Seawater corrosion-Serious Challenge to marine industries

Different materials have long been used in marine environments such as in ships. Recently, new industries with new materials problems have developed.

Major industries are desalination and offshore oil and gas production. The needs for large volumes of cooling water by advanced industry usually resulted in settling of plants near ocean specifically in dry areas like Middle East.

It has increased the use of materials for dealing with seawater, specifically as marine condition is proven as the most corrosive natural environment, the designers usually face problems due to seawater corrosivity however many factors like marine fouling, flow velocity and aeration that have be considered in making the suitable technical and economical selection.

Corrosion types in Seawater

General

Seawater contains complex inorganic salts, dissolved gases, suspended solids, organic matter and organisms. Living organisms have an effect on corrosion behaviour. So, a layer of marine growth can decrease corrosion on carbon steel or cause crevice corrosion on stainless steels.

Oxygen concentration has a significant effect on corrosivity of seawater and this is decreases, as in desalination and oil-well injection units, the seawater or brine is nominally corrosive to most materials. It allows designers to use materials like stainless steels that in aerated seawater could experience serious pitting.

Alloys containing copper in high concentration have high corrosion and pitting resistance in low and medium velocity seawater and are not sensitive to pitting in stagnant conditions. At high velocities, they are attacked at high rates. The nickel-copper alloy is sensitive to pitting in stagnant conditions however becomes passive in running seawater and has high resistance even at 40m/sec.

Resistance to deaerated seawater by Monel bar is significant. This type of resistance is now of major interest with the thriving desalination industry that serves mainly in low oxygen brines and here copper base alloys are the definite choice for heat exchanger components.

Lab tests and service experience show that these deaerated environments are less corrosive than natural seawater to copper-base alloys, infact also with increase in temperature.

Copper base alloys are slightly affected by changes in oxygen concentration. So, it can said that copper-nickel alloys also offer good resistance to seawater with a low general corrosion rate and excellent resistance to pitting in static conditions, good resistance at moderate flow rates and quick corrosion at high flow rates. The nickel-copper alloys have a potential to pit in static conditions, however have outstanding resistance at moderate and high flow rates.

The austenitic stainless steels which are basically iron base alloys contain chromium and nickel are similar to Ni-Cu alloys, however they can receive pitting attack in static conditions , specifically crevice corrosion is higher. The corrosion resistance of stainless steels can be enhanced by the addition of molybdenum. Addition of nitrogen has also been found advantageous in enhancing resistance to crevice corrosion. Alloys that resist crevice corrosion also resist pitting. Hence the performance of alloys can be significantly improved. 

Sintered mesh Particle filtration and cleaning for industrial applications

Understanding the fundamental dynamics of particle separation as a fluid stream passes through a filter media and then the after cake removal is crucial to suitable selection of suitable media and to successful filter design and operation. From the standpoint of filtration processes, the two basic modes of filtration are dead-end and cross- flow. Additionally, the location of particle capture further complicated filter media design and selection for a specific application that are the particles basically captured within the depth of the media or on the media surface.

The types of particle filtration used in dead-end filtration are depth filtration and surface filtration. In case of depth filtration, the particles are held in the media while in surface filtration they are retained, at the surface where after a cake of particles is developed. These types should be considered to ensure suitable media design and choice for a specific industrial application.

Depth filtration in gas and liquid service is mainly used in applications where low particle levels should be separated, to secure downstream equipment, for product purification to meet health, safety and environment requirements. The particles penetrate in the media and are subsequently held within its multiple layer structure. The multiple layer structure prevents premature blocking of the media and increases capacity for particle holding and on-stream lifetime. As the particles held in the depth of the media, the filters are meant to be used once or cleaned off-line. This cleaning can be accomplished with solvents, ultrasonic vibration, pyrolysis, steam cleaning or water back flushing.

Surface filtration by sintered wire mesh in liquid applications mainly uses particle capture through straining mechanism where particles larger than the pore size of the filter media are separated at the upstream surface of the filter, their size prevents them from entering or passing through the pore openings. In gas service, particles are held on or near the filter surface through additional capture mechanisms, i.e. primarily impaction, interception and diffusion. For both liquid and gas service, after particles accumulate as a cake that increases in thickness as more particle laden fluid is forced on the filter media. The cake, with its potentially finer pore structure may aid in the separation of finer particles than can be received through its as filtration proceeds. 

As surface filters are not perfectly smooth or have perfectly uniform pore structure, depth filtration of finer particles may occur that will influence the filter life. So, selection of optimal media grade and knowledge of the particle size distribution particularly the finer particles, is important to achieve long filter service life.

