AISI 4340 PROPERTIES

AISI 4340, 1.6511, 36CrNiMo4, SNCM439

AISI 4340 is a type of low alloy steel that can be heat treated and strengthened with 0.8% Cr, 0.2% Mo, and 1.8% Ni alloy elements. In comparison to AISI 4140, AISI 4340 offers higher strength and toughness, along with excellent fatigue, wear, and atmospheric corrosion resistance. Typically provided in a hardened and tempered condition, AISI 4340 has a tensile strength ranging from 930-1080 Mpa and a hardness of 280-320HB. The pre-hardened and tempered material can also be surface-hardened through flame or induction hardening, as well as nitriding. This ultra-high strength steel is classified as a medium-carbon, low-alloy steel, and has superior ductility, toughness, creep resistance, and fatigue resistance compared to most other steels. Depending on the heat treatment, the alloy can achieve high degrees of hardenability, with HRC hardnesses ranging from 24 to 53.

WHAT IS AISI 4340 STEEL?

AISI 4340 Steel is a particular type of steel alloy assigned prefix code by the AISI system. This letter prefix is mainly used to denote the steelmaking process of the AISI 4340 Steel.

The grade number in the steel alloys makes sure to differentiate their industrial applications.

4:  The first number ‘4’ indicates that the steel is ‘Molybdenum’ steel and Molybdenum is most important alloy element for this steel as compared to other steel series.

3:The second number’3′ means that three (3) elements are present, and they include nickel, chromium, and molybdenum.

40:  The last two numbers ‘40’ indicates the amount of carbon present in the steel. For this grade it has 0.40% carbon  same as AISI 4140 steel.

Moreover, this particular number is assigned to almost all the steel alloys by AISI to designate the different steel compositions in its alloys.

Is AISI 4340 Stainless Steel?

Stainless steel has at least 10.5% Chromium, and the maximum carbon content is not more than 1.2%.The main characteristics for these kind materials are good rust resistance and corrosion resistance.

While AISI 4340 is defined as a heat-treatable low-alloy steel containing 0.8% Cr, 0.2% Mo and 1.8% Ni as strengthening alloying elements. Compared with Stainless steel, it has higher strength and toughness, but its wear resistance and atmospheric corrosion resistance are not as good as stainless steel.

Is AISI 4340 Steel Corrosion Resistant?

AISI 4340 steel is a medium-carbon nickel-chromium-molybdenum steel which has excellent tensile strength, toughness and fatigue resistance.

AISI 4340 Steel is highly resistant to atmospheric corrosion because of its combined alloy elements of chromium, molybdenum, nickel and manganese which can not only improve the strength and hardenability of steel, but also improve corrosion resistance.

The corrosion-resistant nature of the AISI 4340 Steel is responsible for its use in the forged hydraulic systems, and it is also used in many other machine appliances, including those involved in the aerospace industry.

Is AISI 4340 Steel Magnetic?

AISI 4340 Steel is manufactured with many basic properties, including high magnetic properties. Other than magnetic properties, the AISI 4340 Steel is also equipped with durable mechanical properties.

This steel allows very substantial magnetic properties because a few percent of alloying elements are present. The magnetization of the AISI 4340 steel is estimated at up to 21500 Gauss.

Can You Machine AISI 4340 Steel?

Yes, you can machine AISI 4340 Steel with the help of almost all types of conventional techniques. No excess carbon contents are present, that’s why AISI 4340 steel can be machined easily.

This grade is easy to process, depending on the size and complexity of the section and the amount of processing to be carried out. The machining of AISI 4340 steel is carried out under an assumed shape.

However, the recommended machining process for AISI 4340 Steel is carried out under annealed, normalized and tempered environments.

How is The Weldability of AISI 4340 Steel?

AISI 4340 Steel is recommended to weld in the annealed condition, but welding in the quenched and tempered state should be avoided as much as possible, because this will affect the mechanical properties. It is not recommended to weld under nitriding, flame or induction hardening conditions.

