Materials for valve design for service in sea water

Valves are a costly part of marine system however the price of valve is based on the design followed. Besides of any kind of production problems, it is seen that a globe valve will be costlier than a butterfly valve due to its higher weight. It is often become more satisfactory to choose consistent materials for valve production like a butterfly valve instead using a costly design of valve, a globe valve and use economical materials. While using the globe valve, for instance for its suitable flow control properties, the additional price of corrosion resistant materials suitable to the design should be accepted.

Few designers tend to prevent the corrosion issues by valve linings. It is associated with the valve design such simple valve’s shape and structure can be offered with dense rubber lining that can be clamped firmly among the flange welding the valve to the pipes and is not based on the suitable adhesion among the rubber and structure. The complex shaped globe vale and lining should adhere perfectly to the metal surface. Test describes that this adhesion is tough to get and linings generally have limited life.

The valves have specific characteristics that should be taken into account to prevent the corrosion issues. For instance, the shafts on the butterfly turns, enter the lining and it is essential to offer a positive seal among the lining and the stem to avoid contact of seawater to cast iron component. Damages to this have caused valve failure due to the corrosion materials accumulated on the lining causing valve penetration.

Second widely used seawater valve is the membrane valve that comprises of a versatile membrane that separates the valve internals from interaction with contact with marine water. While in use, the membrane is elongated into the stream limiting or ceasing the flow. The shape is simple and rubber linings on the body are suitable. Cavitation damage to the rubber memberane is noticed with extreme throttling.

It is considerable to observe the complex flow path inside the globe valve. Various sharp alterations of the direction happens inside the valve that develops extreme turbulence that results into impingement attack on the valve body. Alloys offering good impingement resistance like Copper-Nickel alloy 70/30 are preferred for choosing this kind of valve.

Galvanic factors in valves

It is seen that most of copper base alloys offer equivalent potential and can be utilized without the considering the severe galvanic effects. The stainless steel 310 installed with brass trim offer excellent galvanic security from the wide area of ferrous material and have a significant life.

It is a good idea to use Monel alloy 400, K-500 and stainless steel grades for cathodic protection of the valves. The copper alloys are used in valves to maintain the galvanic compatibility. Do not use the unsecured iron valves in non-iron units.

The systems made from stainless steel grades are free from the galvanic compatibility issues however various alls are used for the various components.

Precautions should be followed, even if stainless steel grade is used with copper alloy based heat exchangers as they can have a significant galvanic influence. It can be taken care by fitting anodes in the water boxes, As iron ions in marine water are advantageous for copper alloys, their implementation is recommended.

Marine pumps

Centrifugal pumps are usually used in the marine systems and are operated by stable speed electric motors. With the standard rotation speed, the speed tip of the pump impeller reaches to 20m/s at this pace, several copper based alloys are attacked in the fast running seawater. Although only specific parts of the pump interact with the high velocities, besides from these parts, the copper alloys can often be successfully utilized in these pumps.

Pump skins

 For the pumps made from copper alloys there is often adequate gap made between the impeller and skins to secure the pump skin get attacked by the running water through the impeller however it is absorbed in the sluggish water flow through the metal surface towards the pipe. Preventing the direct impingement, the materials such as Cu-Ni alloy 70/30 serve efficiently.

Although in few cases, early damages in the pump casing have been seen that resulted into impingement. It can be caused by increased pump speed. In case of such damages, the casing life becomes very small such as only 1.5 years. To prevent damage of this kind, the design should be improved, to decrease the marine velocity at the metal surface, or materials offering greater resistance should be used. Test shows that copper-nickel alloy 70/30 offer greater resistance as compare to tin bronze. They even offer better resistance than various other copper containing alloys in the running seawater.

For the pumps made from welded nickel bronze sheet, a severe phase corrosion is noticed in the heat affected region of the weld that damages when stressed such as by water stroke.

Pump Impellers

It is in connection with the quickly running, turbulent marine water and for distribution pumps that are in service for a long time, they must be constructed from a alloy that prevent attack in such media. Using Nickel- Copper alloy Monel 400 and K500 or stainless steel grade 316 offer excellent resistance to running marine water, their cast forms are recommended for constructing pump impellers. Use of cast iron or low steel can damage the pumps. 

Alloys for use in chemical plants

Consistent upgrade in the metallurgical and fabrications gives rise to the development of various nickel alloys and their wide use in the chemical plants. The nickel alloys provide great corrosion resistance, strength, hardness, metallurgical stability, fabrication and welding characteristics. Various nickel alloys offer good heat resistance and maintain high durability at the elevated temperatures for which they are widely used in chemical applications

The analysis of wrought nickel based alloys includes different corrosion resistance alloys that are widely used in the chemical plants.

