Search Results

The most effective means for preventing stress corrosion cracking SCC are proper design, reducing stress, removing critical environmental contributors (for example, hydroxides, chlorides, and oxygen), and avoiding stagnant areas and crevices in heat exchanger where chlorides and hydroxides might become concentrated.  Low alloy steel are less susceptible than high alloy steel, but they are subject to SCC in water containing chloride ions.  Nickel based alloys are not affected by chloride or hydroxide ions. Two types of SCC are of major concern to a nuclear facility.  Chloride Stress Corrosion Cracking (Stainless Steel)  The three conditions that must be present for chloride stress corrosion to occur are as follows. Chloride ions are present in the environment Dissolved oxygen is present in the environment Metal is under tensile stress Austenitic stainless steel is a non-magnetic alloy consisting of iron, chromium, and nickel, with a low carbon content. This alloy is highly corrosion resistant and has desirable mechanical properties.  One type of corrosion which can attack austenitic stainless steel  is  chloride  stress  corrosion. Chloride  stress  corrosion  is  a type  of intergranular corrosion. Chloride stress corrosion involves selective attack of the metal along grain boundaries. In the formation of the stainless steel, a chromium-rich carbide precipitates at the grain boundaries leaving these areas low in protective chromium, and thereby, susceptible to attack. It has been found that this is closely associated with certain heat treatment resulting from welding.  This can be minimized considerably by proper annealing processes. This form of corrosion is controlled by maintaining low chloride ion and oxygen content in the environment and the use of lowcarbon stainless steel. Environments containing dissolved oxygen and chloride ions can readily be created in auxiliary water systems.  Chloride ions can enter these systems via leaks in condenser or at other locations where auxiliary systems associated with the nuclear facility are cooled by unpurified cooling water. Dissolved oxygen can readily enter these systems with feed and makeup water. Thus, chloride stress corrosion cracking is of concern, and controls must be used to prevent its occurrence. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In normal mechanical and structural engineering design materials are selected primarily for their mechanical properties-corrosion is not an important criteria. The systems are generally protected against corrosion by surface coatings. Most machines are located indoors and are accessible for inspection and maintenance. The exceptions to this are machines used for construction and agriculture. These machines may well be used in corrosive environments but they are generally regularly maintained and some level of corrosion is acceptable. In process engineering corrosion is a very important design factor and material are selected primarily on their corrosion resistance properties. Surface coatings are often not considered because of the risk of contaminating the process stream. Metal Corrosion Properties – Non Chemiscal Environments Ratings 0 = Unsuitable, 1 = poor, 2 = Fair, 3 =Fair to Good, 4 good, 5 = good to excellent, 6= excellent. Fresh WaterSea WaterSteamSteam Cond’teAirMetalStatic/TurbStatic/TurbDryWetCity/IndustGrey Cast Iron- Plain or Low Alloy4/34/3443Ductile Iron (High Strength )4/44/2443Cast Iron Ni_Resist. (14% Ni, 7% Cu, 2% Cr bal Fe)5/55/5554Ductile Iron Ni_Resist. (24 % Ni, bal Fe)5/55/5554Mild Steel- Low Alloy steels4/34/2443Stainless Steel Ferritic (17% Cro)4/61/4653Stainless Steel Austenitic (18% Cro ,8% Ni )6/62/5654Stainless Steel Austenitic (18% Cro 12% Ni, 2.5% Mo )6/63/5666Stainless Steel Austenitic (20% Cro 29% Ni, 2.5% Mo,3.5% Cu )6/64/6666Hastelloy Alloy (55% Ni, 17% Mo,16% Cr, 6% Fe, 4% W)6/66/6666Inconel (78% ni,15% Cr, 7% Fe)6/64/6666Copper Nickel alloys (Up to 30% Ni)6/66/6565Monel 400 (66% Ni, 30% Cu, 4% Si)6/66/6665Nickel Commercial (99% Ni)3/56/6664Copper and Silicon Bronze6/54/1565Aluminium Brass6/64/5565Bronze (88% Cu,5% Sn,5% Ni,2% Zn)6/65/5565Aluminium Alloys4/50-5/4255Lead (Chemical or antimonial)6/55/3025Silver6/65/5566Titanium6/66/6566Zirconium6/66/6566

A significant proportion of the corrosion problems experienced relate to piping systems. Piping systems are used to transfer a wide range of fluids in a wide range of environments.A major lifetime costs for any industrialised plant is the cost of leaking fluids and the cost of repair of piping system to prevent and eliminate leaks. The main methods of preventing corrosion in piping systems are as follows; Selection of materials Corrosion resistant surface coating Location /Geometry of piping systems Cathodic protection methods Piping Materials There is an extremely wide range of pipeline materials available. These are selected on various criteria the two most important of which are suitability for service and cost. The suitability for service is determined primarily on the materials resistance to attack by the fluid being transferred and the external environment. The internal corrosion resistance is more important than the external resistance. It is easier to protect and monitor and repair the external surfaces. Also the environment generally provides a less arduous regime. Carbon Steel Material containing no principle alloying elements. Piping useable up to 430oC. Widely used and design requirements are detailed in all relevant codes.    Corrosion allowed for when necessary by applying corrosion allowances. Low Alloy Steel Material contains small percentages (less than 3%) of alloying elements such as chromium, nickel, molybdenum or vanadium.   The material has higher temperature range compared to carbon steel. A typical range of fluids with suitable pipeline materials is listed below:FluidPipe line materialProcess AirCarbon Steel,  Copper,  PlasticPotable WaterCarbon Steel,  Copper,  PlasticLow Pressure Sat.SteamCarbon Steel,  CopperHigh Pressure Dry SteamCarbon SteelDemineralised Water304 Stainless Steel,Seawater304/316 Stainless steel,  Aluminium Bronzes,  Copper nickel alloys,  Nickel alloys,   Superduplex,   6%(or7%)Mo St. steels,  Duplex steel,  TitaniumNitric Acid304 Stainless SteelNitrogen,Carbon Steel,ArgonCarbon Steel,Instrument AirCarbon Steel, Stainless Steel Steels specifically alloyed for corrosion resistance generally with chromium levels above 18%.   Steels resist oxidisation and specific corrosion of virtually all chemicals over a wide temperature range (-200oC to 900oC ).    The corrosion resistance is related to the grade selected.   Stainless steels are represented in all design codes and are convenient to use.   Stainless steel generally costs a least 4 times more than carbon steels. Cast Iron /Ductile Iron Two types of cast iron are used, grey cast iron and ductile iron.   The former includes graphite as flakes and the latter includes graphite in spherical or nodular form.   Cast iron piping has been widely used over the years for transferring a wide range of fluids as it is a low cost option with excellent corrosion resistance to a wide range of environments and fluids.   The grey cast irons are generally being superseded by the ductile iron options and the ductile iron piping systems are now being generally replaced by plastic piping.    The British Standard for Ductile piping and fittings is BS 4772. Lead Lead has been used in the past for a wide variety of domestic, civil and chemical piping.   It is suitable for most chemicals it is readily available and easily worked.   