Corrosion steam lines

Boiler Water Treatment. Alkanolamines, in general, provide excellent corrosion protection to steel in many appHcations. When used in boiler water treatment, AMP provides excellent protection to steel and copper in steam lines through efficient absorption of CO2, effectual distribution ratio for... 

Boilers and steam systems Steel steam lines can be inhibited by the use of a volatile amine-based inhibitor such as ammonia, morpholine or cyclohexylamine introduced with the feedwater. It passes through the boiler and into the steam system, where it neutralizes the acidic conditions in pipework. The inhibitor is chemically consumed and lost by physical means. Film-forming inhibitors such as heterocyclic amines and alkyl sulphonates must be present at levels sufficient to cover the entire steel surface, otherwise localized corrosion will occur on the bare steel. Inhibitor selection must take into account the presence of other materials in the system. Some amine products cause corrosion of copper. If copper is present and at risk of corrosion it can be inhibited by the addition of benzotriazole or tolutriazole at a level appropriate to the system (see also Section 53.3.2). 

The pipe wall thickness is selected to resist the internal pressure, with an allowance for corrosion. Processes pipes can normally be considered as thin cylinders only high-pressure pipes, such as high-pressure steam lines, are likely to be classified as thick cylinders and must be given special consideration (see Chapter 13). 

And don t forget—round-bottom flasks should be about halfway in the bath. Whether you should let steam rise up all around the flask or not appears to be a matter of debate. Lots of steam will certainly steam up the lab and may expose you to corrosion inhibitors (morpholine) in the steam lines. You should not, however, have steam shooting out the sides of the bath, or any other place. (Fig. 57). 

Corrosion is negligible if suitable traps are installed in the steam lines so that carry-over of water is minimized... 

Water Contamination Water within the degreaser often is the cause of corrosion of the equipment, spotting of processed work, and increased solvent consumption. The corrosion problem stems from the corrosive nature of the water itself and the combined action of the solvent and water. Therefore, introduction of water into a unit should be minimized. Sources of water entry include condensation of atmospheric moisture, leaking condensers or steam lines, and wet processed work. Work contaminated with water-compounded process oils are likely to introduce large amounts of water. Water that enters the machine is removed to a great degree by water separators. 

The preheated vessel is pumped full of hot, inhibited acid, for example. The acid reacts with corrosion products and scale, then the drain valve is opened, and the solvent removed. The rinsing and neutralizing solutions are handled in the same way. The mechanical requirements are simple. There are tank trucks to haul a liquid acid, such as inhibited concentrated muriatic acid, to the site. A water line to the truck position supplies water. A steam line furnishes steam for heating as the... 

The corrosion inhibitors operate by forming a film on pipe and equipment surfaces. The amines used in this service have higher molecular weights and so are less volatile and less soluble in water. They must be injected into steam lines, and high velocity helps their distribution. 

Steam lines with air and CO2 entrained can be very corrosive. To reduce corrosion, oxygen can be removed by the addition of hydrazine (N2H4). 

DR value means that the metal is readily coated with a thin protective film of the amine. Some amines commonly used and their pH and DR are given in Table 10.5. The amine is slowly lost, and it must be replaced continuously. Steam lines invariably have these amines, and the use of brass, bronze, or copper results in the corrosive removal of copper. 

The original design and structure of the Statue of Liberty, built about 100 years ago, took into accoimt the need to avoid using different metals in direct contact with each other. However, the salt sea spray penetrated the structure and corroded the iron frame which supported the outer copper shell. Chloride ions catalyzed the corrosion of iron. The use of brass in a steam line valve resulted in corrosion and the formation of a green solid product. The architect was apparently unaware of the standard practice to use amines such as morpholine as a corrosion inhibitor for steam lines. Amines react with copper in the brass at high temperatures in the presence of oxygen to form copper-amine complexes similar to the dark blue copper ammonium complex, Cu(NH3)J. ... 

Figure 6.37 Pipe wall thinning (a) and corrosion patterns (b) caused by flow accelerated corrosion (FAC) inside a steam line. (Courtesy of Russ Green, TMI)...

The condensate from the condenser is pumped through full flow filters to remove suspended corrosion and erosion products. The flow rate of the feedwater to the reactor is governed by the steam flow in the main steam line plus a water-level-measuring instrument in the reactor. 

In this pyrolysis, sub atmospheric partial pressures are achieved by employing a diluent such as steam. Because of the corrosive nature of the acids (HE and HCl) formed, the reactor design should include a platinum-lined tubular reactor made of nickel to allow atmospheric pressure reactions to be mn in the presence of a diluent. Because the pyrolysate contains numerous by-products that adversely affect polymerization, the TFE must be purified. Refinement of TFE is an extremely complex process, which contributes to the high cost of the monomer. Inhibitors are added to the purified monomer to avoid polymerization during storage terpenes such as t7-limonene and terpene B are effective (10). 

