Welded steel storage vessels used to hold mildly alkaline solution were produced in exactly the same manner from deep-drawn aluminum-killed SAE 1006 low-carbon steel sheet. After the cylindrical shell was drawn, a top low-carbon steel closure was welded to the inside diameter. The containers were then filled with the slightly alkaline solution, pressurized, and allowed to stand under ambient conditions. A small number, less than 1%, were returned because they began to leak in service. Inspection revealed general corrosion and pitting on the inner surfaces. However, other tanks that experienced the same service conditions developed no corrosion. Corrosion was linked to forming defects that provided sites for localized corrosion, and to lack of steam drying after cleaning, which increased susceptibility to general corrosion.

A resistance-welded carbon steel superheater tube made to ASME SA-276 specifications failed by pitting corrosion and subsequent perforation, which caused the tube to leak. The perforation was found to have occurred at a low point in a bend near the superheater outlet header. It was found that the low points of the superheater tubes could not be completely drained during idle periods. Water-level marks were noticed on the inside surface above the area of pitting. It was revealed by microscopic examination that localized pitting had resulted from oxidation. It was concluded that water contained in the tube during shutdowns had accumulated and cumulative damage due to oxygen pitting resulted in perforation of one of the tubes. Filling the system with condensate or with treated boiler water was suggested as a corrective action. Alkalinity was suggested to be maintained at a pH of 9.0 and 200 ppm of sodium sulfite should be added to the water.

A failure analysis was conducted on brass alloy 270 heat exchanger tubes that were pulled from a unit used to cool oil for the speed regulators and thrust bearings of a hydroelectric power plant. The tubes began to leak after approximately 5.5 years of service. Macrophotography and scanning electron microscopy were used to examine samples from the tubes. An energy-dispersive electron microprobe analysis was carried out to evaluate the zinc distribution. Results showed that the failure was due to dezincification. Replacement of the tubes with new tubes fabricated from a dezincification-resistant alloy was recommended.

The Pandia digester is a long cylindrical vessel which uses alkaline sulfite liquor to cook sawdust for pulping. The inlet cone was fabricated from AISI 304L stainless steel with E308 welds. Typical liquor concentration was approximately 80% NaOH, 20% Na2SO3 with chloride concentrations at 2 grams per liter. The operating pressures in the inlet cone were up to 1.2 MN/sq m (170 psig). The inlet cone had developed leaks within a year of service. Liquid penetrant inspection showed significant through-wall cracking near the fillet welds joining the bottom flange and side wall and the butt welds. Metallographic specimens were prepared from the welds to examine the microstructure and nature of the cracks. The cooking liquor at the inlet cone contained over ppm chlorides and was aggressive to 304 stainless steel. The cracking was identified as chloride-induced SCC. The inlet cone was replaced with an Inconel clad carbon steel inlet cone to combat the SCC.

Steel pipes, used for years in a food factory soft water preheater, were found to leak as a result of corrosion. The pipes, made of 18/8 steel, were immersed in steam maintained at 0.5 atm and 150 deg C. They carried desalinated process water, heating it to approximately 100 deg C. Inspection revealed a reddish-brown coating on the outside of the pipe with a few flat pitting holes and incipient cracks. Corrosion was also observed on the inner walls of the pipe, consisting of rust patches with pitting scars, branching out to predominantly transcrystalline cracks. In this case, leaking appears to be the result of a combination of pitting and stress corrosion, most likely due to chlorides. The factory was recommended to use molybdenum-alloyed steels (type 18/10 or 18/12) which are more resistant to local disruption of passivating films and pitting than molybdenum-free types such as 18/8.

Several nickel-base superalloy (UNS N06600) welded heat-exchanger tubes used in processing black liquor in a kraft paper mill failed prematurely. Leaking occurred through the tube walls at levels near the bottom tube sheet. The tubes had been installed as replacements for type 304 stainless steel tubes. Visual and stereoscopic examination revealed three types of corrosion on the inside surfaces of the tubes: uniform attack, deeper localized corrosive attack, and accelerated uniform attack. Metallographic analysis indicated that pronounced dissimilar-metal corrosion had occurred in the base metal immediately adjacent to the weld seam. The corrosion was attributed to exposure to nitric acid cleaning solution and was accelerated by galvanic differences between the tubes and a stainless steel tube sheet and between the base metal of the tubes and their dendritic weld seams. A change to type 304 stainless steel tubing made without dendritic weld seams was recommended.