Although lead is expensive it is can be totally recovered and reused.  Lead has low strength properties and suffers from creep.   It can be alloyed to improve the strength and creep resistance.   Lead is no longer used for domestic piping for human health reasons.   Lead not widely used now because plastic piping provides improved properties at lower costs. Copper, Brass, Copper Nickel Alloys Piping and tubing made from these metals are used for many purposes throughout industry and also for building and domestic use and for ship pipework engineering because of the resistance of the brasses to sea water attack.   Copper and the associated metals generally conform to the relevant standards and are therefore conveniently produced and installed. Copper tubing is used where ease of fabrication is important. 70%/30% – Cu/Zn brass is a good general purpose material used for a variety of applications e.g. heat exchanger tubes, and closed circuit systems. Admiralty brass 70% /1%/29% – Cu/Sn/Zn has slighty improved resistance to polluted water compared to 70/30 brass. Brass with 76%/2%/0,04%- Cu/Al/As and Remainder Zn has good resistance to seawater attack and is used for perse process plants for transferring seawater under turbulent conditions to resist corrosion and impingement attack. Cupro Nickel Containing 31%/2% – Ni/Fe and ” Kunifer” containing 10.5%/1.7% – Ni/Fe are also used for transferring seawater and high good strength at elevated temperatures. Aluminium / Aluminium Alloys Aluminium piping is supplied in two grades to BS 1471: 1972 . Aluminium is used in many industries and provides excellentcorrosion resistance compared to steel for arduous fluid flow applications. Glass and Glass Lined piping Glass piping and glass lined piping provides ideal corrosion resistance to most fluids.  However this material is not coveniently installed and has various mechanical limitations.   It is used mainly for specialised application including laboratories. Titanium This material has only recently been available in quantity.   At this time it is relatively expensive compared to most other materials.   However if lifetime costing is consided it would likely be competitive as it has superb corrosion resistance especially for seawater transfer duties.   When installed in seawater systems titanium piping provides long continuous service compared to virtually all other metals. Elastomer/Plastic Lined Steel Piping This option provides a relatively low cost method of producing a highly corrosion resistant piping system with good mechanical properties.   However if system design, manufacture and installation is not good the lining system may fail resulting in high rates of local corrosion and expensive early repairs. Plastic Piping Systems Piping systems made from plastics including HDPE, ABS, PVC etc. are not subject to the same corrosion problems experienced by metal piping systems. More and more piping systems are being manufactured from plastics. However plastics have severely limited mechanical mechanical and thermal properties and are attacked by some chemicals. Surface Coating Options This area of design is discussed on separate page  Surface coatings Location/Geometry of piping systems The life of a piping system can be significantly improved if the system is correctly designed in respect to geometry and location. The piping should be designed to ensure that there are no low points which are not fully drained. The piping should also be located to minimise the risk of attack from the environment. If possible piping should be protected against environments hich include excessive precipitation in industrial or marine areas. Cathodic Protection Galvanic anode system Buried ferrous or cast iron piping, however well protected cannot be fully isolated from the moist soil and will therefore be at risk of corrosion. Corrosion will occur where the base metal comes into contact with the salts in the ground with the presence of water.   The base metal will behave as an anode.  Cathodic protection involves forcing the buried pipe to become a cathode relative to a buried electrode which will act as an anode.   This involves connecting the pipe using an insulated cable, to a buried bar made from magnesium or other metal with a similar electric potential relative to the pipe material.   As the buried electrode is electrically positive compared to the pipe this forces the pipe to be a cathode.   The buried bar acts as a sacrificial anode.   The pipe therefore acts as a cathode and is not corroded. The sacrificial anodes are buried about 3m from the pipe and are pitched at about 250m.   The anodes are generally engineered to have a life expectancy of upto ten years. Impressed Current System A similar level of protection can be provided by applying a generated DC voltage across the pipe and a buried buried electrode from cast iron or some similar low cost metal which can discharge a current to the soil.   The applied voltage forces the buried electrode to be positive relative to the pipe ensuring that it will behave as an anode Cathodic protection systems require specialised design involvement. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Bi-Metallic corrosion Galvanic Corrosion is the additional corrosion that occurs when dissimilar metals are in contact in the presence of an electrolyte. The corrosion of a metal, the anode, results from the positive current flowing from the anode to the less reactive (more noble) metal, the cathode, through the electrolyte.  This process is similar to the conventional corrosion of a single, uncoupled metal but generally proceeds at a higher rate depending on the difference in electrochemical reactivity of the anode and cathode metal. The requirements for bi-metallic corrosion are as follows: An electrolyte bridging the two metals Electrical contact between the two metals. A difference in potential between the metals to enable a significant galvanic current A sustained cathodic reaction on the more noble of the two metals. Electrolyte The degree of bi-metallic corrosion is affected by the electrolyte pH and conductivity. The intensity of the corrosion can increase with the conductivity of the electrolyte. Typical values of conductivity of various fluids are listed below; Distilled Water0.5-2 μS/cmStored Distilled Water2-4 μS/cmSupply Water50-1500 μS/cmSea Water50,000 μS/cmSat. Sodium Chloride250,000 μS/cmSulphuric Acidup to 800,000 μS/cm Bi-metallic corrosion is seldom a problem when the metals are immersed in pure water. Methods of Reducing Corrosion resulting from Galvanic Corrosion Where contact between dissimilar metals cannot be avoided the following steps should be considered Select metals that are close together in the galvanic series for the relevant environment Avoid relatively small areas of the less noble metal and large areas of the more noble metal Insulate the metals from each other Exclude electrolyte from around the bimetallic junction e.g painting Paint both metals where possible: if impractical paint the most noble metal Provide additional corrosion allowance on the less noble metal Apply compatible metal or sacrificial metal coatings If electrical insulation is used to minimise the risk, then test for the insulation quality as part of maintenance regime Galvanic Series Reference Oxidation Reduction  Galvanic corrosion is driven by the voltage potential between two electrically connected conductors (  To minimize this form of attack, materials in electrical contact, if required, should be selected so as to minimize their relative potential. The galvanic series of metals lists common materials in order of their electrical potential relative to a recognized standard.   