What are Lower Explosive Limits (LEL) and Upper Explosive Limits (UEL)

Written by Anup Kumar Dey in Health & Safety,Piping Interface

Explosive limits give the concentration range of a fuel (gas/vapor) that will cause an explosion or fire in the presence of an igniting source. There are two kinds of explosive limits that are widely used; LEL or Lower Explosive limits and UEL or Upper Explosive limits. Both LEL and UEL are represented by the percentage by volume of the gas in the air. In this article, we will learn the significance of Lower Explosive Limits (LEL) and Upper Explosive Limits (UEL).

What is Lower Explosive Limit or LEL?

The lower explosive limit or LEL of a vapor or gaseous substance is the lowest concentration of the gas in the air required to ignite/burn and explode in the presence of an ignition source. The lower explosive limit is also known as the lower flammable limit or LFL. To give an example, propane can explode once it reaches 2.1% of the air, by volume. So, the LEL of propane is 2.1%.

The LEL or lower explosive limit varies from one gas to another. In general, for most flammable gases LEL is less than 5% by volume. So, these flammable gases can create a high risk even with a very low concentration of the gas/vapor.

What is Upper Explosive Limit or UEL?

The highest concentration of a gas or vapor that will cause an explosion or burn in the air when ignited is defined as the Upper Explosive Limit (UEL). The other term for upper explosive limit is the Upper Flammable Limit or UFL. For example, propane will explode till the concentration does not exceed 9.5% in the air. Hence, the UEL of propane is 9.5%.

For a fire or explosion to take place, all three elements of the fire triangle must be present simultaneously. Those are fuel, an ignition source, and air/ oxygen. The ratio of fuel and oxygen must be above a certain minimum limit and below a maximum certain limit. This limiting minimum value is known as the Lower Explosive Limit and the limiting maximum value is known as the Upper Explosive Limit which varies with each flammable gas/vapor.

Significance of Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL)

Information about the Lower Explosive Limits (LEL) and Upper Explosive Limits (UEL) of a gas/vapor is very important. Below the LEL level, the fuel and oxygen mixture is very lean and it will not cause burning or explosion. Again there will be a maximum concentration of gas (UEL) above which the fuel and air mixture will be very rich to cause an explosion. So, When the fuel and air mixture falls in between LEL and UEL limit, the condition is hazardous and it may cause fire/explosion in presence of an ignition source.

The above explanation can easily be simplified with an example of Methane gas. The Lower explosive limit of Methane is 5% volume in air and the Upper explosive limit is 17% volume in air. Hence, when the volume percentage of methane in an environment falls between 5% to 17%, the environmental condition is highly hazardous. The range of 5% to 17% is the explosive range for methane gas. When the volume percentage of methane is below 5% or above 17%, there will not be an explosion.

Note that even though the concentrations above the UEL are considered non-burning, they are still hazardous because if the concentration is lowered due to the introduction of fresh air, it will easily enter the explosive range.

Lower and Upper Explosive Limits of Various Fuels (Gases/Vapors)

The LEL and UEL values (percentage by volume) for some common gaseous fuels are provided in the following table.

