STANDARDS AND CODES

• TO ENSURE SAFE AND ECONOMICAL DESIGN

• FABRICATION AND TESTING OF – EQUIPMENT– STRUCTURE AND– MATERIALS

WHO ISSUE THESE STANDARDS

• PROFESSIONAL SOCITIES

• TRADE GROUP

• INSURANCE UNDERWRITING COMPANIES

• GOVERNMENT AGENCIES

• LARGER DESIGN ORGANISATION: – Their in house standards. It save timeand money and

also ensure a conformity of projects

• EQUIPMENT MANUFACTURER:– Work to produce standardize designs and size range

for commonly used items

• THE DESIGNER– Use of standardize component size allows for the

easy integration of apiece of equipment in to the rest of plant

• FOR OPERATING COMPANY– The standardization of equipment design and sizes

increases interchangeability and reduces the stock that have to be held in maintenance store

STANDARDS CODES OVER THE FOLLOWING AREA

• MATERIAL PROPERTIESAND COMPOSITION• TESTING PROCEDURE FOR COMPOSITION,

PERFORMANCE AND QUALITY• PREFERRED SIZES OF TUBE ETC• DESIGN METHODS, INSPECTION,

FABRICATION• CODES OF PRACTICEFOR PLANT OPERATION,

SHUT DOWN, SAFETY, STARTUP ETC

VARIOUS STANDRADS

• AICHE: FOR TESTING PROCEDURE• AMERICAL PETROLEUM INSTITUTE: FOR

– REFINERY INSPECTION– EQUIPMENT INSPECTIPN– REFINERY WASTE DISPOSAL– DESIGN AND CONSTRUCTION OF HIGH PRESSURE AND

LOW PRESSURE VESSELS– PRESSURE REIEVING DEVICES– PRACTICES FOR FIRE AND SAFETY

• AMERICAL SOCIETY OF MECHANICAL ENGINEERS• AMERICAN SOCITY FOR TESTING MATERIALS• TUBULAR EXCHANGER MANUFACTUTRERS

ASSOCIATION

MATERIAL OF CONSTRUCTION

Many factors have to be considered when selecting engineering materials, but for chemical process plant the overriding consideration is usually the ability to resist corrosion.The process designer will be responsible for recommending materials that will be suitable for the process conditions. He must also consider the requirements of the mechanical design engineer; the material selected must have sufficient strength and be easily worked.The most economical material that satisfies both process and mechanical requirements should be selected; this will be the material that gives the lowest cost over the working life of the plant, allowing for maintenance and replacement. Other factors, such as product contamination and process safety, must also be considered.

MATERIAL PROPERTIESThe most important characteristics to be considered when selecting a

material of construction are:1. Mechanical properties(a) Strength-tensile strength(b) Stiffness-elastic modulus (Young's modulus)(c) Toughness-fracture resistance(d) Hardness-wear resistance(e) Fatigue resistance(f) Creep resistance2. The effect of high and low temperatures on the mechanical

properties3. Corrosion resistance4. Any special properties required; such as, thermal conductivity,

electrical resistance, magnetic properties5. Ease of fabrication -forming, welding, casting 6. Availability in standard sizes-plates, sections, tubes7. Cost

• The tensile strength (tensile stress) is a measure of the basic strength of a material.

• Stiffness is the ability to resist bending and buckling. It is a function of the elastic modulus of the material and the shape of the cross-section of the member.

• Toughness is associated with tensile strength, and is a measure of the material's resistance to crack propagation.

• The surface hardness, as measured in a standard test, is an indication of a material's ability to resist wear.

• Fatigue failure is likely to occur in equipment subject to cyclic loading; for example, rotating equipment, such as pumps and compressors, and equipment subjected to pressure cycling.