Features

Nickel alloys are more expensive than stainless steel grades. However considering the prolong economical concept, stainless steel types are found to be more expensive because of their costlier maintenance that is needed after some time.

Nickel-Chromium-Molybdenum alloys are five times costlier than chromium-nickel stainless steel and twice times more expensive than super austenitic steel grades. The nickel alloys have alike thermal expansion properties as of carbon steel but smaller than stainless steel 300 types.

The thermal conductivity of pure nickel is superior than carbon steel however many nickel alloys provide low conductivity values, in some conditions even much lower than austenitic steel types.

Except the pure nickel, the nickel based alloys used in chemical units are more durable than steel 300 series. Nickel alloys provide outstanding ductility and hardness.  

The nickel alloys attain fully austenitic microstructures. Many grades utilized in the chemical plants are the solid solution reinforced alloys. They have superior strength properties as compare by the adequate addition of hardeners such as molybdenum and tungsten. Alike to austenitic steel types, solid solution nickel alloys cannot be hardened by heat treatment however but only by cold treatment.

Another primary class of nickel alloys is strengthened by precipitation hardenable heat treatment. They are commonly chosen for ultrahigh strength based applications such as in deep oil and gas production and widely high pressure processes. Except the selected components in valves and rotating machinery, precipitation hardened nickel alloys have a set of applications in the chemical plants. This group of alloys named as heat resistant super alloys that are utilized in the gas turbines, combustion chambers and aerospace industry.

Corrosion resistance properties

Nickel based alloys show a refined form derived from traditional austenitic steel grades and super austenitic iron based alloys in avoiding corrosion in the wide range of acids, alkalis and salts. The outstanding characteristic of nickel alloys is supreme resistance in aqueous media comprising of halide ions. Therefore nickel alloys are superior to austenitic grades for preventing corrosion in wet chlorides and fluorides.

The supreme corrosion resistance characteristics of nickel based alloys not just affects the material loss in fact it also has the potential to prevent the localized attack, pitting and crevice corrosion, intergranular attack and stress corrosion cracking. These types of localized corrosion that are more severe than general corrosion and result into wide material loss in the chemical industry.

The nickel alloys feature corrosion resistance characteristics to nominal reactivity of nickel as compare to iron as seen from its oxidation potential in the EMS series. As compare to stainless steel grades, chromium based nickel alloys develop security layer more quickly. The addition advantage of nickel over iron is the potential to get blended with different chemistry elements without resulting into the development of brittle phases. The common combining elements are molybdenum, chromium and copper. These factors should be considered as the beginning aspects in the material choice.

Welding

Welding in the different alloys is performed by shielded metal arc welding, gas tungsten arc welding and gas metal arc welding. The Nickel alloy weldments are highly ductile and their nominal heat expansion reduces residual stress and warpage. The post weld heat treatment is usually required for precipitation hardenable grades.

The welding process for nickel based alloys is alike to austenitic stainless steels. However due to their higher sluggishness of Nickel based weld puddles and lower penetration characteristics of nickel alloys, the development of complete cut welds may require enhancement of joint structure and welding methods.

The Nickel alloys cannot withstand the contaminants that cause weld embrittlement. The characteristics such as good ductility, small thermal expansion and ability to handle dilution by various metallic elements have made nickel based welding consumables widely accepted for welding with different materials. It only includes welding of nickel base alloys with iron based materials, even also joining stainless steels to carbon and other steel types. In the same way, nickel alloys can be weld gathered on carbon steel without causing cracks.

Nickel based alloys

The Nickel based alloys are developed in the various forms for example wire, sheet, plate, strip, tubes, pipe, fitting and flanges. Various nickel alloys are also created as castings. They generally provide several characteristics unlike to their wrought forms. These alloys are usually classified to their main alloying elements. These are commonly utilized in the chemical units such as:

Pure Nickel:

Nickel 200 called as pure nickel provides outstanding corrosion resistance properties to the wide range of reducing media and salts although it is not fit for use with powerful oxidation materials such as nitric acid. The major characteristics of Pure nickel is prevention of attack by caustic alkalis, also in the melt form. Besides of offering great resistance to dry halogen media, Nickel is not perfect for use at temperature below water dewpoint. In application temperature above 600oF, Nickel 201 is recommended for use.