Sintered mesh filters used in high particle loading applications discovered in both gas and liquid services are usually online back pulsed cleaned to increase filter life. The operative filtration mechanism becomes cake filtration as the media is particularly engineered to ensure surface filtration and the feasibility of cake particulate removal through pulse blowback cleaning. A particle cake is developed on the surface of the filter media that becomes the filtration layer and results into further pressure drop. 

Advanced woven mesh productions for challenging applications

Quality, knowledge and flexibility, these skills feature our design and manufacturing of stainless steel filter systems since the establishment of our organization in 1984. With more than 45 years of experience, we not only received competent technical expertise, however also developed a precise sense for the specific requirements of our customers.

With modern filtration technologies and wide lab equipment, we produce made to measure solutions. Every system is optimized for the customer working process. Our quality management system is accredited with ISO 9001 standard is implemented on all levels of our company to meet the highest demands.

Our flat organizational structures ensure perfect business communication. With our prolong experience and skills with diverse lines of business, we can act fast and reliable. As a manufacturer of Sintered mesh, we set the great standards on quality.

We offer specific mesh solutions for the following industrial domains:

·         Petrochemical and chemical industry

·         Polymer production and processing

·         Pharmaceuticals

·         Food and beverages

·         Hydraulics

·         Mining

·         Power production

With our premium manufacturing and outstanding filtration efficiency, our mesh filter elements offer numerous feasible fields of application and usage. Our mesh filter elements offer the excellent performance as possible. Every element is delivered with a guarantee of reliability.

Regeneration ability

Various practical chemical or mechanical cleaning cycles of a filter element is an essential sign of its quality of manufacturing. Our mesh elements for filters are widely made from corrosion resistant alloys. Considering the configuration of filter media and component geometry of pleated filters, we focus on high mechanical load rating and efficient cleaning. Additionally, the filter media is secured by an external tube. So, every mesh filter element is fit for the repeated cleaning and offers a longer life.

To ensure the highest feasible performance of mesh in process, every element is evaluated for long life and throughput. We stand for the aim to produce the mesh elements that meet the requested parameters. Filter screens can be produced in any size.

For our extensive knowledge in the area of manufacturing, we offer an unrivalled performance ratio.

Application examples

Food and beverages: Filtration of beer and wine, soft drinks, foods, superheated steam sterilization.

Chemical industry- Process liquids, gases, acids, catalyst recycling, high temperature process

Pharmaceutical industry: Pharmaceutical liquids, emulsions, dispersants and catalyst recycling.

Polymer: Polymerization, extrusion, finalizing yarns and films.

We can achieve the quantum leap in the field of high viscosity polymer melt filtration.

With our optimized design and considerably enhanced production techniques, we produce screens that attain a nominal pressure drop. It leads to a significant enhancement of throughout, as a special test.

Maximum dirt-retaining capacity

The filtration area of a filter disc extends from the very end of the outer dia to a few mm close to the hub’s inner dia and hence provides a maximum surface load.

Cost saving

We use the enhanced semi-hard-hub design for our mesh structures. 

Heat Resistant Superalloys for the leading industrial sectors

Heat resistant alloys are group of alloys used in the different industrial sectors-

Aerospace engine, stationary gas turbines, oil and gas and medical.

The characteristics that make them suitable materials are:

·         Retention of strength and hardness as high temperatures

·         Corrosion resistance

Heat resistant alloys are divided in three categories- nickel based, iron based and cobalt based alloys. The physical properties and machining behaviour of each varies significantly due to the chemical nature of the alloy and the precise metallurgical processing it receives during production. Whether the metal is annealed or aged is specifically effective on the after machining characteristics.

Nickel based alloys are commonly used and presently make about 50% of weight of advanced aircraft engines. Commonly used alloys in Heat engines are Inconel 718 wire, Inconel 625 and solution strengthened nickel alloys.

Iron based materials are developed from austenitic stainless steels. Some have low thermal expansion coefficient that make them suitable for shafts, rings and casings. But they lack in hot strength properties such as A286.

Cobalt based alloy show hot corrosion resistance at high temperature as compare to nickel based alloys. They are costlier and also more difficult to machine because of their extreme wearability. The application in turbines is limited to combustion parts in the hottest engine regions. Their main application is observed in surgical implants that use their inherent corrosion resistance.

With above wide range of materials in the generic name of heat resistant alloys, the machining behaviour widely varies even in the same class of alloys. Actually same material can have different machining recommendations.

Material processing condition

The form of heat treatment affects the hardness of the component and thus the wear mechanism. The development of the chip is a good sign of the hardness with hard materials it is easier to crack the chip.