• Creep is the gradual extension of a material under a steady tensile stress, over a prolonged period of time. It is usually only important at high temperatures;

CORROSION RESISTANCE• The conditions that cause corrosion can arise in a variety

of ways. For this brief discussion on the selection of materials it is convenient to classify corrosion into the following categories:

General wastage of material- uniform corrosion: proceeds evenly and entire exposed areaGalvanic corrosion- dissimilar metals in contact: two dissimilar metal joint

Crevice: in holes of fasket surface,lap joints etc Pitting corrosion: between surfaces in close contact

Erosion-corrosion: corrosional fluid + mechanical wearCorrosion fatigue: cyclic loads with corrosionCavitation corrosion: due to repeated collapse of vapor bubbles in metal surfaceFretting Corrosion: occurs at contact area b/w materials under load subjected to vibration

COMMONLY USED

MATERIALS OF CONSTRUCTION

CAST IRON

• Grey cast Iron– Brittle, low tensile strength, not good for high

pressure application, easy to machine

• White cast Iron– Hard, brittle not good for high pressure

application, used for slurry pump

• Carbon steel– Good strength, easy fabrication, good

weldability

Carbon Steel alloys

• Aluminum: surface hardening

• Chromium: high strength at high temperatures

• Copper: provide self healing oxide film

• Molybdenum, Tungsten: high strength and hardness at high temperatures

Iron and steel• Low carbon steel (mild steel) is

the most commonly used engineering material. It is cheap; is available in a wide range of standard forms and sizes; and can be easily worked and welded. It has good tensile strength and ductility.

• The carbon steels and iron are not resistant to corrosion, except in certain specific environments, such as concentrated sulphuric acid and the caustic alkalies. They are suitable for use with most organic solvents, except chlorinated solvents

Stainless steel

• The stainless steels are the most frequently used corrosion resistant materials in the chemical industry.

• To impart corrosion resistance the chromium content must be above 12 per cent, and the higher the chromium content, the more resistant is the alloy to corrosion in oxidising conditions. Nickel is added to improve the corrosion resistance in non-oxidising environments.

TypesA wide range of stainless steels is available, with

compositions tailored to give the properties required for specific applications. They can be divided into three broad classes according to their microstructure:

1. Ferritic: 13-20 per cent Cr, < 0.1 per cent C, with no nickel

2. Austenitic: 18-20 per cent Cr, > 7 per cent Ni3. Martensitic: 12-10 per cent Cr, 0.2 to 0.4 per cent

C, up to 2 per cent NiThe uniform structure of Austenite is the structure

desired for corrosion resistance, and it is these grades that are widely used in the chemical industry.

Type 304 (the so-called 18/8 stainless steels): the most generally used stainless steel. It contains the minimum Cr and Ni that give a stable austenitic structure. The carbon content is low enough for heat treatment not to be normally needed with thin sections to prevent weld decay.

Type 304L: low carbon version of type 304 (< 0.03 per cent C) used for thicker welded sections, where carbide precipitation would occur with type 304.

Type 321: a stabilised version of 304, stabilised with titanium to prevent carbide precipitation during welding. It has a slightly higher strength than 304L, and is more suitable for high-temperature use.

Type 347: stabilised with niobium.Type 316: in this alloy, molybdenum is added to

improve the corrosion resistance in reducing conditions, such as in dilute sulphuric acid, and, in particular, to solutions containing chlorides.

Type 316L: a low carbon version of type 316, which should be specified if welding or heat treatment is liable to cause carbide precipitation in type 316.

Types 309/310: alloys with a high chromium content, to give greater resistance to oxidation at high temperatures. Alloys with greater than 25 per cent Cr are susceptible to embrittlement due to sigma phase formation at temperatures above 500°C.

High alloy content stainless steels

Super austenitic, high nickel, stainless steels, containing between 29 to 30 per cent nickel and 20 per cent chromium, have a good resistance to acids and acid chlorides. They are more expensive than the lower alloy content, 300 series, of austenitic stainless steels.

Duplex, and super-duplex stainless steels, contain high percentages of chromium. They are called duplex because their structure is a mixture of the austenitic and ferritic phases.

They have a better corrosion resistance than the austenitic stainless steels and are less susceptible to stress corrosion cracking. The chromium content of duplex stainless steels is around 20 per cent, and around 25 per cent in the super-duplex grades. The super-duplex steels where developed for use in aggressive off-shore environments.

The duplex range of stainless steels can be readily cast, wrought and machined.

NickelNickel has good mechanical properties and

is easily worked. The pure metal (>99 per cent) is not generally used for chemical plant, its alloys being preferred for most applications.

The main use is for equipment handling caustic alkalies at temperatures above that at which carbon steel could be used; above 70°C. Nickel is not subject to corrosion cracking like stainless steel.