A back wall riser tube in a high pressure boiler failed, interrupting operations in a cogeneration plant. The failure occurred in a tube facing the furnace, causing eight ruptured openings over a 1.8 m section. The investigation consisted of an on-site visual inspection, nondestructive testing, energy dispersive x-ray analysis, and inductively coupled plasma mass spectrometry. The tube was made from SA 210A1 carbon steel that had been compromised by wall thinning and the accumulation of fire and water-side scale deposits. Investigators determined that the tube failed due to prolonged caustic attack that led to ruptures in areas of high stress. The escaping steam eroded the outer surface of the tube causing heavy loss of metal around the rupture points.

The jackscrew drive pins on a landing-gear bogie failed when the other bogie on the same side of the airplane was kneeled for tire change. The pins, made of 300M steel, were shot peened and chromium plated on the outside surface and were cadmium plated and painted with polyurethane on the inside surface. The top of the jackscrew was 6150 steel. Both ends of the pins were revealed to be dented where the jackscrew had pressed into them and were observed to have been resulted due to overdriving the jackscrew at the end of an unkneeling cycle. These dented areas were found to be heavily corroded with chromium plating missing. A heavily corroded intergranular fracture mode was revealed by chromium-carbon replicas of the areas of fracture origin. Deep corrosion pits adjacent to the fracture origins and directly beneath cracks in the chromium plate were revealed by metallographic examination. It was concluded that stress-corrosion cracks grew out from the rust pits. The pin material was changed from 300M steel to PH 13-8 Mo stainless steel, which is highly resistant to rusting and SCC and the jacking control system was modified to prevent overdriving.

A water tube boiler with two headers and 15.5 atm working pressure became leaky in the lower part due to the formation of cracks in the rivet-hole edges. The boiler plate of 20 mm thickness was a rimming steel with 0.05% C, traces of Si, 0.38% Mn, 0.027% P, 0.035% S, and 0.08% Cu. The mean value of the yield point was 24 (24) kg/sq mm, the tensile strength 39 (38) kg/sq mm, the elongation at fracture, d10, 26 (24)%, the necking at fracture 71 (66)% and notch impact value 11.5 (9.4) kgm/sq cm (the values in brackets are for the transverse direction). The specimen from inside surface of the boiler was polished and etched with Fry-solution, which revealed parallel striations formed due to the cold bending of the plate. The zones of slip were concentrated around the rivet holes. The cracks were formed here. The structure examination proved that the cracks had taken an exactly intercrystalline path, which is characteristic for caustic corrosion cracks. It was recommended that the internal stresses be removed through annealing or alternatively lye-resistant steel should be used.

Nickel anodes failed in several electrolysis cells in a heavy-water upgrading plant. Dismantling of a cell revealed gouging and the presence of loosely attached black porous masses on the anode. The carbon steel top, plate was severely corroded. An appreciable quantity of black powder was also present on the bottom or the cell. SEM/EDX studies of the outer and inner surfaces of the gouged anode showed the presence of iron globules at the interface between the gouged and the unattacked anode. The chemical composition of the black powder was determined to be primarily iron. Cell malfunction was attributed to the accelerated dissolution of the carbon steel anode top, dislodgment of grains from the material, and subsequent closing of the small annular space between the anode and the cathode by debris from the anode top. Cladding of the carbon steel top with a corrosion-resistant material, such as nickel, nickel-base alloy, or stainless steel, was recommended.

Grate bars in the traveling grate indurators in several taconite processing units suffered excessive corrosion following a conversion from acid to fluxed pellet production procedures. The campaign life of the HH grade cast stainless steel bars was reduced from more than 7 years to approximately 9 months. Several corroded grate bars were examined metallographically and by electron microscopy to determine the causes of the accelerated corrosion. Chemical and X-ray diffraction analyses were also conducted, along with simulation tests to assess the role of alkali chlorides in the corrosion process. The basic cause of degradation was found to be hot corrosion caused by the deposition of alkali sulfates and chlorides. However this degradation may have been aggravated by thermal cycling and abrasion. The source of the salt was impurities in the flux. Two potential solutions were proposed: modification of the processing parameters to reduce the salt deposition and / or change of bar materials to a more resistant alloy.

This article provides a discussion on the structural ceramics used in gas turbine components, the automotive and aerospace industries, or as heat exchangers in various segments of the chemical and power generation industries. It covers the fundamental aspects of chemical corrosion and describes the corrosion resistance characteristics of specific classes of refractories and structural ceramics. The article also examines the prevention strategies that minimize corrosion failures of both classes of materials.