Flammable Gas/Vapor	Lower Explosive Limit (LEL %)	Upper Explosive Limit (UEL %)	Flammable Gas/Vapor	Lower Explosive Limit (LEL %)	Upper Explosive Limit (UEL %)
Acetone	2.6	13	Ethylene	2.7	36
Acetylene	2.5	100	Ethylene Oxide	3.6	100
Acrylonitrile	3	17	Gasoline	1.2	7.1
Allene	1.5	11.5	Heptane	1.1	6.7
Ammonia	15	28	Hexane	1.2	7.4
Benzene	1.3	7.9	Hydrogen	4	75
1,3-Butadiene	2	12	Hydrogen Cyanide	5.6	40
Butane	1.8	8.4	Hydrogen Sulfide	4	44
n-Butanol	1.7	12	Isobutane	1.8	8.4
1-Butene	1.6	10	Isobutylene	1.8	9.6
Cis-2-Butene	1.7	9.7	Methane	5	15
Trans-2-Butene	1.7	9.7	Methanol	6.7	36
Butyl Acetate	1.4	8	Methylacetylene	1.7	11.7
Carbon Monoxide	12.5	74	Methyl Bromide	10	15
Carbonyl Sulfide	12	29	3-Methyl-1-Butene	1.5	9.1
Chlorotrifluoroethylene	8.4	38.7	Methyl Cellosolve	2.5	20
Cumene	0.9	6.5	Methyl Chloride	7	17.4
Cyanogen	6.6	32	Methyl Ethyl Ketone	1.9	10
Cyclohexane	1.3	7.8	Methyl Mercaptan	3.9	21.8
Cyclopropane	2.4	10.4	Methyl Vinyl Ether	2.6	39
Deuterium	4.9	75	Monoethylamine	3.5	14
Diborane	0.8	88	Monomethylamine	4.9	20.7
Dichlorosilane	4.1	98.8	Pentane	1.4	7.8
1,1-Difluoro-1-Chloroethane	9	14.8	Propane	2.1	9.5
1,1-Difluoroethane	5.1	17.1	Propylene	2.4	11
1,1-Difluoroethylene	5.5	21.3	Propylene Oxide	2.8	37
Dimethylamine	2.8	14.4	Tetrafluoroethylene	4	43
Dimethyl Ether	3.4	27	Toluene	1.2	7.1
2,2-Dimethylpropane	1.4	7.5	Trichloroethylene	12	40
Ethane	3	12.4	Trimethylamine	2	12
Ethanol	3.3	19	Vinyl Bromide	9	14
Ethyl Acetate	2.2	11	Vinyl Chloride	4	22
Ethyl Benzene	1	6.7	Vinyl Fluoride	2.6	21.7
Ethyl Chloride	3.8	15.4	Xylene	1.1	6.6

Table 1: LEL and UEL values of gases

LEL Sensors and Meters

The gas concentration must be closely monitored to safely work in hazardous closed spaces with flammable gases. Various LEL sensors or meters are used in industries that can give a warning signal. Infrared sensing elements of these LEL meters measure the lower explosive limits of various gases in an environment.

In general, when the gas concentration exceeds 20% of the gas LEL, the environment is considered unsafe. These LEL gas sensors provide a warning to the operators whenever the combustible gas in the environment exceeds 10%.

Modern LEL meters are highly sophisticated devices with microprocessors-based modular design and digital display. The most widely used LEL meter is the Wheatstone bridge type, which is proven to be effective for most environments. However, these types of LEL sensors have some limitations.

To overcome the drawbacks of LEL sensors, Photoionization Detectors (PIDs) with higher sensitivity sensors are developed which provide more accurate LEL measurements. PID can measure the concentration of inflammable gases and other toxic gases even when present at very low levels.

What are PPM and PPB?

PPM or “parts per million” is a dimensionless measure that provides the ratio of a substance in a mixture to the whole mixture. Sometimes LEL/UEL and toxicity of gases are provided in ppm. Similarly, PPB is parts per billion, which is also used for certain gases.

How to convert %LEL to PPM?

Both %LEL and PPM ratios indicate Volumes. While converting %LEL to PPM, 1% is considered equal to 10 thousand per million. Means,

1% vol = 10,000 ppm.
0.1% vol = 1,000 ppm
0.01% vol = 100 ppm
0.001% vol = 10 ppm
0.0001% vol = 1 ppm

So, using the above values any %LEL can be easily converted into the corresponding PPM. Let’s take the example of hydrogen sulfide (H₂S), which is both toxic and flammable gas. The LEL vol% for H₂S is 4 (Refer to Table 1). That means,

100% LEL = 4% vol = 40,000 ppm H2S
50% LEL = 2% vol = 20,000 ppm H2S
10% LEL = 0.4% vol = 4,000 ppm H2S

What is Process Engineering and What Do Process Engineers Do?

Written by Animesh Chakraborty in Process

The term “process” can be defined simply as a way to make a product from raw materials. The process engineer’s job is to select process steps for product manufacturing and the required specifications. There will be several processes to make the same product. The best way to manufacture a product has not yet been discovered and it cannot be said that the product can be manufactured in one way only. Process engineers are facing alternative solutions to a production problem.

This possibility arises from a combination of factors such as information, imagination, knowledge, and experience obtained from past processes. However, the economics of production is the key to finding the most optimized process. Therefore, innovation, Ideas, and cost-effectiveness are key elements of process engineering.

What is Process Engineering?

