Corrosion resistance behavior of nickel super alloys in caustic solutions

Nickel based super alloys are widely used in the chemical plants in the targeted applications. For instance, applications of Hastelloywire grade B2 is in handling hot reducing acids as it offers nominal corrosion rates in this media. Commercial nickel grade Ni 200 is used to handle hot caustic solutions. Other grades of Hastelloy family such as C276 containing Ni, Cr and Mo are versatile and can be used in almost each condition, although their function in hot reducing acids would be lower than Nickel-Molybdenum alloys and in hot caustic it would have a higher corrosion rate as compare to Nickel 200. Unlike austenitic stainless steels, nickel alloys prevent stress corrosion cracking in hot chloride conditions. Although nickel alloys may experience stress corrosion cracking in conditions of hot caustic and dilute hydrofluoric acid conditions.

Caustic Conditions

Caustic conditions involve highly concentrated solutions of sodium hydroxide or caustic soda, potassium hydroxide or caustic potash and calcium hydroxide or caustic lime that may be seen in the industries of oil refineries, pulp and paper. It is likely that the cracking sensitivity of Nickel alloys is related to a dealloying phenomenon.

Cross section of 0.6mm thick sheet of C276 that was in use for ten months in a heat exchanger between water and 50% NaOH and traces of perchlorate at temperatures about 100oC. Cracking occurred in the dealloyed layer subjected to the caustic solution. The supreme performing material in caustic conditions is commercially pure Nickel. Large magnitudes of molybdenum in nickel alloys are detrimental and chromium seems to be an advantageous element in high concentrations. During dealloying chromium and molybdenum dissolve leaving behind a porous pure nickel layer even also the alloy is plated on the surface with pure nickel. In slow strain rate conditions, Hastelloy C276 was prone to transgranular cracking in 50% NaOH at 147oC. Mill annealed and aged for 24 hour at 677oC, Hastelloy C22 resist cracking when kept in 50% NaOH solution at 147oC for 720 hours.

Inconel 600 experiences stress corrosion cracking in hot caustic solutions. Lab SCC test was conducted by using cylindrical slow strain rate samples and spring loaded bend beam samples of grades 600 and 800 in deaerated 10% sodium hydroxide solution at 550oF. Stress corrosion racking was noticed in both alloys, although alloy 600 offered better resistant to cracking as compare to alloy 800, feasibly due to higher nickel concentration. It is found that resistance to stress corrosion cracking increases with magnitude of Nickel in tan alloy, however there was an extensive variation in results depending on the hydroxide concentration and temperature. 

Machining of Nickel base super alloys

Machining of Nickel alloys should be done carefully by using sharp tools with positive rake angles. Adequate feed rate and depth of cut are essential and tools should be controlled to prevent rubbing. Even in the supreme conditions, stress can occur that may cause distortion of the work. For the highest dimensional stability, it is recommended to rough the part to size, stress relieve it and then finish it to size. Stress relieving has nominal influence on shapes, however may influence mechanical properties.

Category of alloys

Group A: Alloys comprise of 95% or more nickel. They have average mechanical strength and high hardness. They are hardened by cold processing. The alloys are gummy in the annealed and hot processed condition and cold processed material is preferred for the supreme machinability and smooth finish.

Group B: Comprises of standard nickel-copper alloys. They have higher strength and nominally lower hardness than those in group A. They are only hardened by cold processing. Cold drawn and stress relieved material provides the supreme machinability and smooth finish.

Group C: Comprises of solid solution nickel-chromium-iron alloys that are similar to the austenitic stainless steels. They are only hardened by cold processing and are machined readily in the cold-drawn or cold-drawn and stress relieved condition. These alloys are Inconel 600 wire, 601, Incoloy 800, 825 and Monel K500.

Group D: Comprises mainly of the age hardenable alloys. Group D1 comprises of alloys in the unaged condition. Group D2 comprises of alloys of group D1 in the aged condition, and many other alloys in aged and unaged conditions.

Cutting Fluid

Any cutting fluid can be used in machining nickel alloys. They respond well to general sulfurized mineral oil, sulfur offer enhanced lubricity and anti-weld properties. If the temperature of oil and work material is sufficient during machining to result in brown sulfur staining of the material. The stain can be removed with a cleaning solution of the sodium cyanide. It should be performed before heat processing including welding due to exposure to high temperature the staining may cause intergranular surface corrosion. To prevent intergranular corrosion, the components should be immersed in cleaning solution for sufficiently long time to prevent the stain. High speed machining operations create high temperatures that preclude the use of a sulfurized oil because of sulfur embrittlement of carbide tools. 

Materials for Solid fuel oxide cell for performance at high temperatures

Solid fuel oxide cell serves at high temperature with fuel like hydrogen gas or reformed natural gas on the anode side and air on the cathode zone. Moisture could occur on both electrodes hence in contact with metallic interconnects. Sulfur contaminants present in the fuel gas contact with the metallic interconnects. Sulfur contaminants present in the fuel gas stream are also anticipated to occur, however upstream desulfurization has been applied to reduce the sulfur contamination level to sub ppm or ppb levels. Hence, besides oxidation, interconnect could also experience sulfidation, hot corrosion and carburization. 

