An Issue about USER DEFINED SIFs

Written by Milad Haji Mohammad Karim in Caesar II,Piping Stress Analysis,Piping Stress Basics

User-defined SIF is the stress intensification factor that the user input into the stress analysis program. The SIF values are usually calculated using FEA programs and then manually entered in the input screens of the stress analysis programs. To increase the accuracy of the output results of a stress analysis problem using the beam method, It is always suggested to extract the amount of SIFs from a Finite Element Analysis (FEA) and then implement them in stress programs like CAESAR II, AutoPIPE, Start-PROF, or Rohr II.

With the deletion of Appendix D from the 2020 edition of ASME B31.3, the use of ASME B31J and other FEA programs will be increased while stress analysis of piping systems. Hence, User-defined SIF values will be very important for stress analysis aspects.

For a branch connection (Tee), The user has to put the amount of extracted SIFs in all 3 elements that form the connection, i.e. two elements for the header and one for the branch, considering the fact that the amount of SIFs for the branch and header are different. For example, for the connection shown in the below figure (Fig. 1), the amount of the header SIFs is entered at nodes 20.1 and 20.2 while the branch SIF is defined at node 20.4.

**Fig. 1: Adding User-defined SIF in Tee joints**

In order to do this, the “SIFs & Tees” box in elements 20.4-45 should be checked, and then the In-Plane and Out-Plane SIFs and also torsion and axial SIFs (if it is necessary) are defined at node 20.4. The same method should be implemented for header elements (at nodes 20.1 and 20.2). The key point in this method is that referring to Fig. 2 below, the type of connection must be blanked.

SIF types selection while specifying user defined SIF — **Fig. 2: SIF types selection while specifying user-defined SIF**

Indeed, in the old method of defining of SIFs, when the type of connection (such as UFT, RFT, and …), is determined in one node, the program will consider that node as an intersection and apart from the calculation of the amount of SIFs, the “Effective section modulus” named “Z_e” in B31 codes, is used for the calculation of the amount of the stresses in the branch section.

**Fig. 3: Effective Section Modulus formula**

But, In the new method, since the value of branch SIFs is extracted and defined directly, therefore, the section modulus of the branch pipe must be used instead of the effective section modulus. This issue has been mentioned in the edition 2016 of the B31.3 code:

In Caesar II, When the type of an intersection is left blank, the real section modulus of pipe elements will be used in stress calculation.

However, leaving the type section blanked causes a problem that must be considered by the user and then a proper solution must be implemented as has been described in the following.

What is the problem? What is the solution?

In Caesar II, as soon as the “SIFs & Tees” box is checked for a particular node and then the type of connection is determined, that node will be considered as an intersection and both the in and out planes will be specified automatically. The procedure of how Caesar II determines these planes has been described in the “User Guide” of the program.

But if the type of connection is not determined, the related node won’t be considered as an intersection and then the in and out planes won’t be determined.

Indeed, using the new method for SIFs determination and when the type is not specified, the program will assume that the user is defining the SIFs for 3 straight elements separately. The In-plane and Out-Plane directions are meaningless for a straight element. However, the program will consider these directions even for a straight element based on the procedure that has been mentioned in detail again in the “User Guide” and then each SIF is assigned to the relevant plane(direction).

The main concept of the Caesar II program for the determination of the in and out planes of a straight element is that there are local coordinate directions and axes for each element named a, b, and c and the program always considers the moment around the b axis as the In-plane moment. The local coordinates in Caesar II are defined in this order:

But, sometimes, based on the orientation of an intersection in the global coordinate system, the In-Plane and Out-Plane directions of the 3 straight elements that form that intersection will be different from the real In-Plane and Out-Plane directions of the mentioned connection. In this case, in order to force the program to calculate the stresses correctly, the extracted SIFs from FEA software are needed to be entered in reverse order.

Some examples

Please consider the below example (Fig. 6) for instance:

**Fig. 6: Typical example for SIF definition**

Referring to the above figure it is obvious that for this intersection, the moment around Z-axis is the In-plane bending moment while for the straight element from node 20.4 to node 45, the moment around X-axis will be the In-plane moment. Now, assume that the In-Plane and Out-Plane SIFs related to the branch side of this connection have been extracted from an FEA program as 3 and 11 respectively and the user wants to import them in Caesar II and at node 20.4. Based on what was mentioned above, these amounts need to be imported in reverse order as has been shown in the below figure (Fig. 7).

Inputting user defined SIFs in Caesar II — **Fig. 7: Inputting user-defined SIFs in Caesar II**

Considering the straight elements of the header, it is obvious that the M_Z is the In-Plane moment for both the straight elements and also the connection itself. Therefore, there is no need to import the extracted SIFs of the header in reverse order.

Now, please consider another example referring to the below figure.

This is a welding Tee and the amount of In-Plane and Out-Plane SIFs are 2.55 and 3.067 respectively. The outer diameter and the thickness of the header and branch are shown in the following figure.

In the first try, the “SIFs box” of the connection has been checked at node 4060 and on the element 4040-4060.

Referring to the below figure (Fig. 9), the amount of bending stress at the branch section is 71.25 Mpa

**Fig. 9: Bending Stress at Branch Connection (first try)**

On the next try, the SIFs of the branch element are imported equal to what was obtained on the first try and also the type of the intersection is left blanked. We may expect to obtain the same results!

Entering user-defined SIF in branch connection — **Fig. 10: Entering user-defined SIFs in branch connection**

But, The below figure reveals that the bending stress has changed to 78.41 Mpa.

Fig. 11: **Bending Stress at Branch Connection (second try)**

In the last try, the obtained values of the In-Plane and Out-Plane SIFs are imported again, but, this time in reverse order, and the type is left blanked again.

