Hastelloy C-276: Corrosion resistant and durable

Hastelloy C- 276 is a Nickel superalloy with some great functional and structural properties.

 Hastelloy C-276 is a versatile and corrosion free alloy. It is a Ni-Cr-Mo super alloy which offers strong resistance to acidic and alkali media which results in the prevention of pitting, corrosion and SCC. In addition to this, Hastelloy C-276 offers good resistance to hypochlorite, chlorine dioxide media and chloride gas (wet).

The most common forms of Hastelloy C-276 are wire, plates and bars.

Let us see a few qualities of Hastelloy C- 276, which are as follows:

•    Corrosion resistant        

•    A very versatile alloy

•    Does not erode in conditions of chemical processing

•    It is resistant to both hot organic and inorganic compounds

•    Causes prevention of attack by ferric

•    Prevents attack from acetic acids or cupric chlorides

•    Great resistance to strong acids

•    Withstand all sorts of corrosive substances

Different forms of Hastelloy C- 276:

•    Hastelloy C- 276 wire:

They diverse from 0.03 m.m to 12 m.m in diameter and is a common form of this alloy.

•    Hastelloy C- 276 plates:

These are available in different cut shapes and sizes

•    Hastelloy C- 276 bar:

There could be round, hexagon or square bars and so on.

As Hastelloy C- 276 is a very resistant and corrosion free alloy, we could put it to a number of uses as per the convenience.

Applications of Hastelloy C- 276:

•    It is used for chemical processing.

•    It is used for the purposes of geothermal and solar energy.

•    Used in bleach plants and digesters in paper plants.

•    Used for the treatment of industrial and municipal waste.

•    Even used for fans or covers and transportation pipes and scrubbers.

•    It is used for stack- gas heaters and evaporators.

•    Its apt for oil and gas or food processing system

So, as stated Hastelloy C- 276 has a number of diverse uses in different genres and areas because it is a very reliable alloy; another important fact about Hastelloy C- 276 is that it is easily weldable and could be fabricated in accordance with the requirements. Though there might be a few precautions which need to be taken like the prevention of excessive heat during welding. However, the carbon content is low in Hastelloy C-276 which reduces the carbide precipitation during welding which maintains the corrosion resistance quality of this alloy.

Hastelloy C- 276 is corrosion resistant:

This alloy possesses a great quality of being corrosion free and it resists any such trouble especially in warm and contaminated mineral acids, contaminated media ( both organic as well as inorganic), chlorine dioxide and hypochlorite, formic or strong acetic acids as well as marine solutions and so on.

So this states that Hastelloy C- 276 is sort of a reliable and durable alloy which could be put to a number of uses and is available in different shapes, sizes and forms. The properties of this alloy are strong enough as it is equipment for the chemical industry.

Inconel 600 wire- a perfect alloy for high temperatures

It is an alloy wire of nickel-chromium-iron alloy 600 which has superb performance at high temperatures and is resistant to oxidation and deterioration. The nickel present in this alloy wire makes it resistant to chloride ion stress corrosion fracturing. This alloy wire doesn’t require age-hardening treatment due to strengthening and hardening done by cold work processes. This alloy wire can be used on various platforms because of its flexibility to be manufactured in different shapes such as flat, square etc.

Inconel 600 wire is a heat tolerant alloy that can resist temperatures up to 700 degrees and therefore it is used in high temperature areas such as chemical industries, food industries, automobile industries, gas turbine industries, nuclear industries etc. This alloy wire is also used in baskets, heat treatment fixtures and trays due its reliability in high temperature areas.

Applications of Inconel 600 wire in aerospace, chemical and nuclear industries as they need to rely on their machinery because if machinery fails then there can be a great loss. This alloy wire is also suitable for places having high kinetic energy and pressure because it is corrosion and oxidation resistant. The stable and thick oxide layer is formed when Inconel 600 wire is heated and prevents further damage. This enables it to be strong in high temperature which is not the case with steel and aluminum which tend to have crystal vacancies. At high temperatures, strength is either given by precipitation strengthening or solid solution strengthening as per an alloy that is being used. In both cases, nickel combines with small parts of niobium to create a compound known as “Gamma prime” which doesn’t let the wire creep or slip at high temperature and this keeps on increasing.

Inconel 600 wire has following mechanical properties at room temperature:

Annealed

·        Ultimate Tensile Strength is 552 MPa min (80 KSI min)

·        Yield Strength is 0.2% offset, 241 a min (35 KSI min)

·        30% min Elongation, gauges are of length less than 0.010 inches

Properties: Tempered

·        Alloy 600 is cold rolled to achieve the temper properties as per specific requirements of customers.