Thermal stresses produced in the SOFC stack because of large temperature gradients across the current collector could also speed up the corrosion process due to premature cracking and spallation of the oxide layer. The availability of complex gaseous species in the fuel condition also cause establishment of grain boundary corrosion, internal oxidation and localized metal loss causing overall reduction of component service life. Sulfidation refers to vigorous corrosion resulting into combined effects of oxidation and reactions with sulfur that may present in the fuel gas streams.

The metallic interconnect is also needed to have sufficient strength to help maintain the structural integrity of the stack during Solid oxide fuel cell service at high temperatures and under thermal cycling. The high temperature alloys for interconnect should have thermal fatigue resistance against feasible structure fracture during thermal cycling, creep resistance to maintain the size stability at high service temperature and rupture resistance to withstand peak thermal stresses produced during SOFC operation. The above stated strengths can be more or less correlated to the yield strength. For stainless steels, the compositions with higher yield strength often possess high creep and fatigue strengths.

Many alloys except annealed low carbon steels do not have standard yield strains, the stress is referred as yield strength. When feasible, the yield strength from bar analyses at room temperature and high temperature was gathered.

Nickel based superalloys

Depending on the ratio of chromium and aluminum, nickel based super alloys are classified containing Cr and Al into these categories:

A NiO scale with Cr2O3 and Al2O3 internal oxides for low chromium and aluminum concentrations.

An Cr2O3 scale with Al2O3 internal oxides for high Cr above 15% however low Al below 3%. An exclusive alpha- Al2O3 scale for considerably high chromium above 15% and high aluminum above 3%. The presence of an inner layer drastically decreases the local oxygen activity at the metal –interface so that an enrichment of alumina particles occurs. Alumina layer develops below the Cr3O3 inner layer that significantly improves the oxidation resistance and also acts as an electrical insulating layer. So, an aluminum concentration of 3% was established to be critical maximum. But none of used nickel base alloys contained chromium content higher than 18% and aluminum higher than 3%. Recommended nickel superalloys Inconel bars for use are Inconel 625.

Stainless steels

Stainless steels are popular for their oxidation resistance. They contain the compositions to withstand all temperatures and hence do not strengthening by heat processing although a few grades need. Austenitic steels are featured by larger linear thermal expansion coefficients. 

Development of super alloys for use in challenging industries

Superalloys have the properties that make them special among other materials. Often comprising of various elements they act as a complex entity as compared to traditional materials here often a single element dominates.

Considering the power production, the industrialization that mark the transformation of agrarian society to industrial society has brought social and economic development. It introduces technological innovation that is basically focused on large scale metal extraction and energy production. The power production sector faces new challenges with increasing demand of energy generation.

High temperature materials are developed to sustain their properties at high temperature even also retain their integrity with nominal environmental impacts. Gas turbines such as land based or aero based demanded the development of high temperature materials. These materials should possess the following properties:

a.       Potential to withstand stress at a service temperature near their melting temperature

b.      A significant resistance to mechanical degradation over increased period of time

c.       Withstand extreme service conditions

These high temperature materials are designed to meet the demands of energy efficiency and also reduce the emission of greenhouse gases. Superalloys are widely used in the gas turbine sector thus, it is crucial to understand the function of the different components in a gas turbine. Applications of Inconel bars in different components of gas turbines are volume flow machines. Gas turbines are mainly of the following types: land based and aero/jet engine. Major components of gas turbines are:

Compressor: It includes alternating set of rotating airfoils- rotors and stationary airfoils. It sucks air from outside and compresses it into the combustion chamber to increase in pressure ratio as well as enthalpy.

Combustion chamber: Compressed air enters into combustion chamber to get mixed with fuel and ignition occurs.

Turbine: Hot gas enters the turbine and enlarges resulting into extraction of mechanical work needed to drive the compressor that is performed by a shaft that connects the turbine to compressor.

Exhaust: Gases after combustion find their way through the exhaust. Usually gas turbine emissions are carbon dioxide, carbon monoxide and NOx.

There are different types of gas turbines following their use. The design of a turbine is based on its type like land based gas turbine or jet engine. The basic difference is the variation in thermodynamic cycles and turbine entry temperature that is often stable for land based gas turbine due to fewer start-up or shut down cycles as compared to jet engines where the TET can vary during the full flight cycle.

The hot components in the combustor and turbine are critical considering the thermal and mechanical loads and material used. While designing a gas turbine, main focus is on the TET because of steep increase in TET due to direct association of efficiency of gas turbines and TET and pressure ratio that increases the demands of high temperature functional alloys.

There are different super alloys used for applications in the aircraft industry, chemical plants, power production and nuclear power plants. They are fabricated in cast and wrought forms. 