Referring to the below figure, the amount of bending stress at node 4060 is again 71.25 Mpa similar to what was obtained on the first try.

Fig. 13: **Bending Stress at Branch Connection (third try)**

Indeed, for this intersection, the In-Plane direction of the branch straight element is different from the real In-Plane direction of the connection and therefore the SIFs must be imported in reverse order in order to calculate the bending stress correctly.

Finally, it should be noted that the approach of the B31.3 code is that in the absence of more applicable data, the axial SIF is supposed to be equal to Out-plane SIF (only for branches). Therefore, if the extracted Out and In-Plane SIFs are needed to be imported in reverse order, you will also have to import the amount of axial SIF manually and equal to the real Out-plane SIF of the connection in order to force the program to calculate the total code stress correctly. You may also get the axial SIF from a better source such as an FEA.

Few more related articles for you.

Stress Intensity Factor (SIF), Flexibility Factor: ASME B31.3 vs ASME B31J
Piping Elbow or Bend SIF (Stress Intensification Factor)
How to use ASME B31J-2017 and FEM for SIF and k-factors for Stress Analysis
Importance & Impact of Stress Intensification Factor (SIF) in Piping

What is Petroleum Refining? Crude Oil Refining Process Steps

Written by Anup Kumar Dey in Process

Petroleum refining is a complex process that transforms crude oil into valuable products like gasoline, diesel, jet fuel, heating oil, and various petrochemicals. This article will delve into the intricacies of crude oil refining, detailing the processes involved, the technologies utilized, and the environmental considerations associated with the industry.

What is Crude Oil

Crude oil is a naturally occurring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials. It varies in composition depending on its source, influencing its refining process. The key components include:

Alkanes (paraffins)
Cycloalkanes (naphthenes)
Aromatics
Asphaltenes (heavy compounds)

Crude oil is classified into various categories, including light, medium, and heavy crude, with different refining implications.

What is Petroleum Refining?

Petroleum Refining is defined as the industrial process of production of useful petroleum products from crude oil. Crude oil in its raw form is a dark and sticky liquid which is not useful. To get usable products from crude oil, it needs to be refined. The plant where the useful products are separated from crude oil is known as a petroleum refinery. In this article, we will explore more about the process of Petroleum Refining-the crude oil refining processes.

How is Petroleum Refined? | What are the stages of oil refining?

Crude oil or petroleum consists of various hydrocarbons. The crude oil refining process breaks the crude oil down into various components to make useful new products. This petroleum refining is a very complex process and requires highly expensive industrial facilities. The basic crude oil refining process steps involved in all petroleum refining for the production of usable products are

Distillation/Separation
- Atmospheric Distillation
- Vacuum Distillation
Conversion
- Cracking
- Reforming
- Alkylation
- Polymerization
- Isomerization
- Coking
- Visbreaking
Treatment, and
Blending

Crude Oil Distillation Process in Petroleum Refining

The first process in the crude oil refining process steps is the distillation process inside a fractionation distillation column. The crude oil from the storage tanks is processed through desalters to remove the excess salt. It is then heated to a temperature of about 400⁰C in a crude oil heater and then routed to the Crude Distillation Unit or CDU.

The main principle of distillation is to vaporize a liquid by heating it at its boiling point and then recondensing and collecting. This same principle is used to separate different compounds from crude oil inside the fractionation distillation column. A temperature gradient is maintained throughout the height of the column. The lower boiling, high volatile hydrocarbons are separated at the top of the column while less volatile, higher boiling products are separated towards the bottom of the column. A reboiler supplies heat at the bottom of the distillation column and the top is cooled by an overhead condenser. So, temperature decreases as the height of the fractionation column increases.

The boiled crude oil (liquid/gas mixture) at the bottom of the distillation column creates its vapor which rises through the vertical column passing through the holes in the distillation trays. As temperature decreases when gas rises through the tower, certain hydrocarbon components condense once one component cools below its boiling point. This separation occurs at different temperatures at different height levels and is collected through the trays. Different boiling-point cuts of different hydrocarbons allow them to be separated out in a single distillation process. The typical Crude oil distillation cuts are presented in Table 1 below:

Hydrocarbon Fraction	Boiling Point Cut/Distillation Range (⁰C)
Gases (C₁-C₄)	<=50
Gasoline/Petrol (C₅-C₇)	50-100
Naphtha (C₈-C₁₁)	80-200
Kerosene (C₁₁-C₁₂)	170-280
Light Diesel (C₁₃-C₁₇)	220-320
Heavy Diesel (C₁₈-C₂₅)	290-350
Atmospheric Residue (C₂₅+)	350-390

Table 1: Typical Crude Oil Boiling-Point Cuts

Refer to Fig. 1, which shows the compounds of crude oils separated at different temperatures in a fractionation distillation column.

**Fig. 1: Crude oil distillation process in Distillation Column**

Conversion Processes in Crude Oil Refining

In this process, residual oils, fuel oils, and light ends are converted to high-octane gasoline, jet fuel, and diesel fuel. Processes like cracking, coking, visbreaking, etc. are used to break large petroleum molecules into smaller ones.

Cracking in Petroleum Refining

Cracking during the crude oil refining process is a very important process where heavy hydrocarbon molecules from the crude oil are broken down into lighter shorter molecules. There are three cracking processes that are used in petroleum refineries. They are

Thermal Cracking: Uses intense heat to break down the heaviest hydrocarbon molecules into smaller ones. Usually used to convert residual oil to fuel oil, petrol, diesel, and naphtha.
Hydro Cracking: This process breaks down the larger molecules of gas oil, kerosene, and naphtha and produces petrol. The Hydrocracking process consists of using hydrogen in the presence of a catalyst at high pressure at around 400⁰C. This process also removes impurities like sulfur, nitrogen, and metal traces.
Catalytic Cracking: In the catalytic cracking process, the gas oil or residual oil is broken down into petrol and diesel using intense heat in the presence of a catalyst. This method produces high-quality products compared to other cracking methods.