Tempered: Hard

·        Ultimate Tensile Strength is 860 MPa min (125 KSI min)

·        Yield Strength is 0.2% offset, 620 MPa min (90 KSI min)

·        Elongation is 2% min, gauges are of length less than 0.010 inches

·        Hardness is Rc 30 min

Inconel 600 wire has various types of standard finishes such as

·        Grease (round wire): It is used for decorations as it has an ultra bright finish due to being drawn in heavy grease and this finish is only available for round wire.

·        Plated: A variety of plating options are there for Inconel 600 wire.

·        Extra clean: It is also known as “Bright annealed and cold rolled” or simply “bright annealed”.

·        Soap (round wire): This finish is for tempered products and is available only for round wire. Soap is not removed which acts as a lubricant for drawing and part forming operation of the customer.

Inconel 600 wire can be formed into various forms such as

·        Precision cutting

·        Cut to lengths

·        Continuous coils

High strength Material for turbine engine components

There are essential differences in the structure and service conditions of industrial and aero-gas turbines that prevent the direct use of standard alloys in the design of industrial engines. Different alloys are used. Blades for industrial gas turbines are often made from super alloys containing high chromium concentration that have been evaluated for service in vigorous conditions whilst those for aero gas engines are made from low carbon high strength alloys.

Blades made for industrial gas turbines are significantly larger than those for aero-engines. It results into significant differences in the process factors during directional solidification that could influence the structural and properties of the casting. In specific, slow heat flow through larger castings will influence the cooling rate and the larger mass of molten metal could cause issues in the containment by current moulding materials.

Industries demand longer lives from the aero-gas turbines that requires better corrosion resistance. Practical engine trials that are significant in the evaluation of aero engines, are impractical for industrial gas turbines, consequently suitable component design by using materials required for service in the required environment.

The industrial gas turbines are made from alloy that is directionally solidified by using lab and commercial observation. The operation of industrial gas turbines with specific emphasis on long term properties and on both the anisotropy and heterogeneity of the castings.

A major part of the turbine design is the selection or development of alloys suitable for application in the turbine. As long as candidate alloys are chosen, basic tests are performed on the alloys that are already selected such as nickel base super alloys Inconel 617. These alloys have very high strength and oxidation resistance at atmospheric pressure.

Initial oxidation tests are performed on the test materials to ensure that they can perform properly and can benefit the boiler research. Higher heating value also signifies the performance of alloys. Ferritic stainless steels comprising of 9 to 12% are presently used at steam temperatures up to 600oC. Most studies of the upper temperature limit are up to 650oC with high temperature strength as a limiting factor.

Austenitic stainless steels keep their strength at higher temperature as compare to ferritic alloys. Although vigorous thermal fatigue issues prevented their regular use at the original design temperatures and pressures. As thermal fatigue becomes more a problem in thicker component parts, austenitic alloys are still useful in the specific thinner components. They are used in boiler sections of advanced power stations.

Advancements in the application materials have contributed in a major way in the development of gas turbine engines with higher power ratings and efficiency levels. Enhancements in the design of gas turbine engines over the years have been possible due to the development f materials with improved performance. Gas turbines are widely used in aircraft engines and land based applications for power production.

The major use of Inconel wire made from alloy 617 is in the improvement of high temperature creep rupture strength without affecting oxidation and corrosion resistance. It is commonly used in manufacturing combustion system components for higher creep rupture strength.

Insight of Woven Mesh screens used in industrial services

Woven wire mesh is processed in various ways to develop the filter screen. Wire cloth and gauze are commonly use words to refer meshes made from fine wire grades. Bolting cloth refers to lightweight forms of square mesh clothes made from the finest wires.

A wide range of mesh screens are made by weaving wires separately. Two major categories of mesh screens are plan weave and zero aperture filter clothes.

In a woven mesh screen, each warp or weft wire bends where it passes over or beneath the wire of other type. Wire crimping occurs during the weaving process for fine wires, however the crimp has to be imposed on the wire above a specific thickness, before it is fed into the position. However this includes a stage to the weaving process, it has a significant advantage of retaining the crossing wire in a place.

Woven wire mesh screens are widely used for filtration for more than a century. They are made in diverse range of materials and specification. The mesh can be woven from virtually a metal with sufficient ductility to be drawn into wire form, specifically nickel-chrome steels, Monel mesh screens and other nickel base alloys. Nickel and nickel alloys are used for high temperature services. These alloys include Inconel, Hastelloy and Incoloy.

The least useful size of wire used is based on the alloy from which it is made, the mesh strength, the service temperature and corrosion level and abrasion probably occur during the service. So, the finer wire diameters in aluminium, copper etc are not usually used for other than ordinary applications. Stainless steel mesh are made from wires under 15 micro-m.