Mesh applications in Electrowinning and fuel cells

Wire mesh is a porous media that is used in electrowinning cells. It can be installed in new or existing electrowinning cells. They can be fabricated to fit the cathodes. They can be reused by nominally washing off the precious metal while on the cathode. Specialists in the high performance metals describe the benefits of stainless steel mesh:

a.       Extensive reduction in slag: Decreased slag loss, enhanced metal recovery and smaller melting furnace needed.

b.      Durable mesh offers long service life

c.       Flux costs decreased

d.      Furnace liner life increased

e.      Extensive labor savings: The cathode is easy to install and installed once over the life of the mesh and does not need drying or meltdown

f.        Size stability: Prevents sag even after prolong use

g.       Stable wire size: Offers outstanding solution flow over large surface areas

h.      Prevents wire in bottom of cell

i.       

      Clean handling – user performance – No steel wool type and doesn’t harm the environment

Saves on labor and longer lasting. Durable mesh cathode wire size permits better wash results and prevents loose wire in the bottom of the cell. Cleaner handling with operator performance. More stable dimension.

The recycling of used fuel is a major problem for the sustainable use of nuclear energy. Pyroprocessing technology has attracted wide interest in terms of recycling of used oxide fuels from nuclear power plants and using them as fuels for fast reactors. By the integrated unit processes of pyroprocessing, the used oxide fuel is electrolytic reduction and electrorefining.

In the oxide reduction process as a front end process of pyrprocessing, the used oxide fuel contained in a permeable cathode basket is electrochemically reduced to metal in molten Li2O-LiCl salt at 650oC.

Usually stainless steel mesh is used as permeable basket containing fuel in oxide reduction and electro-refining process. The reduction product received after the oxide reduction is used as an anode in the ER process by loading it in a mesh basket. The separation of the reduction product from the oxide reduction cathode basket is needed. Although, it is difficult to separate the reduction product received after the oxide reduction from the stainless steel wire mesh cathode basket at ambient temperature without damaging or deforming the basket as the residual salt in the basket is frozen. It should be noted that the surfaces of the cathode basket including the walls of the side and the bottom made of permeable stainless steel wire meshes, except the welds for suitable salt draining after the oxide reduction. It was developed by sintering multiple layers into a single piece.

At the center of the cathode basket, the electrical conductor was brought into contact with the simfuel at the center of the basket. The anode assembly comprises of platinum connected to electrical conductor and the metal shroud. An anode shroud comprised of a lower porous shroud made of the same material. 

Function of Nickel based super alloys in powerful acids media

However wide corrosion data is available for prolong functional stainless steels, although data still lacks for the high performance alloys. It includes Nickel based super alloys with relatively high molybdenum concentration of about 30% for the chemical industry and super alloys for the gas turbine plant.

The corrosion rates in different acids are noticed. As anticipated, the highest corrosion rate occurred in boiling 10% HCl acid, the most powerful reducing acid. Highest corrosion resistance by Hastelloy wiregrade B2 is seen in HCl acid. Unlikely, it showed minimum resistance in boiling 10% nitric acid. As already seen in other study, the concentration of molybdenum is a major factor in deciding the corrosion function in hydrochloric acid, whilst the concentration of chromium is decisive in nitric acid.

The extent of corrosion resistance of Hastelloy B2 is not severely affected by cold deformation and welding. For cold forming of about 50%, cold forming with after welding and cold forming subsequent to welding, the stable corrosion rate was below 0.25 mm/a.

Behavior of alloys with regards to types of local corrosion called pitting, crevice and stress corrosion cracking is investigated. The concentration of chromium and molybdenum concentration is crucial for the resistance to pitting and crevice corrosion. These types of corrosion occurred by chloride ions and the availability of oxidizing agents increases the effect. 10% FeCl3 solution is normally used to evaluate the pitting and crevice corrosion of stainless and chemically resistant steels. 

Although this test solution is not sufficiently extreme for nickel based alloys that usually contain large magnitudes of molybdenum. To evaluate the pitting corrosion of nickel based alloys, solution comprising of 7% sulfuric acid + 3% HCl + 1% FeCl3 + 1% CuCl2 was used to stimulate the conditions in scrubbers. In these test solutions and at the higher temperatures of 323K and 375K, Hastelloy C276 did not receive pitting or crevice corrosion due to high pitting index of about 70. It should be considered that at this stage in presence of crevices, crevice corrosion occurs before pitting. The materials active in crevice and pitting corrosion on the surface is prevented by cathodic protection by the anodic crevice region.

Incoloy 825 was also evaluated. The main objective to correctly determine the critical pitting corrosion potential using electrochemical methods because this potential allows a reliable comparison of the pitting corrosion behaviour of different material in a medium. The problem related with the early appearance of crevice corrosion on surface should be understood as it prevents the correct determination of the critical pitting corrosion potential. Besides, it is observed that the potentiodynamic quick test with a ramping rate of 1000mV/min that is usually used, does nt permit differentiation of the pitting corrosion specifically of the nickel based alloy.

The study aimed on potentiostatic holding analyses with the holding periods of 24 hours for every potential step of 100mV, measured against a saturated calomel electrode. The sample was evaluated for local corrosion after each holding period. For practical applications, there is a damage limit, irrespective of different types of corrosion. Hastelloy G is evaluated for 24 hours tests in five different solutions at 343K or 70oC. Nickel based alloys Inconel 625, Hastelloy C22 and Hastelloy C276 showed suitable performance. 