Reforming in Crude Oil Refining

The reforming process in Petroleum refining increases the production volume of gasoline from each barrel of crude oil. The reforming process basically rearranges the hydrocarbon molecules of similar carbon atoms and naphtha molecules to convert them into gasoline molecules.

The Alkylation or Catalytic Polymerisation process in crude oil refining converts propene and butene molecules into high-octane hydrocarbons by combining them in the presence of an acid catalyst. This process combines smaller hydrocarbons, such as isobutane and olefins, in the presence of an acid catalyst to produce high-octane gasoline components. Alkylation is vital for enhancing the octane rating of fuels.

The Isomerisation process in petroleum refining converts straight-chain hydrocarbons to branched chains which improves hydrocarbon quality. Isomerization rearranges hydrocarbon structures to improve octane ratings. For example, converting normal butane to isobutane enhances fuel quality.

Treating in Crude Oil refining Process

Treating in petroleum refining processes stabilizes and upgrades petroleum products by removing less desirable products and contaminants or objectionable elements. Products like sulfur, nitrogen, oxygen, salts, dissolved metals, etc are usually present which must be removed to improve the petroleum quality. Various processes used in treating are hydrodesulfurization, hydrotreating, chemical sweetening, desalting, deasphalting, hydrogen sulfide scrubbing, and acid gas removal.

The selection of a proper treatment method is dependent on various factors like:

the nature of the petroleum fractions,
amount and type of impurities in the fractions to be treated,
the extent to which the process removes the impurities, and
end-product specifications.

The treating process can be an intermediate stage in the crude oil refining process, or the products can be treated just before sending the finished product to storage. Various treating materials include acids, alkalis, oxidizing, solvents, and adsorption agents.

Key treatment processes include:

Hydrotreating

Hydrotreating uses hydrogen to remove sulfur, nitrogen, and oxygen from petroleum fractions. It is critical for meeting environmental regulations regarding sulfur content in fuels.

Desulfurization

Specific desulfurization processes are employed to lower sulfur levels, essential for producing ultra-low sulfur diesel (ULSD).

Sweetening

Sweetening processes remove sour compounds (mercaptans and hydrogen sulfide) from products, improving odor and stability.

Petroleum Blending Process in Crude Oil Refining

Blending is the last step in the petroleum refining process and is quite complicated. The blending process involves the optimal mixing of various petroleum components to achieve the final finished product requiring specific octane specifications. The final cost of the product is also decided based on the proper blending of the components. The blending processes in crude oil refining are very important to achieve desired properties like viscosity, flashpoint, pour point, octane number, etc. Different processes are used to blend components like:

In-line blending through a manifold system
Batch blending in tanks
Onboard blending into marine vessels

Usually, four product blending pools are typical in a refinery. They are:

LPG Pool for blending saturated C3s and C4s.
Gasolene Pool: Most important and complex blending pool to produce premium and regular gasolene products by blending appropriate amounts of n-butane, reformate, light naphtha, alkylate and light cracked naphtha.
Gas Oil/Diesel Pool to blend Kerosene, slurry, LGO, and LVGO.
Fuel oil/Bunker Oil Pool to blend LVGO, slurry, and cracked residue.

Products from Crude Oil Refining Process

The various usable end products that are produced after petroleum refining in a refinery are:

Light distillates
- C1 and C2 components
- Gasoline (petrol)
- Light naphtha
- Liquified petroleum gas (LPG)
- Heavy naphtha
Middle distillates
- Automotive and railroad diesel fuels
- Kerosene
- Residential heating fuel
- Other light fuel oils
Heavy distillates
- Wax
- Lubricating oils
- Heavy fuel oils
- Asphalt
Others
- Coke (similar to coal)
- Elemental sulfur

The image in Fig. 2 below shows a schematic flow diagram of the petroleum refining processes in a crude oil refinery.

**Fig. 2: Petroleum Refining Process Flow Diagram**

Online Courses on Petroleum Refining

To learn more about the petroleum refining process steps, the following three online courses are highly recommended:

These online petroleum refining courses will guide you step-by-step in processes like Distillation, Isomerization, Alkylation, Reforming, Hydrofining, and Fluid Catalytic Cracking. You will learn how the main petroleum products like LPG, gasoline, kerosene, diesel fuel, heating oil, heavy fuel, asphalt, lubricants, etc are made.

Petroleum refining is a multifaceted process essential to modern society. Understanding the intricacies of crude oil refining, from distillation to blending, highlights the technological and economic complexities involved. As the world shifts toward sustainability, the refining industry must adapt, embracing innovations and prioritizing environmental stewardship.

What are Vessel Trims? / Examples and Characteristics of Pressure Vessel Trims

Written by Anup Kumar Dey in Mechanical,Piping Design Basics

What are Vessel Trims?

Vessel trims are independent piping and instrument items that are directly attached to the pressure vessel. These pressure vessel trims are required for displaying the process parameters inside the vessel and for operation and maintenance purposes. By reading such working process parameters of a horizontal or vertical vessel, the performance and working of the pressure vessel can be known. The vessel trims provide various information like:

the utilization capacity of the vessel
the working temperature
the working pressure
fluid flow
fluid level

Examples of Vessel Trims

Typical examples of pressure vessel trims are:

pressure gauge
temperature transmitter,
pressure transmitter
temperature gauge
sparge tubes
rotameter
dip tubes
potential difference transmitter
level gauge
overflow and vent piping
spray ball assemblies, etc.

