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Stainless steel is known for its ability to be a clean surface that resists corrosion and rust. Because of this stainless steel is a popular choice in products. If you’ve had stainless steel around in your home for very long, you know that it has the potential to live up to its name. Dirt, dust and grime, however, put stainless steel at risk for corrosion and rust. Luckily, it responds well to cleaning, as long as certain rules are followed. Always attempt the mildest cleaning method first. Repeat it a fair number of times before resorting to the more severe cleaningmethods. Routine Cleaning. Stainless Steel’s best friends are quite simply soap, mild detergent or ammonia solutions in warm water, applied with a soft cloth or nylon sponge. Occasionally the use of the least coarse nylon scouring pad may be required. Rinse and dry with a soft cloth. Stainless steel articles are ideally suited for washing in a dishwasher. Only if cookware is heavily soiled is any prewashing required. (Note: Don’t wash in diswashers which have galvanised (Zinc Plated) components. Indelible stains can result on thesurface of Stainless Steel). Such simple Routine Cleaning will easily remove normal soiling. Repeated application will often remove heavier soiling and stains will become less noticeable and may completely disappear. Cleaning of Stainless Steel – Moderate Soiling, Light Staining. Apply the mildest household abrasive cleaner, or a paste made from fine chalk or soda bicarb, using a soft cloth or a fine nylon scouring pad. A soft bristle brush may also be used. Rub the surface as softly as possible using long even strokes in the direction of the polished finish if this exists. Avoid using a circular rubbing action. Rinse well and wash as described under Routine Cleaning. Cleaning of Stainless Steel – Heavy Soiling, Heavier Staining. Presoak in warm/hot detergent or ammonia solution. If this does not sufficiently soften burnt food or carbon deposits, household caustic cleaners will have to be used. Follow by cleaning as for Moderate Soiling, Light Staining. Repeat if necessary. If this does not suffice final resort may have to be made to the use of both coarser abrasive cleaners and nylon scouring pads, but with the risk that the surface may become slightly affected. Follow by a thorough rinse and Routine Cleaning. It is usually only the inside surfaces of cookware that are heavily soiled. If the more severe cleaning methods therefore have to be used – take care – Do not apply them to the outside surfaces where they are not required. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless steels are selected for applications where their inherent corrosion resistance, strength and aesthetic appeal are required. However, dependent on the service conditions, stainless steels will stain and discolour due to surface deposits and so cannot be assumed to be completely maintenance-free. In order to achieve maximum corrosion resistance and aesthetic appeal, the surface of the stainless steel must be kept clean. Provided the grade of stainless steel and the surface finish are correctly selected, and cleaning schedules carried out on a regular basis, good performance and long service life will result. Why Maintenance is Necessary Surface contamination and the formation of deposits are critical factors which may lead to drastically reduced life. These contaminants may be minute particles of iron or rust from other non-stainless steels used in nearby construction and not subsequently removed. Industrial, commercial and even domestic and naturally occurring atmospheric conditions can result in deposits which can be quite corrosive. An example is salt deposits from marine conditions. Working environments can also create more aggressive conditions, such as the warm, high humidity atmosphere above indoor swimming pools. These environments can increase the speed of corrosion and therefore require more frequent maintenance. Modern processes use many cleaners, sterilisers and bleaches for hygienic purposes. All these proprietary solutions, when used in accordance with their makers’ instructions are safe, but if used incorrectly (e.g. warm or concentrated) can cause discolouration and corrosion on the surface of stainless steels. Strong acid solutions (e.g. hydrochloric acid or “spirits of salts”) are sometimes used to clean masonry and tiling of buildings but they should never be permitted to come into contact with metals, including stainless steel. If this should happen the acid solution must be removed immediately by copious water flushing. Maintenance During Installation Cleaning of new fabrications should present no special problems, although more attention may be required if the installation period has been prolonged. Where surface contamination is suspected, immediate attention to cleaning will promote a trouble-free service life. Food handling, pharmaceutical and aerospace applications may require extremely high levels of cleanliness. On Going Maintenance Advice is often sought concerning the frequency of cleaning of products made of stainless steel, and the answer is quite simply “clean the metal when it is dirty in order to restore its original appearance”. This may vary from once to four times a year for external applications or it may be once a day for an item in hygienic or aggressive situations. In many applications the cleaning frequency is after each use. Good Housekeeping During Manufacturing Stainless steel can be contaminated by pick-up of carbon steel (“free iron”) and this is likely to lead to rapid localised corrosion. The ideal is to have workshops and machinery dedicated to only stainless steel work, but in a workshop also processing other steels avoid pick-up from: •         Tooling used with other metals •         Grinding wheels, wire brushes, linishing belts •         Steel storage racks •         Contamination by grinding or welding sparks •         Handling Equipment •         Adjacent carbon steel fabrication Cleaning Methods Stainless steel is easy to clean. Washing with soap or a mild detergent and warm water followed by a clean water rinse is usually quite adequate for domestic and architectural equipment. An enhanced appearance will be achieved if the cleaned