In addition to this, the weldability of the AISI 4340 steel is carried out by preheating the material at 200 to 300 degrees. This high temperature for the welding is maintained to ensuring the sustainability of the substrate. The welded parts should be cooled slowly in the ashes or sand, and the stress should be relieved as much as possible.

EQUIVALENT INTERNATIONAL GRADES

We can see the differences between different national standards from the table below.

Chemical Composition

Standard	Grade	C	Si	Mn	P	S	Cr	Ni	Mo
ASTM A29	4340	0.38-0.43	0.15-0.35	0.6-0.8	≤ 0.035	≤ 0.04	0.7-0.9	1.65-2.0	0.2-0.3
EN10250	36CrNiMo4	0.32-0.4	≤ 0.4	0.5-0.8	≤ 0.035	≤ 0.035	0.9-1.2	0.90-1.2	0.15-0.3
	1.6511
BS 970	EN24	0.36-0.44	0.1-0.4	0.45-0.7	≤ 0.035	≤ 0.04	1.0-1.4	1.3-1.7	0.2-0.35
	817M40
JIS G4103	SNCM439	0.36-0.43	0.15-0.35	0.6-0.9	≤ 0.03	≤ 0.03	0.6-1.0	1.6-2.0	0.15-0.3
GB 3077	40CrNiMoA	0.37-0.44	0.17-0.37	0.5-0.8	≤ 0.025	≤ 0.025	0.6-0.9	1.25-1.65	0.15-0.25

 

Physical Property

Density g/cm3	7.85
Melting point °C	1427
Poisson's ratio	0.27-0.30
Machinability (AISI 1212 as 100% machinability)	50%
Thermal expansion co-efficient µm/m°C	12.5
Thermal conductivity W/(m.K)	44.5
Modulus of elasticity 10^3 N/mm^2	210
Electric resistivity Ohm.mm2 /m	0.19
Specific heat capacity J/(kg.K)	460
Modulus of elasticity 10^3 N/mm2	100 ℃	200 ℃	300 ℃	400 ℃	500 ℃
	205	195	185	175	165
Thermal expansion 10^6 m/(m.K)	100 ℃	200 ℃	300 ℃	400 ℃	500 ℃
	11.1	12.1	12.9	13.5	13.9

4. Mechanical Property

Mechanical Condition	T	U	V	W	X	Y	Z
Ruling Section (mm)	150	100	63	30	30	30	30
Tensile Strength Mpa	850-1000	930-1080	1000-1150	1080-1230	1150-1300	1230-1380	>1550
Yield Strength, Mpa	≥665	≥740	≥835	≥925	≥1005	≥1080	≥1125
Elongation %	≥13	≥12	≥12	≥11	≥10	≥10	≥5
Izod Impact J	≥54	≥47	≥47	≥41	≥34	≥24	≥10
Charpy Impact J	≥50	≥42	≥42	≥35	≥28	≥20	≥9
Brinell Hardness HB	248-302	269-331	293-352	311-375	341-401	363-429	>444

5.High Temperature Strength

For quenched and tempered heavy forgings
Diameter mm	Yield strength MPa
	20 ℃	100 ℃	200 ℃	250 ℃	300 ℃	350℃	400℃
≤250	590	549	510	481	441	412	371
250-500	540	505	471	451	412	383	353
500-750	490	466	441	422	392	363	343

Forging

Forging temperature should be carried out between 1150℃-1200℃,The lower the forging-ending temperature ,the finer the grain size .hold suitable time for the steel to be thoroughly heated before forge, but don’t forge below minimum forging temperature 850°C. AISI 4340 has good forging characteristics, but crack is easily occured when improper cooling way after forged, so it  should be cooled as slowly as possible in still air or in sand after forged.

Normalizing

Normalizing is used to refine the structure of forgings that might have cooled non-uniformly after forged, and considered as a conditioning treatment before final heat treatment. Normalizing temperature for AISI 4340 steel should be carried out between 850℃-880℃. hold suitable time for the steel to be thoroughly heated to complete the ferrite to austenite transformation. Cool in still air.

