Purging Gas in Gas Tungsten Arc Welding: Enhancing Weld Quality and Integrity

Introduction:

In the realm of welding, achieving high-quality welds with excellent integrity is paramount. One crucial technique that aids in this endeavor is the use of purging gas. Purging gas plays a vital role in preventing oxidation and ensuring a clean, controlled environment during welding. In this blog, we will explore the significance of purging gas, its purpose, techniques, and benefits in various welding applications. Join us as we delve into the world of purging gas and its impact on weld quality.

Back purging is most important phenomenon in GTAW process because this process is mostly used in Stainless steel. Stainless steel is widely used fabrication of chemical, petrochemical, food etc. plant. All thin section and root welding is performed by GTAW process. GTAW process is also very popular in Aluminum welding.

In all large diameter pipe the root pass welding is done by GTAW process where the back purging is mandatory. Purging gas protect the weld metal from atmospheric contamination & oxidation because due to contamination & oxidation porosity, oxides, cracks like defect generates in welding.

1. Understanding the Purpose of Purging Gas:

1.1 Controlling Oxidation: Purging gas is used to displace oxygen from the vicinity of the weld joint, preventing the formation of oxides that can weaken the weld.

1.2 Protecting Reactive Materials: Certain materials, such as stainless steel and titanium, are highly reactive and prone to oxidation during welding. Purging gas helps shield these materials from oxygen exposure.

2. Techniques for Purging Gas:

2.1 Back Purging: This technique involves introducing the purging gas on the backside of the weld joint, creating a protective environment. We'll explain the process and benefits.

2.2 Flow Rate and Direction: Controlling the flow rate and direction of purging gas is crucial for effective shielding. We'll discuss optimal practices for achieving a consistent purge.

Argon and helium is most common purging gases .The properties of Argon and Helium gases is explained below.

	Argon Gas	Helium Gas
Chemical name	Ar	He
Atomic number	18	2
Atomic mass	39.948 g.mol -1	4.00260 g.mol -1
Density	1.78.10 -3 g.cm -3 at 0 °C	0.178*10 -3 g.cm -3 at 20 °C
Melting point	-189 °C	- 272.2 (26 atm) °C
Boiling point	-185.7 °C	- 268.9 °C
Ionization potential	15.8eV	24.6eV
Arc initation	Good	Poor
Cleaning	Good	Poor

 

These gases are chemically inert, colorless and odorless in liquid and gaseous forms.

Argon gas:-
Pure Argon is generally used in GTAW & GMAW welding but some time mixture of Helium and Argon is also very useful in weld quality point of view. Helium has higher ionization potential and thermal conductivity. So greater heat generates during welding using Helium as purging gas.

During GTAW Argon is preferred gas in AC Current. Because pure argon gives following characteristics in AC Current.

1.Lower cost.
2. Due to its lower ionization potential, Argon produces consistent high frequency arc.
3. Reduced penetration during welding.
4. Lower gas consumption during welding.
5. Greater metal cleaning action on aluminum and magnesium in AC.
6. Better cleaning action in DCEP.

The atomic number of argon is 18. It has 18 electrons. K, L and M shells contain 2,8,8 electrons respectively. The valence shell contains 8 electrons. Thus, argon has completed its octet and is highly stable. Usually, argon does not form compounds. So, it is chemically unreactive inert gas, also called noble gas. Thus there is no reaction between argon and the metal to be welded. Due to low reactivity of argon, during welding, argon can be used to create an inert gas shield.

Due to High heat generation characteristics, Helium/Argon mixture is used for high heat generation during welding. 25% Helium and 75% Argon gas mixture is used in AC-GTAW Process but Helium more than 25% creates instability in AC Current.  

Helium Gas:-

90%Helium and 10% Argon mixture is useful in DCEN-GTAW process. High heat generation in DC Current provide increased welding speed, full penetration  weld. Following characteristics of Helium gas is given below.

1. Lightest Inert Gas.
2. Helium yields a much higher available heat on metal than Argon. Due to this helium is used for welding of heavy section.
3. Higher welding speed with any defect like undercut.
4. Better cleaning action in DCEP.

Mixture of Helium & Argon also used to provide combination of characteristic of each gases. It provides good arc starting with arc stability, deep penetration and welding speed.

1. So High Helium gas are very useful for GMAW on thicker and GTAW welding with DCEN Polarity.

2. Pure Argon is useful for GTAW & GMAW. Pure Argon is very useful in Orbital welding of Bimetallic tube (25Ni:22Cr:2Mo).

3.Helium is expensive than Argon so many times Argon is preferred gas for purging & Shielding gas.

4. Due to higher density of Argon than Helium low flow rate of Argon required  during welding.

3. Benefits of Purging Gas in Welding:

3.1 Minimizing Weld Defects: Purging gas helps reduce the likelihood of weld defects such as porosity, excessive oxidation, and lack of fusion, leading to improved weld quality.

3.2 Enhanced Corrosion Resistance: By minimizing oxidation, purging gas contributes to the formation of corrosion-resistant welds, particularly in materials like stainless steel.