Materials widely separated on this list will rapidly corrode in the presence of electolyte (e.g. Seawater) when in electrical contact, the anodic material suffering rapid material loss.   Materials close together on this list will suffer less damage due to corrosion. Anodic – Least Noble Magnesium Magnesium Alloys Zinc Cadmium Aluminum Mild Steel , Wrought Iron Cast Iron, Low Alloy High Strength Steel Chrome Iron (active) Stainless Steel, 430 Series (active) Stainless Steel 302, 303, 321, 347, 410,416, (Active) Ni – Resist Stainless Steel 316, 317, (Active) Aluminum Bronze Hastelloy C (active) Inconel 625 (active) Titanium (active) Lead – Tin Solders Lead Tin Inconel 600 (active) Nickel (active) Hastelloy B (active) Brasses Copper Manganese Bronze , Tin Bronze ( Nickel Silver Copper – Nickel Alloy 90-10 Copper – Nickel Alloy 80-20 s Stainless Steel 316, 430 Nickel, Aluminum, Bronze Monel Silver Solder Nickel (passive) 60 Ni- 15 Cr (passive) Inconel 600 (passive) 80 Ni- 20 Cr (passive) Chrome Iron (passive) Stainless Steel 302, 303, 304, 321, 347,(PASSIVE) Stainless Steel 316, 317,(PASSIVE) Incoloy 825nickel – Molybdeum – Chromium Iron Alloy (passive) Silver Titanium (pass.) Hastelloy C (passive) Inconel 625(pass.) Graphite Zirconium Gold Platinum Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Intergranular corrosion is sometimes also called “intercrystalline corrosion” or “interdendritic corrosion”. In the presence oftensile strength, cracking may occur along grain boundaries and this type of corrosion is frequently called “interranular stress corrosion cracking (IGSCC)” or simply “intergranular corrosion cracking”. Such precipitation can produce zones of reducedcorrosion resistance in the immediate vicinity. The microstructure of metals and alloys is made up of grains, separated by grain boundaries. Intergranular corrosion is localized attack along the grain boundaries, or immediately adjacent to grain boundaries, while the bulk of the grains remain largely unaffected. This form of corrosion is usually associated with chemical segregation effects (impurities have a tendency to be enriched at grain boundaries) or specific phases precipitated on the grain boundaries. The attack is usually related to the segregation of specific elements or the formation of a compound in the boundary. Corrosion then occurs by preferential attack on the grain-boundary phase, or in a zone adjacent to it that has lost an element necessary for adequate corrosion resistance – thus making the grain boundary zone anodic relative to the remainder of the surface. The attack usually progresses along a narrow path along the grain boundary and, in a severe case of grain-boundary corrosion, entire grains may be dislodged due to complete deterioration of their boundaries. In any case the mechanical properties of the structure will be seriously affected. A classic example is the sensitization of stainless steel or weld decay. Chromium-rich grain boundary precipitates lead to a local depletion of Cr immediately adjacent to these precipitates, leaving these areas vulnerable to corrosive attack in certain electrolytes. Reheating a welded component during multi-pass welding is a common cause of this problem. In austenitic stainless steel, titanium or niobium can react with carbon to form carbides in the heat affected zone (HAZ) causing a specific type of intergranular corrosion known as knife-line attack. These carbides build up next to the weld bead where they cannot diffuse due to rapid cooling of the weld metal. The problem of knife-line attack can be corrected by reheating the welded metal to allow diffusion to occur. Many aluminum base alloys are susceptible to intergranular corrosion on account of either phases anodic to aluminum being present along grain boundaries or due to depleted zones of copper adjacent to grain boundaries in copper-containing alloys.Alloys that have been extruded or otherwise worked heavily, with a microstructure of elongated, flattened grains, are particularly prone to this damage. “Intergranular” or ‘intercrystalline” means between grains or crystals. As the name suggests, this is a form of corrosive attack that progresses preferentially along interdendritic paths (the grain bourdaries). Positive identification of this type of corrosion usually requires microstructure examination under a microscopy although sometimes it is visually recognizable as in the case of weld decay. The photos above show the microstructure of a type 304 stainless steel. The figure on the left is the normalized microstructure and the one on the right is the “sensitized” structure and is susceptible to intergranular corrosion or intergranular stress corrosion cracking. What causes intergranular corrosion?  This type of attack results from local differences in composition, such as coring commonly encountered in alloy castings. Grain boundary precipitation, notably chromium carbides in stainless steels, is a well recognized and accepted mechanism of intergranular corrosion. The precipitation of chromium carbides consumed the alloying element – chromium from a narrow band along the grain boundary and this makes the zone anodic to the unaffected grains. The chromium depleted zone becomes the preferential path for corrosion attack or crack propagation if under tensile stress. Intermetallics segregation at grain boundaries in aluminum alloys also causes intergranular corrosion but with a different name – “exfoliation”. How to prevent intergranular corrosion?  Intergranular corrosion can be prevented through: Use low carbon (e.g. stainless steel 304, stainless steel 304L, stainless steel 316L) grade of stainless steel tube Use stabilized grades alloyed with titanium (for example type 321) or niobium (for example type 347). Titanium and niobium are strong carbide- formers. They react with the carbon to form the corresponding carbides thereby preventing chromium depletion. Use post-weld heat treatment. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

When austenitic stainless steel tubes are heated or cooled through the temperature range 425-900C (800-1650F), chromium tends to combine with carbon to form chromium carbides. The carbides precipitate preferen- tially at grain boundaries depleting chromium from the adjacent areas. This reduces the corrosion resistance of the chromium depleted areas, sensitizing the alloy to Intergranular Attack (IGA). The extent of carbide formation is dependent upon time at temperature and the carbon content of the alloy. Thus, exposure in the temperature range stated does not automatically mean that sensitization, or IGA will occur. Sensitization may also result from slow cooling from solution annealing temperatures, or stress relieving – after welding – in the 425 to 900C (800 to 1650F) temperature range. In welded fabrications, sensitization and IGA may occur in corrosive environments in a rather narrow band on either side of or on the side opposite the weld, known as the heat affected zone (HAZ). It is important to note that even if sensitization does occur, it is not of significant consequence unless the alloy is exposed to a corrosive environment. Sensitized stainless steel performs in a normal manner and safe manner in non-corrosive applications. Order of Resistance904L stainless steelHighest This table lists some of the common stainless steels as to general resistance to pitting or crevice corrosion in aqueous environments where corrosive conditions may exist.317L stainless steel 329 stainless steel 316/316L stainless steel 304/304L stainless steel 430 stainless steel 410 stainless steel 420 stainless steelLowest Methods of Minimizing Intergranular Attack – IGA 1) Solution anneal above 1040C (1900F) followed by a rapid quench. 