Monel Alloy

The corrosion resistance performance of Monel 400 wire is supreme as of pure nickel, however it cannot perform well in aeration and oxidizing conditions. Alloy 400 attains outstanding security from attack of halogen media particularly hydro-fluoric acid, hot gases containing fluoride or hydrogen fluoride. It is commonly used in dealing with sulfuric acid solutions, sea water and brine solutions. The components that require high strength such as valve and pump fittings, demand Monel K-500 that is a precipitation hardenable form of alloy 400.

Inconel 600: Chromium in addition of nickel improves the service of Inconel alloy 600 in the oxidizing conditions. Although only fit for mineral acids, Inconel 600 provides extreme resistance to organic acids and is commonly used in fatty acid treatment. It is also commonly used in the development and dealing with caustic and alkali media. Alloy 600 is also fit for serve in the high temperature conditions that demand heat and corrosion resistance. The alloy offers outstanding service in the hot halogen media therefore it is fit for use in the organic chlorination processes. In the various elevated temperature degradation processes, Inconel 600 offers good resistance to oxidizing, carburizing and nitriding media.  

Inconel 625: An inclusion of molybdenum to Ni-Cr combination provides security from mineral attack and also from oxidizing and reducing salts corrosion. The presence of molybdenum improves pitting and crevice resistance in wet chlorides. The alloy offers good mechanical strength and fatigue strength. Alike to alloy 600, corrosion resistant Inconel 625 wire is a super alloy material that is a proven candidate for use in chemical and petrochemical processing units for service in the severe and elevated temperature applications.

Incoloy 825: It is a member of austenitic stainless steel group and is commonly used in handling sulfuric and phosphoric acid, they are the major challenges to be met by alloy 825. Although suitably resistant to HCl, alloy 825 prevents attack of chloride pitting and crevice in sluggish and unaerated conditions. However alloy 825 is mildly resistant to alkali and halogen media unlike to high nickel alloys.

Hastelloy G: Alloy G3 offers improved corrosion resistance than Monel 400, alloy 600 and alloy 825 in the various media. It is specifically resistant to sulfuric acid and contaminated H3PO4 and can serve excellent in the vigorous oxidizing and reducing conditions. The advanced Hastelloy G30 provides improved weldability and resistance to different kinds of corrosion and also in the weld heat affected regions.

Hastelloy C: Alloy C276 is the main material that is used in the chemical processing systems for service in the highly corrosive media where the stainless steel grades do not withstand. Hastelloy C276 provides outstanding resistance to different acids, salts and various media that are involved in the chemical industry. It is particularly significant in the extreme conditions involving wet chlorine and hypochlorites. The materials offering superior metallurgical and corrosion resistance properties as compare to Hastelloy C276 has led to the development and popularity of different kinds of alloys for example Hastelloy C22, C2000 and Inconel 622. They have higher molybdenum and chromium content as compare to Hastelloy C276. Few grades also contain tungsten and copper. The effect of nominally alloying elements on the metallurgical properties and corrosion resistance is not focused in this article.

Hastelloy B grades: Hastelloy B2 provides excellent resistance to sulfuric acid, phosphoric acid and hydrochloric acid in the reducing media. It is ideally fit for use in systems that deal with HCl at whole concentration and temperature up to the boiling temperature.

The oxidation media severely decrease the corrosion resistance, particularly the powerful oxidizers like ferric and cupric salts that may be present as contaminants. Hastelloy B3 provides superior service than alloy B2. The main benefit of new grade is limited development of unnecessary matrices during the production that may result into embrittlement. 

Corrosion behavior of Nickel and its alloys in Alkalies

Corrosion rates in chemical media usually reduce with increase in pH values. In alkaline media, the hydrogen ion is available in small contents. However various metal receive nominal corrosion at some pH, usually basic and then become quickly corrosive as pH increases. Often corrosion because of alkaline media causes localized and pitting attack by the development of cathodic layers and corrosion is extreme at the sensitive anodic areas. Austenitic grades and various nickel based alloys receive stress corrosion cracking or general corrosion in hot concentrated caustic.

Addition of nickel in an alloy increases corrosion resistance in alkaline media. Nickel 200 and various high nickel alloys provide suitable service in dealing with this media. The commonly used nickel alloys in alkali media are nickel 200, Monel 400, Inconel 600 and alloy 625.

Nickel 200

The great corrosion resistance characteristic of alloy 200 is its potential against caustic soda and other alkalies. The alloy is not affected by anhydrous ammonia or ammonium hydroxide in contents of 1%. Larger contents are resulted by fast corrosion in the presence of dissolved oxygen.