Commonly used Cleaning methods for filter elements

If you are considering the filter from HYDAC Process technology, choose the following factors:

·         Inline filters in single and duplex versions

·         Strainer filters in single and duplex types

·         High pressure filters in stainless steel

·         Automatic backflushing filters

·         Filter systems with combinations of wide range of components

There are main design principles that should be taken into consideration:

a.       Material resistance to the medium, for which variety of materials and solutions are chosen.

b.      Flow rate

c.       Pressure

d.      Pressure drop

e.      Temperature

f.        Connection sizes

g.       Filtration rating

h.      Economic factors

The core of every filter is the filter element. It provides solutions for the varied filtration applications, diverse filter materialsof sintered wire mesh and element models are chosen. Many filter materials can be cleaned, hence preventing the significant costs of purchase and storage.

Filtration Process

Nominal filtration rate: The filtration ratings are based on a factory standard filter test, that is conducted by introducing a large magnitude of dust, in the beginning of the filter test and after separating the contamination particles over 60 minutes. The test filter retains 90 to 95% of all particles larger than the specific filtration rating.

Absolute retention rate: The filtration ratings are found by the multi-pass test performed on the test rig. At nominal 99% of particles larger than the specific filtration rating should be helped and this up to the maximum permissible differential pressure across the filter element.

Cleaning Filter elements

The filter elements should be divided into cleanable and noncleanable filter materials. The selection of filter materials should be made as per economic, ecological and system specific factor. For process filtration, a cleanable filter material is often used.

The selection of cleaning methods is based basically on the type of contamination and filter material. For a better cleaning effect, specific processes can be combined together. It ensures that the cleaning parameters and selected solvents do not corrode the filter material.

Not all types of cleaning can be performed by the operator. Specialized firms can perform this by using cleaning elements. Common cleaning methods used are:

High pressure cleaning: Fit for cleaning coarse and loose particles manually and automatically with high pressure jets.

Ultrasound cleaning: Cleaning filter elements in ultrasound bath works by breaking down and flushing the contamination particles that is embedded in the element. The ultrasound bath is conducted in the range of 20 to 40 kHz using water and surfactant additive. Or specific solvents can be used.

Scalding in solvents: Scalding of the filter elements used where the elements are kept in a closed circuit, acting as a rinsing machine. The system operates with solvents at the elevated temperatures.

Scalding of the filter elements used where the elements are kept in a closed circuit, acting as a rinsing machine. The system operates with solvents at the elevated temperatures.

Pyrolysis: This cleaning method is based on the degradation of organic material that has accumulated on the element. The organic material is vaporized at high temperatures in a low oxygen condition. 

Corrosion performance of Incoloy 825 and Monel 400 in sulfuric acid

The corrosion resistance of precipitation hardening stainless steels is based on their structure and chemistry. Aging causes chromium carbide precipitation and reduces corrosion resistance. There are various alloys in this classification.

As end grain and side grain corrosion occurred to a larger extent on the bar stock than on the sheet samples, the corrosion rates on the bar samples were much higher than on the sheet samples.

Manganese and nitrogen have austenite stabilizers and in durations of short nickel supply, these elements have replaced a part of nickel in austenitic stainless steels. Normally, the corrosion resistance of SS 316, 216L is superior to SS 316, SS 316l. Although in dilute sulfuric acid, nickel is an essential alloying element and the corrosion resistance of SS 216 is lower to SS 316.

Besides to stabilizing austenite, manganese and nitrogen reinforce austenitic stainless steels and enhance resistance to abrasion and galling.

Incoloy 825 has outstanding resistance to sulfuric acid, particularly in the concentration range of 40%. It provides suitable performance in sulfuric solutions to 40% at atmospheric boiling temperature, to 78% concentration at 80oC and in all concentrations of the acid up to 65oC or 150oF. It is stabilized against carbide precipitation by inclusion of titanium so that it can be used in the as-welded condition.

Corrosion rate of Incoloy 825 is independent of specific heat of alloy or if the corrosion analyses were conducted in technical grade. The corrosion rate was based on the type of condenser used for the test equipment. Metal ions exist in acid from dissolution of the stainless steel act as oxidizing agents and lower the corrosion rate by a factor of about 10. This prevention was independent of the concentration of dissolved stainless steel in the range of 5 – 50 g/l of dissolved stainless steel. This influence was higher than that received by bubbling air in the solution, feasibily due to the limited solubility of oxygen in the boiling acid solution. It also shows that prevention could also be achieved by anodic protection.

Corrosion rates were about the same in liquid and vapour on samples of 1/4^th inch thick plate welded by the Tungsten insert-gas process.

Use Monel 400 bar for handling sulfuric acid is popular in reducing conditions. It provides an alternative to stainless steels and other alloys of similar behaviour when the sulfuric acid solutions are not firmly oxidizing. Alloy 400 attains low corrosion rates in air-free sulfuric acid up to 85% concentration at 30oC and about 60% concentration at 95oC. At the boiling temperature, Monel 400 has supreme resistance to 20% sulfuric acid concentrations are nominal.

While air saturation speeds up the corrosion of Monel 400 in various applications the corrosion rate will be approximate to the air-free rates as continuous air saturation is rare.