Process engineering is the understanding and application of the basic principles and laws of nature that enable humans to transform raw materials and energy into products useful to society on an industrial scale. By taking advantage of natural forces such as pressure, temperature, concentration gradients, and the law of conservation of mass, process engineers can develop methods to synthesize and purify desired chemical products in large quantities. Process engineering deals with the design, operation, control, optimization, and enhancement of chemical, physical and biological processes.

What is the key difference between Chemical Engineering and Process Engineering?

For all practical purposes, it makes no difference, process engineers are often chemical engineers.

A chemical engineer does not have to be a process engineer, but can be a project engineer or project manager.

A process engineer in the E&C business is a chemical engineer who practices chemical engineering, designs processes, and performs unit operations in the petroleum refining, petrochemical, food processing, biotechnology, pharmaceutical, oil and gas, and gas processing industries.

Skills required by a Process Engineer

A good process engineer should have the following capabilities:

Technical drawing interpretation
Good analytical and mathematical ability.
Excellent written and verbal communication skills
Ability to change existing practices.
Strong attention to detail.
Solid ability to identify, assess and solve problems.
Good Software knowledge
Commercial awareness

What Does a Process Engineer Do?

Process engineers perform calculations, analyze results, and create designs within safety and control parameters to achieve the desired product. A process engineer’s job begins with a block diagram that consists of the major operations involved. As the design progresses, block diagrams are transformed into process flow diagrams showing key controls and required process parameters, and finally, detailed drawings called Piping and Instrumentation Diagrams (P&IDs). The P&ID represents all control layouts and piping layouts for the various unit operations involved in the process.

A unit operation is a piece of machinery that is also indicated by a P&ID along with details such as sizing, process data, and operating parameters. This P&ID will continue to serve as a guideline for developing process and functional specifications. In basic engineering, the process engineer plays a key role, in initiating and establishing the process flow based on the specifications received from the customer and working on the created design layout.

Some of the other responsibilities of a process engineer can be listed as follows:

Design and development of the complete process using simulation software packages.
Developing P&IDs, PFDs, Line Parameters, Equipment Sizing, Line Sizing, etc for further activities.
Facilitating HAZOP, HAZID requirements, etc
Performing regular tests of existing equipment.
Commissioning and decommissioning of a plant or part of a plant.
Monitoring and Maintaining equipment.
Designing new equipment.
Researching, pricing, and assisting in the equipment purchase of new equipment
Redesigning/Improving the flow of the process in the factory or plant
Overseeing processes to guarantee efficient performance of the line to maximize output with minimum defects in the production line.
Overseeing the operations of the plant
Overseeing the safety of employees
Writing, maintaining, and collecting required paperwork to show compliance with safety protocols
Assisting in budgeting.
Verifying every detail of the production process to improve efficiency and productivity and cut costs.

Click here to learn the deliverables that a process engineer produces during the design phase of an EPC project.

Process Engineering Jobs

Process engineers are required in various industries. They usually got an opportunity to work in permanent or contract jobs. The majority of their jobs are in large and small factories, plants, and manufacturing facilities. Some of the industries where process engineers get jobs are:

Oil and Gas Industries.
The refinery, Chemical, and Petrochemical facilities.
Private process safety companies
Nuclear plants
Insurance firms
Companies that inspect chemical refineries
Water treatment facilities
Chemical manufacturers
Steel Industries
Pharmaceutical companies
Biochemical and biopharmaceutical Industries
Process Licensing
Mining Industries
Food and beverage manufacturers
Finance companies that fund chemical manufacturers
Environment-friendly and recycling groups
Offshore Industries
Process safety industries
Dairy industries
Cosmetics Industry
Mineral processing

Salary of a Process Engineer

The salary of a process engineer varies based on the education, experience, and location of the work.

In India, the salary of a fresh process engineer varies in the range of 300,000 INR to 600,000 INR per year. A mid-range process engineer with 10 years of experience usually earns 1,200,000 INR to 2,000,000 INR per year.

In the USA, the salaries of process engineers range from $35,000 to $162,000 per year.

How do you become a better Process Engineer?

It is by Years of experience. More specifically, it’s more than the ability to do lightning-fast calculations and estimates in your head, a good process engineer looks at an object, compares it to known measurements, and translates that information into formulas. For example, you can estimate the height and number of floors of a distillation column by looking at the number of rungs one foot apart on the attached ladder. Little tricks like this are compiled from years of experience.