Nickel 200 offers good resistance to whole concentration percentage of caustic soda or sodium hydroxide at the different temperature limits including the melting point. Below 50% concentration, corrosion rates are low, usually below 0.1 mpy or 0.003 mm/a actually in boiling points. The increased content and temperature limits result in slightly accelerated corrosion rates.

The major influencing factor of nickel alloy in highly concentrated caustic soda is the same nature of layer developed while exposing the caustic soda. In the diverse media, a security layer of black nickel oxide is developed that results in a considerable reduction in the corrosion rates during prolong experience. For example, specimens of alloy 201 were exposed to caustic solutions consisting of 500 cc of water to 2kg of technical caustic flakes followed by heating in nickel 201 at temperature limit of 790oF – 830oF. The corrosion rate in the first 24 hours was average 21 mpy. The specimens were exposed to test without the elimination of oxide layer. During the weekends the overall corrosion rates decrease to 2.8 mpy or 0.07 mm/a.

The presence of chlorates in caustic soda solutions accelerates the corrosion of alloy 200 considerably. Taking the damaging effects into account, it is preferred to avoid chlorates fully prior evaporation at the high temperatures in the presence of nickel. It is also known that the presence of oxidizable sulphur compounds increases the corrosivity of caustic for nickel. This effect is noticed normally with sulphides such as hydrogen sulphide, mercaptans, sodium sulphide and to a small limit with slightly oxidizing media containing thiosulfates and sulphates.

The effect of oxidizable sulfur compounds can be eliminated by the addition of caustic solution of suitable sodium peroxide to oxidize them to sulfates. Wide peroxide does not appear to alter the corrosiveness of caustic soda to nickel.

In the other media, when nickel is used at temperatures above 600oF, the preferred metal is a low carbon alternative for example Nickel 201.

Monel 400

The high nickel content, alloy 400 provides good resistance identical to the Pure Nickel alloy 200 to caustic soda for the several concentration limits, although causing stress corrosion cracking in the strong alkalis at the elevated temperatures. The corrosion rates of alloy 400 are higher in concentrated caustic soda and caustic potash at the high temperatures. Alloy 400 also offers good resistance to anhydrous ammonia and ammonium hydroxide solutions comprising of 3% alkali concentration in the absence of dissolved oxygen.

Incoloy Grades

The alloys provide excellent resistance to alkaline solutions, getting a corrosion rate of 0.5 mpy or 0.01 mm/a in the boiling 50% sodium hydroxide, their resistance is below that provided by Nickel 200, are used in alkaline conditions except other corrosive media is included. They can also get stress corrosion cracking in warm concentrated alkalis. They also prevent corrosion in ammonia and ammonium hydroxide solutions in the various service media.

Inconel 600

In the high temperature caustic conditions containing sulfur, alloy 600 offers superior performance than alloy 201. However alloy 600 can receive stress corrosion cracking in specific alkali media. So it should be stress relieved prior service and service stresses must be used to the minimum. Alloy 600 provides good resistance to sodium hydroxide at the boiling temperatures in concentrations about 80%.

For nickel 200, the presence of chlorates in caustic soda accelerates the corrosion rates. For its con

For Nickel alloy 200, the availability of chlorates in caustic soda increases the corrosion rates. Due to its concentration of chromium, Inconel alloy 600 is fully resistant to corrosion by ammonia for a complete range of concentrations and temperatures.

While offering good corrosion resistance, Inconel grades are not often required for service in absolute caustic media. They can be advantageous for use in halide media.

Salt

Salt and water combination offers good conductivity of salts and therefore they become able to take higher corrosion currents. Therefore the galvanic effects are more noticeable in the salt solutions instead in pure water.

The commonly used nickel alloys in the process media involving sulfate salts are Incoloy 825, Inconel 625, Hastelloy C276 etc. For media containing chloride salts, the commonly used alloys are alloy 400, alloy 825, alloy 625, etc.

Applications of materials in marine water

Cupronickel alloys

Copper-Nickel alloys such as 90/10 and 70/30 are used for heat exchanger tubings for several years. The demand for high consistency in major modern plants has preferred the service of cupronickels instead the conventional brass.

In the major significance has been the development of desalination market. Around 75% of this capacity includes distillation procedures, multistage flash distillation is very popular.

The plants include heavy duty heat exchangers and they demand tubing in the large scale. For every meter cube per day of output needs around 25 kg of tubing, the installed capacity is around 200,000 tonnes.