The rate at which air can be reused at a quite solution air interface is nominally compared to the rate at which oxygen can be eliminated by corrosion. As a result, in an open tank, a high level of aeration would occur only at the liquid line.

Decorative Wire Mesh Screens for Operational Structures

Heanjia is specialized in weaving and fabrication of comprehensive line of mesh cloth. Many mesh specifications are made using different metals like mild steel, stainless steel, aluminium, copper and super alloys. Our screens provide flexibility in design, uniform fit and minimum waste. Combining different mesh patterns, different metals, custom sizes and shapes allow a designer a wide range of flexibility.

Different metal surfaces of mesh screens create optical contrast with other materials. The screens it takes on the color of surroundings and reflects them. Used indoors or outdoors, mesh screens assist to merge design and environment.

Wire mesh terms

Mesh: Number of openings in a lineal inch measured from the center of one wire to point one inch distant.

Clear opening: Space between adjacent parallel wires.

Crimp: Corrugations in wires to allow locking in place when perpendicular to each other.

Double crimp: Wires pre-crimped before weaving, wires in every crimp

Slotted opening: Weave where the wires are organized to offer rectangular openings.

Material Properties

Sizes: The architectural wire meshes can be developed to required specifications. It allows in preventing many measurement restrictions. Standard applications without seams are possible with materials having own stability.

Resistance to corrosion or weathering: Choosing a stainless steel or aluminium, corrosion and weathering are virtually eliminated in any condition.

Nominal maintenance: Mesh needs no special maintenance after its configuration.

Sound absorption: Outstanding acoustic values are attained mesh is used for suspended ceilings and wall covers. Sound is obstructed through mesh structure.

Flexibility:  Different requirements can be met by using mesh. Air and light can pass through large opening weaves or can be limited with tighter and smaller holes.

Flammability: Mesh screens are not flammable hence they can be used in residential, commercial and domestic buildings without concerns for the fire.

Turn your place from drab to dramatic. Hide mechanicals in plain sight with bold shapes and colors. Make you place memorable. The possibilities are numerous. With unlimited shape options, a modern, aesthetic profile is added providing clear and pen sightlines.

The contoured screens provide an attractive contrast to the wing shaped roofline, that blend harmoniously with a wide expanse of glass, adding light, airy and attractive look. The horizontal screens have an added bonus of helping to reduce sun glare and heat gain like sunshade.

The screen profile adds a strong exterior providing great lift from clean and graceful lines. Although conventionally used on the rooftop as a visual barrier for mechanical system, the screen clothes look graceful. Made from extruded aluminium in different styles, they are long lasting, economical and attractive and needs nominal maintenance.

Using architectural decorative wire mesh screens, parking structures are made to not look like parking structures. The screens add one step further in the beauty of parking structures maintaining the ventilation and vision control properties. Heanjia has extensive experience in designing screening systems to meet specific parking requirements like free area, load and fire resistance. Use of durable decorative screens reduces the magnitude of material required as well as labor that adds up to an economical way to add texture and span. 

Why Nickel base superalloys are recommended for high stress applications

The nickel base super alloys used for jet engine structural components are subjected to high stresses and extreme environmental conditions. At the high temperatures in the jet engines, molten salts form, and thin films of salt coat the internal components. An extremely corrosive gas phase comprising of oxygen, SO2 and SO3. A combination of stress and corrosive environment results in decreased component life and eventual failure. Research on high temperature materil properties and environmental degradation is a crucial part of the technology base for engine life prediction and alloy development.

This study evaluates the effect of a molten salt condition on the high temperature creep properties of Inconel 718. Sustained-load creep tests were conducted at a temperature about 1472oF, in lab air at stress levels about 10 ksi – 30 ksi. High strength round Inconel bars are coated with 90% Na2SO3/ 10% NaCL salt mixture by spraying a heated sample with an aqueous salt solution.

Creep data is studied over a 72 hour test period. Tests conducted with salt coated samples were compared with tests  conducted with uncoated samples.

Degradation of high temperature creep properties of Inconel 718 due to the presence of molten salt. It is because of primarily to oxide penetration in metal that has been depleted of alloying elements and after cracking oxide-metal interfaces. Additionally, grain boundary sliding and void developed along the grain boundaries occurred in the alloy- depleted region of corrosion attack. The influence of stress in the corrosion process and the microstructural changes and mechanisms that occur during corrosion mechanical property interactions .

Static hot corrosion tests on samples were also conducted. Cylindrical pins were salt coated and analyzed for 72 hours at a temperature of 1652oF in lab air.

Nickel base super alloys are high temperature, heat resistant alloys retain high strength in the temperature range of 1400oF to 1000oF. These complex alloys have supreme oxidation and corrosion resistance and supreme resistance to creep and cracking at high temperatures. Nickel base super alloys are precipitation hardenable alloys. The major phase of these alloys is gamma phase and gamma prime phase and carbides. The phase is reinforced by solid solution elements like chromium, molybdenum, tungsten, cobalt, columbium, titanium and aluminium.