2) Use type 347 stainless steel, a Cb stabilized grade, or 321 stainless steel, a Ti stabilized grade. 3) Use a low carbon, 0.03% max. carbon steel grade such as 304L stainless steel, 316L stainless steel, 317L stainless steel or 904L stainless steel. With today’s technology, carbon steel is economically reduced to very low residuals. The low carbon grades are the standard forwelded fabrication. ASTM A262 practice A to E are standard tests to determine susceptibility to IGA. Practice E, the Huey test, is widely used. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In our product programme we offer our customers two classes of Stainless Steel grades that have an excellent resistance to corrosion stainless steel. Austenitic-ferritic Duplex stainless steels are characterised by their excellent mechanical qualities, particularly their high stress corrosion cracking resistance. They are especially well-suited for maritime applications and in the chemical industry. Their excellent resistance to corrosion enables them to withstand a chloride medium, particularly under mechanical stress. This makes them superior to austenitic steel in many cases. The category of austenitic corrosion resistant stainless steel tube primarily includes materials with higher alloys (e.g. nickel, chrome and molybdenum). They are resistant to different types of corrosion caused by wet chemical influences, and are still able to maintain an austenitic face centred cubic matrix. This creates a range of highly versatile stainless steel. Although one of the main reasons why stainless steels are used is corrosion resistance, they do in fact suffer from certain types of corrosion in some environments and care must be taken to select a grade which will be suitable for the application.Corrosion can cause a variety of problems, depending on the applications: Perforation such as of tanks and pipes, which allows leakage of fluids or gases, Loss of strength where the cross section of structural members is reduced by corrosion, leading to a loss of strength of the structure and subsequent failure. Degradation of appearance, where corrosion products or pitting can detract from a decorative surface finish, Finally, corrosion can produce scale or rust which can contaminate the material being handled; this particularly applies in the case of food processing equipment. Corrosion of stainless steels can be categorised as one of:- ·         General Corrosion ·         Pitting Corrosion ·         Crevice Corrosion ·         Stress Corrosion Cracking ·         Sulphide Stress Corrosion Cracking ·         Intergranular Corrosion ·         Galvanic Corrosion ·         Contact Corrosion General Corrosion Corrosion whereby there is a general uniform removal of material, by dissolution, eg when stainless steel is used in chemical plant for containing strong acids. Design in this instance is based on published data to predict the life of the component. Published data list the removal of metal over a year. Tables of resistance to various chemicals are published by various organisations and a very large collection of charts, lists, recommendations and technical papers are available though stainless steel manufacturers and suppliers. Pitting Corrosion Under certain conditions, particularly involving high concentrations of chlorides (such as sodium chloride in sea water), moderately high temperatures and exacerbated by low pH (ie acidic conditions), very localised corrosion can occur leading to perforation of pipes and fittings etc.  This is not related to published corrosion data as it is an extremely localised and severe corrosion which can penetrate right through the cross section of the component. Grades high in chromium, and particularly molybdenum and nitrogen, are more resistant to pitting corrosion. Pitting Resistance Equivalent number (PRE) The Pitting Resistance Equivalent number (PRE) has been found to give a good indication of the pitting resistance of stainless steels. The PRE can be calculated as: PRE = %Cr + 3.3 x %Mo + 16 x %N One reason why pitting corrosion is so serious is that once a pit is initiated there is a strong tendency for it to continue to grow, even although the majority of the surrounding steel is still untouched. The tendency for a particular steel to be attacked by pitting corrosion can be evaluated in the laboratory. A number of standard tests have been devised, the most common of which is that given in ASTM G48. A graph can be drawn giving the temperature at which pitting corrosion is likely to occur, as shown in Figure 1. Figure 1. Temperature at which pitting corrosion is likely to occur This is based on a standard ferric chloride laboratory test, but does predict outcomes in many service conditions. Crevice Corrosion The corrosion resistance of a stainless steel is dependent on the presence of a protective oxide layer on its surface, but it is possible under certain conditions for this oxide layer to break down, for example in reducing acids, or in some types of combustion where the atmosphere is reducing.  Areas where the oxide layer can break down can also sometimes be the result of the way components are designed, for example under gaskets, in sharp re-entrant corners or associated with incomplete weld penetration or overlapping surfaces. These can all form crevices which can promote corrosion. To function as a corrosion site, a crevice has to be of sufficient width to permit entry of the corrodent, but sufficiently narrow to ensure that the corrodent remains stagnant. Accordingly crevice corrosion usually occurs in gaps a few micrometres wide, and is not found in grooves or slots in which circulation of the corrodent is possible. This problem can often be overcome by paying attention to the design of the component, in particular to avoiding formation of crevices or at least keeping them as open as possible. Crevice corrosion is a very similar mechanism to pitting corrosion; alloys resistant to one are generally resistant to both. Crevice corrosion can be viewed as a more severe form of pitting corrosion as it will occur at significantly lower temperatures than does pitting. Stress Corrosion Cracking (SCC) Under the combined effects of stress and certain corrosive environments stainless steels can be subject to this very rapid and severe form of corrosion. The stresses must be tensile and can result from loads applied in service, or stresses set up by the type of assembly e.g. interference fits of pins in holes, or from residual stresses resulting from the method of fabrication such as cold working. The most damaging environment is a solution of chlorides in water such as sea water, particularly at elevated temperatures. As a consequence stainless steels are limited in their application for holding hot waters (above about 50°C) containing even trace amounts of chlorides (more than a few parts per million).  