In wetted-wall units, the walls of a tall circular, slightly tapered combustion chamber are protected by a high volume curtain of cooled acid flowing down inside the wall. Phosphoms is atomized by compressed air or steam into the top of the chamber and burned in additional combustion air suppHed by a forced or induced draft fan. Wetted-waU. plants use 25—50% excess combustion air to reduce the tail-gas volume, resulting in flame temperatures in excess of 2000°C. The combustion chamber maybe refractory lined or made of stainless steel. Acid sprays at the bottom of the chamber or in a subsequent, separate spraying chamber complete the hydration of phosphoms pentoxide. The sprays also cool the gas stream to below 100°C, thereby minimising corrosion to the mist-collecting equipment (typically type 316 stainless steel). 

The term steam quaUty refers to the amount of dry steam present relative to Hquid water in the form of droplets. The steam deUvered from the boiler usually contains some water. Excessive amounts can result in air entrapment, drying problems following exposure, and unacceptable steam levels (>3% water or <97% quaUty steam). Excessive amounts of water deposits dissolve boiler chemicals onto the load to be sterilized. Boiler chemicals are used to prevent corrosion in the lines. Inappropriate boiler chemicals, also called boiler amines, may introduce toxicity problems (see CORROSION AND CORROSION control). 

The buildup of carbonaceous materials in the sulfuric acid presents one of the most serious problems of acid concentration (76—80). Acid concentration also presents a corrosion problem. The vessels are mild steel lined with lead or brick the steam heating elements are composed of siUcon, iron, or tantalum, and pipelines are generally constmcted of lead (81). 

Apphcations requiring accurate temperature control are generally limited to electric tracing. For example chocolate lines cannot be exposed to steam temperatures or the product will degrade and if caustic soda is heated ove 150°F it becomes extremely corrosive to carbon steel pipes. 

In water-wall incinerators. The internal walls of the combustion chamber are lined with boiler tubes that are arranged vertically and welded together in continuous sections. When water walls are employed in place of refrac toiy materials, they are not only useful for the recovery of steam but also extremely effective in controlling furnace temperature without introducing excess air however, they are subject to corrosion by the hydrochloric acid produced from the burning of some plastic compounds and the molten ash containing salts (chlorides and sulfates) that attach to the tubes. 

Leaky valves are also a cause of erosion. Most turbine erosion-corrosion problems come from damage that takes place when the unit is not running. A shght steam leak into the turbine will let the steam condense inside the turbine, and salt from the boiler water will settle on the inside surfaces and cause pitting, even of the stainless blading. There must be two valves with a drain between them, i.e., a block valve on the header and an open drain in the line before it reaches the closed trip-throttle valve. 

Carbon Dioxide CO2 Corrosion in water lines and particularly steam and condensate lines Aeration, deaeration, neutralization with alkalies, filming and neutralizing amines... 

Steam used in the sidestream strippers and in the stripping section of the main column is condensed in the overhead condenser. This water settles to the bottom of the distillate dmm and is drawn off through a small water pot in the bottom. In most installations, ammonia gas is injected into the overhead line to raise the pH of this water and reduce corrosion. 

Carbon dioxide COj Results in the corrosion of water lines, especially steam and condensate lines. 

Condensate returns lines are often copper. Copper has good corrosion resistance to oxygen and carbon dioxide individually. When both gases are present in the condensate, copper is susceptible to corrosion. Copper picked up in the condensate system and returned to the boiler causes serious corrosion problems in the boiler and any steel feedwater and steam pipework. Boiler tubes should last for 25 years but can fail within one year in a mismanaged or ill-designed boiler system suffering from these faults. 

Where the acid condensate is corrosive and neutralisers cannot be used, then a condenser of resistant materials has to be employed. However, by steam tracing the lines leading the vapour to the condenser, premature condensation can be avoided (Fig. 9.6) and in consequence a cheaper material may be used. 

Where steam is used for sterilization, hospital duty, food and drug manufacturing processes, or steam humidification purposes, there generally is a reluctance (or mandated prohibition) to employ amines as a treatment for steam-condensate line corrosion protection. Clean-steam... 

Also, no specific amine-based inhibitor is generally provided to protect LP steam condensate pipework against the ravages of carbonic acid (H2C03)-induced condensate line corrosion. 

Where problems develop, there is always a cause-and-effect process. In this case, as oxygen infiltrates the CR system, enhanced condensate line corrosion results (i.e., corrosion over and above the level that may be caused by the carbonic acid formed during steam condensation). This enhanced corrosion, in turn, creates the potential for further downstream corrosion debris pickup by the returning condensate and transporting this material back to the FW system. 

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