surface is finally wiped dry. Specific methods of cleaning are as in Table 1. Sections below give passivation treatments for removal of free iron and other contamination resulting from handling, fabrication, or exposure to contaminated atmospheres, and picklingtreatments for removal of high temperature scale from heat treatment or welding operations. Passivation Treatments •         Grades with at least 16% chromium (except free machining grade such as 303), 20-50% nitric acid, at room temperature to 40oC for 30-60 minutes. •         Grades with less than 16% chromium (except free machining grades such as 416), 20-50% nitric acid, at room temperature to 40oC for 60 minutes. •         Free machining grades such as 303, 416 and 430F, 20-50% nitric acid + 2-6% sodium dichromate, at room temperature to 50oC for 25-40 minutes. Pickling Treatments •         All stainless steels (except free machining grades), 8-11% sulphuric acid, at 65 to 80oC for 5-45 minutes. •         Grades with at least 16% chromium (except free machining grades), 15-25% nitric acid + 1-8% hydrofluoric acid, at 20 to 60oC for 5-30 minutes. •         Free machining grades and grades with less than 16% chromium such as 303, 410 and 416, 10-15% nitric acid + 0.5-1.5% hydrofluoric acid, at 20 to 60oC for 5-30 minutes. “Pickling Paste” is a commercial product of hydrofluoric and nitric acids in a thickener – this is useful for pickling welds and spot contamination, even on vertical and overhanging surfaces. Table1. Methods of Cleaning Stainless Steel Problem Cleaning Agent Comments Routine Cleaning All finishes Soap or mild detergent and water (Preferably warm) Sponge, rinse with clean water, wipe dry if necessary. Follow polish lines. Fingerprints All finishes Soap and warm water or organic solvent (eg acetone, alcohol, methylated spirits) Rinse with clean water and wipe dry. Follow polish lines. Stubborn Stains and Discolouration. All finishes. Mild cleaning solutions, eg. Jif, specialty stainless steel cleaners. Use rag, sponge or fibre brush (soft nylon or natural bristle. An old toothbrush can be useful). Rinse well with clean water and wipe dry. Follow polish lines. Lime Deposits from Hard Water. Solution of one part vinegar to three parts water. Soak in solution then brush to loosen. Rinse well with clean water. Oil or Grease Marks. All finishes. Organic solvents (eg. acetone, alcohol, methylated spirits, proprietary “safety solvents”). Baked-on grease can be softened beforehand with ammonia. Clean after with soap and water, rinse with clean water and dry. Follow polish lines. Rust and other Corrosion Products. Embedded or Adhering “Free Iron”. Rust stains can be removed by adding one part of nitric acid to nine parts of warm water. Leave for 30 to 60 minutes, then wash off with plenty of water, and flush any drains thoroughly. See also previous section on Passivating. Rinse well with clean water. Wear rubber gloves, mix the solution in a glass container, and be very careful with the acid. (see Precautions for acid cleaners) Routine Cleaning of Boat Fittings. Frequent washing down with fresh water. Washing is recommended after each time the boat is used in salt water. Cooking Pot Boiled Dry. Remove burnt food by soaking in hot water with detergent, baking soda or ammonia. Afterwards clean and polish, with a mild abrasive if necessary. See comments re steel wool. Dark Oxide From Welding or Heat Treatment. “Pickling Paste” or pickling solutions given on previous page. Must be carefully rinsed, and use care in handling (see Precautions for acid cleaners). Scratches on Polished (Satin) Finish. Slight scratches – use impregnated nylon pads. Polish with scurfs dressed with iron-free abrasives for deeper scratches. Follow polish lines. Then clean with soap or detergent as for routine cleaning. Do not use ordinary steel wool – iron particles can become embedded in stainless steel and cause further surface problems.Stainless steel and “Scotch-brite” scouring pads are satisfactory. Precautions Acids Acids should only be handled using gloves and safety glasses. Care must be taken that acids are not spilt over adjacent areas. All residues must be flushed to a treated waste stream. Always dilute by adding acid to water, not water to acid. Use acid-resistant containers, such as glass or plastics. If no dulling of the surface can be tolerated a trial treatment should be carried out; especially for pickling operations. All treatments must be followed by thorough rinsing. Solvents Solvents should not be used in confined spaces. Smoking must be avoided when using solvents. Chlorides Chlorides are present in many cleaning agents. If a cleaner containing chlorides, bleaches or hypochlorites is used it must be afterwards promptly and thoroughly cleaned off. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Stainless steel Tubing and hose can be thought of as a cylindrical thin-walled pressure vessel. The strength of thin walled pressure vessels is determined by: 1. The material strength 2. The wall thickness, and 3. The size of the tubing. The formula is: strength, psi = yield*(wall thickness/radius) This last item, stainless steel tubing size, is unusual. One can understand how strength is related to how strong the material is and how thick it is but size (radius)? The relationship between stainless steel tubing size and strength is inverse; the larger the tube diameter the less strength it has. When you look at pressure ratings for tubing and hose you will notice that for the same hose, maximum recommended operating pressure goes down as the size goes up. You can use the properties to your advantage. For example, you might have a choice of stainless steel tubing or hose size for a particular application. Everything else being equal, a smaller diameter line holds more pressure than a larger diameter line. Another advantage is that a smaller size weights less. Inspection: When you inspect a hose or line, you are inspecting a pressure vessel. As with all pressure vessels, they should be protected from damage that reduces the wall strength. Inspect for nicks, cuts, chafing, and corrosion.  Make sure that the line does not vibrate. When working with large pressure vessels, such as aircraft fuselage, don’t be fooled by the low pressures. Because of their large size, these pressure vessels are under a lot of stress. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Painting galvanized steel requires careful preparation and a good understanding of both painting and galvanizing. Many products have been galvanized and painted successfully for decades, including automobiles and utility towers. Past experience provides excellent historical data for how best to achieve good adhesion. By studying past adhesion failures and successes, galvanizers, paint companies, researchers, paint contractors, and other sources have created an ASTM specification (ASTM D 6386) detailing the process and procedures for preparing hot dip galvanized steel for painting. When the galvanized surface is prepared correctly, paint adhesion is excellent and the duplex system becomes an even more successful method of corrosion protection. Galvanized steel can be pided into three categories: newly-galvanized steel, partially weathered galvanized steel, and fully weathered galvanized steel. Each type of galvanized steel must be prepared differently because the galvanized surface has different characteristics at each stage of weathering. It is important to know the age of the galvanized steel that will be painted. Different paint selections are also important to know. Newly-Galvanized Steel Newly-galvanized steel is zinc-coated steel that has been hot-dip galvanized after fabrication within the past 48 hours. The newly-galvanized steel should not be water or chromate quenched, nor should it be oiled. This type of galvanized surface is typically very smooth and the surface may need to be slightly roughened – using one of the profiling methods described in this publication – to improve paint adhesion. A newly galvanized surface has little or no zinc oxides or zinc hydroxides, so no major cleaning is necessary. Partially Weathered Galvanized Steel Partially weathered galvanized steel is classified as steel that has been galvanized more than 48 hours ago but has been in service for less than two years. At this stage in the life of the galvanized steel, the formation of zinc corrosion products is evident by a light white film present on the galvanized steel. This layer of oxidation must be removed to promote good adhesion between the paint and the galvanized steel. Cleaning of the light corrosion products can be done using many methods mentioned below. Before painting partially weathered galvanized steel, it is important to know if the coating was chromate quenched. Spot testing the galvanized steel according to ASTM B 201 can determine the presence of chromate conversion coatings. If a chromate coating is detected, the chromate layer must be removed, either by brushing off by abrasive blast cleaning, abrading, sanding or allowing the steel to weather for six months. Partially weathered galvanized steel also should be slightly roughened to improve paint adhesion. Any of the surface profiling methods described below can be used to prepare the surface. Fully Weathered Galvanized Steel Fully weathered galvanized steel has been in service for approximately two years and has completely formed the protective layer of corrosion products known as the zinc patina. The patina has a very stable and finely etched surface, which provides excellent paint adhesion. The only surface preparation needed is a warm water power wash to remove loose particles from the surface. In order to protect the surface, the power wash should not exceed 1450 psi. Allow the surface to completely dry before application of the paint system. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Maximum working temperature and pressure rating of carbon steel flanges conforming dimensions ASME B16.5 Pipe Flanges  and Flanged Fittings- and materials specification ASTM A-105 Specification for Carbon Steel Forging for Piping Applications -temperature in Fahrenheit and pressure in psi.Gauge Pressure (psi)Temperature  (oF) Flange Class15030040060090015002500< 10028574099014802220370561702002606759001350202533755625300230655875131519703280547040020063584512701900317052805001706008001200179529954990600140550730109516402735456065012553571510751610268544757001105357101065160026654440750955056701010151025204200800804105508251235206034308506527035553580513402230900501702303455158601430950351051402053105158601000205070105155260430 ASME B16.5 Pipe Flanges and Flanged Fittings: NPS 1/2 through NPS 24 Metric/Inch Standard covers pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings for pipe flanges and flanged fittings.  Included are: flanges with rating class designations 150, 300, 400, 600, 900, and 1500 in sizes NPS 1/2 through NPS 24 and flanges with rating class designation 2500 in sizes NPS 1/2 through NPS 12, with requirements given in both metric and Customary units with diameter of bolts and flange bolt holes expressed in inch units;  flanged fittings with rating class designation 150 and 300 in sizes NPS 1/2 through NPS 24, with requirements given in both metric and U.S. Customary units with diameter of bolts and flange bolt holes expressed in inch units;  flanged fittings with rating class designation 400, 600, 900, and 1500 in sizes NPS 1/2 through NPS 24 and flanged fittings with rating class designation 2500 in sizes NPS 1/2 through NPS 12 that are acknowledged in Non-Mandatory Appendix E in which only Customary units are provided. B16.5 is limited to flanges and flanged fittings made from cast or forged materials, and blind flanges and certain reducing flanges made from cast, forged, or plate materials.  Also included in this Standard are requirements and recommendations regarding flange bolting, flange gaskets, and flange joints. This Standard is to be used in conjunction with equipment described in other volumes of the ASME B16 Series of Standards as well as with other ASME standards, such as the Boiler and Pressure Vessel Code and the B31 Piping Codes. Careful application of these B16 standards will help users to comply with applicable regulations within their jurisdictions, while achieving the operational, cost and safety benefits to be gained from the many industry best-practices detailed within these volumes. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Pressure Rating for standard seamless stainless steel pipes, temperature from 100oF to 750oF. All ratings in psig based on ANSI/ASME B31.1.The operating (allowable) internal pressure of a vessel, tank, or piping used to hold or transport liquids or gases.The pressure ratings of pipes, valves, etc. must be matched throughout a hydraulic system in order for the system to function.  For example, if a hydraulic system was rated at 2,000 PSI, you should not install a valve rated at 125 PSI. The pressure of the water will quickly cause the valve to fail since its pressure rating is too low. Pressure Rating (psig)Pipe Size (inches)Pipe ScheduleTemperature (oF)1002003004005006006507007501″403048262923622171201919241867182418101″804213363432653002279126592580252825011″1606140529647594375406838763761368436461.5″402257194717501608149614251383135413401.5″803182274424662267210820091949190918891.5″1604619398435803291306029162829277227432″401902164014741355126012011165114111292″802747236921291957182017341682164816312″1604499388034863205298028402755269926713″401806155814001287119611401106108410723″802553220219791819169116121564153215163″1603840331229762736254424242352230422804″40153113211187109110149679389199094″802213190917151577146613971355132813144″1603601310627912566238622732206216121385″401342115810409568898478228057975″801981170915351411131212501213118911765″1603414294526462433226221552091204920276″40121910529458698087707477327246″801913165014831363126712081172114811366″1603289283625492343217920762014197319538″4010739268327657116786576446378″801692145913111205112110681036101510058″16031752738246022622103200419441905188510″4097484075569494561559658457810″8016091388124711471066101698696695610″160314727142439224220851986192718801868 The outside housing of most seamless pipes have pressure ratings listed. Seamless pipes made from different materials will have different pressure ratings. The rating of copper tubing is 700 PSI. Schedule 40 steel has a rating of 2,000 PSI. The higher rating of the steel pipe means that the pipe is stronger. Of course, factors other than pressure ratings have to be taken into account when choosing piping. For example, though steel pipe is strong, it is not widely used because it is labor intensive and highly corrosive. In contrast, copper pipe is toxic to living organisms and has been known to keep the water flowing through it fresh for over two thousand years. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Barlow’s formula can be used to estimate burst pressure of steel pipes or tubes. P = 2 s t / (do SF) where P = max. working pressure (psig) s = material strength (psi) t = wall thickness (in) do = outside diameter (in) SF = safety factor (in general 1.5 to 10) The Barlow’s estimate is based on ideal conditions at room temperature. Material Strength The strength of a material is determined by the tensile strength tension test, which measure the tension force and the deformation of the test specimen. the stress which gives a permanent deformation of 0.2% is called the yield strength the stress which gives rupture is called the ultimate strength steel pipes Strength of some common materials: MaterialYield Strength  (psi)Ultimate Strength  (psi)Stainless Steel, 30430,00075,0006 Moly, S3125445,00098,000Duplex Stainless Steel, S3180365,00090,000Nickel Stainless Steel, N0220015,00055,000 1 psi (lb/in2) = 6,894.8 Pa (N/m2) = 6.895×10-2 bar steel pipes Bursting Pressure Bursting pressure of low carbon steel pipes are indicated in the table below:OD (in)Bursting Pressure (psi)Wall Thickness (in)0.0280.0350.0490.0650.0950.120.1340.1480.1650.180.203 0.221/413475173255/1610588134753/888001100016088233751/2646381131168815950246135/8646392131251318975250253/45363756310175155382021322963257137/8453964638663130631691319250214502447513988563875631100014575165001842520900231001 1/4605089681141312925144381622517875204881 1/24950728893501058811825132001457516775182881 3/46188797589381003811275123751402515400255006875783886639763107251210013200 1 in (inch) = 25.4 mm Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

A power plant engineer has many choices when selecting steel tubing materials for his condenser, feedwater  heater or balance-of-plant application. The wide variety of stainless steel choices available (ASTM lists  over 75 alloys) gives the engineer greater flexibility to choose the best candidate to meet budgetary  constraints and still provide the performance needed for the lifetime of the plant. Unfortunately, upset  conditions can be common in power generation, and these can result in premature unexpected failure of  steel tubing and piping materials. These may include differences in operation modes from design, changes in  water chemistry due to leaks in other parts of the system, corrosion from unexpected sources, impact of  improper lay-up practices, and the effect of corrosion product transport to other parts of the system. The  motivation to build modern combined-cycle power plants for the lowest cost per kilowatt has stretched the  envelope for materials performance.  This paper provides an overview on a number of factors known to cause failure of a tube or pipe material.  Knowing the limitations of material is crucial when making a selection for a specific application. This  paper helps to identify the factors that need to be considered when selecting a material. Properties  compared in this paper include corrosion resistance, stress corrosion cracking potential, thermal and  mechanical properties, erosion resistance, vibration potential, and temperature limitations. The property  comparison guides are intended to be quick tools to assist the user in selecting a cost-effective material  for a specific application.  Corrosion  Corrosion may be grouped into two broad categories, general corrosion and localized corrosion  accelerated by an electrochemical mechanism. The latter group can be pided into several well-known  specific mechanisms.  