This form of corrosion is only applicable to the austenitic group of steels and is related to the nickel content. Grade 316 is not significantly more resistant to SCC than is 304. The duplex stainless steels are much more resistant to SCC than are the austenitic grades, with grade 2205 being virtually immune at temperatures up to about 150°C, and the super duplex grades are more resistant again. The ferritic grades do not generally suffer from this problem at all. In some instances it has been found possible to improve resistance to SCC by applying a compressive stress to the component at risk; this can be done by shot peening the surface for instance. An other alternative is to ensure the product is free of tensile stresses by annealing as a final operation. These solutions to the problem have been successful in some cases, but need to be very carefully evaluated, as it may be very difficult to guarantee the absence of residual or applied tensile stresses. From a practical standpoint, Grade 304 may be adequate under certain conditions. For instance, Grade 304 is being used in water containing 100 – 300 parts per million (ppm) chlorides at moderate temperatures. Trying to establish limits can be risky because wet/dry conditions can concentrate chlorides and increase the probability of stress corrosion cracking. The chloride content of seawater is about 2% (20,000 ppm). Seawater above 50°C is encountered in applications such as heat exchangers for coastal power stations. Recently there have been a small number of instances of chloride stress corrosion failures at lower temperatures than previously thought possible. These have occurred in the warm, moist atmosphere above indoor chlorinated swimming pools where stainless steel (generally Grade 316) fixtures are often used to suspend items such as ventilation ducting. Temperatures as low as 30 to 40°C have been involved. There have also been failures due to stress corrosion at higher temperatures with chloride levels as low as 10 ppm. This very serious problem is not yet fully understood. Sulphide Stress Corrosion Cracking (SSC Of greatest importance to many users in the oil and gas industry is the material’s resistance to sulphide stress corrosion cracking. The mechanism of SSC has not been defined unambiguously but involves the conjoint action of chloride and hydrogen sulphide, requires the presence of a tensile stress and has a non-linear relationship with temperature. The three main factors are Stress Level, Environment and Temperature. Stress Level A threshold stress can sometimes can be identified for each material – environment combination. Some published data show a continuous fall of threshold stress with increasing H2S levels. To guard against SSC NACE specification MR0175 for sulphide environments limits the common austenitic grades to 22HRC maximum hardness. Environment The principal agents being chloride, hydrogen sulphide and pH. There is synergism between these effects, with an apparently inhibiting effect of sulphide at high H2S levels. Temperature With increasing temperature, the contribution of chloride increases but the effect of hydrogen decreases due to its increased mobility in the ferrite matrix. The net result is a maximum susceptibility in the region 60-100°C. A number of secondary factors have also been identified, including amount of ferrite, surface condition, presence of cold work and heat tint at welds. Intergranular Corrosion Intergranular corrosion is a form of relatively rapid and localised corrosion associated with a defective microstructure known as carbide precipitation. When austenitic steels have been exposed for a period of time in the range of approximately 425 to 850°C, or when the steel has been heated to higher temperatures and allowed to cool through that temperature range at a relatively slow rate (such as occurs after welding or air cooling after annealing), the chromium and carbon in the steel combine to form chromium carbide particles along the grain boundaries throughout the steel. Formation of these carbide particles in the grain boundaries depletes the surrounding metal of chromium and reduces its corrosion resistance, allowing the steel to corrode preferentially along the grain boundaries. Steel in this condition is said to be “sensitised”. It should be noted that carbide precipitation depends upon carbon content, temperature and time at temperature. The most critical temperature range is around 700°C, at which 0.06% carbon steels will precipitate carbides in about 2 minutes, whereas 0.02% carbon steels are effectively immune from this problem. It is possible to reclaim steel which suffers from carbide precipitation by heating it above 1000°C, followed by water quenching to retain the carbon and chromium in solution and so prevent the formation of carbides. Most structures which are welded or heated cannot be given this heat treatment and therefore special grades of steel have been designed to avoid this problem. These are the stabilised grades 321 (stabilised with titanium) and 347 (stabilised with niobium). Titanium and niobium each have much higher affinities for carbon than chromium and therefore titanium carbides, niobium carbides and tantalum carbides form instead of chromium carbides, leaving the chromium in solution and ensuring full corrosion resistance. Another method used to overcome intergranular corrosion is to use the extra low carbon grades such as Grades 316L and304L; these have extremely low carbon levels (generally less than 0.03%) and are therefore considerably more resistant to the precipitation of carbide. Many environments do not cause intergranular corrosion in sensitised austenitic stainless steels, for example, glacial acetic acid at room temperature, alkaline salt solution such as sodium carbonate, potable water and most inland bodies of fresh water. For such environments, it would not be necessary to be concerned about sensitisation. There is also generally no problem in light gauge steel since it usually cools very quickly following welding or other exposure to high temperatures. It is also the case that the presence of grain boundary carbides is not harmful to the high temperature strength of stainless steels. Grades which are specifically intended for these applications often intentionally have high carbon contents as this increases their high temperature strength and creep resistance. These are the “H” variants such as grades 304H, 316H, 321Hand 347H, and  also 310. All of these have carbon contents deliberately in the range in which precipitation will occur. Galvanic Corrosion Because corrosion is an electrochemical process involving the flow of electric current, corrosion can be generated by a galvanic effect which arises from the contact of dissimilar metals in an electrolyte (an electrolyte is an electrically conductive liquid).  In fact three conditions are required for galvanic corrosion to proceed; the two metals must be widely separated on the galvanic series (see Figure 2), they must be in electrical contact and their surfaces must be bridged by an electrically conducting fluid. Removal of any of these three conditions will prevent galvanic corrosion. Figure 2. Galvanic series for metals in flowing sea water. The obvious means of prevention is therefore to avoid mixed metal fabrications. Frequently this is not practical, but prevention can also be by removing the electrical contact – this can be achieved by the use of plastic or rubber washers or sleeves, or by ensuring the absence of the electrolyte such as by improvement to draining or by the use of protective hoods. This effect is also dependent upon the relative areas of the dissimilar metals. If the area of the less noble material (the anodic material, further towards the right in Figure 2) is large compared to that of the more noble (cathodic) the corrosive effect is greatly reduced, and may in fact become negligible. Conversely a large area of noble metal in contact with a small area of less noble will accelerate the galvanic corrosion rate. For example it is common practice to fasten aluminium sheets with stainless steel