrosion debris and salt scales. The material typically is present as carbonized organic components and may originate from water treatment chemicals such as quebracho, wattle, pymgallol, or other tannin derivatives. Also, acrylates, starches, sulfonated lignins, and other sludge dispersants may be present. 

Where serious problems develop, typically the waterside chemistry is poor and iron corrosion debris, sludges, and general deposition are evident. Perhaps there is no softener or the water treatment program is unsuitable for actual operating conditions. Possibly the protocol for BD is inappropriate (either too much or too little, or it is unrelated to steam demands) or flushing, cleaning, and boil-out programs have not been properly instituted. 

Low pH MU water sources are likely to adversely affect first preboiler equipment, such as economizers and other front-end components a severely low pH incursion (say, below pH of 5.0-5.5) also results in general corrosion of boiler section components, including the boiler itself. Under these conditions, iron corrosion debris may form composed of particulate magnetite needles. 

Table 7.5 Summary notes iron oxide and other boiler section corrosion debris...

Corrosion of condensate lines is a serious problem. It is compounded where both oxygen and carbon dioxide are present because it causes considerable quantities of hematite (Fe203) to develop. Corrosion of other boiler plant components, such as FW heaters, adds more metals to the mix, and corrosion debris typically includes iron, copper, nickel, zinc, and chromium oxides. 

Notwithstanding the seriousness of these pre-boiler problems, however, it is material (especially iron oxide corrosion debris) originating in the condensate system, then transported back to the boiler itself, which carries the greatest risks of long-term operational problems. 

Today, all-membrane processes are also employed to ensure the integrity of high-purity primary coolant water and the removal of chlorides and fluorides. Crud (iron/steel corrosion debris) is removed by filtration. 

Once a filmer program starts, feeding of amine must be continuous because with the gradual removal of old iron oxide debris, the clean metal surface is subject to rapid corrosion should the continuous film cease to be maintained. 

Where the rapid removal of corrosion debris occurs or where amine feed rates are initially kept low and the condensate still contains iron oxide, the dirty condensate should be polished or simply dumped until the condition improves. 

Very visible form of corrosion in which voluminous layers form of brittle, iron oxide corrosion debris, usually covering a pit or deep crevice. 

Iron oxide and other corrosion debris deposition 231... 

Silicates and other common minerals, deposition by (Cont.) iron oxide and other corrosion debris deposition... 

Whatever caused this stunning blue sheen, it represented a unique opportunity to test the theory of how massive stars explode and how nucleosynthesis takes place within the explosion. This theory predicted that isotopes of mass 44, 56 and 57 would be produced by the sudden, explosive grafting of alpha particles (helium nuclei) and protons onto silicon nuclei (see Appendix 3). They would be synthesised in their radioactive forms, nickel-56, nickel-57 and titanium-44, in that order of importance (see Table 7.1). After a suitable series of decays, these sparsely scattered nuclei in the supernova debris would arrive at their stable forms, iron-56, iron-57 and calcium-44. 

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