Besides of tubing applications, a vast growth in various applications where weldability and fabricability are needed in addition of resistance to attack. Cupronickel 90/10 offers good weldability  and is producible in complex shapes like water boxes and ship hulls. Major increase has been observed in recent times in the applications where making is included such as seawater pipes. Large tones of cupronickel 90/10 alloy pipes are installed in the various plants in the coastal oil industry.

Initially in the Gulf of Mexico practice, galvanized steel marine units were utilized. They couldn’t offer consistent performance and in the vigorous service conditions their maintenance expenses were very intolerable. The cupronickel alloy 90/10 has offered economical and consistent service. The application of cupronickel has now increased surpassing North Sea to the areas like Arabian Gulf and Brazil.

Cupronickel 90/10 alloy is also made as clad plate that carbon steel is cladded with a cupronickel alloy’s layer. It is used in large magnitudes in the desalination plants for water boxes and pipes of big diameters and also prevented the corrosion issues that occurred with coated steel water boxes and pipes.

In the latest times in Italy, an array of fireboats with hulls made from cupronickel 90/10 alloy steel has been built. These vessels prevent attack of fouling and corrosion because of copper alloy hull. The attractive characteristics of cupronickel alloy 90/10, combining with its fabricability and weldability, confirms that this versatile material is used widely in marine applications.

Stainless Steel

Issues of pitting and crevice attack have forced designers to use stainless steel grades in marine water. The benefits of other characteristics can be received, although the resistance to rapidly flowing marine water for outstanding service in few applications. The common use is for pump impellers and shafts. Several pumps use Super Duplex Stainless steel 2507 for these components and offered the pump is not left standing for prolong periods, issues with crevice corrosion are nominal.

Where static conditions are assumed, benefit is usually taken of the cathodic security offered to
austenitic steel grades by Nickel Resist cast irons. The alloys containing high nickel content offer supreme corrosion resistance in marine conditions and are usually used for pump casing components like inlet bell mouths, column pipes and discharge heads in big vertical pumps like are used for flowing marine water in MSF and power production units. Various factors apply to valve stems and valve trim offer good resistance to turbulent marine water makes stainless steels captivating.

The rapid use of steel grades in heat exchanger tubes is noticed. The steel grades are perfect for power plant condenser tubing and to control pollution of marine water specifically where it contains hydrogen sulfide- rules the use of cupronickel alloys.

In the desalination plants, large magnitudes of steel grades are used in applications like vent piping, distillate trays and transfer troughs, evaporator vessel linings and demisters.

In the latest plants, the whole distillate system is usually in stainless steel 316 as test has described that this highly pure water can be attacking to carbon steel. The low oxygen levels in these plants allow stainless steels are used to handle boiling sea water and brine. These grades also avoid stress corrosion cracking in the hot conditions.

The advanced use for stainless steels is in reverse osmosis, a membrane process allows fresh water to be developed from marine water by pressure. In the RO process, natural aerated marine water is utilized that means stainless steel 316 experiences crevice attack at the various joints related with the numerous modules used to fabricate these plants.

The piping material in the plants is being enhanced to high alloy steels as in the piping system. The major marine markets include the development of ship tanks for handling chemicals, solvents and wine, fittings for craft and fasteners.

This method of weld overlaying of crucial areas with a very resistant material like alloy 625 is commonly used for marine and offshore applications.

Conclusions

Nickel based alloys like cupronickels, stainless steels and nickel based alloys have characteristics featured for marine applications. Advanced needs for high reliability and small life cycle costs are preferable to result in enhanced used of these alloys in the marine fields.

Nickel alloys are used in pollution control, nuclear power, solar energy, coal gas plants, gas turbines and in various phases of industrial production features high temperature service is allowing the designers to further test the high temperature properties of construction materials. The latest processes are commercialized and as production capacities are improved, temperature normally becomes necessary factor in the selection of materials.

The stainless steels are normally selected initially, depending on the corrosion resistance and on the base of their mechanical properties. With improvement in the service temperature, high temperature characteristics quickly become the major concern. The stainless steels are highly versatile in its potential to meet the requirements of high temperature applications.

FeCrAl resistance heating element- Scaling resistance

FeCrAl heating element is used as catalytic substrate that is a metallic substrate providing different advantages as compare to ceramic substrates. A metallic substrate provides higher resistance to shock and vibration, it provides greater conductance to heat instead ceramic. Additionally, it can be fabricated easily in thin foil and provides honeycomb structure to deliver wide surface area and is lightweight.