screws, but aluminium screws in a large area of stainless steel are likely to rapidly corrode. Contact Corrosion This combines elements of pitting, crevice and galvanic corrosion, and occurs where small particles of foreign matter, in particular carbon steel, are left on a stainless steel surface. The attack starts as a galvanic cell – the particle of foreign matter is anodic and hence likely to be quickly corroded away, but in severe cases a pit may also form in the stainless steel, and pitting corrosion can continue from this point. The most prevalent cause is debris from nearby grinding of carbon steel, or use of tools contaminated with carbon steel. For this reason some fabricators have dedicated stainless steel workshops where contact with carbon steel is totally avoided. All workshops and warehouses handling or storing stainless steel tubing must also be aware of this potential problem, and take precautions to prevent it. Protective plastic, wood or carpet strips can be used to prevent contact between stainless steel tube and carbon steel storage racks. Other handling equipment to be protected includes fork lift tynes and crane lifting fixtures. Clean fabric slings have often been found to be a useful alternative. Passivation and Pickling If stainless steel does become contaminated by carbon steel debris this can be removed by passivation with dilute nitric acid or pickling with a mix of hydrofluoric and nitric acids. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

The first major undersea stainless steel pipeline was built during World War II. Nicknamed Operation PLUTO (Pipe Line Under The Ocean), this stainless steel pipeline stretched 70 miles across the English Channel, connecting the Isle of Wight with the coast of France. The construction required 46 tons of building materials per mile. Operation PLUTO was intended to provide a safe way to transport fuel to Allied tankers. To keep the stainless steel pipeline secret, pumping stations along the route were disguised as garages and other inconspicuous buildings. Over sixty years later, the basic purpose of underwater stainless steel pipelines remains fuel transport. As natural gas deposits are discovered under the ocean, raw fuel must be transported to refining facilities. Stainless Steel Pipelines serve to fill this need. When the gas has been refined, separate stainless steel pipelines are used to load the liquefied natural gas to fuel tankers. Undersea stainless steel pipelines also provide an environmentally-friendly method of fuel transportation. Since the installation of stainless steel pipelines does not require a prolonged disturbance of the seabed, biologically fragile areas can be spared needless disruption. As technology has improved, polyethylene piping has begun to be used in underwater stainless steel pipelines. These pipes are generally coupled using screw anchors and saddle clamps. Steel buckles are also used in marine applications. Stainless steel pipe flanges are also common in undersea stainless steel pipelines, and indeed 316 stainless steel as used by manufacturers like ISO Stainless Steel is preferred by many for marine applications. That is because the 316 type of stainless steel is particularly resistant to corrosion. 316 stainless steel is composed of several types of metals added to the steel to protect it from corroding. A stunning example of undersea stainless steel pipeline technology at use is the recent Langeled Pipeline, which connects Norwegian North Sea oil fields with processing plants in Britain. It stretches an astonishing 746 miles to bridge the gap between the two countries, over underwater terrain so rough and rocky it required two robotic diggers working tirelessly to clear the space for it. At its deepest the stainless steel pipeline lays in 2953 feet of water (with water pressure of 1500+ psi!). The $3.3 billion stainless steel pipeline was laid piece by piece with pipe welded on two floating “pipe factories” – ships on which the pipes were secured before being placed on the ocean bottom. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Laying pipe on the seafloor can pose a number of challenges, especially if the water is deep. There are three main ways that subsea stainless steel pipe is laid — S-lay, J-lay and tow-in — and the pipelay vessel is integral to the success of the installation. ​ Buoyancy affects the pipelay process, both in positive and negative ways. In the water, the stainless steel pipe weighs less if it is filled with air, which puts less stress on the pipelay barge. But once in place on the sea bed, the stainless steel pipe requires a downward force to remain in place. This can be provided by the weight of the oil passing through the Stainless Steel Pipeline, but gas does not weigh enough to keep the stainless steel pipe from drifting across the seafloor. In shallow-water scenarios, concrete is poured over the stainless steel pipe to keep it in place, while in deepwater situations, the amount of insulation and the thickness required to ward of hydrostatic pressure is usually enough to keep the line in place. Tow-In Stainless Steel Pipeline Installation While jumpers are typically short enough to be installed in sections by ROVs, flowlines and Stainless Steel Pipelines are usually long enough to require a different type of installation, whether that is tow-in, S-lay or J-lay. Tow-in installation is just what it sounds like; here, the stainless steel pipe is suspended in the water via buoyancy modules, and one or two tug boats tow the stainless steel pipe into place. Once on location, the buoyancy modules are removed or flooded with water, and the stainless steel pipe floats to the seafloor. Surface Tow Stainless Steel Pipeline Installation There are four main forms of tow-in Stainless Steel Pipeline installation. The first, the surface tow involves towing the Stainless Steel Pipeline on top of the water. In this method, a tug tows the stainless steel pipe on top of the water, and buoyancy modules help to keep it on the water’s surface. Using less buoyancy modules than the surface tow, the mid-depth tow uses the forward speed of the tug boat to keep the Stainless Steel Pipeline at a submerged level. Once the forward motion has stopped, the Stainless Steel Pipeline settles to the seafloor. Off-bottom tow uses buoyancy modules and chains for added weight, working against each other to keep the stainless steel pipe just above the sea bed. When on location, the buoyancy modules are removed, and the stainless steel pipe settles to the seafloor. Lastly, the bottom tow drags the stainless steel pipe along the sea bed, using no buoyancy modules. Only performed in shallow-water installations, the sea floor must be soft and flat for this type of installation. S-Lay Stainless Steel Pipeline Installation When performing S-lay Stainless Steel Pipeline installation, pipe is eased off the stern of the vessel as the boat moves forward. the stainless steel pipe curves downward from the stern through the water until it reaches the “touchdown point,” or its final destination on the seafloor. As more pipe is welded in the line and eased off the boat, the stainless steel pipe forms the shape of an “S” in the water. S-Lay Stainless Steel Pipeline Installation Stingers, measuring up to 300 feet (91 meters) long, extend from the stern to support the stainless steel pipe as it is moved into the water, as well as control the curvature of the installation. Some pipelay barges have adjustable stingers, which can be shortened or lengthened according to the water depth. Pipe being lowered into the water via