Characteristics of Vessel Trims

All such pressure vessel trims are linked with the DCS system for control room operation for reading purposes. Few of the vessel trims are considered piping items while a maximum is considered instrumentation items.

Vessel trims are independent items and are not manufactured along with the pressure vessel. However, the exact location of such vessel trims must be informed to the vessel manufacturer prior to the fabrication of the vessel. Usually, the piping engineer is responsible to consider and locate the pressure gauge, potential difference transmitter, level gauge, temperature gauge, level bridal, rotameter, and future connections with valve and blind flanges and inform the vendor of the exact locations. All these items can be removed from the vessel. Vessel trims are usually bolted with a vessel nozzle with a flanged connection.

All vessel trims must be easily accessible. They should be visible easily to the plant operators and hence, must be installed at a reasonable height. A ladder and access platform must be provided for big-diameter vessels when vessel trims are mounted on the top of the vessel. Usually, a separate vessel trim drawing is prepared to identify all these items. The scope and supply of vessel trims must be decided with the vendor prior to order finalization.

All vessel trims must be indicated in the process P&IDs. Usually, these are added in the detailed engineering phase of any project. All vessel trims are loose items and are generally identified by a trim number (line number). The design and materials of vessel trims are the responsibility of the piping engineer. The vessel trim materials are usually selected according to the designated piping material class.

Online Course on Pressure Vessels

If you wish to learn more about Pressure Vessels, their design, fabrication, installation, etc in depth, then the following online courses will surely help you:

A36 Steel | Composition, Applications, and Properties of ASTM A36 Steel

Written by Anup Kumar Dey in Civil,Engineering Materials,Piping Interface

A36 Steel is the most extensively used structural steel material for construction purposes. This carbon steel material is designated by ASTM as ASTM A36 or A36 steel. Containing a maximum of 0.29% carbon, A36 steel is strong, ductile, formable, tough, and weldable. All these properties help A36 steel to be used for multipurpose applications. A36 steel is produced in a variety of forms like plates, bars, girders, structural shapes, etc. In the following paragraphs, we will learn about A36 steel properties and their key attributes.

Chemical Composition of A36 steel

ASTM A36 is mild steel or low-carbon steel having a carbon amount of less than 0.3% by weight. The presence of a low amount of carbon makes A36 steel have properties like good formability, weldability, machinability, and ductility. A36 usually contains some other elements like Silicon, Copper, Manganese, Phosphorus, Sulfur, etc. Also, depending on the product form the chemical compositions of A36 steel vary slightly. Typical chemical compositions for ASTM A36 steel are provided in Table 1 below.

A36 Steel Product form	C (wt%)	Si (wt%)	Mn (percentage by weight)	P (wt%)	S (wt%)	Cu (wt%)
A36 Structural Shapes with thickness <=75 mm	0.26	0.4	No specific requirement	0.04	0.05	0.2
A36 Structural Shapes with thickness >75 mm	0.26	0.4	0.85-1.35	0.04	0.15-0.40	0.2
Plates with thickness <=20 mm	0.25	0.4	No specific requirement	0.03	0.03	0.2
A36 Steel Plates with thickness >20 mm to up to 40 mm.	0.25	0.4	0.80-1.20	0.03	0.03	0.2
A36 Steel Plates with thickness >40 mm to up to 65 mm.	0.26	0.15-0.40	0.80-1.20	0.03	0.03	0.2
A36 Steel Plates with thickness >65 mm to up to 100 mm.	0.27	0.15-0.40	0.85-1.20	0.03	0.03	0.2
A36 Steel Plates with a thickness >100 mm	0.29	0.15-0.40	0.85-1.20	0.03	0.03	0.2
A36 bars with thickness <=20 mm	0.26	0.4	no requirement	0.04	0.05	0.2
A36 Steel Bars with thickness >20 mm to up to 40 mm.	0.27	0.4	0.60-0.90	0.04	0.05	0.2
A36 Steel Bars with thickness >40 mm to up to 100 mm.	0.28	0.4	0.60-0.90	0.04	0.05	0.2
A36 Steel Bars with a thickness >100 mm	0.29	0.4	0.60-0.90	0.04	0.05	0.2

Table-1: Chemical Compositions of A36 Steel

Properties of A36 Steel

The properties of A36 steel can be grouped into two classes:

Mechanical properties of A36 Steel and
Physical properties of A36 Steel.

A36 Steel Mechanical Properties

The mechanical properties of A36 steel relevant for structural steel application are provided in Table 2 below:

Mechanical properties of A36 Steel	Values	A36 steel product types/Notes
Ultimate tensile strength, MPa (KSI)	400-550 (58-80)	For Shapes, Plates, and Bars
Yield strength, MPa (KSI)	250 (36)	Thickness ≤ 200mm (8 in)
Yield strength, MPa (KSI)	220 (32)	Steel plate thickness > 200mm (8 in.)
Elongation, %	20	Plates and Bars in 200 mm (8 in.)
Elongation, %	23	Plates and Bars in 50 mm (2 in.)
Brinell hardness, HB	119-162	As per the conversion from tensile strength
Rockwell Hardness, Rockwell B	67-83	As per the conversion from tensile strength
Charpy V-Notch Impact Test, J ( ft·lbf)	27 (20)	Structural shapes, alternate core location
Modulus of elasticity (Young’s modulus), GPa (KSI)	200 (29×10³)
Shear modulus, GPa (KSI)	79.3 (11.5×10³)
Bulk Modulus, Gpa (KSI)	140 (20.3X10³)
Poissons ratio	0.26

Table 2: A36 Steel Mechanical Properties

Physical properties of A36 Steel

The physical properties of A36 steel are listed below:

The density of A36 Steel: 7850 Kg/m³
Range of Melting Point: 1425 to 1538⁰ C (2600-2800⁰F).