Hardened materials have increased cutting temperatures and show a potential to notching of the cutting edge at the depth of cut. The combination of a low entering angle and a hard substrate with a heat barrier coating is needed. Softer materials machine in a similar way to the stainless steel family.

Insert grades with greater toughness and decreased hot hardness, resistance to high temperatures, are needed due to reduced cutting temperatures and increased chip hammering. The damage to areas outside the real cutting edge is caused by the chip breaking against the insert. Considering the size, shape and strength requirements of the component, different production methods for the empty material will be used. The production methods depends used depends on the machinability of the material and will alter the wear characteristics.

These raw material types directly affect the microstructure of an alloy and also its after machining behaviour.

Forged materials have a finer grain size as compared to in castings that enhances the strength and grain flow of the component. When machining forgings, decreasing the speed and increasing the feed normally gives the maximum feasible metal removal rate with good tool life.

The opposite rule is applied in castings and using low feeds ad higher speeds can be advantageous. Castings have poor machinability and tend to be most sensitive to notch wear and abrasive wear. They can be easily recognized due to their visibly mottled surface. 

Evaluation of Laminated Porous Metal sintered felt as catalyst support

A laminated porous metal fiber sintered felt acting as a catalyst support was used in a cylindrical methanol steam reforming microreactor for hydrogen generation.

Microreactor is widely used in diverse chemical reactions for its small size, high specific surface area and outstanding heat and mass transfer properties. Liquid hydrocarbon as fuel can be instantly transformed into hydrogen-rich gas in suitable catalytic reaction conditions. This post gives a feasible idea to solve the hydrogen source problem for fuel cell. The microreactor with porous materials used as catalyst support is featured by a reaction flow path and low pressure drop. The catalyst supports have three dimensional porous structure and large specific surface area, so the catalyst can be easily coated on the porous material to develop a stable catalyst structure.

Metal foams are developed by direct forming of metals comprising of three dimensional pore structure, high specific surface area and low density. Although the fabrication of metal foam requires the specialized equipment with high production cost. It prevents the widespread application of metal foams. The foams made from copper, Nickel and FeCrAl materials are widely used in different types of catalytic reaction processes.

Porous copper sintered fiber felt had a relatively uniform three dimensional interconnect structure, that was advantageous to the homogenous loading of the catalyst. Additionally it is very easy to find out that copper/zinc/aluminium/zirconium catalyst could be effectively loaded on the sintered fiber felt with 80% porosity by using two layer impregation method.

Catalyst support by sinteredfiber felt  with uniform porosity structure offered good performance. When the reaction temperature was up to 300oC, the methanol conversion was reduced, and hydrogen gas flow rate increased. The sintered fiber felt with 80% porosity showed a much better reaction performance of microreactor.

A performance comparison of fiber felt with uniform porosity structure and gradient porosity structure serving as catalyst support operated at different reaction temperatures. When the reactant was into sintered fiber felt with gradient porosity changing from 90% to 70%, the maximum methanol conversion and hydrogen gas flow rate was discovered at different reaction temperatures. When the reaction was performed at temperature up to 380oC, the methanol conversion and hydrogen gas flow rate could be above 98%. This result can be attributed to the gradient porosity structure that could increase the capillary diffusion to enhance the heat and mass transfer of gas reactants in the sintered fiber felt. Additionally the reactant diffusion rate could match with the reactant chemical rate in the sintered fiber felt featuring a gradient pore structure because of optimal catalyst distribution.

It can be easily concluded that a higher reaction performance can be received when the reactant is fed from high porosity to low porosity part for the sintered felt with a gradient porosity structure.

To increase the hydrogen production, the laminated sintered mesh fiber felt as the catalyst support was used in the cylindrical methanol steam reforming microreactor for hydrogen development. It is found that sintered fiber felt attained better reaction performance . 

Corrosion resistant alloys for use in oil and gas plants

Corrosion resistant alloys are important for offering prolong resistance to corrosion for various components used in oil and gas production processes. These components include downhole tubing and safety critical elements, wellhead, valves, pipelines, piping, heat exchangers and various other pieces of equipment in facilities. There are different corrosion resistant alloys to choose and they can be featured by their resistance to specific conditions.

Major environmental parameters influencing the corrosion characteristics of these alloys are:

·         Temperature

·         Magnitude of chloride ions

·         Partial pressure of Carbon dioxide

·         Partial pressure of H2S

·         Environment pH

·         Sulfur

Above factors influence

a.       Stability of the passive layer

b.      Ease of repassivation of created pits

c.       Dissolution rate of metal from pits

d.      The chance of stress corrosion cracking initiating and propagating

The selection of corrosion resistant alloys for development and transport of corrosive oil and gas can be a complicated procedure and if not done correctly can cause problems in application as well as misguidance about the performance of a CRA in a specific service condition.