Iron in the austenitic matrix decreases the cost and enhanced workability and weldability, however it also significantly lowers the strength and oxidation resistance of alloy. The gamma prime phase can be precipitated in nickel-phase super alloys by precipitation hardening heat processing. Gamma prime precipitate in high nickel matrices is usually the intermetallic phase Ni3(Al,Ti). In presence of cobalt, it replaces nickel as (Ni,Co),(Al,Ti).

The gamma prime phase has outstanding long term stability and a high volume fraction of gamma prime provides the significant high temperature strength. As carbides are harder and more brittle than alloy matrix, their distribution along the grain boundaries will influence the high temperature strength, ductility and creep properties. If continuous chains of carbides extend along the grain boundaries, grain boundary sliding will be prevented. Wide stresses will develop during deformation and result to premature failure along the regular fracture paths at the carbide interfaces. 

Durable woven mesh filtration media for heavy duty applications

Replacement of sensitive, low-grade filter components is common place. The automatic self-cleaning filters are used in upstream of UV disinfection systems. High grade alloys are used in saline lake beds, shipboard reverse osmosis desalination, plant desalination, and designed water applications to minimize replacement components due to corrosion, to enhance sustainability and decrease maintenance and labor costs.

Applications

·         Petrochemical

·         HVAC

·         Metal works

·         Seawater

·         Water-car wash

·         Food processing

·         UF pre-filtration

·         Membrane safety

·         Drinking water

·         Wastewater

·         Recycled water and reuse

·         Desalination

·         Golf- turf

·         Agriculture

·         Greenhouse

·         Nursery

100% of particles removed above the degree of filtration, even one can also receive a significant particle reduction of 25 to 50% in 5 to 50 micron size due to the filter cake effect. The filter cake effect simply shows the fact that degree of filtration becomes finers as a screen accumulates dirt. It explains 25% reduction in particles at 5 to 15 range.

Advantages

·         Automatic backwash

·         No need to replace cartridges

·         Less system downtime

·         Less time used on regular maintenance

·         Nominal water used for backwash

·         Durable stainless steel design

·         Predictable solid filtration barrier

·         Does not need a minimum velocity

·         Removes solids, irrespective of density

·         Static filtration barrier

·         Higher flow rates

·         Robust MOC

Custom automatic self-cleaning water filter for shipboard reverse osmosis desalination, the custom fabricated sintered wire mesh filter screens are developed using duplex stainless steel to withstand corrosive seawater conditions.

Advanced automatic self-cleaning filters used in the reverse osmosis desalination system, conventional solid-liquid separation technologies in various aspects including decreased service costs. The level of pre-filtration allows continuous operation without any reduction in system performance or increase in service costs or maintenance.

Surface finishes and processes

·         Mill finishes

·         Mechanical smoothing

·         Sandblasting

·         Beadblasting

·         Electropolishing

·         Chemical vapour deposit

·         Hydrogen annealing

Second generation of duplex steels was developed with enhanced welding properties through nitrogen alloying. Common duplex grade is 2205 that has a nominal composition of 22% chromium, 5% Nickel, 3% Molybdenum and 0.16% Nitrogen. The steel is used in varied applications in a wide range of product forms. Various grades have become popular for their chromium and nickel concentrations. Alloy 2205 is a nitrogen improved duplex stainless steel grade. Nitrogen significantly improves the corrosion resistance properties that also include a yield strength that is more than double of conventional austenitic stainless steels particularly in the welded condition.

Earlier duplex grades had medium resistance to general corrosion and chloride stress corrosion cracking, however experienced a major loss of properties when used in the as-welded condition. Duplex 2205 stainless steel offers corrosion resistance in various conditions that is better than SS 304, 316 and 317 austenitic stainless steels. The duplex stainless steel is usually used in the form of welded pipe or tubular components and formed sheet product and welded sheet product in conditions where resistance to general corrosion and stress corrosion cracking is crucial. High strength develops opportunities for reduction in tube wall thickness and prevents damage. 

Welding Procedure of Nickel base superalloy Inconel 718

Inconel 718 is age hardenable because of the inclusion of columbium instead of titanium and aluminium as present in other nickel base age hardenable alloys. Studies have described that Inconel 718 is hardened basically by Ni3(Al-Ti-Cb), a columbium bearing gamma prime. It is special in this fact. Due to its particular age hardening properties, Inconel 718 is welded in the age hardened condition and in more highly restrained conditions than the other alloys. In regions up to minimum 0.5 inch it is not essential to use stress-relief treatments after welding. Some heat affected zone softening is occurred when welding the hardened alloy. The sluggish precipitation of submicroscopic age hardening columbium bearing compounds allows annealing and welding without extreme hardening during heating and cooling.

The usual joint preparation and cleaning needs are feasible to Inconel 718. Fusion welding often is done by the inert gas tungsten gas tungsten arc process. Good gas coverage on face and root of the joint is needed. Various filler metals are evaluated for Inconel 718. Inconel 718 and Hastelloy X are some of them. When the joints are restrained, Rene 41 is the recommended filler metal because of the higher melting point.

