The document discusses factors to consider when selecting materials for engineering equipment and piping in petrochemical process plants. It covers mechanical properties, corrosion resistance, common material types including various grades of steel, and other factors. The most important considerations are the material's ability to resist corrosion in the process conditions and satisfy both process and mechanical requirements at the lowest cost over the plant's lifetime.

1. Material selection and design
Mohamed Saad
Material selection and design
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2. Introduction
• This section covers the selection of materials of construction for equipment and piping
• Many factors have to be considered when selecting engineering materials such as
(Mechanical properties, Cost ,Corrosion resistance, Design condition, Easy working ) , but
for petrochemical process plant the consideration is usually the ability of material to resist
corrosion.
• The Process designer will be responsible for recommending materials that will be suitable
for the process conditions. He must consider the requirements of mechanical designer.
• The most economical material that satisfies both process and mechanical requirements
should be selected (material that gives the lowest cost over the working life of the plant)
• Maintainability, replacement, Process safety, shall be consider during selection of material.
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3. Mechanical Properties
Tensile strength:
It is the maximum stress that the material will withstand, measured by a standard tensile test.
The older name for this property, which is more descriptive of the property, was Ultimate
tensile Strength (UTS)
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4. Mechanical Properties
Toughness :
The ability of a material to absorb energy and plastically deform without fracturing.
One definition of material toughness is the amount of energy per unit volume that a
material can absorb before rupturing. It is also defined as a material's resistance to
fracture when stressed.
Hardness :
Generally defined as resistant of material to permanent deformation. It's usually indicates to
abrasion, scratching, cutting or shaping.
Fatigue :
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 :
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;
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5. Mechanical Properties
The effect of high and low temperatures on the mechanical properties:
At higher temperature:
• The tensile strength: decrease with increasing temperature.
For (low carbon steel, C < 0.25 )
The tensile strength is 450 N/mm2 @ 25C but failing to 210 @ 500C,
• Creep resistance , in case of material is subjected to high stresses at elevated
temperatures the creep may be occurred depending on the type of material. Special alloys,
such as Inconel are used for high temperature equipment such as furnace tubes.
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6. Mechanical Properties
At lower temperature :
• For low-temperature equipment, such as cryogenic plant and liquefied-gas storages,
austenitic stainless steel or aluminum alloys are preferable to be utilized.
• V-notch impact tests, such as the Charpy test, are used to test the susceptibility of
materials to brittle failure , by applying this test we can check if material can withstand the
lower temperature or not, depending on many factors such as minimum design metal
temperature, material and its grade, material treatment condition, thickness …..etc.
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7. Mechanical Properties
Specific effects of the addition of some elements
Material selection and design
Nickel (Ni) (2-20%): alloying element critical to stainless steels, nickel is added at over 8%
content to high chromium stainless steel. Nickel increases toughness, and strength,
while also improving resistance to oxidization and corrosion. It also increases
toughness at low temperatures when added in small amounts.
Chromium (Cr) (0.5-18%): alloying element critical to stainless. At over 12% content, chromium
significantly improves corrosion resistance. The metal also improves hardenability,
strength, response to heat treatment and wear resistance.
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8. Mechanical Properties
Carbone ( C ) It raises tensile strength, hardness, and resistance to wear and abrasion. It lowers
ductility, toughness and machinability.
Molybdenum (Mo) (0.2-5.0%) molybdenum increases hardenability and strength, creep resistance at high
temperatures. molybdenum protects against pitting corrosion caused by chlorides and
sulfur chemicals.
Aluminum (Al) A (0.95-1.30%): deoxidizer. Used to limit the growth of austenite grains.
Manganese (Mn) (0.25-13%): a deoxidizer and Increases strength at high temperatures by eliminating
the formation of iron sulfides. Manganese also improves hardness, hardenability,
ductility and wear resistance.
Silicon (Si) (0.2-2.0%): silicon is used in a deoxidizing agent in the production of steel, it is almost
always found in some percentage in all grades of steel, improves tensile and yield
strength, hardness and magnetic permeability
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9. Mechanical Properties
Material selection and design
Phosphorus Phosphorus is often added with sulfur to improve machinability in low alloy
Sulfur (S) (0.08-0.15%): Added in small amounts, sulfur improves machinability without
resulting in hot shortness. With the addition of manganese hot shortness is further
reduced due to the fact that manganese sulfide has a higher melting point than iron
sulfide (eliminating the formation of iron sulfide). But without manganese it decrease
weldability, impact toughness and ductility
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10. Corrosion resistance
Corrosion resistance
The following factors shall be considered:
• Temperature - affects corrosion rate and mechanical properties.