The plain dutch weave is a zero aperture weave. It is a plain weave with larger diameter wires similar to warp and straight, while the weft wires are crimped at each pass. The mesh developed from this weave extends from 340 micro-m to 15 micro-m in aperture size. The holes are small, and not straight through the mesh. The cloth is durable and compact with high strength. Two differences of this type of mesh occur, first that includes two warp wires rather one and that is usually selected for holes below 14 micro-m or when higher strength is needed. Other type includes finer warp and weft wires leading to better flow rates and higher tolerance.

In a reverse plain dutch weave, everything followed is similar, except the factor that thicker wire treats as weft. This type of mesh is substantially stronger and is even the most durable weave to produce filter mesh for commercial filtration applications. It features good flow and high dirt retaining capacity, for which it is widely used on the industrial scale.

With similar combination of warp and weft wires, two basic types of twilled dutch weave are developed. Using heavy warp wires in this weave allows the production of the finest grades of woven wire cloth, while also offering the benefit of smooth surface on both sides of the mesh. Dutch weave has less flow resistance and also rough surfaces on both sides.

Recommended super alloys for control on corrosion

It is well known that the major saving is great by using available and economic practices to enhance corrosion prevention and control. The designer should consider the initial material cost and also include maintenance cost, service life, downtime cost and replacement cost. This type of analysis helps better understand the cost-effectiveness of corrosion resistant materials.

Studies have stated that the overall cost of corrosion is surprising. The total cost of corrosion in U.S. is about $276 billion a year. About 25 to 305 of cost of corrosion is preventable and can controlled by using corrosion resistant materials and application of best anticorrosion technology from the design through maintenance. As becoming commercially available material, Nickel has become a crucial material in preventing corrosion. It is a major element in the coating and claddings applied to steels, copper-nickel and nickel-copper alloys as well as high performance nickel alloys. Nickel is not just a corrosion resistant element, it also has high tolerance for alloying that makes it possible to develop various high performance, special purpose alloys.

Nickel-Chromium alloys can be considered as the base for other alloys. Chromium offers resistance to oxidizing conditions and high temperature strength. It helps alloys resist stress corrosion cracking and corrosion in nitric acid, steam, and oxidizing gases. Alloys with high chromium contnent resist melting sulphates and vandates found in the fuel ash. Resistance to high temperature oxidation is also enhanced by alloying with aluminium in conjunction with high chromium. Nickel is used as a corrosion resistant material in food processing and in high temperature caustic and gaseous chlorine or chloride conditions.

Alloys offering significant performance in aqueous reducing acids, alloys for oxidizing chloride conditions and seawater- Inconel 625 and Hastelloy C276. Cobalt and other alloying element inclusions create materials for use in jet engines that combine high temperature strength with resistance to gaseous oxidation and sulfidation.

Other technologically important materials are high iron alloys that are made to conserve nickel and are usually considered as moderate in performance and cost between nickel alloys and stainless steels. Incoloy 800 is a general purpose alloy that has good high temperature strength and resistance to seam and oxidizing or carburizing gases. Addition of molybdenum and chromium similar to in Incoloy 825 and Hastelloy G enhances resistance to reducing acids and localized corrosion in chlorides.

Other essential group of alloys is nickel-copper alloys. Containing higher nickel, Monel alloys are the best for use in corrosive chemical conditions such as with hydrofluoric acid and vigorous marine conditions. Alloys with higher copper content such as copper-nickel alloys are commonly used in marine conditions for providing high fouling resistance.

Nickel base alloys offer outstanding resistance to corrosion in nitridingconditions and in chlorine or chloride gases. Corrosion in the chloride conditions at the high temperatures speeds up with the formation and volatization of chloride layers and high nickel alloys offer suitable performance because nickel develops least volatile chlorides. On the other hand, in sulfidiing conditions, high nickel alloys without chromium content can be corroded due to the development of low melting temperature Ni-Ni3Si2 eutectic.  Here Nickel-Chromium alloys are fit to use.

In demand grades of Nickel-Chromium-Iron alloys

Inconel 600

Inconel 600 offers outstanding mechanical properties and high strength and supreme workability.  It adequately performs up to 1200oF. Inconel 600 resists corrosion in fresh waters, including the highly corrosive natural waters comprising of free carbon dioxide, iron compounds and dissolved air. It remains free from stress corrosion cracking in fact in boiling magnesium chloride.

Alloy 600 offers supreme resistance to sulfuric acid in the oxidizing conditions than Nickel 200 or Monel 400. Inclusion of oxidizing salts to sulfuric acid passivates Inconel 600 that makes it fit for use with acid mine waters where Monel  400 cannot be used.