Advantages of A36 Steel

There are various advantages of A36 steel like

Cheaper.
Very good performance and strength
High durability.
Easily recyclable.
Can be easily joined by bolting/riveting.

Applications of A36 Steel Material

Because of the above-mentioned benefits, A36 steel is used as the base material for structural and construction applications. Based on the thickness and corrosion resistance of the material, A36 steel is used for the following applications:

Structural shapes like H-beams, I-beams, and channels
Used in the construction of warehouses, industrial and commercial structures, buildings (including pre-fabricated buildings), pipes, enclosures, tubings, cabinets, and housings.
Used in tanks, forming bins, rings, jigs, bearing plates, cams, templates, stakes, fixtures, sprockets, forgings, brackets, gears, base plates, automotive equipment, machinery parts, ornamental works, stakes, agricultural equipment, and frames.
To make components in the automotive, construction, heavy equipment, and oil and gas industrie s.

A36 Steel Equivalent

EN S275 and S235J2 steel is equivalent to A36 Steel

A36 Steel vs 1018 Steel

Both 1018 and A36 steel are highly useful mild steel grades. 1018 steel comes in cold-drawn or hot-rolled form and contains 0.18% carbon. The main differences between A36 steel vs 1018 steel are provided in Table 3 below:

Parameter	A36 Steel	1018 Steel
Composition	A36 Steel contains 0.26% Carbon, and 0.75% Manganese	1018 Steel contains 0.18% Carbon and 0.6 to 0.9 % Manganese.
Strength	The tensile strength of A36 steel is 58 ks and the yield strength is 36.3 KSI.	The tensile and yield strength of 1018 steel is higher than A36 steel. The yield strength is 53.7 KSI and the tensile strength is 63 KSI.
Elongation	The elongation of A36 steel is more than 1018 steel	Less elongation as compared to A36 steel
Cost	A36 steel is cheaper than 1018 steel	1018 steel is costlier than A36 steel.
Uses	A36 Steel is widely preferred for structural applications.	1018 Steel is preferred for machining and finishing applications.

Table-3: A36 steel vs 1018 Steel

A36 Steel FAQs

1. What is A36 grade steel?

ASTM A36 is a structural grade mild carbon steel with excellent strength, formability, and welding properties. The material is widely used in construction.

2. What is A36 steel used for?

A36 steel is one of the most common types of alloy steel finding a range of applications including, oil and gases, bridges, building services, chemical industries, heavy equipment industries, etc.

3. Is A36 steel strong?

A36 steel is a strong material. s you can see from table 2 above, it has a yield strength of 36 KSI, and tensile strength ranges from 58 to 80 KSI.

4. Why is A36 steel so popular?

The popularity of A36 steel lies in its favorable properties. It has high strength, and durability, and can be easily fabricated. Moreover, A36 steel is economic.

5. What is the difference between A36 and A572 steel?

A572 has a higher yield point and tensile strength than A36. So, A572 is stronger as compared to A36 steel.

6. Is 1018 steel the same as A36?

No, A36 and 1018 steel are different. The differences between 1018 and A36 steel are provided in Table 3 above.

7. Is A36 stainless steel?

No, A 36 is carbon steel. Refer to Table 1 above to know its chemical compositions.

8. What is A36 steel yield strength?

The yield strength of A36 steel is 32 KSI.

9. What is A36 steel density?

The density of A36 steel is 7850 Kg/m³

What is Crude Oil? / Crude Oil Price and Types

Written by Anup Kumar Dey in Mechanical,Process

Crude oil, a naturally occurring petroleum product is a type of fossil fuel extracted from the earth. Consisting of hydrocarbons and other organic materials, crude oil is refined to produce a wide variety of usable products including gasoline, diesel, and various other forms of petrochemicals.

As crude oil can not be replaced naturally at the same rate that we consume, It is a nonrenewable limited resource. To date, crude oil is the single most important primary source of energy production, and hence, it plays a significant role in the world energy scenario. Due to its high market value in the energy scenario, Crude oil is often compared to gold and referred to as “black gold”. In the year 1859, Col. Edwin Drake drilled the first successful well through rock and produced crude oil at Titusville, Penn. In this article, we will explore more about crude oil: its definition, composition, types, and factors that determine crude oil price.

What is Crude Oil?

Crude oil can be defined as a naturally occurring, yellowish-black colored, liquid fossil fuel made up of a mixture of hydrocarbons, extracted through drilling from beneath the earth’s surface. Crude oil consists of a mixture of hydrocarbons, nitrogen, sulfur, oxygen, and other miscellaneous organic compounds. Crude oil is formed due to the transformation of large quantities of dead organisms by intense heat and pressure under the sedimentary rock of the earth.

Upon extraction of this crude oil by the oil drilling method, its components are separated by fractional distillation technique in a fractionating column. Numerous oil and gas industry products like gasoline, kerosene, diesel, asphalt, plastics, pharmaceuticals, pesticides, chemicals, etc are produced from crude oil.

Composition of Crude Oil

The composition of crude oil varies from one formation to another. However, it falls approximately in the range provided in Table 1 below.

Element	Weight Percent Range
Carbon	83 to 85%
Hydrogen	10 to 14%
Nitrogen	0.1 to 2%
Oxygen	0.05 to 1.5%
Sulfur	0.05 to 6.0%
Metals	< 0.1%

Table-1: Elements in Crude Oil

Crude oils are characterized by hydrocarbon compound types present in them: alkanes or paraffin, naphthenes, aromatics, and asphaltic. The most common hydrocarbons in crude oil are Alkenes. Naphthenes are also an important part of all liquid refinery products. Aromatics and asphaltic usually constitute a small percentage of most crudes. The relative percentage of these four groups of hydrocarbons that determine the exact properties of crude oil is provided in Table 2.