Annealing

Full annealing is recommended for AISI 4340 before machining, AISI 4340 should be carried our at a nominal temperature of 830℃-850℃,hold suitable time for the steel to be thoroughly heated, then furnace cooling to 610℃ at a rate of 11℃ per hour, finally air cooling.

Hardening

This heat treatment will obtain martensite structure after quenched. It will increase the surface hardness and strength.AISI 4340 should be carried out between 830℃-865℃, hold suitable time for the steel to be thoroughly heated, soak for 10-15 minutes per 25 mm section, oil quench is recommended. Tempering should be followed  immediately after quenched.

HOW TO HARDEN AISI 4340 STEEL?

AISI 4340 alloy structural steel belongs to gear steel which has high strength, toughness and outstanding hardenability and anti-thermal stability.

AISI 4340 Steel is used for heavy machinery high-load shafts, turbine shafts with a diameter greater than 250 mm, helicopter rotor shafts, turbojet engine turbine shafts, blades, high-load transmission parts, crankshafts, gears,etc.

But before we use them for above applications, we need to harden the materials according to requirements. In the actual production process,we often use water quench and oil quench to harden AISI 4340 Steel.

	Water Quench	Oil Quench
Quench Medium	Water	Oil
Quench Temperature	850~870℃	850~870℃
Quench Time	Normal	Longer
Cooling ability	Better	Normal
Crack Resistance	Poor	Normal
Deformation	Bigger	Normal
Hardness	Higher	Normal
Hardenability	Better	Normal
Tempering Following	Immediately	Immediately

HARDNESS OF AISI 4340 STEEL

When we use AISI 4340 steel for applications, we choose its high strength, high hardness and excellent toughness. Normally, AISI 4340 steel has a hardness below 229 HBW under annnealed conditon, 248-302HBW under quenched and tempered condition. With suitable hardening process, it can even achieve surface hardness up to 60HRC.

But can it be considered that the higher the hardness, the better the performance? Of course not.

The higher the hardness, the greater the strength, but the plasticity and toughness decrease. Especially in the case of quenching and tempering conditon, in order to ensure the strength, it is necessary to find a balance point between the strength and the toughness.

Tempering

AISI 4340 alloy steel should be in the heat treated or normalized and heat-treated condition before tempering. Tempering is usually carried out to relieve stresses from the hardening process, but primarily to obtain the required  hardness and mechanical properties. The actual tempering temperature will be chosen to meet the required properties.it is usually carried out at 450℃- 660℃, hold until temperature is uniform throughout the section, soak for 1 hour per 25 mm of section, and cool in still air. Tempering between 250℃-450℃ is not avoided as tempering within this range will seriously reduce the impact value, result in temper brittleness.

Application

AISI 4340 is often used in preference to AISI 4140 at the higher strength levels because of its better hardenability and improved CVN impact toughness.

Typical applications include: Heavy-duty axles, shafts, heavy-duty gears, spindles, pins, studs, collets, bolts, couplings, sprockets, pinions, torsion bars, connecting rods, crow bars, conveyor parts, forged hydraulic, forged steel crankshafts etc.

 

What is CD4MCuN Hardened?

CD4MCuN is a duplex stainless steel alloy that is known for its excellent corrosion resistance properties. It is not typically hardened through traditional heat treatment methods like quenching and tempering, as these methods are not suitable for duplex stainless steels.

Duplex stainless steels like CD4MCuN have a two-phase microstructure consisting of austenitic and ferritic phases. This microstructure provides the alloy with excellent strength and corrosion resistance properties, but it also makes it difficult to harden through traditional heat treatment methods.

Instead of heat treatment, duplex stainless steels like CD4MCuN are typically hardened through cold working or work hardening. This involves subjecting the alloy to mechanical deformation processes like rolling, bending, or forging, which can increase its strength and hardness. The extent of work hardening can be controlled by adjusting the amount and type of deformation applied to the alloy.