General electric has also evaluated the weldability of Inconel 718 by using a circular patch weld restraint test. The outcomes showed that the alloy could be welded and heat processed under restraint without cracking. The material was 0.063 inch thick was the filler metal used. Tensile and rupture properties were determined. The joint efficiencies received for tensile and 100 hour rupture life were very good, about 92% for tension tested and 88% for rupture tested welds. The welding procedures were not mentioned.

Welding of thick Inconel bar by a multipass welding technique and the manual inert gas tungsten arc process is evaluated. Sufficient weld joints were made up to 0.5 inch thick. Hastelloy R 235 filler metal provided the best tensile and rupture properties. It was noticed that argon gas in the torch and backup was not sufficient for thicknesses above 0.125 inch. Helium was recommended for the thicker material. Helium allowed better penetration and provided less porosity. Double U- joints were chosen to aid penetration. The weldability of Inconel 718 has made it an attractive alloy for use where age hardenable nickel base alloys are required.

Resistance Welding

 The standard methods of resistance welding are useful for the welding of nickel base precipitation hardening alloys. Low thermal conductivity and high resistivity of nickel base alloys as compared with steel should be taken into consideration when using the welding cycles. The complex heat treatments and high strength of nickel base alloys at high temperatures also influence the welding factors. Cleanliness cannot be over emphasized.

Normally these alloys can be welded using the same welding factors as are implemented for the non-heat treatable nickel alloys. Commonly more pressure and less current is needed. It is due to higher strength and supreme resistance of these alloys. Inadequate pressure results into cracking. Extensive current supply causes ejection of the molten metal. 

Materials fit for Heat exchanger applications

Vigorous pitting occurred in moderator heat exchanger tubed with Incoloy 800 in pickering nuclear production unit. Pitting occurred on the cooling water side of the tubes and perforation occurred within 24 months. It was known from corrosion evaluation at CRNL that Incoloy 800 was not sensitive to pitting in Lake Ontario water in isothermal conditions. Corrosion evaluation with heat transfer around the tube wall was conducted and it was found that extreme pitting may occur in deposits developed on the tubes in Ontario lake water. After testing conducted to find the pitting resistance of other eligible alloys : Incoloy 825, stainless steel 904l, Inconel 625, CuNi alloy 70/30 and titanium. Among these materials titanium did not received pitting corrosion in silt containing lake Ontario water. In absence of slit, so deposits, no pitting occurred on the tested alloys.

All alloys tested at room temperature in natural fresh waters did not show any sign of corrosion after exposure to 24 hours. These alloys that suffered some extent of corrosion at  45oC and 70oC are Cu-Ni alloy 70/30 and 90/10. It was invariably crevice corrosion. In availability of silt and chloride contamination, nickel based and copper based alloys experienced some corrosion at room temperature. The extent of corrosion found to increase with temperature, however this study is based on visual testing only.

Incoloy 800 was sensitive to crevice corrosion in room temperature chloride-contaminated river water, the corrosion rate was 0.1mm/a. No direct comparison of pitting rate can b made with service data for Incoloy 800, 0.5mm/a or the heat flow test results, as the isothermal tests at 70oC for contaminated Lake Ontario water were not conducted. Although, it is evident that chloride contamination seems to be important in these isothermal tests to induce pitting corrosion of Incoloy 800 and the nickel based alloys.

The comparisons of the admiralty brass results with in-service data are sufficient. In-service admiralty brass condenser tube pitting rates of 0.13 mm/a over a 10 years duration seems to be standard and this value is in good agreement with isothermal lab test results varying from 0.03 – 0.2 mm/a depending on temperature and water composition. Similarly Cu-Ni alloy 70/30 in operation in PNGS has show nominal corrosion, often an insignificant surface etching and dealloying that is consistent with results received. Cu-Ni alloy 70/30, nickel and brass increase the corrosion rate in heat transfer conditions.

Heat transfer tests

The results showed limited alloys suitable formoderator heat exchanger service Inconel 625 wire. Where no slit crevices were used, no pitting was found on the tested materials. In cases, the results were very reproducible within the duplicates, however insufficient sampling was conducted to offer statistically considerable predictability. The outcomes in these cases offer a clear guide to type the alloy that would be fit for corrosion free service as tubing in moderator heat exchangers.

Incoloy 800 is quite sensitive to pitting corrosion, Incoloy 825 less however still sensitive and stainless steel 904L subjected to occasional deep pitting. The pit shapes are feature of under deposit chloride corrosion.

PNGS has operated adequately with CuNi alloy 70/30 tubes for couple of years. The only sign of corrosion on the material was under very adherent deposits where redeposition of leached copper was found. The corrosion in this region was limited to nominal etching that had penetrated below 1 micro in six months.

In various cases, the noticed corrosion on alloys experiencing corrosion was related with dark green or black deposits that had developed at formed at the tube-silt deposit interface. Evaluations of the dark areas showed to enriched of calcium, silicon and chlorine and containing considerable magnitudes of chromium. 