What is a Heavy Hex Nut? Dimensions of Heavy Hex Nuts

Written by Anup Kumar Dey in Mechanical

We all know that nuts are manufactured in different forms like Square nuts, Hexagonal nuts, Ring nuts, cap nuts, cylindrical nuts, dome nuts, wing nuts, etc. Among all of these types of nuts, Hexagonal nuts or Hex nuts are one of the most widely used nuts. Hex nuts also come in different types like standard hex nuts and heavy hex nuts. In this article, we will learn about Heavy hex nuts and their dimensions.

What are Heavy Hex Nuts?

Heavy hex nuts are six-sided (hexagonal) internally threaded fasteners and larger versions of common/standard hex nuts. They are widely used for structural applications and because of this, heavy hex nuts are also known as structural nuts. Hex-heavy nuts are used for high-strength threaded fastening with large diameters. They are thicker and wider than standard hex nuts.

Similar to all other nuts, the heavy hex nuts are also used along with other fasteners mainly with a bolt to secure two or more materials together. To provide a long-lasting experience, heavy hex nuts are produced in zinc, plain, stainless steel, and galvanized finishes.

Paired with heavy hex bolts, these types of nuts are most common in construction and engineering applications. Hex-heavy nuts are available in various grades and selected based on the application.

Heavy Hex Nut Standards and Specifications

The most popular Heavy Hex nut standard is the ASME B18.2.2 which covers the complete general and dimensional data for the various types of inch series square and hex nuts. Widely used ASTM standards that cover the Heavey Hex Nuts are:

ASTM A194
ASTM A563

Heavy Hex Nut Dimensions

Heavy hex nut dimensions basically consist of three specific dimensions as listed below:

Nut thickness (T)
Width across flats (F), and
Width across corners (C)

Hex heavy nut thickness, T is the overall distance from the top of the nut to the bearing surface measured parallel to the nut axis. Nut thickness also includes the thickness of the washer plate if available.

Nut’s width across flats, F is the distance between two opposite sides of the heavy hex nut measured perpendicular to the nut axis. Similarly, width across corners is the distance between two opposite corners as shown in Fig. below.

**Nomenclature for Heavy Hex Dimensions for Table-1**

Heavy hex dimensions based on ASME B18.2.2 are given in table 1 below.

	Width Across Flats, F (inches)	Width Across Flats, F (inches)	Width Across Flats, F (inches)	Width Across Corners, C (inches)	Width Across Corners, C (inches)	Thickness, T (inches)	Thickness, T (inches)	Thickness, T (inches)
Size	Basic	Max	Min	Max	Min	Basic	Max	Min
1/2	7/8	0.875	0.850	1.010	0.969	31/64	0.504	0.464
5/8	1-1/16	1.062	1.031	1.227	1.175	39/64	0.631	0.587
3/4	1-1/4	1.250	1.212	1.443	1.382	47/64	0.758	0.710
7/8	1-7/16	1.438	1.394	1.660	1.589	55/64	0.885	0.833
1	1-5/8	1.625	1.575	1.876	1.796	63/64	1.012	0.956
1-1/8	1-13/16	1.812	1.756	2.093	2.002	1-7/64	1.139	1.079
1-1/4	2	2.000	1.938	2.309	2.209	1-7/32	1.251	1.187
1-3/8	2-3/16	2.188	2.119	2.526	2.416	1-11/32	1.378	1.310
1-1/2	2-3/8	2.375	2.300	2.742	2.622	1-15/32	1.505	1.433
1-5/8	2-9/16	2.562	2.481	2.959	2.828	1-19/32	1.632	1.556
1-3/4	2-3/4	2.750	2.662	3.175	3.035	1-23/32	1.759	1.679
1-7/8	2-15/16	2.938	2.844	3.392	3.242	1-27/32	1.886	1.802
2	3-1/8	3.125	3.025	3.608	3.449	1-31/32	2.013	1.925
2-1/4	3-1/2	3.500	3.388	4.041	3.862	2-13/64	2.251	2.155
2-1/2	3-7/8	3.875	3.750	4.474	4.275	2-29/64	2.505	2.401
2-3/4	4¼	4.250	4.112	4.907	4.688	2-45/64	2.759	2.647
3	4-5/8	4.625	4.475	5.340	5.102	2-61/64	3.013	2.893
3-1/4	5	5.000	4.838	5.774	5.515	3-3/16	3.252	3.124
3-1/2	5-3/8	5.375	5.200	6.207	5.928	3-7/16	3.506	3.370
3-3/4	5-3/4	5.750	5.562	6.640	6.341	3-11/16	3.760	3.616
4	6-1/8	6.125	5.925	7.073	6.755	3-15/16	4.014	3.862