However, it is important to note that excessive cold working can also lead to a loss of toughness and ductility, which can make the alloy more susceptible to brittle fracture. Therefore, it is essential to balance the amount of work hardening with the desired mechanical properties and the intended application.

In summary, CD4MCuN is not typically hardened through traditional heat treatment methods like quenching and tempering. Instead, it can be hardened through cold working or work hardening, which involves subjecting the alloy to mechanical deformation processes. It is important to balance the amount of work hardening with the desired mechanical properties and the intended application to avoid excessive loss of toughness and ductility.

SAE 904L: Chemical Composition, Propertes and Applications

SAE 904L is a non-stabilized austenitic stainless steel alloy that is known for its high corrosion resistance properties. It contains high levels of nickel and molybdenum, which give it excellent resistance to a wide range of corrosive environments. In this article, we will discuss the properties of SAE 904L stainless steel in detail.

Equivalent grades include:

• EN 1.4539 (X1NiCrMoCuN25-20-5)
• UNS N08904
• AISI 904L
• DIN 1.4539
• ASTM A182 F904L
• JIS SUS 890L
• AFNOR Z2 NCDU 25-20

Chemical Composition:

The chemical composition of SAE 904L stainless steel includes high levels of nickel, chromium, and molybdenum. It also contains copper, which enhances its resistance to acids. The low carbon content in the alloy minimizes the risk of intergranular corrosion.

The chemical composition of SAE 904L stainless steel typically includes:

• Carbon (C): Maximum of 0.020%
• Silicon (Si): Maximum of 1.00%
• Manganese (Mn): Maximum of 2.00%
• Phosphorus (P): Maximum of 0.045%
• Sulfur (S): Maximum of 0.035%
• Chromium (Cr): 19.0% - 23.0%
• Nickel (Ni): 23.0% - 28.0%
• Molybdenum (Mo): 4.0% - 5.0%
• Copper (Cu): 1.0% - 2.0%
• Nitrogen (N): Maximum of 0.10%
• Iron (Fe): Balance

Corrosion Resistance: SAE 904L stainless steel is known for its excellent corrosion resistance properties. It is highly resistant to a wide range of corrosive environments, including sulfuric acid, hydrochloric acid, and phosphoric acid solutions. It also has good resistance to pitting and crevice corrosion. The high nickel and molybdenum content in the alloy provide it with excellent resistance to stress corrosion cracking.

Mechanical Properties:

SAE 904L stainless steel has good strength and ductility. Its high tensile strength and yield strength provide the necessary strength for structural applications. The alloy also has good elongation, which means it can undergo plastic deformation without cracking or breaking. The low carbon content in the alloy minimizes the risk of sensitization and intergranular corrosion. The alloy's high nickel and molybdenum content provide it with excellent toughness and resistance to stress corrosion cracking.

The mechanical properties of SAE 904L stainless steel typically include:

• Tensile strength: 490 MPa (71 ksi) minimum
• Yield strength: 220 MPa (32 ksi) minimum
• Elongation: 35% minimum
• Hardness: Brinell 70 maximum; Rockwell B 90 maximum

Physical Properties:

SAE 904L stainless steel has a density of 7.98 g/cm³ (0.289 lb/in³) and a melting point of 1350°C (2460°F). It has a thermal conductivity of 13.1 W/m·K (9.03 BTU/hr·ft·°F) and a specific heat capacity of 500 J/kg·K (0.12 BTU/lb·°F).

Applications:

SAE 904L stainless steel is commonly used in applications that require high corrosion resistance, such as in the chemical processing, oil and gas, and pulp and paper industries. It is also used in medical and laboratory equipment due to its high corrosion resistance and bright finish. The alloy is also used in heat exchangers, condensers, and other equipment that requires high resistance to corrosive environments.

In conclusion, SAE 904L stainless steel is a highly versatile alloy with excellent corrosion resistance properties. Its high nickel and molybdenum content provide it with excellent resistance to a wide range of corrosive environments. The alloy's good mechanical and physical properties make it suitable for use in a wide range of applications, including chemical processing, oil and gas, and medical equipment.