There are several ways companies and people choose Corrosion resistant alloys for the required well and flowline conditions. With extensive research facilities start a test program that involves simulating the particular application environment. A group of alloys using the information is chosen that shows a possible range of alternatives. Instead testing alloys, it is more economical and less time consuming to test some alloys that are possibly eligible. This method easily takes 1 – 3 years to accomplish at a large cost.

Another method is to check the corrosion data that applies to the anticipated field conditions. It can help in eliminating those materials that do not perform well and hence shortlist the number of testing alloys.

Austenitic stainless steel 316L

It shows the resistance of AISI 316L to deaerated, non-H2S containing conditions. It is widely used in surface piping, linepipe, cladding etc. In the presence of oxygen, stainless steel 316 will develop pits if exposed to cold seawater. In H2S condition, the performance of this alloy is very sensitive to the presence of chloride ions. In chloride-free conditions, this steel gives reliable service in sour gas handling facilities, however pitting readily develops in presence of chloride ions. So you should evaluate completely for the specific application.

Alloy 825, 625 and C276

The increased resistance of Inconel 625 wire to corrosion in H2S with increasing temperature as well resistance to all concentrations of CO2 make it fit to use in oil and gas applications. These alloys are not much susceptible to chloride concentration except at very high chloride levels. Although this factor should be more explored.

A common component of gas streams that has a profound effect on alloys is elemental sulphur that is called as free sulphur. It causes pitting and catastrophic damage to alloys in specific conditions but Hastelloy C276 is the most resistance however it cannot prevent this kind of corrosion and damage.

Why thermal spray coating dominates other spray processes

Absolute customer focus is our priority. We are a provider of solutions to challenging welding applications. We ensure that our customers get the right materials, use them optimally and that the whole process parameters are followed for the best possible performance. We consider it as our responsibility to ensure that we deliver the value to our customers and offer the best feasible solutions. We also endeavor to develop new products, evaluate existing products and streamline processes to achieve the short turnaround times. We focus on technologically advanced industrial sectors and offer products that are geared to their special requirements.

We efforts to afford our customers the best feasible support and promote development in line with specific targets we have built our core competences in the joint welding, repair and maintenance, welding and soldering and brazing. We offer our customers the largest and most comprehensive products of filler materials.

Customers and distributed are supported by experienced welding engineers. In addition our aim is to be best in class motivates constant evolution through our complete dedication to research and development and ensures our customers are using the technically advanced welding products available today. Our product maintenance consists of innovative and tailored welding consumables from our own production facilities:

Flame Spraying

Flame spraying is a common thermal coating process. In powder flame spraying, the spray material, in powder form, is melted with an oxy-fuel gas flame, accelerated towards a component by the combustion gases and sprayed on the surface of the component.

The plastic powders can be processed by using spray guns particularly designed for those materials. Spray guns that commonly take the form of manual torches, specifically by using acetylene as a fuel gas because of its high flame temperature are selected for metallic alloys based on nickel, iron or cobalt. The powder particles that are partially melted by the flame, deform on impact with the surface of the component and are deposited there to develop a spray coating with a lamellar structure. The main application areas for thermal coatings are corrosion protection and wear protection.

Power flame spraying can be subdivided in cold and hot processes. In cold procedures, the powders are applied by the spray gun and spray coating is not subjected to any after thermal treatment.

Plasma Powder Surfacing

Plasma powder surfacing also called as plasma transferred arc process, is a thermal coating process. Unlike to the spraying process, this is a welding process and involves metallurgical bonding of the applied material to the base material.

Although if the parameters are suitably set, the extent to which it blends with the base material can be reduced to a minimum. It is used for surfacing of wear resistant and corrosion resistant coatings on to a base material. The process is featured by using two separately controllable electric arcs. One arc is pilot and the plasma nozzle. The grain sizes are chosen according to the system type.

Thermal spray wire coating

Besides of above coating processes, commonly used coating process is thermal spray wire coating that offers reliable coating. The scope of thermal spray wire is to repair the damaged components and increase component life. 

How to clean strainers for long life

Our strainers are designed for the continuous removal of entrained solids from liquids in pipeline systems. They are fit for applications that need constant flow, a key factor in plant operations. Our mesh strainers are available in various sizes and materials as per application requirement. They are used for straining cooling water from ponds, lakes or rivers, cooling towers, plan service water, boiler feed water, secondary effluent irrigation and municipal water intake for system protection.