• Pressure.
• PH.
• Presence of traces- impurities stress corrosion.
• The amount of aeration - differential oxidation cells.
• Stream velocity and agitation , erosion-corrosion.
• Heat-transfer rates - differential temperatures.
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11. Material types and grades
• Steel : is a combination of iron and carbon. Steel is alloyed with various elements to improve
properties such as (strength, toughness, corrosion resistance, creep resistance,…..etc).
• Carbon steel
Steels that do not have alloying elements intentionally added. However, there may be small amounts
of elements permitted by specifications such as SA516 and SA106, for example that can affect
corrosion resistance, hardness after welding, and toughness. Elements which may be found in small
quantities include Cr, Ni, Mo, Cu, S, Si, P, Al, V and B.
• Stainless steel
Stainless steels categories that are characterized by their metallurgical structure at room
temperature: austenitic, ferritic, martensitic and duplex. One more category is precipitation hardening,
These alloys have varying amounts of chromium and other alloying elements that give them
resistance to oxidation and improve corrosion resistance and mechanical properties depending on the
alloy content.
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12. Iron – Carbon Phase Diagram
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13. Material types and grades
• Austenitic stainless steels
• 300 series SS grades including 304, 304L, 304H, 309, 310, 316, 316L, 316, 316L, 316H, 321, 321H, 347,
347H.
• “L” & “H” suffixes refer to low and high carbon content respectively.
• 300-series grades contain enough nickel to stabilize austenite at room
• Austenitic steels are non-magnetic stainless steels that contain high levels of chromium and nickel and low
levels of carbon.
• Contains about 16 to 22 %chromium and 8 to 14 % nickel
• SS 304 contains 18 Cr and 8Ni , SS 316 similar like SS 304 with adding 2% Mo for more corrosion resistance
• Straight grades of austenitic stainless steels have a maximum carbon content of 0.08 percent. Low carbon
grades or "L" grades contain a maximum carbon content of 0.03 percent in order to avoid carbide
precipitation.
• Carbide precipitation can be reduced through the use of grades with lower carbon content
• show great corrosion resistance, tensile strength, ductility and toughness at cryogenic temperatures also
show high formability, easy weldable
• austenitic stainless steels can be cold worked to improve hardness, strength
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14. Material types and grades
• Applications for austenitic SS:
• 304 and 304L: Tanks,Storage vessels and pipes for corrosive liquid ,Mining, chemical,
cryogenic, food and beverage, and pharmaceutical equipment,Sinks
• 309 and 310 (high chrome and nickel grades): Furnace, and catalytic converter
components, Flare tip
• 316 and 316L (high moly content grades): Chemical storage tanks, pressure vessels, and
piping
• 321 and 316Ti ("stabilized" grades): Afterburners, Super heaters, Compensators ,
Expansion bellows
• 200 Series (low nickel grades):Dishwashers and washing machines, Cutlery and cookware
, In-house water tanks, Indoor and nonstructural architecture, Food and beverage
equipment, Automobile parts
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15. • Ferritic stainless steels
• Include 405, 409, 430, 422 and 446.
• Ferritic stainless steel usually contains at least 12% chromium and is considered a
“straight chromium” stainless steel.
• Ferritic grades have high ductility (but not like austenitic SS) and are easily formed, but
they do not retain their strength at high temperatures like austenitic stainless steel, lower
cost than other grades
• Applications: Solar heaters, slate hooks, coins
Material selection and design
Material types and grades
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16. Material types and grades
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17. • Duplex stainless steels.
• Are called duplex because of the microstructure consists of two phase (50% austenite and 50%ferrit)
including alloy 2205, 2304 and 2507.The welds of 300 series may also show a duplex structure.
• Strength: are twice as strong as regular austenitic SS and ferritic SS
• Corrosion resistance :duplex show corrosion resistance for chloride pitting and crevice corrosion due to
chromium ,molybdenum and nitrogen content so duplex SS grades have a range of corrosion resistance
similar to austenitic SS (except for SCC)
• Stress corrosion crack resistance SCC: duplex SCC show very good SCC resistance.
SCC can be problem for certain circumstances such as (chlorides, humidity,……) for austenitic SS 304, 316,
So duplex SS show better SCC resistance than austenitic SS
• Toughness and ductility: duplex SS show better toughness and ductility than ferritic SS but still does not
reach the excellent value of austenitic SS
• Cost: will be lower than austenitic due to the lower required thickness which lead to lower weight which
means lower cost.