References:

1.     "904L Datasheet" (PDF). Atlas Steels.

2.     ^ "904L Datasheet" (PDF). Rolled Alloys.

3.     ^ "904L Datasheet" (PDF). ATI Metals.

Properties of CD4MCuN Duplex Stainless Steel

CD4MCuN is a duplex stainless steel that is commonly used in harsh environments, such as offshore oil and gas production, due to its superior corrosion resistance properties. This alloy is a modified version of CD4MCu, which also contains nitrogen for improved corrosion resistance. In this article, we will explore the properties of CD4MCuN in detail.

Equivalent steel grades of CD4MCuN: 

UNS S32750; UNS S32550; SAE 904L; SUS 904L; UNS N08904; EN 1.4539; SS2562

The chemical composition of CD4MCuN is as follows:

• Carbon (C): 0.030% max
• Silicon (Si): 1.00% max
• Manganese (Mn): 1.50% max
• Phosphorus (P): 0.040% max
• Sulfur (S): 0.030% max
• Chromium (Cr): 24.0-26.0%
• Nickel (Ni): 3.0-5.0%
• Molybdenum (Mo): 1.5-2.5%
• Copper (Cu): 1.5-3.0%
• Nitrogen (N): 0.20-0.35%

The addition of nitrogen in CD4MCuN improves its corrosion resistance properties compared to its predecessor CD4MCu. The high levels of chromium, molybdenum, and copper in CD4MCuN also contribute to its excellent corrosion resistance properties, while the low carbon content enhances its weldability

Corrosion Resistance:

One of the most significant properties of CD4MCuN is its exceptional corrosion resistance. This alloy offers superior resistance to pitting and crevice corrosion in chloride-containing environments, making it well-suited for use in offshore and marine environments. CD4MCuN also offers good resistance to general corrosion in a wide range of corrosive media.

Mechanical Properties:

Here are the mechanical properties of CD4MCuN:

• Tensile Strength: The tensile strength of CD4MCuN ranges from 550 to 700 MPa (80 to 101 ksi). Tensile strength is the maximum stress that a material can withstand before it fractures under tension.
• Yield Strength: The yield strength of CD4MCuN ranges from 350 to 450 MPa (51 to 65 ksi). Yield strength is the stress level at which a material begins to deform permanently.
• Elongation: The elongation of CD4MCuN is typically around 25%. Elongation is the amount of deformation that a material can undergo before it fractures.
• Hardness: The hardness of CD4MCuN is typically in the range of 25 to 30 HRC (Rockwell C). Hardness is a measure of a material's resistance to deformation or scratching.
• Fatigue Strength: The fatigue strength of CD4MCuN is also high, which means that it can withstand repeated loading and unloading cycles without suffering from fatigue failure.

The mechanical properties of CD4MCuN are largely unaffected by high temperatures, making it suitable for use in high-temperature environments. CD4MCuN is also highly weldable using conventional welding techniques, such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and shielded metal arc welding (SMAW). However, due to its high strength and hardness, CD4MCuN can be more difficult to machine than some other stainless steels.

Weldability:

CD4MCuN is highly weldable using conventional welding techniques, such as gas tungsten arc welding (GTAW), gas metal arc welding (GMAW), and shielded metal arc welding (SMAW). This alloy exhibits good weldability due to its low carbon content and high chromium and molybdenum content.

Heat Resistance:

CD4MCuN has excellent heat resistance properties, making it suitable for use in high-temperature environments. It has a maximum service temperature of 300°C (572°F), and its mechanical properties are largely unaffected at elevated temperatures.

Machinability:

CD4MCuN has good machinability, but it can be more difficult to machine than some other stainless steels due to its high strength and hardness. Carbide tools are recommended for machining CD4MCuN.

Applications:

CD4MCuN is commonly used in offshore and marine environments, such as in offshore oil and gas production facilities, seawater desalination plants, and marine equipment. It is also used in chemical processing, pulp and paper production, and other corrosive environments where superior corrosion resistance is required.