Different FeCrAl resistance heating elements consists of Yttrium that offers considerable oxidation resistance characteristics and conserve oxide layer, however Yttrium has some drawbacks. It is expensive and reduces weight while melting and pouring of iron alloys. Because of high reactivity of yttrium, it reacts with various elements such as oxygen and loses to slag and furnace refractory materials. Because of high reactivity of Yttrium, a costly vacuum induction melting is used for development of FeCrAl Cr25Al5 that have Yttrium as a compositional element. Additionally, while vacuum melting and casting, receiving Yttrium in alloy is below 49.9% of that was added in the molten metal. Unfortunate delays, or problems that prevent the quick pouring of melt, efficiency % decreases significantly.

Additionally, vacuum induction heating method is not adequate to attain considerable magnitude of Yttrium by remelting the scrap of FeCrAl alloys.

The catalytic system that comprises of aluminum bearing ferrite steel that treats as substrate, particularly a FeCrAl alloy has Yttrium. FeCrAl heating element is subjected to keep the characteristic of development of stable alumina layer while the substrate surface heating that the alumina film secures the material from oxidation to make it corrosion resistant.

To adjust the drawbacks of Yttrium, various cheap elements are excluded. FeCrAl alloy is a heating element that consists of silicon, titanium and various rare earth metals. FeCrAl alloys consist of 10-15% chromium, 1-3.5% aluminum, 0.8-3% silicon, 0.01-0.5% calcium, cerium and other rare earth metals have scale adherence. The patent also requires aluminum and silicon concentration from 2-5%, titanium reduction about 0.2% and combination of oxygen and nitrogen concentration below 0.05%.

The high temperature oxidation resistance alloys have nominal concentration of cerium states that a FeCrAl alloy with significant magnitude of cerium provide prolong oxide coating. These alloys comprise cerium magnitudes from 0.01- 0.37%. FeCrAl alloy nominal content of cerium of 0.01% receives spaling whereas FeCrAl alloy with cerium by .04% - 0.37% describe no signs of spalling. Cerium is available in the latter alloys in the development of cerium-iron intermetallic compounds that is precipitated at the grain levels.

FeCrAl heating element has cerium about 5% cerium and also has 0.5% carbon and 0.5% nitrogen.

The key reason of developing FeCrAl alloys is to improve the oxidation resistance, scaling resistance and hardness at the elevated temperatures above 2102oF – 1150oC.

FeCrAl heating element

FeCrAl has good heat absorption and radiation characteristics for combustion units. It is also featured for use in combustion units and is also used in glass sealing by an inclusion of 2% rare earth metals in its main chemistry.

Although, industry still needs an alloy that is cheap to fabricate by small cost alloying composition that can be made by cheap melting methods and that provides resistance to heat cyclic oxidation from very low to high temperature of 1600oF, in the internal combustion exhaust conditions and offers good hot workability. Additionally, the heating element should be fit to provide an improved aluminum oxide surface that lasts on the metallic surface in the heat cyclic conditions. It then needs heating element that is fit for additional processing to provide an improved aluminum oxide layer to offer wide surface area and strengthen more catalytic materials to be used on the alloy by aluminum oxide layer.

The FeCrAl alloy must be fit to get stabilized in the high temperatures with wide creeping strength characteristics. A hot processing iron stainless steel alloy is offered to provide outstanding resistance to heat cyclic oxidation and scaling at the high temperatures. It is then fit for fabrication on the retainable aluminum oxide layer. The alloy consisting of up to 25% chromium, 8% aluminum and various 0.002- 0.05% rare earth elements like cerium, lanthanum, neodymium and praseodymium with the whole content of rare earth metals about 0.06% silicon, 1% manganese and general steel contaminants.

The FeCrAl heating element is also stabilized by inclusion zirconium or niobium that stabilizes and offers high temperature creeping resistance. An oxidation resistance catalytic substrate that offers consistent aluminum oxide layer also offers catalytic system with substrate. The production of hot working ferrite steel is also delivered that comprises of steps of development of alloy melt and hence producing an aluminum bearing ferrite steel. It is also then processed to develop a reliable aluminum oxide layer.

Normally, a FeCrAl alloy is developed with an addition of rare earth metals particularly cerium or lanthanum that provides hot processing alloy and prevents heat cyclic oxidation and has scaling resistance at the high temperatures. It is then fit for the development reliable aluminum oxide.