a stinger for S-lay installation Proper tension is integral during the S-lay process, which is maintained via tensioning rollers and a controlled forward thrust, keeping the stainless steel pipe from buckling. S-lay can be performed in waters up to 6,500 feet (1,981 meters) deep, and as many as 4 miles (6 kilometers) a day of pipe can be installed in this manner. J-Lay Stainless Steel Pipeline Installation Overcoming some of the obstacles of S-lay installation, J-lay Stainless Steel Pipeline installation puts less stress on the Stainless Steel Pipeline by inserting the Stainless Steel Pipeline in an almost vertical position. Here, stainless steel pipe is lifted via a tall tower on the boat, and inserted into the sea. Unlike the double curvature obtained in S-lay, the stainless steel pipe only curves once in J-lay installation, taking on the shape of a “J” under the water. J-Lay Stainless Steel Pipeline Installation The reduced stress on the stainless steel pipe allows J-lay to work in deeper water depths. Additionally, the J-lay Stainless Steel Pipeline can withstand more motion and underwater currents than stainless steel pipe being installed in the S-lay fashion. J-Lay Pipelay Vessel S7000 Types Of Pipelay Vessels There are three main types of pipelay vessels. There are J-lay and S-lay barges that include a welding station and lifting crane on board. The 40- or 80-foot (12- or 24-meter) pipe sections are welded away from wind and water, in an enclosed environment. On these types of vessels, the stainless steel pipe is laid one section at a time, in an assembly-line method. On the other hand, reel barges contain a vertical or horizontal reel that the stainless steel pipe is wrapped around. Reel barges are able to install both smaller diameter pipe and flexible pipe. Horizontal reel barges perform S-lay installation, while vertical reel barges can perform both S-lay and J-lay Stainless Steel Pipeline installation. Vertical Reel Barge When using reel barges, the welding together of stainless steel pipe sections is done onshore, reducing installation costs. Reeled pipe is lifted from the dock to the vessel, and the stainless steel pipe is simply rolled out as installation is performed. Once all of the stainless steel pipe on the reel has been installed, the vessel either returns to shore for another, or some reel barges are outfitted with cranes that can lift a new reel from a transport vessel and return the spent reel, which saves time and money. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Carbon steel suffer from ‘general’ corrosion, where large areas of the surface are affected. Stainless steel tubes in the passive state are normally protected against this form of attack, however, localised forms of attack can occur and result in corrosionproblems. The assessment of corrosion resistance in any particular environment, therefore, usually involves a consideration of specificcorrosion mechanisms. These mechanisms are principally: Crevice corrosion Pitting corrosion Intergranular corrosion (or intercrystalline)(IC) Stress corrosion cracking (SCC) Bimetallic (galvanic) corrosion Other related mechanism can also occur, which include: Erosion – corrosion Corrosion fatigue Localised corrosion is often associated with chloride ions in aqueous environments. Acidic conditions (low PH) and increases in temperature all contribute to localised mechanisms of crevice corrosion and pitting corrosion. The addition of tensile strength, whether applied by loading or from residual stress, provides the conditions for stress corrosion cracking (SCC). These mechanisms are all associated with a localised breakdown of the passive layer. A good supply of oxygen to all surfaceof the steel is essential to maintaining the passive layer but higher levels of chromium, nickel, molybdenum & nitrogen all help in their inpidual ways to prevent these forms of attack. Resistance to localised forms of corrosion As a general rule increased corrosion resistance can be expected by moving through the grades: 1.4512 to 1.4016409 to 430increasing chromium from 11 to 17%1.4301304adding nickel which aids the reformation of the passive layer if it is disturbed1.4401316adding molybdenum reduces the effectiveness of chloride ions in locally breaking down the passive layer1.4539 and 1.4547904L and 6% molybdenum gradesfurther increases in chromium, nickel and molybdenum result in overall improved localised corrosion resistance Duplex stainless steel grade such as 2205 (1.4462/S31803) are specifically designed to combat SCC by ‘balancing’ the structure to increase its strength, but additionally molybdenum and nitrogen enhance the pitting resistance, which in turn has the additional benefit in improving their SCC resistance. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

One of the first major subsea stainless steel pipeline was built between Great Britain’s Isle of Wight and the coast of France during World War II and since then, their use has expanded exponentially. Today, undersea stainless steel pipes are mostly used to move oil and gas. Companies mine both from the ocean floor and the stainless steel pipes are used to bring these fossil fuels ashore. After oil or gas has been refined, different stainless steel pipelines are used to move oil, or the liquefied natural gas, to fuel tankers. One of the most impressive examples of a subsea stainless steel pipeline is the Langeled Pipeline, which connects the North Sea oil fields near Norway to processing plants in the United Kingdom, stretching nearly 750 miles between the two countries. The stainless steel pipeline passes over rough underwater terrain and at its deepest point, it sits underneath nearly 3000 feet of water with a pressure of over 1500 pounds per square inch. Installation of Subsea stainless steel Pipes The $3.3 billion Langeled Pipeline was laid with the help of two floating “pipe factories,” or ships where the stainless steel pipes were welded together before being placed on the bottom of the North Sea. However, before that or any other undersea stainless steel pipeline can be laid, the seabed must be carefully surveyed for any sunken ships, sensitive reefs or other objects which may be along the route. If an obstacle is along the route, it is either moved or bypassed. Surveyors also determine if any sections of pipe should be backfilled or buried. Tow-in Installation In this technique, sections of stainless steel pipeline are attached to buoys and a tugboat drags the entire setup out to sea. Once the boat arrives at its destination, the buoys are either removed or flooded and the pipe is allowed to sink to the seabed. This technique is called surface tow and there are three variations to it: mid-depth tow, off-bottom tow and bottom tow. Mid-depth tow involves using the speed of the tugboat to keep the dragging pipe sections from banging along the ocean floor. Off-bottom tow uses chains to weigh the buoyed stainless steel pipe down into the water. After the tugboat arrives at its destination, the buoys are removed. Bottom-tow involves dragging sections of stainless steel pipe along the seafloor and is only used for shallow installations. S-lay Installation After the survey is complete, a small convoy of ships is sent out to lay pipe. Small barges supply floating “pipe factories” with sections of stainless steel pipe while a lead ship watches the seabed. Stainless Steel Pipes from the barges are unloaded into storage sites on the decks of the stainless steel pipe factory ships. The factory ships typically have enough stainless steel pipe segments for 12 hours of work. Aboard the