Behavior of high functional Nickel alloys in oil and gas wells

In the recent years the new face of oil and gas exploration will be in deep wells, and specifically those in deepwater. As compare to shallow wells, deep wells normally need equipment made with high performance nickel base alloys. Wells are classified as sweet or sour. Sweet wells are mildly corrosive whilst sour wells are extremely corrosive and contain hydrogen sulfide, carbon dioxide, chlorides and free sulfur. Besides to different levels of corrosive media compounded by temperatures up to 260oCand pressures to 25000 psi and normally deep wells have higher temperatures and pressures.

Material choice is particularly critical for sour gas wells. The materials of choice should be corrosion resistant, economical, reliable and have the desired strength for the well conditions. These conditions become more vigorous material selection varies from carbon steels for sweet wells to duplex stainless steel to nickel base alloys like Incoloy 825 and Inconel 725.

Materials required to meet criteria for corrosion resistance and mechanical properties in application media need increased reliability throughout the life of well. Age hardened nickel based alloys and cold worked solid worked nickel base alloys offering various benefits like high strength, hardness, low magnetic permeability and outstanding corrosion resistance. The choice of material for specific set of well environments depends on wide selection factors such as:

• ·         Mechanical properties
• ·         General corrosion resistance
• ·         Pitting and crevice corrosion resistance
• ·         Chloride stress cracking resistance
• ·         Sulfide stress corrosion cracking resistance

The strength levels of age hardened materials are increasing in significance, specifically for offshore applications showing high pressure deep well reserves where weight factors can influence the economic feasibility of a project. Material choice for down hole and wellhead equipment including hangers, sub surface safety valves, pump and packers need age hardenable alloys to receive the resuired strength  in heavier cross section that cannot be reinforced by cold processing.

Nickel alloys used in oil well applications are Monel 400wire, Incoenl 718, Inconel X750 and 725. The age hardened alloys are used at different strength levels considering the applications. Incoloy 925 is used at 758 MPa minimum yield strength level. The minimum yield strength level for Inconel 718 is 827 Mps. Inconel 725 is used at 965 Mpa minimum yield strength level. The improved strength properties of Inconel 725 HS have been received by suitable thermal and mechanical processing.

Galvanic Compatibility

Galvanic corrosion occurs when different materials are placed in contact in a conductive fluid. The Inconel grades are usually noble materials. In galvanic compatibility, tests conducted in ambient temperature seawater for three months for corrosion mechanism. Inconel 725 and alloy 625 were found to be galvanically compatible. Coupling a large area of Inconel 725 to Monel K500, increased corrosion of the component of Monel K500.

General Pitting and Crevice Corrosion

Traditionally corrosion resistant alloys are graded first by their PREN and then by the equivalent cracking data produced in sour brine condition.

The critical pitting temperature for an alloy is found by subjecting samples in acidified 6% ferric chloride solutions. New unexposed test samples and fresh ferric chloride solution are used at every test temperature. The minimum critical pitting temperature for alloy is 40oC for various offshore applications. 

How choosing insect screens is a wise decision?

Insect screens are ideally developed for regular vents, even are also fit for other types of vent. We work closely with roof suppliers on greenhouse construction projects. The insect screen gauze is virtually invisible and prevents any light loss.

The systems cannot always be fully configured on all types of existing vent even light loss remains negligible. Screens are installed in a way so they are less vulnerable to wear and tear and more durable that traditional screens. To decrease the amount of cold air on the crop, we develop advanced screens.

Why should you choose Heanjia insect screen

·         Feel your home more: Open windows and doors to allow fresh air without the insects

·         Wide range of options and individual safety: Precision fit screens are made in large range of choices.

·         Eco-friendly and durable : Certified screens for protection against insects without the need of chemicals

·         Safe and user-friendly : Simple to use and easy to remove screens

·         Easy care and clean: Wear resistant mesh has insect screen supplier have long service life.

·         Advanced and proven effectiveness: Latest insect protection technology that has proved itself in millions of houses.

·         Timeless design: Unobtrusive and elegant screens are of fine quality

·         Individual service: You receive individual service and specialized installation

·         Outstanding production means value for your money

      

We manufacture high quality and eco-friendly insect screens. The screens are recognized as the leading name in made to measure insect protection. We manufacture precision-fit screens for your doors and windows to prevent unwelcome visitors.

When it is about insect protection, we do the best for you. People love bright and air are good for wellbeing. As you don’t want to entertain unpleasing species, the best way to keep pests like flies and mosquitoes at bay with an insect screen, made to your specific measurements. It gives you a good night sleep with open windows, fresh air and reassurance of understanding that you have made the best choice for your family’s health.

The insect screens are available in different options to suit your situation, from simple screens to multi layers screens and with different mesh types.

Our window screens are safe and easy to handle and can be easily installed without drilled. They can be used anywhere, robust and unobtrusive. The screens are durable and suitable for small spaces. They are easy and convenient to use. Insect protection is provided whenever required. 

Advanced design, durable functionality and fit for roof windows. The screens are robust, modern and user friendly. They are made from sturdy and ideal material for excellent versatility.

The mesh produced by Heanjia is made by patented technology. As compare to traditional insect screens, it offers decisive benefits such as more light transmittance and outstanding transparency. The screens are made in different formats and variants for different types of structures. They are secured, robust and durable. So contact us for your special window screen requirements.