Chromium content offers needed characteristics such as oxidation and corrosion resistance. The chromium concentration is limited to avoid unnecessary hardness and strength that prevent formability of FeCrAl heating element. The concentration of chromium below 8% offers inadequate resistance to heat cyclic oxidation. The key role of chromium is to provide outstanding corrosion resistance, oxidation resistance and there is a link between number of heat cycles to fail and enhanced content of chromium.

Concentration of chromium above 25% enhances the service of FeCrAl heating element and also creates problem in the development of alloy.

Applications of cupronickel alloys in seawater

Cupronickel clad steel

The applications that require economic or engineering considerations solid cupronickel alloy is not perfect hence using the cupronickel clad steel is suggested. Mining, MIG spot welded linings and adhesive bonding are used successfully however for few applications clad steel is bonded.

The clad plate is developed by hot roll bonding, bursting bonding or weld overlaying. The economical breakpoint for specific thickness in three ways is a part of some assumption and thumb rule, cupronickel alloy is roll bonded about 35 mm thickness. Bursting bonding is usually covered above 35mm and weld overlay is the recommended method for thickness above 100mm. Normally the cladding thickness is above 1.5mm and 2 – 3mm is usually considered, wide accumulations are hardly discovered excluding the explosively bonded tube plates or weld overlayerd components.

Besides of lucrative factors, the  application of clad plate, take the advantage of higher strength of the steel bases, are a significant factor in design, if the developed components need to withstand large loads or high pressures.

Cupronickel clad plate is easily welded based on the availability from steel or clad side, welding processes are adequately made. Normally, to avoid the embrittlement because of copper entrance in the steel, root runs are made with cupronickel alloy with high tolerance to iron dilution. If cupronickel alloys are selected for their anti-fouling characteristics, their capping layer on the weld must be made from cupronickel alloy 90/10 to prevent biofouling.

Cupronickel clad plate is a new material and its main application is in water boxes and flash chambers in multistage flash desalination plant in the middle east also used large magnitude of cupronickel clad plate. The major applications for this material are noticed in marine industry.

Cupronickel alloy Welding

While considering the welding of cupronickel alloy, it is important to avoid local changes in chemical composition of weld metal. Specific control on the welding is important. Larger content of nickel creates nominal iron corrosion problems, and it is significant to improve the composition of filler metal slightly through continuous cycles to use the maximum nickel concentration as filler metal for the initial stack and to end with normal cupronickel chemical chemistry.

The choice of filler metals is also influenced by taking the corrosion strength into account with cupronickel alloy 70/30 and 90/10. These are easily solderable. This technique is not normally followed due to insignificant weld strength in the application media in which the use of these materials is recommended and problems of bimetallic corrosion may occur in vigorous conditions.

For the conventional brazing methods, the filler alloys comprising high silver concentration are recommended to decrease the specific corrosion issues.

The alloys of copper-phosphorus, copper-silver-phosphorus brazing alloys must not be used due to their sensitivity to intergranular attack and embrittlement. The extremely cold processed material must be annealed before brazing to avoid extensive penetration and cracking of base metal by brazing of alloy.

Cupronickel alloy for seawater plants

The  cupronickel alloy super metals are widely used for their outstanding resistance to biofouling, corrosion on the running and static marine water. The ships and many offshore plants use marine water cooling applications and various industrial configurations cooling applications. The marine pipes are also configured for conveying ballast, tank cleaning water and steam for emergency fire extinguishing applications.

Seawater is a severe mixture of salts, abrasive solids, gases dissolved and bubbles and organic matter and organisms and its chemistry may change in composition as per the tide and weather. The types of problems noticed in pipeline materials are general corrosion in the fresh marine water, impingement attack by turbulent flow round bends or objects, pitting attack by the interaction with neighbor materials , crevice attack in area of insufficient oxygen and erosion by the mounted solids. Therefore, the piping units are designed to be suitable and affordable during the service life of the configuration rather the economical price.

Normally considered as the very economical material for pipes, carbon steel offers a costlier service as compare to cupronickel alloys, it requires to be replaced one or two times in its service. Comparing the installation costs, it may be more expensive due to the corrosion wastage, it needs to be thicker and heavier than cupronickel alloy. The welding costs for thin gauge cupronickel alloy can be smaller for the same weight of steel. As the water flow resistance of cupronickel alloy is smaller than steel, it is feasible for designs to use the smaller internal diameter without the need to allow for increase in hardness of the surface while in use.

Using noble materials for pipes or organic lines inside the  pipes may result into troubles besides the system. Although fouling may be limited at service speeds, quiescent conditions may result into connection among germs that will then continue to grow while service in seawater units.