General Corrosion  General corrosion is the regular dissolution of surface metal. The two most common encountered are the  rusting of carbon steel and the wall thinning of copper alloys. General corrosion is normally not  catastrophic. With proper planning, a heat exchanger can be designed to accommodate general  corrosion, and in many instances, an alloy susceptible to this type of corrosion may be a cost-effective  design option. Heat exchanger designers commonly add a “corrosion allowance” to a high-pressure carbon steel feedwater heater to allow for a 10 to 25 year lifetime. Copper alloys are often chosen for condensing and BOP heat exchangers, and 25-year lifetimes are not  uncommon. In some applications, copper alloys are expected to slowly dissolve to maintain some  resistance to biofouling as the copper ion can be toxic to the microorganisms that attach to the tube wall.  Unfortunately, on the steam side of the tubing, copper transport to other locations due to this slow  dissolution may cause other problems. The copper can replate on turbine blades, resulting in a loss of  efficiency, or on boiler tubes, resulting in premature failures. Although the discharge values on the  cooling water side may be in the ppb concentration range, total copper metal discharge for a mediumsized condenser over the tubes’ lifetime can exceed several hundred thousand pounds per unit. In some  North American regions, high discharge levels have prevented the reuse of copper alloys in power plant  heat exchangers.  Electrochemically Driven Mechanisms  Several corrosion-related mechanisms are electrochemically driven, and these can be very unpredictable.  Therefore, they cannot be accommodated by design. These failure mechanisms usually have two  stages: an incubation or initiation period, and a propagation mode. The time of initiation can be very  unpredictable. It could happen in a few days or last for years. Once initiated, the second mode can occur  rather quickly, driven by the electropotential between the two regions. Conductivity of the water may be a  dominant factor. Higher conductivities allow higher current densities. Higher current densities are  proportionately related to metal removal rates.  Pitting  Pitting corrosion is a highly localized attack that can result in through-wall penetration in very short  periods of time. Failures may occur in less than four weeks. Once a pit is initiated, the environment in  the pit is usually more aggressive than the bulk solution because of the pit’s stagnant nature. Even if the  bulk solution has a neutral or basic pH, the pH in a pit can drop below two. When this occurs, the surface  inside the pit becomes active. The potential difference between the pit and the more noble surrounding  area is the driver for the galvanic attack. As the surface area of the anode (pit) is small and the cathode  (the passive surface surrounding the pit) is large, a very high current density in the pit is possible. This  drives the very high corrosion rates.  The most common cause of pitting of stainless steels in the power industry is chlorides. Several alloying  elements, such as chromium, molybdenum, and nitrogen, promote chloride resistance in this group of  alloys. Not all have the same effect. By investigating the impact of each element, Rockel developed a  formula to determine the total stainless steel resistance to chloride pitting (1):  PREn = % Cr + 3.3 (% Mo) + 16 (N) (1) PREn represents the “Pitting Resistance Equivalent” number. Using this formula, various stainless steels  can be ranked based upon their chemistry. In this formula, nitrogen is 16 times more effective and  molybdenum is 3.3 times more effective than chromium for chloride pitting resistance. The higher the  PREn, the more chloride resistance an alloy will have. It is interesting to note that nickel, a very common  stainless steel alloying element, has little or no effect on chloride pitting resistance. However, it does  have a profound impact in stress corrosion cracking which will be discussed later.  Crevice Corrosion  Crevice corrosion is very similar to pitting corrosion. However, since the tighter crevice allows higher  concentrations of corrosion products (less opportunity to flush with fresh water), it is more insidious than  pitting. This drives the pH lower. The end result is that crevice corrosion can happen at temperatures  30°-50° Centigrade lower than pitting in the same environment.  Crevice corrosion is commonly measured by the ASTM G 48 test. Kovach and Redmond evaluated a  large database of existing crevice corrosion data and compared it to the PREn number described earlier  (2). They developed relationships between the PREn and the G 48 critical crevice temperature (CCT) and plotted the relationships. Figure 1 is a modified version to be used as a tool for comparing alloys and  determining maximum chloride levels.  Figure 1  Critical Crevice Temperature and Maximum Chloride Levels Versus PREn of Various Stainless  Steels parallel correlations. After a typical or minimum chemistry is determined, the PREn can be calculated. To  compare the corrosion resistance of two or more alloys, a line is drawn vertically from the calculated  PREn for each alloy to the appropriate sloped line for the structure. The vertical line should stop at the  bottom line for austenitics, such as TP 304, TP 316, TP 317, 904L, S31254, and N08367. Duplex grades,  such as S32304, S32003, S33205, and S32750, fall on the center line. The ferritics, such as S44660 and  S44735, follow the top sloped line. From this intersection, a horizontal line should be drawn to the left  axis to determine an estimated CCT. A higher CCT indicates more corrosion resistance.  Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Tubes Heat exchangers with shell diameters of 10 inches to more than 100 are typically manufactured to industry standards. Commonly, 0.625 to 1.5″ tubing used in exchangers is made from low carbon steel, Admiralty, copper, copper-nickel, stainless steel, Hastelloy, Inconel, or titanium. Tubes can be drawn and thus seamless, or welded. High quality electro resistance welded tubes display good grain structure at the weld joints. Extruded tubes with fins and interior rifling are sometimes specified for certain heat transfer applications. Often, surface enhancements are added to increase the available surface or aid in fluid turbulence, thereby increasing the operative heat transfer rate. Finned tubes are recommended when the shell-side fluid have a considerably lower heat transfer coefficient than the tube-side fluid. Note, the diameter of the finned tube is slightly smaller than the un-finned areas thus allowing the tubes to be