In conclusion, CD4MCuN is a duplex stainless steel alloy with excellent corrosion resistance, mechanical properties, weldability, heat resistance, and machinability. Its unique combination of properties makes it well-suited for use in harsh environments where other alloys may fail. Understanding the properties of CD4MCuN can help engineers and designers select the appropriate material for their specific application, ensuring optimal performance and reliability.

 

ASTM A990: Standard Specification for Duplex Stainless Steel Castings

ASTM A990 is a standard specification for duplex stainless steel castings used in pressure-containing applications such as valves, flanges, and fittings. This standard covers five different grades of duplex stainless steel castings, each with unique properties and characteristics.

The five grades covered by ASTM A990 include CD3MN, CD4MCu, CD4MCuN, CE3MN, and CE8MN. CD3MN is a duplex stainless steel with a high chromium content and moderate amounts of nickel, molybdenum, and nitrogen. It offers good corrosion resistance in various environments, including seawater, and is often used in valves, pumps, and other pressure-containing components.

CD4MCu is a duplex stainless steel with higher levels of chromium, molybdenum, and copper than CD3MN. It has excellent resistance to pitting and crevice corrosion and is commonly used in marine and chemical processing applications.

CD4MCuN is a modified version of CD4MCu that also contains nitrogen for improved corrosion resistance. This grade is well-suited for applications in harsh environments, such as offshore oil and gas production.

CE3MN is a duplex stainless steel with a high nitrogen content and low nickel content. It offers good resistance to corrosion and stress corrosion cracking in chloride-containing environments and is often used in chemical processing and pulp and paper production.

CE8MN is a duplex stainless steel with higher levels of nitrogen and molybdenum than CE3MN. It has excellent resistance to pitting and crevice corrosion and is often used in seawater applications.

The mechanical properties of the duplex stainless steel castings specified in ASTM A990 depend on the grade and the heat treatment process. The minimum tensile strength and yield strength requirements for each grade are specified in the standard, as well as the maximum hardness values.

ASTM A990 also specifies the chemical composition and testing requirements for each grade of duplex stainless steel castings. The chemical composition requirements ensure that the castings meet the specified corrosion resistance and mechanical properties, while the testing requirements ensure that the castings meet the quality standards set forth in the specification.

In conclusion, ASTM A990 is an important standard specification for duplex stainless steel castings used in pressure-containing applications. Understanding the different grades and their properties can help engineers and designers select the appropriate material for their specific application. By following the requirements set forth in ASTM A990, manufacturers can ensure that their duplex stainless steel castings meet the necessary quality and performance standards

 

Erosion and Erosion-Corrosion in Process Equipment and Piping

Summary:

Erosion and erosion-corrosion are forms of damage that can occur in process equipment and piping exposed to moving fluids and/or catalysts. These damages can cause a localized loss in thickness in the form of pits, grooves, gullies, waves, rounded holes, and valleys. The metal loss rates depend on various factors, including the velocity and concentration of the impacting medium, the size and hardness of the impacting particles, the hardness and corrosion resistance of the material subject to erosion, and the angle of impact.

Preventing and mitigating erosion and erosion-corrosion involve improvements in design, changes in shape, geometry, and materials selection, and utilizing impingement plates and specialized corrosion coupons. Visual examination and specialized corrosion monitoring electrical resistance probes are among the inspection and monitoring techniques used to detect the extent of metal loss.

Electrical Resistance (ER) probes and instruments determine metal loss from corrosion or erosion by the electrical resistance method.

1. Description of Damage

a) Erosion is the accelerated mechanical removal of surface material as a result of relative movement between, or impact from solids, liquids, vapor or any combination thereof.

b) Erosion-corrosion is a description of the damage that occurs when corrosion contributes to erosion by removing protective films or scales, or by exposing the metal surface to further corrosion under the combined action of erosion and corrosion.

2. Materials Affected by Erosion-Corrosion

 All metals, alloys, and refractories are susceptible to erosion-corrosion.