3.3 Increased Strength and Integrity: Purging gas helps maintain the mechanical strength and integrity of the weld joint by minimizing oxygen-induced embrittlement.

4. Applications of Purging Gas:

4.1 Stainless Steel Welding: Purging gas is extensively used in stainless steel welding, where it helps achieve welds with superior corrosion resistance and aesthetic appearance.

4.2 Titanium Welding: Given the reactivity of titanium, purging gas is crucial in titanium welding to prevent contamination and maintain its exceptional properties.

4.3 Pipe Welding: Purging gas finds widespread use in pipe welding, ensuring clean and defect-free welds in critical applications such as oil and gas pipelines.

5. Types of Purging Gases:

5.1 Inert Gases: Inert gases, such as argon and helium, are commonly used as purging gases due to their low reactivity and ability to displace oxygen effectively.

5.2 Gas Mixture Considerations: Depending on the specific welding application, gas mixtures with controlled oxygen content may be employed. We'll discuss the considerations involved in gas selection.

6. Safety Considerations:

6.1 Ventilation: Proper ventilation is essential when working with purging gases to prevent the accumulation of potentially hazardous gases in the welding environment.

6.2 Gas Monitoring: Regular monitoring of gas levels, especially in confined spaces, ensures a safe working environment for welders.

Conclusion:

The use of purging gas in welding is a critical technique that contributes to the production of high-quality welds with superior integrity. By effectively displacing oxygen and preventing oxidation, purging gas minimizes weld defects, enhances corrosion resistance, and maintains the mechanical strength of the weld joint. Whether in stainless steel, titanium, or pipe welding applications, the controlled environment provided by purging gas ensures clean, reliable welds. Understanding the purpose, techniques, and benefits of purging gas allows welders to optimize their welding processes, resulting in welds that meet stringent quality standards.

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Minimum required thickness of process pipeline (Engineering calculation)

Calculator:Minimum required thickness of pipeline for service as per ASME B31.3

Design Pressure (PSI):
Diameter (inch):
Stress 'S' (PSI):
Quality Factor 'E':
Weld Joint Reduction Factor 'W':
Coefficient 'Y':

Results:

Min. Reqired Thickness tm (inch):
12.5% Allowance (inch):
Mini. Required Thicknes (mm):

After getting 12.5% allowance (inch) value again check ASME B36.10 or API 574 piping thickness table and choose thicknes value higher then this value for service.

Calculating the Minimum Required Thickness of Pipelines for Service as per ASME B31.3

Introduction:

In the field of engineering, designing safe and reliable pipelines is of utmost importance. The American Society of Mechanical Engineers (ASME) B31.3 code provides guidelines for the design and construction of process piping systems. One critical aspect is determining the minimum required thickness of pipelines to ensure structural integrity and safety. In this blog post, we will focus on calculating the minimum required thickness of pipelines when the corrosion allowance (T) is less than D/6, where D represents the outside diameter of the pipe.

Understanding ASME B31.3:

ASME B31.3 is a widely recognized code that establishes requirements for the design, materials, fabrication, inspection, and testing of process piping systems. It provides guidelines to ensure the safe operation of piping systems handling various fluids under different operating conditions.

Calculation Methodology:

When T is less than D/6, ASME B31.3 provides specific equations to calculate the minimum required thickness of the pipeline. The formula is as follows:

Where:

- t: Minimum required thickness of the pipe

- P: Design pressure (Psi)

- D: Outside diameter of the pipe (Inch)ASME B36.1

- S: Allowable stress of the material at the design temperature (Psi) Stress factor table (ASME B31.3)

- E: Quality factor Table A1-B (ASME B31.3)

- C: Corrosion allowance factor (C)

- W: Weld joint reduction factor

Weld joint quality factor

                               

Coefficent Y Table 304.1.1
	Temperature °C(°F)
Material	482(900) & Below	510(950)	538(1000)	566(1050)	593(1100)	621(1150)	649(1200)	677(1250) & above
Ferritic steels	0.4	0.5	0.7	0.7	0.7	0.7	0.7	0.7
Austenitic steel	0.4	0.4	0.4	0.4	0.5	0.7	0.7	0.7
Nickel alloys UNS Nos N06617 & N08810 &N08825	1.4	0.4	0.4	0.4	0.4	0.4	0.5	0.7
Gray Iron	0	…	…	…	…	…	…	…
Other Ductile metals	0.4	0.4	0.4	0.4	0.4	0.4	0.4	0.4

In the above equation, the numerator represents the primary membrane stress while the denominator represents the primary longitudinal stress. The difference between these two values determines the minimum required thickness.

Practical Application:

To calculate the minimum required thickness of a pipeline, follow these steps:

1. Determine the design pressure (P) based on the operating conditions and system requirements.

2. Determine the outside diameter (D) of the pipe.

3. Determine the allowable stress (S) of the material at the design temperature. This value depends on the material used and can be obtained from material specifications or ASME standards.

4. Determine the quality factor (E) based on the material and construction quality. This factor considers the reliability of the material and fabrication processes.