Mechanical characteristics of Inconel 617

Alloy 617 attains good mechanical characteristics at the high temperatures. Its supreme characteristic is its strength level that is retained at the wider limits. Alloy’s high resistance to the high points increases the significance of its room temperature mechanical properties.

The mechanical characteristics of different forms of alloy 617 are shown as following:

Hot rolled Inconel 617 plate

Yield strength – 46.7 ksi

Tensile strength – 106.5 ksi

Elongation – 62%

Reduced Area- 56%

Hardness – 172 BHN

Hot rolled Inconel 617 bar

Yield strength – 46.1 ksi

Tensile strength – 111.5 ksi

Elongation – 56%

Reduced Area- 50%

Hardness – 181 BHN

Cold rolled Inconel 617 tube

Yield strength – 55.6 ksi

Tensile strength – 110 ksi

Elongation – 56%

Hardness – 193 BHN

Cold rolled Inconel 617 sheet and strip

Yield strength – 50.9 ksi

Tensile strength – 109.5 ksi

Elongation – 58%

Hardness – 173 BHN

This information is ideal for materials that are in solution annealed form. The characteristics of the above stated forms are crosswise. The analytics materials are selected in the standard configuration. The big cycle fatigue strength of alloy 617 at the room and high temperatures about 1600oF is determined. The rotating light test is conducted on the coarse grain, solution annealed and hot processed rod. The combined evaluation of test results s observed for the welded joints. The alloys joints are connected by gas metal arc method by using the similar constituted filler metal.

The development of alloy 617 sheet depends on the requirement of maximum creeping strength at the elevated points. The solution annealing is selective to provide the coarse grain necessary for the extreme high temperature creep resistance. Presently, the hot gas turbine experts understand the need of finding low cycle fatigue strength and creep strength. The preparation depends performing this evaluation. The tension- tension axial load controlled test is conducted at 1100 – 1400oF.

An improvement in LCF function with ASTM grain size up to 4-5% is crucial. After the vast thermochemical processing, the controlled practice is performed that controls the grain size around 3 – 6%. Nominal changes in alloy’s chemistry offer improved grain size and stress rupturing characteristics. The combination of alloy chemistry optimization and controlled processing offer significantly improved LCF performance of alloy 617 sheet with nominal or no change in creeping resistance characteristics in coarse grain material. An improved LCF service is also maintained at the high temperatures. Alloy 617 retains prolong metallurgical consistency and strength.

Alloy 617 is known for its supreme metallurgical stability and high strength. The alloy specimen are used in the solution annealed form before exposing it in the service media. The strengthening is achieved to carbide development and exposure temperature at 1200oF to 1400oF to the precipitation of gamma prime. Alloy 617 attains large level of creeping strength at high temperatures about 1800oF and above. The characteristics combined with outstanding resistance to oxidation and carburization offer alloy potential to introduce extended large stress at the elevated limits.

The creeping resistance of alloy 617 in the solution annealing form  upto 2000oF is evaluated. The rupture characteristics of solution annealed metal at the same limit are evaluated. The studies are performed on various forms such as bar, tube and sheet components. The design standards permitted design stress for alloy 617 forms is received.

Alloy 617 contains nickel, chromium and aluminum in significant magnitudes to offer good resistance to oxidation and carburization at the high temperatures. These constituents with molybdenum also offer strength to prevent corrosion in severely corrosive media.

The corrosion resistance characteristic of alloy 617 to cyclic oxidation at temperature around 2000oF is crucial. The study is conducted on thin alloy strip and consisting of exposure cycle to temperature for a small length of time after air quenching is done. The outcomes describe the potential of alloy to develop and retain the security oxide layer in the strict conditions of severe heat cycling. The specimen of thin alloy 617 sheet and plate was subjected to the testing temperature for 50 hour cycles to find the loss in magnitude of alloy after each cycle.

The corrosion resistance of Inconel alloy 617 offers significant strength, heat resistance and prevent continuous oxidation in the moisture at temperatures around 1832oC. The excellent resistance characteristics of alloy 617 to oxidation are received by the availability of aluminum and chromium elements. These elements result into the development of thin oxide layer that is developed upon heating at the elevated temperatures. The oxidized layer provides the complete diffusion media for the development of security chromium oxide layer on the metallic surface. It also offers spalling of the security layer developed during oxidation.


It retains wide resistance to aqueous corrosion to the vast range of corrosive conditions. Inconel alloy is widely used in the high temperature applications.