Table 1: Heavy Hex Nut Dimensions

Standard Hex Nuts vs Heavy Hex Nuts

The shape of both Standard hex nuts and heavy hex nuts are the same. However, there are some differences between a heavy hex nut and a standard hex nut as listed below:

For the same nominal size, a finished hex nut or standard hex nut has a smaller width across the flats and corners than a heavy hex nut.
The thickness of a heavy hex nut is slightly more as compared to a standard hex nut of the same nominal size.
As heavy hex nuts are 1/8” larger across the flats than a standard hex nut for all sizes, Larger wrenches and sockets are required to install a heavy hex nut.
As can be seen in ASTM A563, heavy hex nuts have a higher proof load strength compared to standard hex nuts.

What is ASTM A105 Material? A105 vs A105N

Written by Anup Kumar Dey in Engineering Materials,Piping Design Basics

ASTM A105 or ASME SA105 is a specification for forged carbon steel piping components suitable for ambient and high-temperature services. They cover various pipe fittings (Tee, elbow, coupling, etc) and components like ﬂanges, valves, etc.

All A105 components are made by forging with a weight limitation of a maximum of 4540 Kg (10,000 lb). Larger forgings beyond 4540 Kg are covered under specification A266. ASTM A105 material finds wide application in the piping and pipeline industry and is suitable for a range of services within a range of -29 Deg C to +425 Deg C. This carbon steel specification does not cover tube sheets and hollow cylindrical forgings for pressure vessel shells

Properties of A105 Steel

Killed carbon steel materials are used for making A105 forged components. A105 materials have a Specific Gravity of 7.9 and a melting point of 2740 Deg F. They have very good machinability and weldability.

The chemical composition of A105 Steel consists of the following elements:

Carbon: ≤0.35 %
Manganese: 0.60-1.05 %
Phosphorus: ≤0.35 %
Sulfur: ≤0.40 %
Silicon: 0.10-0.35 %
Copper: ≤0.40 %
Nickel: ≤0.40 %
Chromium: ≤0.30 %
Molybdenum: ≤0.12 %
Vanadium: ≤0.08 %

Additionally, there are two other criteria for ASTM A105 material that must meet. Those are:

The sum of copper, nickel, chromium, molybdenum, and vanadium must be ≤ 1.00 %, and
The sum of chromium and molybdenum must be ≤ 0.32 %.

The mechanical properties of A105 steel forgings are as listed below:

Minimum Tensile Strength: 70,000 psi (485 MPa)
Minimum Yield Strength: 36,000 psi (250 MPa)
Minimum Reduction of area (0.2 % offset method or the 0.5 % extension-under-load method ): 30%
Maximum Hardness: HBW 197. The usual hardness range for ASTM A105 carbon steel forge material is 137 to 197 HBW.

The maximum Carbon Equivalent [CE= C + (Mn/6) + (Cr+Mo+V)/5 + (Ni+Cu)/15] for A105 steel material shall be limited to a maximum of 0.48

Difference between A105 and A105N

Many a time we find the letter N is attached to A105 steel material. So, a question automatically arises if A105 and A105N are the same or not. If different then what are the differences between A105 and A105N materials?

The base material for both the above are the same and is A105 and both have the same chemical composition. The letter N in ASTM A105N denotes a specific heat treatment type. In general, A105 does not have specific heat treatment requirements while A105N needs normaliz i n g heat treatment. This heat treatment makes A105 and A105N materials different from each other. The main differences between A105N and A105 can be mentioned as follows:

Due to normalization treatment, A105N has a better mechanical properties than regular A105 steel. The strength of A105N is improved by the normalization heat treatment. Also, A105N provides better performance in low-temperature service. Because of this A105N is recommended for critical applications.

What is ASTM A106? Different Grades of ASTM A106 and their Differences

Written by Anup Kumar Dey in Engineering Materials,Piping Design Basics

ASTM A106 is an international (American) specification of carbon steel pipe. ASTM A106 is a widely used standard specification for seamless carbon steel pipes used for high-temperature service. The specification covers pipes from NPS 1/8 (DN6)to NPS 48 (DN 1200). All pipes under ASTM A106 are suitable for bending, welding, and other forming operation. A106 is also known as SA106.