3. Key Considerations

a) In most cases, erosion-corrosion occurs as a result of the combined action of mechanical erosion and chemical corrosion, with pure erosion (abrasive wear) being rare. Thus, it is important to consider the role of corrosion in contributing to damage.

b) Metal loss rates are influenced by several factors, including the velocity and concentration of the impacting medium (such as particles, liquids, droplets, slurries, and two-phase flow), the size and hardness of the impacting particles, the hardness and corrosion resistance of the material subject to erosion, and the angle of impact.

c) Softer alloys, such as copper and aluminum, may be more vulnerable to erosion-corrosion under high-velocity conditions due to their susceptibility to mechanical damage.

d) While increasing the hardness of the metal substrate is often considered a means to minimize damage, it may not necessarily improve resistance to erosion, especially if corrosion plays a significant role.

e) For each environment-material combination, there is usually a threshold velocity above which impacting objects may cause metal loss. Increasing velocities beyond this threshold results in higher metal loss rates, as shown in Table 1, which demonstrates the relative susceptibility of different metals and alloys to erosion-corrosion by seawater at varying velocities.

f) The size, shape, density, and hardness of the impacting medium also affect the rate of metal loss. 

g) Increasing the corrosivity of the environment can reduce the stability of protective surface films and increase the susceptibility to metal loss. Metal can be removed from the surface as dissolved ions or solid corrosion products that are mechanically swept from the metal surface.

h) Factors that increase the corrosivity of the environment, such as temperature and pH, can also increase the susceptibility to metal loss.

Table 1– Typical erosion-corrosion rates in seawater (API 571 Section 4.2.14)

4. Affected Equipment and Components

a) Erosion and erosion-corrosion can affect all types of equipment exposed to moving fluids and catalysts. This includes piping systems, such as bends, elbows, tees, and reducers, as well as downstream piping systems from letdown valves and block valves. Additionally, pumps, blowers, propellers, impellers, agitators, agitated vessels, heat exchanger tubing, measuring device orifices, turbine blades, nozzles, ducts, vapor lines, scrapers, cutters, and wear plates can be affected.

b) Erosion can be caused by gas-borne catalyst particles or particles carried by a liquid, such as a slurry. Refineries are particularly susceptible to this type of damage, as it can occur in catalyst handling equipment (valves, cyclones, piping, reactors) and slurry piping in FCC reactor/regenerator systems, coke handling equipment in both delayed and fluidized bed cokers (figure 1), and as wear on pumps (figure 2 and figure 3), compressors, and other rotating equipment.

Figure 1: Erosion of a 9Cr coker heater return bend (API 571 Section 4.2.14)

Figure 2: Cast iron impeller in untreated cooling water after four years of service (API 571 Section 4.2.14)

Figure 3: Close-up of Figure 2 showing both erosion-corrosion at the vane tips and pitting on the pressure side of the vanes (API 571 Section 4.2.14).

c) Hydroprocessing reactor effluent piping may be subject to erosion-corrosion by ammonium bisulfide, with the degree of metal loss dependent on several factors, including the concentration of ammonium bisulfide, velocity, and alloy corrosion resistance.

d) Crude and vacuum unit piping and vessels exposed to naphthenic acids in some crude oils may suffer severe erosion-corrosion metal loss depending on temperature, velocity, sulfur content, and TAN level.

5. Appearance or Morphology of Damage

a) Erosion and erosion-corrosion result in a localized loss of thickness, typically in the form of pits, grooves, gullies, waves, rounded holes, and valleys. These losses often exhibit a directional pattern.

b) Failures can occur quickly, making it crucial to address and monitor these types of damage.