installed easily through the baffles and tube supports during assembly while minimizing fluid bypass. A U-tube design finds itself in applications when the thermal difference between the fluid flows would otherwise result in excessive thermal expansion of the tubes. Typical U-tube bundles contain less tube surface area as traditional straight tube bundles due to the bended end radius, on the curved ends and thus cannot be cleaned easily. Furthermore, the interior tubes on a U-tube design are difficult to replace and often requiring the removal of additional tubes on the outer layer; typical solutions to this are to simply plug the failed tubes. Tube Sheets Tube sheets usually constructed from a round, flattened sheet of metal. Holes for the tube ends are teen drilled for the tube ends in a pattern relative to each other. Tube sheets are typically manufactured from the same material as tubes, and attached with a pneumatic or hydraulic pressure roller to the tube sheet. At this point, tube holes can both be drilled and reamed, or they are machined grooves (this significantly increases tube joint strength) (figure A). The tube sheet comes in contact with both fluids in the exchanger, therefore it must be constructed of corrosion resistant materials or allowances appropriate for the fluids and velocities. A layer of alloy metal bonded to the surface of a low carbon steel tube sheet would provide an effective corrosion resistance without the expense of manufacturing from a solid alloy. The tube-hole pattern, often called ‘pitch’, varies the distance between tubes as well as the angle relative to each other allowing the pressure drop and fluid velocities to be manipulated in order to provide max turbulence and tube surface contact for effective heat transfer. Tube and tube sheet materials are joined with weld-able metals, and often further strengthened by applying strength or seal weld to the joint. Typically in a strength weld, a tube is recessed slightly inside the tube hole or slightly beyond the tube sheet whereas the weld adds metal to the resulting edge. Seal welds are specified when intermixing of tube liquids is needed, this is accomplished whereas the tube is level with the tube sheet surface. The weld fuses the two materials together, adding no metal in the process. When it becomes critical to avoid the intermixing of fluid, a second tube sheet is designed in. In this case, the outer tube sheet becomes the outside the shell path, and the inner tube sheet is vented to atmosphere, so that a fluid leak can be detected easily effectively eliminating any chance of cross contamination. Shell Assembly The shell is constructed either from pipe or rolled plate metal. For economic reasons, steel is the most commonly used material, and when applications involving extreme temperatures and corrosion resistance, others metals or alloys are specified. Using off-the-shelf pope reduces manufacturing costs and lead time to deliver to the end customer. A consistent inner shell diameter or ‘roundness’ is need to minimize the baffle spacing on the outside edge, excessive space reduces performance as the fluid tends to channel and bypasses the core. Roundness is increased typically by using a mandrel and expanding the shell around it, or by double rolling the shell after welding the longitudinal seam. In some cases, although extreme, the shell is cast and then bored out until the correct inner diameter is achieved. When fluid velocity at the nozzle is high, an ‘impingement’ plate is specified to distribute fluid evenly in the tubes, thereby preventing fluid-induced erosion, vibration and cavitation. Impingement plates effectively eliminate the need to configure a full tube bundle, which would otherwise provide less available surface. An impingement plate can also be installed above the shell thereby allowing a full tube count and therefore maximizing shell space (figure B). Bonnets and End Channels Bonnets / end channels regulate the flow of fluid in the tube-side circuit, they are typically fabricated or cast. They are mounted against the tube sheet with a bolt and gasket assembly; many designs include a ‘machine grooved’ channel in the tube sheet sealing the joint. If one or more passes are intended, the head may include pass ribs that direct flow through the tube bundle (figure C). Pass ribs are aligned on either end to provide effective fluid velocities through an equal number of tubes at a time ensuring a constant, even fluid velocity and pressure drop throughout the bundle. Figure C. Heads contain pass ribs that direct flow on the tube-side fluid for one or more passes across the tube bundle. Shell and tube configurations with up to (4) passes are the most common, however specialty designs do allow 20 or more crossings. The tube sheet configuration in a multi-pass shell and tube design must have provisions for the pass ribs, requiring either removal of tubes to allow a low cost straight pass rib or alternately a pass rib with curves around the tubes adding cost to the manufacture process. When a full bundle count is needed for the thermal requirement, machine pass ribs usually prevent the need to ‘upsize’ to the next larger shell diameter. The material used in the cast bonnets / heads used in smaller diameters (ie 15” or less) are typically, poured from iron, steel, bronze, Hastelloy, nickel plated, or stainless steel. Pipe connections are normally NPT, others including SAE, tri-clamp, ASME flanged, BSPP, and others types are available. Baffles Baffles function in two ways, during assembly they function as tube guides, in operation they prevent vibration from flow induced eddies, last but most importantly they direct shell-side fluids across the bundle increasing velocity and turbulence effectively increasing the rate of heat transfer.  