Grades of ASTM A106 Materials

Depending on the chemical composition (mainly Maximum Carbon percentage) of A106 material, there are three grades of ASTM A106 materials. They are:

A106 Grade A, having a maximum of 0.25% carbon.
A106 Grade B, having a maximum of 0.30% carbon, and
A106 Grade C, having a maximum of 0.35% carbon.

In the chemical composition of the different grades as mentioned above, the percentage range of manganese also varies slightly with respect to grade. A106 Grade A usually has 0.27 to 0.93% manganese while A106 Grade B and C generally have 0.29 to 1.06% Manganese. The maximum percentage of other elements like phosphorus, sulfur, silicon, copper, chromium, molybdenum, nickel, vanadium, etc are usually the same in all three grades of ASTM A106 carbon steel material. However, ASTM A106 provides a note of caution for these other elements saying the total combined percentage of all these other materials shall not exceed 1%.

As the maximum carbon percentage of different grades of A106 material varies in chemical composition, so vary their mechanical strengths. While A106-A has a minimum yield strength of 30 KSI (205 MPa) and A106-B has a minimum yield strength of 35 KSI (240 MPa), the other grade A106-C has the largest minimum yield strength of 40 KSI (275 MPa). In a similar way, the tensile strength also varies. Both tensile and yield strength increase when we move on from Grade A to Grade C but at the same time, the percentage elongation reduces.

Difference Between A106 Grade A, B, and C

The main difference between ASTM A106 Grade A, B, and C are their maximum carbon percentage in the chemical composition and corresponding change in mechanical properties like tensile and yield strength, elongation, etc as discussed above.

Properties of A106

In general, A106 pipes have the following properties:

Density: 7800 – 8000 kg/m3
Elastic Modulus: 190 GPa (27557 KSI) – 210GPa (30458 KSI)
Poisson’s Ratio: 0.27 – 0.30.

**Mechanical Strength of A106 materials**

Difference between ASTM A106 and ASTM A53

Both A106 and A53 are carbon steel pipes having wide applications. However, there are some differences between ASTM A106 and ASTM A53 pipe materials. The major differences that differentiate A106 pipe material from A53 pipes are provided in the following table:

ASTM A106	ASTM A53
ASTM A106 pipes are seamless pipes.	On the other hand, ASTM A53 pipes can be seamless or welded.
As per chemical analysis, A106 has silicon in its chemical composition.	ASTM A53 pipes do not have silicon in their composition.
A106 pipes are generally costlier than A53 pipes.	A53 pipes are usually cheaper than A106 pipes.
A106 pipes are usually used for high-temperature pressure applications.	A53 pipes are usually not applied for high-temperature applications.

ASTM A106 vs ASTM A53

Difference between A106 and SA106

As a piping engineer, you must have heard that some are referring to the pipe as A106 while some are referring to SA106. So, a question always arises in our mind, “what is the difference between A106 and SA106 pipe materials”?

In general, there is no difference between pipe material A106 and SA106. The only difference is in their material standards. ASTM standard uses the callout A whereas the ASME standard uses the SA callout for pipe materials. The 2013 edition of the ASME II material chapter has confirmed that SA106 is consistent with ASTM A106. So basically, SA106 is a grade of American ASME while A106 is the grade of ASTM.

Is ASTM A106 killed carbon steel?

Yes, all three grades of ASTM A106 carbon steel seamless pipe materials are killed carbon steel.

Difference between A106-Gr. B and A333-Gr. 6

The main difference between A106 Gr B and A333 Gr 6 is that A333-6 is an LTCS material whereas A106-B is CS material. The lower temperature at which A106 Gr B pipe material can be subjected without impact testing and stress ratio checking is -28.9⁰C (For thickness up to 12.7 mm as per table 323.2.2A of ASME B31.3 ) Whereas A333 Gr 6 material is already proven for use up to a temperature of -46⁰C (Refer Table A-1M). Moreover, A106-B pipes are seamless whereas A333-6 pipes can be seamless or welded.