Hydrocarbon Type	Weight Percent Range
Alkanes (paraffin)	15 to 60%
Naphthenes	30 to 60%
Aromatics	3 to 30%
Asphaltic	Remainder

Table-2: Amount of Hydrocarbon types in crude oil

The appearance and color of crude oil depend greatly on its composition. The usual color of raw crude oil is black or dark brown.

What are the Types of Crude Oil?

Depending on various parameters crude oil is categorized into several groups as follows:

Crude Oil type based on API gravity scale

Depending on the API gravity of crude oils, they are classified into the following three types:

Heavy Crude (10-20⁰ API gravity)
Medium Crude (20-25⁰ API gravity), and
Light Crude (>25⁰ API gravity)

Types of Crude Oils based on the amount of sulfur

Depending on the presence of sulfur or hydrogen sulfide (one of the major pollutants), crude oil is grouped into the following two categories:

Sweet Crude oil (Sulfur content less than 0.5%)
Sour Crude oil (Sulfur content >0.5%)

Usually heavier crude has greater sulfur content.

Crude oil Types based on geographic location

The classification of crude oil based on the geographic location where it is produced is very important as it directly affects transportation costs. Depending on the geographic production location, crude oil is classified into the following classes

WTI (West Texas Intermediate) crude: High quality, sweet, light oil crude.
Brent crude: Oil production from Europe, Africa, and the Middle Eastern oil is usually considered as Brent crude.
Dubai-Oman crude
Tapis crude: from Malaysia
Minas crude: from Indonesia
OPEC reference basket crude: crude oil blends from various OPEC countries.
Midway sunset crude: heavy crude oil of California
Western Canadian Select crude

Crude Oil Price

The price of crude oil refers to the spot price of a barrel of benchmark crude oil. Depending on the type of crude oil the price also varies significantly. The factors on which the crude oil price depends are:

Extraction cost: With an increase in the cost of extraction due to technology cost, the crude oil price increases.
Specific gravity or API gravity of the crude oil: Lighter crudes cost more as compared to heavier grades.
The sulfur content of the crude oil type: Sour crude oil is cheaper than sweet crude oil.
Location of the crude oil: WTI crude is costlier compared to other grades.
Oil Demand: Similar to other products, when demand rises crude oil price also increases.
Production Volume: When crude oil extraction is more than the demand, the price of crude oil drops.
Natural Disaster: Natural disasters or extreme weather conditions in major oil-producing regions affect production which results in an increase in crude oil price.
Dependency on other energy sources: With an increase in energy dependency on other energy sources like renewable energy sources the price of crude oil decreases.
Political factors: War, terrorism, attacks, political instability, etc. reduce oil prices.
The exchange value of the Dollar: The fluctuation of the dollar price globally affects the crude oil price locally.
Economic factors: Crude oil prices reduce during recession periods.
Brokers and Speculators: The crude oil price is also influenced by the brokers and speculators of trading.
OPEC decisions: OPEC or the Organization of Petroleum Exporting Countries (15 countries: Iran, Iraq, Kuwait, Saudi Arabia, Venezuela, Nigeria, Libya, Algeria, Angola, Congo, Ecuador, Gabon, UAE, Qatar, Equatorial Guinea) have a major influence on the global oil price. Their decisions affect the price of crude oil.

Crude Oil Barrel

A Crude oil barrel is a unit of crude oil that represents the volume of crude oil. It is represented as bbl in short. The price of crude oil is provided in terms of “crude oil price per barrel”. In the worldwide oil industry, a crude oil barrel is defined as 42 US gallons or 35 imperial gallons which are approximately 159 liters. The production of oil companies is represented as barrels (bbls) per day unit.

What are the differences between Crude oil and Shell oil? Crude oil vs Shale oil

The primary difference between crude oil and shale oil is the way they are collected. The shale oil is usually found in smaller batches within the rock shale. The differences between crude oil and shale oil are tabulated below:

Crude Oil	Shale Oil
Crude oil is extracted directly from reservoirs	Shale oil is generated by processing the organic matter present in the rock shale with pyrolysis, hydro-generation, or thermal dissolution.
Extraction of crude oil does not require high-end technology.	High-end technology is required for extracting shale oil.
The crude oil extraction method is old but used worldwide.	The shale oil extraction method is newer and widely used in the USA.

Table-3: Crude Oil vs Shale Oil

Crude Oil Frequently Asked Questions

1. What are the top oil-producing countries?

The top five oil-producing countries are the USA, Russia, Saudi Arabia, Canada, and Iraq.

2. When will the Oil production come to an end?

This is not easy to answer. However, the oil firm BP has estimated that as per the existing oil reserve estimate in different counties and consumption rates, the oil production will end in the year 2067. But not to worry, scientists will create other renewable sources to depend on.

Click here to know about Crude Desalting and Dehydration Processes

Rockwell Hardness Scale for Hardness Test

Written by Anup Kumar Dey in Engineering Materials,Mechanical

The hardness of a material can be defined as the resistance of that material to indentation and scratching. It is characteristic of materials and a very important material property. Different applications required hard materials and the hardness of that material quantifies that property. The more the value of hardness, the more hard the material is, and the more difficult will be to create an indentation under a given load. There are various industry-approved methods for hardness testing like Brinell Hardness, Rockwell Hardness, Vickers Hardness, etc. However, Rockwell hardness testing is one of the widely used, efficient, and industry-recognized methods of hardness testing that is represented using Rockwell Hardness Scales.