stainless steel pipe factories, segments of stainless steel pipe are welded together and each joint is then checked for defects using ultrasound. Next, all the joints receive an anticorrosion coating. A custom-built conveyor then moves the weldedstainless steel pipes toward a special boom called a ‘stinger’ that juts into the water at an angle. Stainless Steel Pipes are then gradually lowered onto the seabed over the stinger. J-Lay Installation J-Lay installation is similar to S-Lay. However, instead of letting the stainless steel pipes pass over the stinger, which makes an ‘S’-shape, J-Lay involves angling the stainless steel pipe being welded off the deck of the factory ship and letting it ease into the water at a more vertical angle – forming a ‘J’-shape. Lifting the stainless steel pipe at an angle reduces the stress on the stainless steel pipeline during the manufacturing process. This method also allows for work at depths deeper than can be achieved with the S-Lay process. Attaching the Pipeline The entire process of laying subsea gas pipelines generally begins not on the shore, but in the sea. Gas pipelines incorporate quite a large number of sections all constructed at different times from several vessels, and then they are all linked to each other later. Gas pipelines must be able to endure pressures in various sections and because of this, pipes with several thicknesses are used. Upon the completion of the initial subsea portion of the line, stainless steel pipes are pulled up shore with a special winch placed on solid ground. The pipeline is then linked with its land-based section. Stainless Steel Pipe builders must also conduct hydro-testing of the stainless steel pipeline. To do this, the stainless steel pipeline is loaded with water under mandatory strain and left for a while to detect possible defects. The condition of gas pipelines are meticulously monitored after commissioning as well. Special electronics for in-pipe inspection are also used to monitor pipelines. Corrosion Marine-grade stainless steel, or 316 stainless steel, is one of the most popular alloys for subsea stainless steel pipes and it has been known to corrode at the bottom of the ocean. There are two kinds of corrosion seen in subsea piping: pitting and crevice. Pitting is easily recognizable and can be caused by any number of factors. Crevice corrosion is much harder to identify however. Pitting Pitting corrosion begins when the chromium-rich film on 316 breaks down in a high-chloride environment. The greater the chloride quantity and the higher the temperature, the higher chance the film will break down. Once the film is permeated, an electrochemical cell is set up. Iron goes into solution in the more anodic base of the pit, it then spreads in the direction of the top and oxidizes to produce iron oxide. The concentration of the iron-chloride solution rises as the pit deepens, which results in an accelerated rate of pitting, perforation of tubing walls and leakages. Pitting can go deep into the tubing walls, developing into a situation where tubing could be compromised. Crevices Crevices can be found between piping and pipe supports, between neighboring pipes and below deposits that may build up onstainless steel pipe surfaces. Fairly tight crevices are the ones that pose the greatest danger to subsea stainless steel pipe integrity. Standard corrosion of piping in a tight crevice leads to the oxygen concentration in the fluid that was in the crevice to decrease. A reduced oxygen concentration in crevice fluid increases the chance for breakdown of the surface film, and therefore the initiation of pitting. Dealing with Corrosion Some companies find that replacing 316 stainless steel tubes with a different stainless steel alloy reduces the amount of corrosion. Another possibility is to jacket the subsea piping with a material that resists corrosion, such as thermoplastic polyurethane. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

In the oil and gas industries, valves are key components involved in the control of the flow of corrosive, abrasive and erosive gases and fluids. However, resistance to wear and galling in valves poses a material problem to oil and gas companies across the globe. Hard materials are generally used in extreme environments. However, the brittleness of hard materials affects their performance. In addition, such materials can be highly expensive. Some valve components tend to deform with the application of high pressures and shock loads, resulting in chipping, fracture and even catastrophic malfunction of equipment. Pipelines, pumps and valves are generally corroded by acidic fluids, sour oil and gas containing aggressive H2S and different grades of crude containing CO2. Even under normal operating conditions, these valves may undergo microcracking and fatigue erosion that lead to premature failure. Hard chromium electroplating was considered a reliable solution to prolong the service life valves. However, this technique is restricted under REACH and OSHA environmental and health and safety guidelines, owing to the use of carcinogenic hexavalent chromium salts. Unlike other alternatives, CVD coatings can be precision-applied to complex geometries and internal surfaces. For instance, HVOF is a type of thermal spray coating technology that deposits tungsten carbide grains contained in a softer metal matrix. This line-of-sight technique is not suitable for coating undercuts. The resultant coatings have a porous structure and rough surface, and require machining post-coating, which is not always possible on intricate shapes. For cages and plug trim in choke valves, the conventional line-of-sight methods may clad the component surface without coating the inner diameters of the through holes that pass along the sleeve. The choke valves are subjected to abrasive media and high velocities owing to their pressure reducing role which can result in additional wear and erosion issues. Ball valves can also be subjected to severe abrasion by sand or stone chippings in fluids, and from erosion by accelerating flow while being opened or closed. The CVD coatings make the valve parts resistant to wear and scratches. The metal to metal seals in ball valves can suffer hard wearing, and there is often need for flex in the material. Traditional carbides, however, cannot meet this requirement as they are conducive to cracking due to their rigid nature. Ball valve spray coating needs to be performed at a 90º angle to ensure the generation of a mechanical bond to avoid any impact on the adhesion of the coating. Choosing an inappropriate approach angle can result in edge chipping. The CVD coating process avoids this potential pitfall, and is suitable for more intricate and smaller valves. Other advantages of CVD include cost savings achieved by avoiding the need for machining after coating, the strength of the chemical bond and shorter lead times through batch processing. Conclusion Although there are a number of choices to resolve valve wear issues, some of them may not meet the heavy duty requirement of oil and gas pipelines. Coatings not only add value to the components by providing corrosion and wear resistance combined with toughness and ductility, but they also reduce operational costs by saving downtime, improving performance and increasing productivity. The CVD process paves the way for the development of design of valves capable of operating in extreme oil and gas pipeline conditions, providing greater engineering flexibility not possible with other technologies. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)