6. Prevention and Mitigation Techniques for Erosion and Erosion-Corrosion

Erosion and erosion-corrosion can cause serious damage to equipment and structures, leading to costly repairs and downtime. Fortunately, there are several prevention and mitigation techniques that can be employed to minimize the impact of these damaging processes.

a) Design improvements are a crucial aspect of preventing erosion and erosion-corrosion. Changes in shape, geometry, and materials selection can all play a role. Examples of design improvements include increasing pipe diameter to decrease velocity, streamlining bends to reduce impingement, increasing wall thickness, and using replaceable impingement baffles.

b) Improving resistance to erosion is often achieved by increasing substrate hardness using harder alloys, hardfacing, or surface-hardening treatments. Erosion-resistant refractories, such as those used in cyclones and slide valves, have also been effective.

c) Erosion-corrosion can be mitigated by using more corrosion-resistant alloys and/or altering the process environment to reduce corrosivity. Techniques such as deaeration, condensate injection, or the addition of inhibitors can all help to reduce corrosion. It is important to note that increasing substrate hardness alone generally does not improve resistance to erosion-corrosion.

d) Heat exchangers can utilize impingement plates and tube ferrules to minimize erosion problems.

e) In applications where naphthenic acid corrosion is a concern, higher molybdenum-containing alloys can be used to improve resistance to this specific form of corrosion.

By employing these prevention and mitigation techniques, the impact of erosion and erosion-corrosion can be minimized, ensuring the longevity and reliability of equipment and structures.

7. Inspection and Monitoring

a) Metal loss can be detected through visual examination of suspected or troublesome areas as well as through ultrasonic (UT) or radiographic testing (RT).

b) In some applications, specialized corrosion coupons and on-line corrosion monitoring electrical resistance probes are used for monitoring purposes.

c) Infrared (IR) scans are employed to detect refractory loss in service.

8. Related Mechanisms

Specific terminology has been developed for various forms of erosion and erosion-corrosion in particular environments and/or services. These terms include cavitation, liquid impingement erosion, fretting, and other similar terms.

9. Conclusion

Erosion and erosion-corrosion can cause severe damage to equipment and facilities in the refining and petrochemical industry, leading to safety hazards, production losses, and increased maintenance costs. Effective prevention and mitigation measures are crucial to minimize the impact of these damaging mechanisms. This requires a combination of proper material selection, design improvements, and regular inspection and monitoring.

10. Future Scope

Further research and development in materials science and corrosion engineering can lead to more effective solutions for preventing erosion and erosion-corrosion in the refining and petrochemical industry. This includes the development of new alloys and coatings with improved erosion and corrosion resistance, as well as the advancement of non-destructive testing techniques for early detection of damage. Additionally, continued education and training for industry professionals on the importance of erosion and erosion-corrosion prevention and mitigation can help reduce the frequency and severity of incidents caused by these mechanisms.

11. References

1. ASM Metals Handbook, Volume 13, “Corrosion,” ASM International, Materials Park

2. ASM Metals Handbook, Volume 11, “Failure Analysis and Prevention,” ASM International, Metals Park.

12. Case Studies and Examples of Erosion and Erosion-Corrosion in Refining and Petrochemical Industry

Here are some examples of erosion and erosion-corrosion in the refining and petrochemical industry:

1. Erosion-corrosion in a crude oil unit atmospheric distillation column: In this case, the metal loss occurred due to the presence of naphthenic acid corrosion in the column's top tray. The damage was detected during an inspection, and the tray had to be replaced.
2. Erosion in FCC regenerator cyclones: The cyclones in an FCC regenerator were suffering from erosion due to the high-velocity flow of catalysts. The damage was addressed by replacing the existing cyclones with erosion-resistant ceramic cyclones.
3. Erosion-corrosion in hydroprocessing units: Ammonium bisulfide was causing erosion-corrosion in the effluent piping of hydroprocessing units. The problem was mitigated by using more corrosion-resistant alloys and altering the process environment.
4. Erosion in piping downstream of letdown valves: In a petrochemical plant, the piping downstream of letdown valves was experiencing erosion due to high-velocity flow of fluids. The problem was solved by installing replaceable impingement baffles.
5. Erosion-corrosion in FCC reactor feed nozzles: The nozzles in an FCC reactor were experiencing erosion-corrosion due to the high-velocity flow of catalysts. The damage was addressed by changing the material of the nozzles to a more erosion-resistant alloy.

By NTS