For material selection, process and quality control, and acceptance testing of commercial products, the Rockwell hardness test is useful. In this article, we will learn the procedure of the Rockwell hardness test, related formulas, standards, the Rockwell hardness scale, and its advantages.

What is the Rockwell Hardness Test?

Rockwell hardness test using the Rockwell hardness scale is one of the extensively used and accurate hardness test methods prevalent in industries. This testing is easier to perform as compared to Brinell or Vickers hardness test. As per the name of the inventors, Mr. Hugh M. Rockwell and Mr. Stanley P. Rockwell, this hardness test is well-known as Rockwell hardness testing.

Rockwell hardness test is widely used for thin steel, lead, brass, zinc, aluminum, cemented carbides, iron, titanium, copper alloys, and certain plastics. This test is considered one of the simple and quick hardness testing methods.

Rockwell hardness testing is performed by comparing the penetration depth measurement of an indenter under a large load known as a major load and a smaller preload known as a minor load.

Types of Rockwell Hardness Tests

Depending on the applications of minor and major loads during the test, the Rockwell hardness test is categorized into two groups. They are:

Regular Rockwell Hardness Test where the minor load is 10 kgf and major load is 60, 100, or 150 kgf.
Superficial Rockwell Hardness Test where the applied minor load is 3 kgf and the major loads are 15, 30, or 45 kgf.

Rockwell Hardness Test Procedure

The procedure for the Rockwell Hardness test consists of the application of a minor load followed by a major load. The minor load is applied to establish the zero position from where the measurement will be taken. Next, the major load is applied and then removed while still maintaining the minor load. The penetration depth (d) from the zero datum position is measured by a dial.

A pre-decided minor and major load are applied on the test specimen by a diamond or ball indenter. The minor load (3 kgf to 10 kgf) reduces the effect of the surface finish. After that, the additional load or major load (15 kgf to 150 kgf) is applied for a specified dwell time. Now the major load is released and the final depth of indentation from the preload position to the combined load position is measured which is converted to the Rockwell hardness number. Then the preload is released and the indenter is removed from the sample. Refer to Fig. 1 below that explains the Rockwell hardness test procedure.

**Fig. 1: Rockwell Hardness Test Procedure**

The procedure of the Rockwell hardness test consists of the following steps:

Setting the test specimen sample on a flat, solid surface.
Applying the minor load to create a slight impression (zero point position).
Setting the measuring gauge and measuring the initial indentation depth under minor load.
Applying the major load and holding for the dwell time.
Removing the major load, keeping the minor load.
Measuring the depth of penetration from zero position.
Finding the Rockwell hardness number from the penetration depth.

Rockwell Hardness Test Formula

Rockwell hardness test is directly read from the equipment. However, there is a formula to convert the measured depth (d) into the Rockwell hardness number. A Rockwell hardness number for a material is a unitless number indicating the hardness value on a specified Rockwell scale.

The equation for Rockwell Hardness Number is given by

HR=N-(d/s)

Where,

N and s are scale factors depending on the test being used. The value of N is either 100 or 130 depending on the Rockwell hardness scale used. Similarly, the value of s is either 0.001 mm or 0.002 mm.
d is the penetration depth measured from zero points (in mm).

Rockwell Hardness Scale

Rockwell hardness scale is a type of scale that indicates the hardness of a material measured using the Rockwell hardness test. It is a unitless number. The Rockwell hardness scale is symbolized by HR followed by a letter indicating any of the possible scales. For example, “HRC 96” for a metal means the hardness of that metal is 96 when measured using Rockwell hardness scale C.

Manufactured products are made of different types of materials. To accommodate the hardness testing of this diverse range, several different indenter types are used in the Rockwell hardness testing along with a range of standard force levels. Each combination of indenter type and applied force levels has been defined using a distinct Rockwell hardness scale. As per ASTM E 18, there are thirty (30) different Rockwell scales divided into two categories: regular Rockwell scales and superficial Rockwell scales.

There are several different Rockwell Scales denoted by various letters requiring different loads or indenters during hardness testing. The Rockwell hardness scale chart for regular Rockwell scales and superficial Rockwell scales are provided in table 1 and 2 below:

Rockwell Scale Symbol	Type of Indenter/Diameter in case of Ball	Minor Load	Major Load	Typical use
HRA	Spheroconical diamond	98.07 N (10 kgf)	588.4 N (60 kgf)	Cemented carbides, thin steel, and shallow case hardened steel.
HRB	Ball, 1.588 mm (¹⁄₁₆ inches)	98.07 N (10 kgf)	980.7 N (100 kgf)	Copper alloys, soft steels, aluminum alloys, malleable iron, etc.
HRC	Spheroconical diamond	98.07 N (10 kgf)	1471 N (150 kgf)	Steel, hard cast irons, pearlitic malleable iron, titanium, deep case hardened steel, and other materials harder than 100 on the Rockwell B scale.
HRD	Spheroconical diamond	98.07 N (10 kgf)	980.7 N (100 kgf)	Thin steel and medium case hardened steel, and pearlitic malleable iron.
HRE	Ball, 3.175 mm (⅛ inches)	98.07 N (10 kgf)	980.7 N (100 kgf)	Cast iron, aluminum and magnesium alloys, and bearing metals.
HRF	Ball, 1.588 mm (¹⁄₁₆ inches)	98.07 N (10 kgf)	588.4 N (60 kgf)	Annealed copper alloys, and thin soft sheet metals.
HRG	Ball, 1.588 mm (¹⁄₁₆ inches)	98.07 N (10 kgf)	1471 N (150 kgf)	Malleable irons, copper-nickel-zinc and cupronickel alloys.
HRH	Ball, 3.175 mm (⅛ inches)	98.07 N (10 kgf)	588.4 N (60 kgf)	Aluminum, zinc, and lead.
HRK	Ball, 3.175 mm (⅛″)	98.07 N (10 kgf)	1471 N (150 kgf)	Bearing metals and other very soft or thin materials.
HRL	Ball, 6.350 mm (¼ inches)	98.07 N (10 kgf)	588.4 N (60 kgf)	Bearing metals and other very soft or thin materials.
HRM	Ball, 6.350 mm (¼ inches)	98.07 N (10 kgf)	980.7 N (100 kgf)	Bearing metals and other very soft or thin materials.
HRP	Ball, 6.350 mm (¼ inches)	98.07 N (10 kgf)	1471 N (150 kgf)	Bearing metals and other very soft or thin materials.
HRR	Ball, 12.70 mm (½ inches)	98.07 N (10 kgf)	588.4 N (60 kgf)	Bearing metals and other very soft or thin materials.
HRS	Ball, 12.70 mm (½ inches)	98.07 N (10 kgf)	980.7 N (100 kgf)	Bearing metals and other very soft or thin materials.
HRV	Ball, 12.70 mm (½ inches)	98.07 N (10 kgf)	1471 N (150 kgf)	Bearing metals and other very soft or thin materials.