MonelMonel, the classic nickel-copper alloy with the

metals in the ratio 2 : 1, is probably, after the stainless steels, the most commonly used alloy for chemical plant. It is easily worked and has good mechanical properties up to 500°C. It is more expensive than stainless steel but is not susceptible to stress-corrosion cracking in chloride solutions. Monel has good resistance to dilute mineral acids and can be used in reducing conditions, where the stainless steels would be unsuitable. It may be used for equipment handling, alkalies, organic acids and salts, and sea water.

Inconel• Inconel (typically 76 per cent Ni, 7 per cent Fe, 15 per

cent Cr) is used primarily for acid resistance at high temperatures. It maintains its strength at elevated temperature and is resistant to furnace gases, if sulphur free.

The Hastelloys• The trade name Hastelloy covers a range of nickel,

chromium, molybdenum, iron alloys that were developed for corrosion resistance to strong mineral acids.

• The corrosion resistance, and use, of the two main grades, Hastelloy B (65 per cent Ni, 28 per cent Mo, 6 per cent Fe) and Hastelloy C (54 per cent Ni, 17 per cent Mo, 15 per cent Cr, 5 per cent Fe),

Copper and copper alloysPure copper is not widely used for chemical equipment. It has been

used traditionally in the food industry, particularly in brewing. Copper is a relatively soft, very easily worked metal, and is used extensively for small-bore pipes and tubes

The main alloys of copper are the brasses, alloyed with zinc, and the bronzes, alloyed with tin. Other, so-called bronzes are the aluminium bronzes and the silicon bronzes.

Copper is attacked by mineral acids, except cold, dilute, unaerated sulphuric acid. It is resistant to caustic alkalies, except ammonia, and to many organic acids and salts.

• Brass:5-45%Zinc; Muntz, yellow, red(40,30 and 15% Zinc resp.• Bronze: 12% Tin, high strengthThe brasses and bronzes have a similar corrosion resistance to the

pure metal. Their main use in the chemical industry is for valves and other small fittings, and for heat-exchanger tubes and tube sheets. If brass is used, a grade must be selected that is resistant to dezincification.

The cupro-nickel alloys (70 per cent Cu) have a good resistance to corrosion-erosion and are used for heat-exchanger tubes, particularly where sea water is used as a coolant.

Aluminium and its alloysPure aluminium lacks mechanical strength but has higher resistance to

corrosion than its alloys. The main structural alloys used are the Duralumin (Dural) range of

aluminium copper alloys (typical composition 4 per cent Cu. with 0.5 per cent Mg) which have a tensile strength equivalent to that of mild steel.

The pure metal can be used as a cladding on Dural plates, to combine the corrosion resistance of the pure metal with the strength of the alloy. The corrosion resistance of aluminium is due to the formation of a thin oxide film (as with the stainless steels). It is therefore most suitable for use in strong oxidising conditions. It is attacked by mineral acids, and by alkalies; but is suitable for concentrated nitric acid, greater than 80 per cent.

It is widely used in the textile and food industries, where the use of mild steel would cause contamination. It is also used for the storage and distribution of demineralised water.

• LeadLead was one of the traditional materials of

construction for chemical plant but has now due to its price, been largely replaced by other materials, particularly plastics. It is a soft, ductile material, and is mainly used in the form of sheets (as linings) or pipe. It has a good resistance to acids, particularly sulphuric.

• TitaniumTitanium is now used quite widely in the chemical

industry, mainly for its resistance to chloride solutions, including sea water and wet chlorine. It is rapidly attacked by dry chlorine, but the presence of as low a concentration of moisture as 0.01 per cent will prevent attack. Like the stainless steels, titanium depends for its resistance on the formation of an oxide film.

PLASTICS AS MATERIALS OF CONSTRUCTION FOR CHEMICAL PLANT

Plastics are being increasingly used as corrosion-resistant materials for chemical plant construction. They can be divided into two broad classes:

1. Thermoplastic materials, which soften with increasing temperature; for example,polyvinyl chloride (PVC) and polyethylene.

2. Thermosetting materials, which have a rigid, cross-linked structure; for example, the

polyester and epoxy resins.