Cavitation damage of diesel engine cylinder liners is due to vibration of the cylinder wall, initiated by slap of the piston under the combined forces of inertia and firing pressure as it passes top dead center. The occurrence on the anti-thrust side may possibly result from bouncing of the piston. The exact mechanism of cavitation damage is not entirely clear. Two schools of thought have developed, one supporting an essentially erosive, and the other an essentially corrosive, mechanism. Measures to prevent, or reduce, cavitation damage should be considered firstly from the aspect of design, attention being given to methods of reducing the amplitude of the liner vibration. Attempts have been made to reduce the severity of attack by attention to the environment. Inhibitors, such as chromates, benzoate/nitrite mixtures, and emulsified oils, have been tried with varying success. Attempts have been made to reduce or prevent cavitation damage by the application of cathodic protection, and this has been found to be effective in certain instances of trouble on propellers.

High temperature corrosion may occur in numerous environments and is affected by factors such as temperature, alloy or protective coating composition, time, and gas composition. This article explains a number of potential degradation processes, namely, oxidation, carburization and metal dusting, sulfidation, hot corrosion, chloridation, hydrogen interactions, molten metals, molten salts, and aging reactions including sensitization, stress-corrosion cracking, and corrosion fatigue. It concludes with a discussion on various protective coatings, such as aluminide coatings, overlay coatings, thermal barrier coatings, and ceramic coatings.

This article provides an overview of the electrochemical nature of corrosion and analyzes corrosion-related failures. It describes corrosion failure analysis and discusses corrective and preventive approaches to mitigate corrosion-related failures of metals. These include: change in the environment; change in the alloy or heat treatment; change in design; use of galvanic protection; use of inhibitors; use of nonmetallic coatings and liners; application of metallic coatings; use of surface treatments, thermal spray, or other surface modifications; corrosion monitoring; and preventive maintenance.

Corrosion is the deterioration of a material by a reaction of that material with its environment. The realization that corrosion control can be profitable has been acknowledged repeatedly by industry, typically following costly business interruptions. This article describes the electrochemical nature of corrosion and provides the typical analysis of environmental- and corrosion-related failures. It presents common methods of testing of laboratory corrosion and discusses the processes involved in the prevention of environmental- and corrosion-related failures of metals and nonmetals.

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to analyze an automotive polyoxymethylene (POM) sensor housing that was depolymerizing during service. It was found that a combination of heat, oxygen, and sulfuric acid attacked and caused premature failure of the part. POM should not be selected for automotive applications where elevated temperatures and acidic environments can exist. If exposure to acid is suspected, sodium bicarbonate should be applied to neutralize the surrounding environment, followed by copious quantities of water, and repeated until no effervescence is observed.

A spiral heat exchanger made from 316L stainless steel developed a leak after eight years of service as a condenser on a distillation tower. Examination identified the leak as being located on the cooling water side in the heat affected zone (HAZ) of a weld joining two plates. Cooling water deposits were observed in a V-shaped corner formed by the weld. A metallurgical examination identified the presence of transgranular cracks in the HAZ on the cooling water side. Analysis of the cooling water revealed the presence of chlorides. Based on the metallurgical analysis and other findings, it was determined that the cracks and associated leak were the result of chloride stress-corrosion cracking.

The phenomenon of on-load corrosion is directly associated with the production of magnetite on the water-side surface of boiler tubes. On-load corrosion may first be manifested by the sudden, violent rupture of a boiler tube, such failures being found to occur predominantly on the fire-side surface of tubes situated in zones exposed to radiant heat where high rates of heat transfer pertain. In most instances, a large number of adjacent tubes are found to have suffered, the affected zone frequently extending in a horizontal band across the boiler. In some instances, pronounced local attack has taken place at butt welds in water-wall tubes, particularly those situated in zones of high heat flux. To prevent on-load corrosion an adequate flow of water must occur within the tubes in the susceptible regions of a boiler. Corrosion products and suspended matter from the pre-boiler equipment should be prevented from entering the boiler itself. Also, it is good practice to reduce as far as possible the intrusion of weld flash and other impedances to smooth flow within the boiler tubes.

A pipe in the lateral wall of a boiler powering an aircraft carrier flat-top boat failed during a test at sea. The pipe was made from ASTM 192 steel, an adequate material for the application. Microstructural analysis along with equipment operating records provided valuable insight into what caused the pipe to rupture. Although the pipe had been replaced just 50 h before the accident, the analysis revealed incrustations and corrosion pits on the inner walls and oxidation on the outer walls. Microstructural changes were also observed, indicating that the steel was exposed to high temperatures. The combined effect of pitting, incrustations, and phase transformations caused the pipe to rupture.