Table 1: Regular Rockwell hardness scale chart

Rockwell Scale Symbol	Type of Indenter/Diameter in case of Ball	Minor Load, N (kgf)	Major Load, N (kgf)	Typical use
15N	Spheroconical diamond	29.42(3)	147.1 (15)	Similar to A, C, D scales in table-1 but for thinner gage material.
30N	Spheroconical diamond	29.42(3)	294.2 (30)	Similar to A, C, D scales in table-1 but for thinner gage material.
45N	Spheroconical diamond	29.42(3)	441.3 (45)	Similar to A, C, D scales in table-1 but for thinner gage material.
15T	Ball; 1.588 mm (1/16 inches)	29.42(3)	147.1 (15)	Similar to B, F, G scales in table-1 but for thinner gage material.
30T	Ball; 1.588 mm (1/16 inches)	29.42(3)	294.2 (30)	Similar to B, F, G scales in table-1 but for thinner gage material.
45T	Ball; 1.588 mm (1/16 inches)	29.42(3)	441.3 (45)	Similar to B, F, G scales in table-1 but for thinner gage material.
15W	Ball; 3.175 mm (1/8 inches)	29.42(3)	147.1 (15)	Very Soft Material
30W	Ball; 3.175 mm (1/8 inches)	29.42(3)	294.2 (30)	Very Soft Material
45W	Ball; 3.175 mm (1/8 inches)	29.42(3)	441.3 (45)	Very Soft Material
15X	Ball; 6.35 mm (1/4 inches)	29.42(3)	147.1 (15)	Very Soft Material
30X	Ball; 6.35 mm (1/4 inches)	29.42(3)	294.2 (30)	Very Soft Material
45X	Ball; 6.35 mm (1/4 inches)	29.42(3)	441.3 (45)	Very Soft Material
15Y	Ball; 12.70 mm (1/2 inches)	29.42(3)	147.1 (15)	Very Soft Material
30Y	Ball; 12.70 mm (1/2 inches)	29.42(3)	294.2 (30)	Very Soft Material
45Y	Ball; 12.70 mm (1/2 inches)	29.42(3)	441.3 (45)	Very Soft Material

Table 2: Superficial Rockwell hardness scale charts

Factors for Selecting Appropriate Rockwell Scale

Choosing the right Rockwell scale is difficult as various parameters affect the selection process. The major factors to be considered for Rockwell scale selection are:

the type of hardness test material
the thickness of the test material
the area or width of the test material
the limitations of each Rockwell hardness scale
the test material homogeneity.

Standards for Rockwell Hardness Testing

The widely used standards that govern the Rockwell hardness testing methodology are:

ASTM E18 for Metals
ISO 6508 for Metals,
ASTM D785 for Plastics
ISO 2039 for Plastics

Rockwell Hardness Test Machine

A wide range of Rockwell hardness tester machines is available to find out the hardness values of materials. It can vary from manual and semi-automatic to fully automatic advanced ones. Refer to Fig. 2 below that provides the major components of a typical Rockwell hardness testing machine.

**Fig. 2: Typical Rockwell hardness testing machine**

Factors Affecting the Accuracy and Reliability of Rockwell Hardness Testing

There are various parameters that affect the accuracy, precision, and reliability of the Rockwell hardness testing method. Those are:

Rockwell test machine: Test results can vary due to variability from the equipment, operator, and environmental conditions. So, it must be ensured that the machine condition, and specimen set-up by the operator are correct.
Presence of dirt or grease in the contact area.
Specimen Surface: Surface conditions must be of good quality to get more accurate and reproducible test results.
Operator Skill: the operator must be highly skilled in proper fixing and testing techniques. Otherwise, test results can vary significantly.

Typical Rockwell Hardness Values

The following table (Table 3) provides some typical values of Rockwell hardness

Material	Rockwell Hardness Values
Very Hard Steel	HRC 55 to HRC 66
Axes	HRC 45 to HRC 55
Brass	HRB 55 to HRB 93
Hard Impact Steel Blades	HRC 52 to HRC 55

Table 3: Typical Rockwell Hardness Values

Advantages of Rockwell Hardness Testing

Rockwell hardness testing provides significant advantages with respect to other hard test methods as listed below:

Rockwell hardness test displays hardness values directly. So no calculation is required to find the hardness value.
It is a fast, reliable, and robust method with a small area of indentation.

Rockwell Hardness Test vs Brinell hardness Test

The details of the Brinell hardness test and the main differences between the Rockwell and Brinell hardness test are published in a separate article. Kindly click here to visit that article.

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