• The mechanical strength and operating temperature of plastics are low compared with that of metals. The mechanical strength, and other properties, can be modified by the addition of fillers and plasticisers. When reinforced with glass or carbon fibres thermosetting plastics can have a strength equivalent to mild steel, and are used for pressure vessels and pressure piping. Unlike metals, plastics are flammable. Plastics can be considered to complement metals as corrosion-resistant materials of construction.

• They generally have good resistance to dilute acids and inorganic salts, but suffer degradation in organic solvents that would not attack metals. Unlike metals, plastics can absorb solvents. causing swelling and softening. The properties and typical areas of use of the main plastics

used for chemical plant are reviewed briefly in the following sections.

Poly-vinyl chloride (PVC)

PVC is probably the most commonly used thermoplastic material in the chemical industry.

Of the available grades, rigid (unplasticised) PVC is the most widely used.

It is resistant to most inorganic acids, except strong sulphuric and nitric, and inorganic salt solutions.

It is unsuitable, due to swelling, for use with most organic solvents. The maximum operating temperature for PVC is low, 60 °C.

Polytetrafluroethylene (PTFE)PTFE, known under the trade names Teflon and

Fluon, is resistant to all chemicals, except molten alkalies and fluorine, and can be used at temperatures up to 250°C.

It is a relatively weak material, but its mechanical strength can be improved by the addition of fillers (glass and carbon fibres).

It is expensive and difficult to fabricate. PTFE is used extensively for gaskets and gland packings, reaction vessel, pipeline, plugging leakage.

As a coating, it is used to confer non-stick properties to surfaces, such as filter plates.

It can also be used as a liner for vessels.

Glass-fibre reinforced plastics (GRP)The polyester resins, reinforced with glass fibre, are the

most common thermosetting plastics used for chemical plant.

Complex shapes can be easily formed using the techniques developed for working with reinforced plastics.

Glass-reinforced plastics are relatively strong and have a good resistance to a wide range of chemicals. The mechanical strength depends on the resin used; the form of the reinforcement (chopped mat or cloth); and the ratio of resin to glass.

By using special techniques, in which the reinforcing glass fibres are wound on in the form of a continuous filament, high strength can be obtained, and this method is used to produce pressure vessels.

The polyester resins are resistant to dilute mineral acids, inorganic salts and many solvents. They are less resistant to alkalies.

Glass-fibre-reinforced epoxy resins are also used for chemical plant but are more expensive than the polyester resins.

The chemical resistance of GRP is dependent on the amount of glass reinforcement used. High ratios of glass to resin give higher mechanical strength but generally lower resistance to some chemicals.

Rubber• Rubber, particularly in the form of linings for tanks and

pipes, has been extensively used in the chemical industry for many years.

• Natural rubber is most commonly used, because of its good resistance to acids (except concentrated nitric) and alkalies. It is unsuitable for use with most organic solvents.

• Synthetic rubbers are also used for particular applications. – Hypalon has a good resistance to strongly oxidising chemicals and

can be used with nitric acid. It is unsuitable for use with chlorinated solvents.

– Viton has a better resistance to solvents, including chlorinated solvents, than other rubbers. Both Hypalon and Viton are expensive, compared with other synthetic, and natural, rubbers.

GlassBorosilicate glass (known by several trade names,

including Pyrex) is used for chemical plant as it is stronger than the soda glass used for general purposes; it is more resistant to thermal shock and chemical attack.

Glass equipment is available from several specialist manufacturers. Pipes and fittings are produced in a range of sizes, up to 0.5 m. Special equipment, such as heat exchangers, is available and, together with the larger sizes of pipe, is used to construct distillation and absorption columns. Teflon gaskets are normally used for jointing glass equipment and pipe.

Where failure of the glass could cause injury, pipes and equipment should be protected by external shielding or wrapping with plastic tape.

Glass linings, also known as glass enamel, have been used on steel and iron vessels for many years. Borosilicate glass is used, and the thickness of the lining is about 1 mm.