All baffles must have diameter slightly smaller than the shell in order to fit, however tolerances must be tight enough to avoid a performance loss as a result of fluid bypass around the baffles. This is where the concept of ‘shell roundness’ is of up most importance in sealing off the otherwise would be bypass around the baffle. Baffles are usually stamped / punched, or machined drilled; such configurations vary based on size and application. Material selection must be compatible with the shell side fluid to avoid failure as a result of corrosion. It is not uncommon for some punched baffle designs to include a lip around the tube hole to provide more surfaces against the tube to reduce wear on the adjoining parts. Tube holes must be precisely manufactured to allow easy assembly and possible field tube replacement, all the while minimizing fluid flow through the hole and against the tube wall. In typical liquid applications, baffles occupy between 20-30% of the shell diameter; whereas in a gas application with a necessary lower pressure drop, baffles with 40-45% of shell diameter are used (figure D). Baffle placement requires an overlap at one or more tubes in a row to provide adequate tube support. Additionally baffles are spaced evenly throughout the shell to aid in reducing pressure drop and even fluid velocity. In a ‘single-segmental’ configuration, baffles move fluid or gas across the full tube count. When high velocity gases are present, this configuration would result in excessive pressure loss thus calling fourth a ‘double-segmental’ layout. In a ‘double-segmental’ arrangement, structural effectiveness is retained, yet allowing gas to flow in a straighter overall direction. While this configuration takes full advantage of the full available tube surface, a reduction in heat transfer performance should be expected. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Selection of stainless steel and nickel alloys, the first element is choose the correct stainless steel and nickel alloy grades. Stainless steel and nickel alloy that contains many of the standard level, between the level of chemical composition, corrosion resistance, physical properties, mechanical properties,  there is a big difference. For a particular application to select the most appropriate grade, can be obtained with the least cost to you satisfied with the results. In the choice of grade, consider the material properties.  ​ Select a grade to consider the properties include:  Corrosion resistance; anti-sulfur resistance; use of strength, ductility, and environmental temperature; on the processing technology adaptation; on the adaptability of washing procedures; use the stability of performance; strength anti-wear, anti-erosion; anti- sticky corrosive; reflex; magnetic; thermal conductivity; thermal expansion; resistivity; sharpness; hardness; dimensional stability. Corrosion resistance of stainless steel or heat-resistant steel is usually the most important features, but in the application, corrosion resistance, the most difficult assessment. Under natural conditions, and in pure chemical solution, the corrosion resistance is relatively easy to determine. However, localized corrosion, such as: stress corrosion cracking, crevice corrosion, pitting corrosion, intergranular corrosion (present in the HAZ) is much more complex than the general corrosion. Although there is no such localized corrosion on the structural damage to a large area, but may not be expected to result from, or even fatal failure. Therefore, construction and choice of stainless steel in the design must carefully consider these factors. Corrosion may be through the media, alarming increase in minor impurities, the impurities in the media is difficult to predict, but even if it is the concentration of parts per million can cause serious consequences. In the case of warming, although minor changes in the atmosphere will greatly accelerate the corrosion of metals, may affect the corrosion rate, curing and carburization. Despite these complexities exist, we can combine the steel manufacturer’s recommendations to select the appropriate rule of thumb for most applications of steel. However, to understand one thing: the material obtained by the corrosion test data for predicting performance of a particular kind of deviation from time to time. Even the work the data have been limited because of corrosion similar to some of these media may be due to slight changes in the erosion factors have substantial differences. For demanding applications that require extensive data for these two studies, comparative analysis, and sometimes will follow the lead testing or operation test. The mechanical properties of the working temperature is the primary consideration, but sometimes overlook other temperature requirements to achieve a satisfactory performance. Therefore, the products used for low temperature below zero must have for the performance of the work, although a constant operating temperature may be much higher, at room temperature in work performance are also important. The choice of products not only need to consider the needs of performance, but also consider the handling of processing andcleaning needs. Can be processed with a particular characteristic (easy to shape or weldability) of the material would normally be used, not the other, but that relatively good performance of the high cost of materials processing. Even the cleaning process will also affect the choice of steel. Sometimes, even if the working conditions in the degree of sensitization is not important, but need to be adopted by the welding process of the stable carbon materials that may be ignored. The welding process of the material needs to be placed in a washing medium, such as nitric acid – hydrofluoric acid, sensitized by the media will corrode stainless steel or nickel alloy. For some specialized applications, other properties listed in the list is critical. but in many other applications are rarely considered. Surface finish are important for many applications, sometimes using stainless steel, because it has a beautiful surface for a variety of options. According to the appearance, smoothness and other characteristics, or to select the cleaning surface. Surface in terms of cleaning is not as easy as it is sometimes, the existing test surface may be desirable. The choice of surface layer may affect the type of choice, the choice of the surface layer in turn may affect the choice of material grade, because the different levels of surface layer, the durability of the surface layer are also different. Strong level of corrosion resistance in corrosive solution (the lower alloy content will corrode steel) in the surface layer remains bright. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Hardness testing of seamless stainless steel pipes need to take into account its mechanical properties, performance and quality of this is related to the deformation of stainless steel as raw materials, stamping, cutting and other processing. Therefore, all seamless staineless steel tubes for mechanical properties testing. Mechanical properties of the test method is mainly pided into two categories, a tensile test,hardness test. Stainless steel thickness greater than 1.2mm, with Rockwell hardness tester, testing, HRB, HRC hardness. 0.2 ~ 1.2mm thicknessstainless steel pipe plate surface Rockwell hardness test HRT, HRN hardness. Less than 0.2mm thick stainless steel plate surface Luo Hardness tester with diamond anvil, test HR30Tm hardness. Metal materials in the United States, the standard in on the hardness test has a prominent feature is the precedence Rockwellhardness test, supplemented by Brinell hardness test, Vickers hardness test uses very little the U.S. believes Vickers hardness test primarily. The research for metal and thin small parts test. Chinese and Japanese standards are also used three types of hardness test, users can thickness and the material conditions of state and choose one of their own to test the stainless steel pipes material. Japanese stainless steel pipes on the tensile strength test and hardness test requirements and the corresponding Chinese standard forms the same value close to the Chinese standard reference here to see the traces by Japanese standards. Stainless steel hardness, the Rockwell hardness is a worthy priority to the use of equipment, simple equipment, easy to operate without professional inspector, the hardness value can be directly read, test efficiency,suitable for factory use. On the use of Rockwell hardness testing hardness of stainless steel, stainless steel pipes standard generally provides for HRC and HRB two rulers. For the annealing stainless steel usually corresponds to each grade stainless steel varieties provides hardness values should not be HRB certain a large value, typically 88-96HRB range. As for the quenching and tempering of martensite stainless steel, generally corresponding to each grade stainless steel pipes variety, provides a hardness HRC is not smaller than a certain value, usually in the range of 32-46HRC Inside. Provided only in stainless steel pipes with Rockwell hardness of HRB and HRC scale. In fact, Rockwell superficial hardness testing stainless steel also can be fully applied. Because its principle is identical with the Rockwell hardness tester, test power is relatively lesser. And its hardness can be easily converted to HRB, HRC, or Brinell hardness HB, Vickers hardness HV. The corresponding conversion tables in the company’s website can be found in these conversion tables from the U.S. standard ASTM or international standards ISO. For thin-walled stainless steel tube, thin stainless steel pipe plate, thin stainless steel, fine stainless steel wire, surface hardness of Rockwell will be very convenient. In particular, developed the company’s latest portable surface Rockwell hardness, Rockwell hardness tester tube, can be as thin as 0.05mm stainless steel pipe Plate, stainless steel and fine to 4.8mmstainless steel tube for rapid, accurate hardness, making it difficult to resolve the past in the country’s problems immediately. Tiny tube in stainless steel, electric pipe in stainless steel, decoration pipe in stainless steel, product pipe in stainless steel, precision pipe in stainless steel,industrial pipe in stainless steel, antenna pipe in stainless steel, rectangle pipe in stainless steel, special pipe in stainless steel, punching pipe in stainless steel, tiny pipe in stainless steel without seam. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)

Chromium in stainless steel performance decision has become the main element, the fundamental reason is to add chromium steel as an alloying element, the internal contradictions of its campaign in favor of resistance to the development of corrosiondamage. Such a change can be obtained from the following description: 1. Chromium Fe-based solid solution so that the electrode potential to improve  2. Chromium electronic absorption of iron so that iron-passivated  Anodic passivation is due to be prevented from arising from reaction of metal and alloy corrosion resistance phenomenon can be improved. Passivation of metals and alloys constitute the theory of many major film theory, deals with the electronic order of adsorption. Valency states of chromium The valency (oxidation state) of chromium metal as an alloying constituent of stainless steel is 0 (zero). Chromium atoms are present in stainless steel in ‘substitutional’ lattice positions, replacing iron atoms. This is the same as other ‘large’ atoms from elements such nickel. The atoms are held together in the lattice structure by the ‘metallic bond’. This involves the sharing of electrons between atoms with no loss or gain of electrons from atom to atom. The valency state is therefore taken as 0 (zero). The chromium in solid stainless steel should not be regarded as a health hazard. In contrast ionic bonding in compounds, such as sodium chloride (common salt), involves the exchange of electrons between atoms and hence valency states of 1, 2, 3 etc depending on how many electrons the element has lost or gained. It is compounds involving chromium ‘ions’ with a valency state of 6 (which includes chromates) that have been identified as a cause for health concerns. This valency state is also referred to as ‘chromium 6’, ‘hexavalent chromium’ or ‘Cr6+’ Release of chromium if stainless steel corrodes If stainless steel are subject to corrosion metal ions are released from the alloy into the surrounding environment. Under these conditions, chromium ions should be in the trivalent state (Cr3+), which like the chromium in the un-corroded steel, should not be a health hazard. Chromium in stainless steel welding fumes Fumes from welding stainless steel may contain hexavalent chromium ions, depending on the process and any fluxes used Efficient local exhaust ventilation systems should normally be suitable for maintaining exposure limits below the 0.05 mg/m3 limit for hexavalent chromium ions. Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)