5. Determine the corrosion allowance (T) based on the expected corrosion rates and material compatibility.

6. Determine the weld joint reduction factor (Y) considering the type of weld joint used in the pipeline.

7. Substitute the values into the formula: 

8. Calculate the minimum required thickness (t) using the above equation.

9. Compare the calculated value with the available pipe thickness options. If the required thickness exceeds the available options, select the next higher available thickness.

Conclusion:

Calculating the minimum required thickness of pipelines is a crucial step in ensuring the safety and reliability of process piping systems. By following the guidelines outlined in ASME B31.3 and using the appropriate formula, engineers can determine the minimum required thickness when the corrosion allowance is less than D/6. It is essential to consider the design pressure, outside diameter, allowable stress, quality factor, corrosion allowance, and weld joint reduction factor in the calculation process. Adhering to these calculations helps ensure the integrity of pipelines and enhances overall system performance and safety.

All see: Maximum Allowable reinforcement Video ASME Sec VIII Div 1

Ultrasonic Flaw Detection: Unveiling the Power of Sound in Non-Destructive Testing

Introduction:

Non-destructive testing (NDT) techniques play a vital role in ensuring the integrity and safety of structures, materials, and components in various industries. Among the array of NDT methods available, ultrasonic flaw detection stands out as a powerful and versatile technique. In this blog, we will explore the fundamentals of ultrasonic flaw detection, its applications, and the benefits it offers in detecting and characterizing defects without causing damage. Join us as we dive into the world of sound waves and their ability to reveal hidden flaws.

1. Understanding Ultrasonic Flaw Detection:

1.1 The Basics of Ultrasonics: We'll introduce the principles of ultrasonics, explaining how sound waves are generated, propagated, and detected.

1.2 Interaction with Materials: We'll explore how ultrasonic waves interact with different materials, including their reflection, transmission, and absorption behaviors.

2. How Ultrasonic Flaw Detection Works:

2.1 Transducers: We'll discuss the role of transducers in ultrasonic flaw detection, which convert electrical energy into sound waves and vice versa.

2.2 Pulse-Echo Technique: The pulse-echo technique is a fundamental method in ultrasonic flaw detection. We'll explain how it works, including the emission, propagation, and reception of ultrasonic waves.

1. Skip distance & Beam path Calculator for Ultrasonic Flaw  

     Detection (Ultrasonic Flaw Detection, ASME Sec V)

Formula for Skip distance 

1. Half skip Distance = T x Tanθ

2. Full Skip distance =  2 x T x Tanθ

3. 1-1/2 Skip distance =  3 x T x Tanθ 

    

Formula for Beam Path

 1. Half Beam path = T x Secθ

2. Full Beam path =  2 x T x Secθ

3. 1-1/2 Beam path =  3 x T x Secθ 

Note:-  θ = Probe angle

Probe used for Ultrasonic testing

Following probes we can use during testing

1. 0° = Normal Beam Probe 

2. 45° = Angle Beam Probe

3. 60° = Angle Beam Probe

4. 70° = Angle Beam Probe

3. Applications of Ultrasonic Flaw Detection:

3.1 Weld Inspection: Ultrasonic flaw detection is widely used for weld inspection in various industries, including manufacturing, construction, and oil and gas. We'll delve into the specifics of weld inspection and the types of defects it can identify.

3.2 Material Characterization: Ultrasonics can provide valuable information about material properties, such as thickness measurement, sound velocity determination, and attenuation analysis. We'll explore these applications in detail.

3.3 Defect Detection in Components: Ultrasonic flaw detection is effective in identifying defects in a wide range of components, such as pipes, pressure vessels, and aerospace structures. We'll highlight its importance in ensuring component integrity and safety.

4. Advantages and Limitations of Ultrasonic Flaw Detection:

4.1 Advantages: We'll discuss the key advantages of ultrasonic flaw detection, including its non-destructive nature, high sensitivity, real-time imaging capabilities, and portability.

4.2 Limitations: While ultrasonic flaw detection is a powerful technique, it has certain limitations. We'll examine factors such as material properties, surface conditions, and operator skill that can affect its effectiveness.

5. Recent Advancements and Future Directions:

5.1 Advanced Imaging Techniques: We'll explore the advancements in ultrasonic flaw detection, such as phased array ultrasonics and time-of-flight diffraction, which offer improved imaging capabilities and defect characterization.

5.2 Automation and Data Analysis: The integration of automation and advanced data analysis techniques, such as artificial intelligence and machine learning, is revolutionizing ultrasonic flaw detection. We'll discuss the potential benefits and challenges of these developments.

Conclusion:

Ultrasonic flaw detection has revolutionized the field of non-destructive testing, allowing us to uncover hidden defects and ensure the integrity of critical structures and components. By harnessing the power of sound waves, this technique provides invaluable information about material properties and helps identify flaws in a non-invasive and efficient manner. As technology continues to advance, we can expect further improvements in imaging capabilities, automation, and data analysis, enhancing the accuracy and reliability of ultrasonic flaw detection. With its versatility and wide-ranging applications, ultrasonic flaw detection remains a cornerstone in ensuring safety and quality across numerous industries.