LINING OF VESSEL

• PROVIDE PROTECTION TO COSTLY MATERIALS

• PREVENT WEAR AND TEAR

• PREVENT CONTAMINATION

• COST BENEFICIAL

•LEAD LINING

•RUBBER LINING

•GLASS LINING

•EPOXY LINING

LEAD LINING

LOOSE LEAD SHEET LINING• Lead sheets applied to surface• Thickness 3-10 mm• Air pocket shd be avoided

HOMOGENEOUS LEAD LINING• Lead is bonded with some flux applied on

surface drop by drop• Used in high temp agitation vessels, vacuum

operations

RUBBER LINING

• TECHNIQUE:– Surface is suitably prepared and treated and bonding

agent is applied– Unvolcanized rubber sheet is then applied and then

the vessel is vulcanized

• ADVANTAGE– Light weight– Uniform– Leak proof– Cheaper– Non adsorbent

uses• Ebonite:

(1)hard rubber lining, used for transporting acids, non porous and highly resistant to chemicals(2) It Can be damaged due to impact, high temp. variation, repairs not easy

• Soft rubber: uses in chemical tanks and pipelines; can withstand temperature fluctuations

• Neoprene: use for strong alkali, organic compound, not suitable for sulphuric acid, nitric acid, ammonia, acetic acid etc

GLASS LINING

• Good for processing highly corrosive chemicals under high degree of temp and pressure

• When long operating time and economy is desired

• Prevention of adhesion of product to the wall of vessel is required

• High purity product is required• Major advantage: same vessel can be used for

different product after giving a water wash

It is done by imparting a chemical bond with mild steel where steel is first oxidized and iron oxides goes into chemical solution in glass

FABRICATION1. Fabrication of steel plant:Steel shd have low carbon content and good surface quality

tensile strength: 3400kg/m3Yield strenght (min): 1800 Kg/cm2

Sharp corner should be avoidedCasting shd be freefrom cracks,holes, porosity etc

2. Manufacturing of glass frit:Borax: a frit that tears easliyClay, Pigments: act as opaying agent but reduce acid

ressistantSilica: High= leads to chipping off

Low = promote crack formation(a)other chemical added and send to smelter(b) smelter glass is slowly quenched(c)Glass frit is grounded in wither a wet mill or dry mill

3. Techniques for Glass liningWet Spray: (1) Ground coated enamel is applied in slip form by

spraying, the coat is dried(2) The equipment is fired in a furnace then cooled slowly

to ambient temperature(3) Several coats can be applied

Dry Spray: (1) Same as above step 1(2) The equipment is then removed from furnace and dry

powder coat enamel is duslet till the surface is red hot(3) Send again to furnace, several coats can be applied

Spray Dust: It is a combination of above two

(1) Wet coat of enamel is sprayed, powdered frit is sprayed over it in cold condition, and then allowed to dry.

(2)Send to furnace

• 4. Baking operation: After Lining process coat is air dried and then baked in a furnace at a temperature of 900oC

EPOXY LINING• Epichlorohydrin+ Bisphenol A• Component added:

– Plasticizers: e.g. pine oil is added to increase flexibility– Tropic agents : preventing resin from flowing off from surface– Flow control agents like n-octanol to improve brushability of

coating– Reactive diluent used to reduce the viscosity of formulation

• Preparation:• Surface is first cleaned, sand blasted and made free of

grease and made rough– Resin is then applied by 2 component spray equipment

• Property: It has good chemical resistance and excellent flexibility good

• USES: in paper and pulp industry, waste water treatment plant, formaldehyde storage tank, food processing and beverages

FIBRE GLASS REINFORCED PLASTICS LINING

• COMPONENTS:– Glass: provide strength– Resin: provide rigidity and stability– Epoxy: chemical resistant, adhesiveness and low shrinkage– Clays: To smoothen curves– Graphite: Thermal resistance

• FROP Lining steps– Base metal surface is cleaned by solvent, scraped to remove

dust– Covered with thin layer of resin coat– Putty of suitable resin is applied to produce smooth corners– FRP components are then sprayed– Top layer is then covered with resin rich formulation

Principle Methods of Depositing Films

(1) The object to be coated is heated above melting point of epoxy or FRP and is immersed in fluidized bed of polymer

(2) Polymer powder is sprayed under pressure through hot air where particles get softened and on impact with surface, fuse together

(3) Suspension of polymer in water or in a volatile organic medium is first deposited on the metal object which on evaporation leads to fusion of polymer with the surface