Inconel 600 is not susceptible to stress corrosion cracking in the chloride salts and has supreme resistance to the nonoxidizing halides. It offers outstanding resistance to dry halogens at high temperatures and is used successfully in the chlorination plants up to 1000oF. This alloy replaces Nickel 201 in specifically high temperature applications where sulfur offers enhanced resistance.

Incoloy 800

It is basically used for oxidation resistance and strength at high temperatures. Alloy 800 is used in high temperature equipments because it does not develop the embrittling delta phase after long exposures up to 1600oF. It offers high creep and rupture strengths that add in its functionality in the numerous applications.

At moderate temperatures the general corrosion resistance of Incoloy 800 is similar to other austenitic nickel-iron-chromium alloys. With increase in temperature, alloy 800 attains supreme corrosion resistance whilst other austenitic steel grades fail to perform.

Incoloy 800 offers supreme resistance to nitric acid up to 70% concentrations. Its Inconel bars resist corrosion in diverseoxidizing salts however except halide salts. It offers good resistance to organic acids like formic, acetic and propionic acids. Incoloy 800 is specifically fit for use in hot corrosive gases.

Incoloy 825

Alloy 825 is an enhanced version of Incoloy 800 containing higher nickel concentration that makes it resistant to chloride ion stress corrosion cracking. Inclusions of molybdenum and copper resists pitting in the reducing conditions for example sulfuric or phosphoric acid. Incoloy 825 prevents corrosion in pure sulfuric acid solutions up to 40% concentrations at boiling points. However it has limited applications in hydrochloric or hydrofluoric acids.

Chromium concentration in Incoloy 825 resists corrosion in diverse oxidizing conditions like nitrates, nitric acid solutions and oxidizing salts. It resists corrosion by stress cracking in neutral chloride conditions. For localized corrosion of stainless steel 300 series, Incoloy 825 is the best replacement. It also prevents corrosion in seawater.

Incoloy 800H

Incoloy 800H is a controlled carbon grade of alloy 800. Carbon concentration is maintained between 0.05% to 0.1% to offer superior high temperature creep and stress rupture properties. It is also used in diverse high temperature applications in the refining and heat processing plants.

Corrosion issues in Pressurized water reactor steam generators

Traditional domestic commercial nuclear power plants were made with austenitic stainless steel generators for their outstanding corrosion resistance, weldability and other properties. A pressurized water reactor steam generator started in 1967, is made of Inconel 600 due to its outstanding resistance to chloride stress corrosion cracking. Although since its use, wastage and intergranular  cracking of alloy 600 has occurred in plants involving the use of sodium phosphate or volatile water treatment.

Intergranular corrosion has been attributed to the presence of free caustic, there have also been cases of intergranular stress corrosion cracking on the tube used in the surface in relatively pure water. Cracking of highly stressed Inconel resulted into steam generator tube failures that was due to corrosion.

In the pressurized water reactor steam generators, the heat released from the primary coolant is used to develop steam that passes through the turbine generators to the condenser where the waste heat is removed. The steam generator tubes made from Inconel 600 and tube shells made from carbon steel, an Inconel 600 cladding to which the tubes are welded. To limit the tubes vibration, a series of carbon steel supports are used for the straight parts of the tubes and for the u tube design, a series of retstraints as antivibration bars are used for the curved part of the tubes.

Both design features and environmental factors have had a determined effect on the integrity of steam generator tubing. Contaminants in the secondary water that are allowed to focus due to their thermal and hydraulic factors that result in regions of low flow, have resulted into degradation of steam generator. The main causes of contaminants are corrosion of materials in the turbine, condenser and feedwater pipes and inleakage of the tertiary coolant in the condenser.

Secondary water chemistry:

Secondary water chemistry focuses on reducing the corrosion and prevent scale development on the high-heat flux surface of the tubing by the contaminants. Types of water chemistries like in PWR secondary water systems- all volatile treatment is increased and the oxygen scavenged by volatile additives like hydrazine or morpholine, a phosphate treatment, in which sodium phosphates are added to the coolant to raise the pH and react with scale developing contaminants to develop harmless soft phosphate precipitates, combined with inclusions of morpholine or sodium sulphite to scavenge oxygen that uses full-flow condensate demineralization to eradicate caustic forming contaminants and scale forming solids from the steam generator.

Phosphate Composition and wastage cracking

Sodium phosphate treatment is commonly used for steam generators that eliminate precipitated or suspended solids by blowdown. Different steam generators with Inconel 600 tubes recieved stress corrosion cracking. The cracking was featured to free caustic that can be developed when sodium ratio exceeds the preferred limit of 2.6.`They accumulate as sludge on the tube sheet and tube supports at the main part of the tube bundle where limited water supply and high heat flux occurs.

With the use of high corrosion resistant nickel alloys, the problems of corrosion are significantly minimized that ensure the considerably longer life of service equipments.