The deciding factors are the extent of solids and the potential to handle the backwash discharge flow. They are significant investment in case of high loading or upset conditions.

The strainers also offer stress-free operations. Regular flow is provided even when the equipment is being backwashed, offering stable protection for pumps, valve, heat exchangers  and other functional systems. Rapid cleaning and servicing of manual strainers is expensive and is not properly done, serious disruptions to the whole piping system may occur. Our mesh strainers will considerably decrease the maintenance costs. They are fit replacements for simple or duplex strainers.

Characteristics

Our mesh strainers are made in accordance with ASME sections and codes.

They prevent any leakage so the strainer remains dry as well as clean in service without leakage of process media down the sides of the strainer.

Unitized modular assembly, the motor, gear reducer, cover and full internal operating mechanism lift off as a unit, making all components easily accessible. It widely simplifies maintenance and decreases costs.

A small part of system flow used during backwash.

Common Strainer mesh can be woven wire or perforated mesh.

Applications of Monel mesh screens are:

·         For coarse straining applications like raw water intakes from pond, streams, perforated elements offer good performance and at economical price.

·         In applications where pre-screening of the fluid is done however fine filtration of the fluids is required, the sintered mesh elements can be chosen.

·         In applications where the fluid to be strained contains fibrous materials, wedge screen elements will reduce the impact of the fibers to the screen.

Cleaning the strainer

·         Cleaning the strainer is performed by using pressure differential among line pressure and atmosphere. During the cleaning cycle, when the backwash valve is opened to atmosphere, a part of the strained fluid reverses flow back across the isolated part of element, lifts off the debris and removes it from the strainer.

·         Sticky or greasy debris are hard to backwash and may need longer backwash cycle durations. Sand, pipe scale backwash easily. The magnitude of debris released from the strainer can also cause a trouble. Make sure that the volume of suspended solids doesn’t increase from the value of 0.02%. If your process needs heavier loading, contact our engineers.

·         The magnitude of fluid needed to clean a straining element is based on the type and magnitude of debris. In normal conditions, around 5% of the line flow will be used for cleaning of straining element during cleaning process. 

Effect of heat processing on Inconel alloy 718 properties

Single step aging treatments are used to develop the mechanical properties in oil and gas applications. The annealing temperatures are often in the range 1850oF – 1950oF or 1210oC – 1265oC followed by one step age at 1200oF to 1450oF or 648oC to 988oC. It offers yield strengths of 130,000 – 140,000 psi. The strength can be receive by underaging near 1275oF or overaging near 1400oF. Considering the needs any of these heat treatments are used for a specific yield strength. The hardness reduces with increase in aging temperature however the yield strength reaches a peak value between 1200oF to 1400oF. Hence for excellent hardness, underaging may be suitable. For instance, grain boundary precipitation may affect hardness, as is shown by either the ductile or intergranular nature of fracture surfaces received in toughness tests.

Some applications demand the highest yields strength about HRC 40 hardness. Inconel 718 is supplied and configured in oil field applications for corrosive media. Using these extreme strength levels is unlike to the justification for the recent amendments made in NACE specification MR0175. User should understand that most of Inconel alloy 718s used in market are designed for high temperature services. They are heat processed to the standard double aging treatments. Reheat treatment of these alloys may not offer the necessary properties for oil and gas applications as the heat treatment history has an effect on the microstructure. For instance, grain boundary precipitates or second phases can retain in the grain boundaries to subsequently coarsen in future heat processing. So the oil and gas industry should consider the heat treatment history.

Inconel alloy 718 is used for oil and gas applications because of its excellent corrosion resistance. As downhole conditions are fully deaerated the chance of general corrosion or pitting attack in production environments is nominal. Inconel alloy 718 is useful in offering excellent resistance to carbon dioxide, hydrogen sulfide and acetic acid based conditions. Corrosion rates of below 1 mil per year occur in high temperatures. Just with acid, oxygen or elemental sulfur significantly corrodes Inconel alloy 718. So the pitting corrosion resistance is considered in the extremely severe conditions occurred in the industry. Various corrosion resistant alloys are used in most production conditions. Inconel 718 offers pitting corrosion resistance similar to duplex stainless steels.

Inconel 718 applications are not only limited to corrosion resistance. Both general corrosion resistance and pitting corrosion resistance properties of Inconel 718 wire are affected by heat processing. Increase in pitting temperatures show enhanced corrosion resistance. Heat processing up to 1350oF do not have a damaging effect on the pitting temperature in the Yellow Death Solution. Although heat processing at 1450oF affects the pitting corrosion resistance. The loss of pitting resistance can be added to precipitation of carbides and to the segregation of alloying composition during the precipitation hardening processing.