Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Identify at least three special welding techniques used in the oil and gas industry.
• Explain the importance of each technique for safety and efficiency.
• Analyze the advantages of different welding techniques.

Lesson summary

This lesson explores the highly specialized and critical welding techniques required in the oil and gas industry. As Ghana continues to develop its petroleum resources (like the Jubilee, TEN, and Sankofa fields), the need for skilled welders who can work under extreme conditions is paramount. The pipes, platforms, and vessels used in this industry contain materials under immense pressure and in corrosive environments. A single faulty weld can lead to catastrophic environmental and economic disaster. Therefore, understanding these advanced techniques is crucial for any student aiming for a career in modern engineering and technology.

Lesson notes

A. Why is Oil & Gas Welding "Special"?

Welding for a gate or a metal chair is very different from welding for a pipeline that will carry natural gas at high pressure. The conditions in the oil and gas industry present unique challenges: High Pressure: Pipelines and pressure vessels operate under immense internal pressure. Welds must be exceptionally strong and completely free of defects like cracks or porosity to prevent explosions. Corrosive Environments: Crude oil, natural gas (especially "sour gas" containing hydrogen sulfide), and saltwater are highly corrosive. The welds must be able to resist this chemical attack over many years. This often requires welding special materials like stainless steel or nickel alloys. Extreme Temperatures: The industry deals with everything from cryogenic (very cold) liquefied natural gas (LNG) to very hot processed fluids. Welds must maintain their integrity across a wide temperature range. Critical Safety: Weld failure can lead to loss of life, environmental pollution (oil spills), and huge financial losses. There is zero tolerance for error. Difficult Locations: Welding often needs to be done on offshore rigs, deep underwater, or in remote, windy locations. B. Key Specialised Welding Processes

Here are the key processes used to meet these challenges. Gas Tungsten Arc Welding (GTAW / TIG) How it Works: Uses a non-consumable tungsten electrode to create the arc. A separate filler rod is added manually. The weld pool is protected from the atmosphere by a shield of inert gas (usually Argon). Application in Oil & Gas: It is the "gold standard" for quality. It is primarily used for the root pass of pipe welds. The root pass is the first, most critical bead of weld laid at the bottom of the joint. A perfect, smooth root pass ensures smooth fluid flow and prevents cracks from starting. It is also used for welding corrosion-resistant alloys like stainless steel and aluminium. Advantages: Extremely high-quality, clean, and precise welds with no spatter. Gives the welder excellent control. Disadvantages: Very slow process, requires a highly skilled operator, and the gas shield is sensitive to wind, making it difficult for outdoor use without protection. Flux-Cored Arc Welding (FCAW) How it Works: This is a semi-automatic process that uses a continuously fed tubular wire filled with flux. The flux melts and creates a protective slag and gas shield over the weld pool. Some FCAW wires are "self-shielded" (requiring no external gas) and are excellent for outdoor conditions. Others are "gas-shielded" for higher quality welds. Application in Oil & Gas: A very popular process for welding pipelines and structural steel for offshore platforms. Its high deposition rate (it lays down a lot of metal quickly) and robustness in windy, outdoor conditions make it ideal for "fill" and "cap" passes on pipes after the GTAW root pass is complete. Advantages: High speed, good penetration, and excellent for outdoor/field use (especially the self-shielded version). Disadvantages: Produces a slag covering that must be cleaned off between passes, and can produce a lot of smoke. Orbital Welding How it Works: This is an automated, computer-controlled version of GTAW. A special machine with a welding torch "head" clamps around the pipe. The torch then rotates (orbits) 360 degrees around the pipe, performing a perfect, continuous weld. A human operator sets the parameters on a computer and monitors the process. Application in Oil & Gas: Used for critical pipeline and tubing connections where weld consistency and quality are non-negotiable. It is increasingly used where many identical, high-quality welds are needed, as it removes the potential for human error and fatigue. Advantages: Extremely consistent, repeatable, and high-purity welds. Faster than manual GTAW for repetitive tasks. Disadvantages: Very expensive equipment, requires specialized training to operate, and is limited to standard pipe sizes the machine can clamp onto. Submerged Arc Welding (SAW) How it Works: A fully automatic process where the welding arc is "submerged" under a blanket of granular flux. A continuous wire is fed into the joint. The flux melts, protecting the weld from the atmosphere, and the unused flux can be collected and reused. Application in Oil & Gas: Used in fabrication shops and factories (not in the field) to make long, straight seams on large-diameter pipes, pressure vessels, and storage tanks (like those at TOR). Its speed and quality are unmatched for this type of work. Advantages: Extremely high deposition rate and speed, deep penetration, excellent weld quality, and no arc flash or smoke. Disadvantages: Limited to flat and horizontal welding positions and requires bulky, expensive equipment. Not portable. Hyperbaric Welding (Underwater Welding) How it Works: This is welding done underwater, mainly for repairing pipelines and offshore structures. There are two main types: Wet Welding: A specially trained diver-welder uses a waterproof electrode holder and special waterproof electrodes (based on SMAW). The arc directly contacts the water, creating a bubble of gas that provides a temporary shield. This is a quick but lower-quality method, often used for temporary repairs. Dry Welding (Hyperbaric): This is the high-quality method. A rigid chamber or "habitat" is sealed around the area to be welded. The water is pumped out and replaced with a breathable gas mixture at the same pressure as the surrounding water. The welders then work inside this dry chamber, allowing them to produce welds of the same quality as those made on the surface. Application in Oil & Gas: Essential for subsea pipeline construction (tie-ins), modifications, and permanent repairs on offshore platforms and subsea infrastructure. Advantages: The only way to perform high-integrity permanent repairs on submerged structures. Disadvantages: Extremely expensive, complex, and dangerous. Requires highly specialized diver-welders and extensive support systems. Summary Table

| Process | Key Feature | O&G Application | Location | | :--- | :--- | :--- | :--- | | GTAW (TIG) | High precision, clean | Pipe root pass, special alloys | Field & Shop | | FCAW | Fast, good outdoors | Pipeline fill/cap passes, structures | Field (Onshore/Offshore) | | Orbital Welding | Automated GTAW, consistent | Critical pipe joints, tubing | Field & Shop | | SAW | High speed, automated | Large vessel/pipe fabrication | Shop/Factory only | | Hyperbaric | Underwater welding | Subsea repairs, tie-ins | Offshore (underwater) |

Evaluation guide

• Explain special welding techniques used in oil and gas industry.
• Group work/collaborative learning:
• In mixed ability groups, assist learners to discuss the special welding processes used in
• the oil and gas industry.