Material selection and design
Material types and grades
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18. • Martensitic stainless steels.
• Include 410, 410S,416,420,440A,440B & 440C.
• It is characterized by its extremely high strength, low fracture resistance, and low ductility.
It can be held at an intermediate temperature for various times, in a process called
tempering, to reduce strength while vastly improving toughness and ductility
• Applications: pumps, valves, boat shafts, cutlery, medical tools (scalpels, razors and
internal clamps),bearings (ball bearings)
Material selection and design
Material types and grades
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19. Material types and grades
• Precipitation hardening stainless steels
• are chromium and nickel containing steels that provide an optimum combination of the properties of
martensitic and austenitic grades. Like martensitic grades, they are known for their ability to gain high
strength through heat treatment and they also have the corrosion resistance of austenitic stainless steels.
• The high tensile strengths of precipitation hardening stainless steel come after a heat treatment process that
leads to precipitation hardening of a martensitic or austenitic matrix. Hardening is achieved through the
addition of one or more of the elements Copper, Aluminium, Titanium, Niobium, and Molybdenum.
• The most well known precipitation hardening steel is 17-4 PH. The name comes from the additions 17%
Chromium and 4% Nickel. It also contains 4% Copper and 0.3% Niobium. 17-4 PH is also known as stainless
steel grade 630.
• Application: aerospace, High strength shafts, Gears., Nuclear waste casks, Turbine blades.
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20. Material types and grades
• Low alloy steel :
A family of steels containing up to 9% chromium and other alloying additions for high
temperature strength and creep resistance. The materials include C-0.5Mo, Mn-0.5Mo, 1Cr-
0.5Mo, 1.25 Cr-0.5Mo, 2.25Cr-1.0Mo, 5Cr-0.5Mo, and 9Cr-1Mo. These are considered
ferritic steels.
• High Strenth low Alloy Steels (HSLA)
A family of low-carbon steels in which the strength levels are achieved by the addition of
moderate amounts of alloying elements such as titanium, vanadium or niobium in amounts of
less than 0.1%. They can be are more sensitive to cracking during fabrication from hydrogen
embrittlement (delayed cracking) or underbead cracking.
• sea water.
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21. Material types and grades
• Monel:
Monel, the classic nickel-copper alloy with the metals in the ratio 2 : 1, is probably, the most commonly used
alloy for chemical plant for specific purpose. It is easily worked and has good mechanical properties up to 500C.
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,
• Inconel:
Inconel (typically 76%Ni, 7% Fe, 15%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, particularly HCl. The corrosion resistance, and use, of the two main
grades, Hastelloy B (65% Ni, 28 %Mo, 6 % Fe) and Hastelloy C (54% Ni, 17 %Mo, 15 %Cr, 5% Fe),
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22. Material types and grades
• Aluminium and its alloys
Pure 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 Cu, with 0.5 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%. 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.
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23. Material types and grades
• Plastic (Nonmetallic) Materials:
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.
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24. Other factors
Surface finish:
• Surface finish can affect on equipment life time especially to equipment that will be subjected to corrosive
environmental.
• Equipment surface should be smooth where corrosive products and other solids can be accumulate.
• Welding joints design should be consider to prevent accumulate and deposition of solids
• Design geometry should be consider to avoid accumulation and erosion-corrosion.
• Refractory: Refractory bricks and cements are needed for equipment operating at high temperatures; such
as, fired heaters, high-temperature reactors and boilers. Which is common composed of mixtures of (Silica
SiO2 and alumina AL2O3)
• Protective coating: Paints are used mainly for protection from atmospheric corrosion.
• Special chemically resistant paints such as epoxy-based have been developed for use on chemical process
equipment. Which requires high surface preparation to ensure good adhesion of painted film
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25. Other factors
• Any special properties required; such as, thermal conductivity, electrical resistance,
magnetic properties
• Ease of fabrication forming, welding, casting. Availability in standard sizes plates, sections,
tubesCost
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26. Conclusion
Material selection and design
The following factors shall be consider during material selection:
1. Mechanical properties
2. The effect of high and low temperatures on the mechanical properties:
3. Corrosion resistance
4. Any special properties required; such as, thermal conductivity, electrical
resistance, magnetic properties
5. Ease of fabrication forming, welding, casting. Availability in standard sizes
plates, sections, tubes
6. Cost
7. Surface finish
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