Publish Time: 2025-05-18 Origin: Site
In modern oil and gas operations, high-pressure environments are increasingly common, especially as operators explore deeper reservoirs, complex well paths, and harsh geological formations. Coiled tubing plays a vital role in servicing these wells, enabling efficient interventions, cleanouts, acidizing, and even drilling without halting production. However, not all coiled tubing is created equal, especially when operating under extreme pressure conditions.
Welded coiled tubing has emerged as a reliable and economical solution for many high-pressure applications. Yet, to use it safely and effectively, operators must understand how it is designed, manufactured, and selected for such demanding environments. This article offers a comprehensive look at everything you need to know about using welded coiled tubing in high-pressure settings—from how it performs to what features you should look for.
In oilfield terms, a “high-pressure” well usually refers to those where the formation pressure exceeds 10,000 psi (pounds per square inch), though many wells today operate at even higher pressures. These conditions are typical in deepwater reservoirs, unconventional shale plays, and ultra-deep vertical or horizontal wells.
High pressure places considerable stress on all equipment exposed to the wellbore, including coiled tubing. The tubing must withstand external hydrostatic pressure, internal pumping pressure, and mechanical stress from coiling, uncoiling, and bending during deployment. In addition, it must maintain integrity when exposed to corrosive fluids, scale, sand, and elevated temperatures.
Failure in such environments is not only costly but potentially dangerous. That’s why selecting the right type of coiled tubing—and ensuring its quality—is critical.
Welded coiled tubing is manufactured by taking flat strips of steel (or corrosion-resistant alloy), forming them into a cylindrical shape, and welding the edges together longitudinally. This contrasts with seamless tubing, which is made from a solid billet without any welding.
While seamless tubing was traditionally favored for high-pressure work due to its uniform structure and perceived superior strength, modern advancements in welding technology and non-destructive testing (NDT) have significantly improved the performance and reliability of welded tubing.
Today, welded coiled tubing can meet or exceed the mechanical and pressure requirements for many high-pressure applications. It also offers several practical advantages:
Cost efficiency: Welded tubing is more economical to produce, making it attractive for operators balancing performance and budget.
Longer lengths: Welded tubing can be manufactured in continuous lengths exceeding 30,000 feet, which is essential for extended-reach wells.
Custom sizes: The manufacturing process allows greater flexibility in wall thickness and diameter combinations.
Shorter lead times: Welded tubing can often be sourced more quickly than seamless alternatives.
These benefits make welded coiled tubing a viable and sometimes preferable option—provided it’s properly engineered and qualified.
To survive in a high-pressure environment, welded coiled tubing must meet several critical criteria:
The tubing must have high yield strength to resist deformation under both internal and external pressures. Depending on the depth and fluid pressure, coiled tubing used in high-pressure environments typically has yield strength ranging from 90,000 to over 125,000 psi. Higher strength means the tubing can carry more weight and resist collapse, especially in deep or deviated wells.
Burst pressure is the maximum internal pressure the tubing can withstand before rupturing, while collapse pressure is the maximum external pressure it can endure before buckling. Both are vital in high-pressure wells. Engineers calculate these limits using industry standards and safety factors, often requiring tubing to perform at 80% or more of its theoretical burst strength under load.
Coiled tubing is continuously spooled and unspooled during operations, causing repeated bending cycles. This can lead to fatigue, especially near the weld seam. High-pressure environments exacerbate this stress. Therefore, the tubing must be made from materials and with processes that enhance fatigue resistance and extend operational life.
Many high-pressure wells also contain corrosive substances like hydrogen sulfide (H₂S), carbon dioxide (CO₂), and chlorides. In such environments, using corrosion-resistant alloys (CRAs) or applying internal coatings is essential. Welded tubing must be made from or lined with materials that resist both uniform corrosion and stress corrosion cracking.
Since welded tubing has a longitudinal seam, the weld must be as strong as the parent metal. Advanced welding techniques such as high-frequency induction welding or laser welding are used. After welding, the seam is heat-treated and inspected with ultrasonic and eddy current methods to detect flaws that could compromise integrity.
The performance of welded coiled tubing under high pressure largely depends on how well it is manufactured. Reputable manufacturers follow strict quality control procedures at every stage:
Edge preparation: Ensures a clean, even surface for welding.
Weld monitoring: Uses real-time sensors to track welding temperature and alignment.
Post-weld heat treatment: Restores metal structure and relieves stress at the seam.
Cold drawing or rolling: Increases strength and dimensional accuracy.
NDT inspections: Detect micro-cracks, porosity, and other defects invisible to the naked eye.
Hydrostatic testing: Applies controlled pressure to verify burst and collapse performance.
It’s important for operators to demand full traceability, including material certifications and NDT results, especially for high-pressure projects.
When selecting welded coiled tubing for high-pressure operations, several project-specific factors must be considered:
Longer and deeper wells require tubing with greater strength and fatigue resistance. The deeper the well, the higher the hydrostatic pressure exerted on the tubing. You’ll also need to account for pump pressures during operations like acidizing or fracturing.
If the well contains corrosive fluids, CRAs or coated tubing may be necessary. Material selection should be based on a chemical analysis of well fluids to avoid unexpected corrosion failures.
High downhole temperatures can weaken the tubing’s mechanical properties over time. Select grades that retain their yield strength at elevated temperatures and have been tested under similar conditions.
Both inner and outer diameters should match the operational requirements and tool compatibility. Wall thickness directly influences burst and collapse resistance, so a careful balance must be struck between strength and flexibility.
If the tubing is expected to be reused across multiple jobs, fatigue resistance becomes even more critical. Some applications may require tubing with special coatings or post-processing to enhance life span.
Using welded coiled tubing in high-pressure wells demands strict adherence to safety and operational protocols. Some best practices include:
Regular inspection before and after each job, including dimensional checks and NDT.
Real-time monitoring during deployment, including bending radius, pressure, and fatigue cycles.
Proper handling and storage to prevent mechanical damage to the tubing or weld seam.
Training for operators and technicians on identifying signs of fatigue, corrosion, or deformation.
Even with high-quality tubing, improper use or overextension beyond design limits can lead to failure. Engineering teams should always evaluate tubing performance based on actual well data and design safety margins accordingly.
Welded coiled tubing has proven its value in a wide range of applications, and with modern advancements in materials, welding, and inspection, it is now a dependable solution even in high-pressure environments. By choosing the right specifications and working with trustworthy manufacturers, operators can enjoy both the cost benefits and the performance reliability that welded tubing offers.
For those seeking high-quality welded coiled tubing solutions, Jiaxing Mt Stainless Steel Co., Ltd. stands out as a manufacturer committed to precision, durability, and safety. Their expertise in advanced stainless steel tubing and high-pressure applications ensures that clients receive tubing products that perform under the most demanding field conditions.
If you are planning a high-pressure project and need reliable coiled tubing, understanding the manufacturing process, testing standards, and proper application will help you make the right decision—saving time, reducing risk, and maximizing success in your operations.