What is a Socket Welding? Socket Welded Pipe Fittings

Written by Anup Kumar Dey in Piping Design Basics

Socket welding is a permanent pipe joining methodology for welding pipe fittings and components. A range of piping applications uses socket-welded pipe fittings because of high leakage integrity and structural strength. In this write-up, we will learn about Socket weld and socket welded fittings.

What is a Socket Weld?

A socket weld involves the welding of pipe with several pipe fittings like elbows, reducers, and tees. Two pipe pieces/components are involved in socket welding. One is having a larger diameter than the other. The smaller diameter pipe is inserted in the other piece and welding is performed on the periphery of the larger piece. As no end preparation is required in socket welding, the process is easy and quick. In general, socket welding is used for small-diameter pipes, usually up to 4 inches.

Working of Socket Welding

As already defined above, socket welding is the name given for welding fittings with pipes inside them. These pipe fittings include recessed sockets where the pipes are inserted before welding. A small gap is maintained between the end of the pipe and the bottom of the socket to allow the pipe to grow/expand by the welding heat. When the gap (usually 1/16 inch) is ensured and the pipe is placed in position, fillet welding is performed at the location where the pipe diameter meets the socket.

Socket welds create effective, leak-proof, high-pressure piping and pipeline configurations for fluid transport.

Types of Socket weld pipe fittings

A range of socket weld pipe fittings and components are used in the piping industry. While welding, the pipe is inserted into the recessed part of the valve, flange, or fitting. Socket weld pipe fittings are usually referred to as SW pipe fittings and they are available in various types as listed below:

SW Full Couplings: Used for joining two pipes together. Have threads at both ends for connecting both pipes.
Socket Weld Half Couplings: Have threads on one end only, and the other end is generally welded.
SW Reducing coupling: Used for connecting pipes of different diameters.
SW equal tees: For making a branch connection of the same size.
Socket welded reducing tees: For making a branch connection of reduced size.
SW elbows: 90-degree and 45-degree designs for changing flow direction.
SW unions
Sockolet: Used to weld a smaller diameter pipe with a larger diameter pipe
Socket Weld Cross
SW flanges,
Socket weld caps: socket weld p i p e cap is connected to the end of a pipe to seal it.

While ordering these types of pipe fittings, you need to mention pipe diameter and pressure rating, class.

Features of Socket Weld Fittings

As socket weld pipe fittings have high-pressure ratings, they are used in a wide range of industrial applications. They are installed in pipelines to transport flammable, toxic, or hazardous chemicals safely with a low possibility of leakage. Socket weld fittings are of high quality as most of them are manufactured following ASME and ASTM specifications and standards.

Socket welding pipe fittings can also be classified based on the type of materials.

Advantages of Socket weld pipe fittings

For pipe joining, socket weld fittings provide a number of advantages like:

Easy alignment for joining. No tack weld requirement for aligning.
Lower risk of leakage.
No weld metal infiltration in the pipe bore
Cheaper to install as compared to butt welded fittings.
No special machining requirements.

Drawbacks of Socket weld pipe fittings

Some of the disadvantages of socket weld pipe fittings are:

Substances can accumulate in the expansion gap and those are difficult to clean.
Internal crevices and expansion gaps associated with socket weld fittings often lead to corrosion.
Not suitable for food industries.

Socket weld vs Butt weld fittings

There are some major differences between socket weld fitting and butt weld fitting. The following table lists the major differences between the two types of fittings.

Socket Weld Fitting	Butt Weld Fitting
ASME B16.11 provides details of socket welded pipe fittings.	Whereas, the governing standard for Butt welded pipe fittings is ASME B16.9
Socket welded fittings have low strength as compared to butt-welded pipe fittings.	More strong as compared to socket weld fittings.
Socket-welded pipe fittings are easy to weld and bevel ends are not required.	Butt welding fittings need proper end preparation for joining.
SW pipe fittings are normally used for lower pipe sizes.	Butt-welded pipe fittings are more suitable for higher pipe sizes.
Socket-welded pipe fittings are usually avoided for high-temperature and pressure applications.	Butt weld fittings are widely used for high-temperature and pressure applications.

Butt Weld vs Socket Weld fittings

Video Courses in Welding

To learn more about welding the following video courses you can refer to:

Introduction to MIG Welding
Understanding Welding Codes and Procedures
The Basics of Gas Tungsten Arc Welding
Certification in Welding Technology
Understand Welding Symbols
AWS-Certified Welding Inspector

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