Vacuum-Insulated Tubing Weld Overlay for HPHT Well Integrity
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Solution Overview
Problem
Existing vacuum insulated tubing (VIT) for deepwater oil and gas wells fails to withstand high pressure and temperature conditions without collapsing and is susceptible to weld corrosion and cracking, leading to loss of vacuum.
Innovation Solution
A VIT apparatus with an inner and outer tubular member having a vacuum gap, where a weld is formed at the inner cylindrical corner and protected by a mechanized gas tungsten arc weld overlay that does not extend into the inner bore, using high-strength 15Cr steel and a nickel-based alloy weld overlay to resist corrosion and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If existing VIT is used in HPHT wells, then vacuum insulation is provided, but the tubing collapses under high pressure
Solution Approach 1:
The patent employs composite material construction by combining inner and outer tubular members made from high-strength alloys (such as 13Cr stainless steel or Inconel) with a vacuum insulation layer between them. This composite structure provides both thermal insulation properties and enhanced collapse resistance, allowing the VIT to withstand HPHT conditions while maintaining temperature differential protection.
2Ease of manufacture
If existing VIT welds are used, then tubing is joined, but welds are susceptible to corrosion and cracking
Solution Approach 1:
The patent applies local quality enhancement by placing a corrosion-resistant weld overlay (such as Hastelloy C-276 or Inconel) specifically on the weld areas and adjacent heat-affected zones. This localized application provides enhanced corrosion and cracking resistance precisely where the base weld metal is most vulnerable, without requiring the entire VIT structure to be made from expensive high-alloy materials.
Solution Approach 2:
The weld structure is designed as a composite system combining the base metal (13Cr stainless steel or Inconel), the heat-affected zone, and a corrosion-resistant overlay material (Hastelloy C-276 or Inconel). This multi-layer composite weld structure leverages the strength of the base metal with the superior corrosion resistance of the overlay, creating a reliable joint that resists both mechanical stress and chemical degradation.
3Reliability
If HVOF coating is applied to protect welds, then corrosion protection is improved, but coating cracks and spalls under tensile stress
Solution Approach 1:
The patent changes the deposition parameters and material composition of the protective coating by using a weld overlay process with controlled heat input and specific alloy compositions (Hastelloy C-276 or Inconel). The overlay is applied with controlled thickness (typically 0.020-0.050 inches) and undergoes post-weld heat treatment to relieve stresses and prevent cracking, thereby maintaining coating integrity under tensile stress while providing superior corrosion protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a VIT capable of withstanding pressures over 15,000 psi and temperatures above 350°F without collapsing and maintains vacuum integrity, preventing corrosion and cracking, thus effectively mitigating annular pressure buildup in deepwater wells.
Implementation Method 1
VIT has a vacuum gap there within between the inner and outer tubes of the VIT to reduce heat transfer from the production fluids within the inner tube into the annulus
Implementation Method 2
A weld overlay is placed over the weld for protecting the weld formed using a mechanized gas tungsten arc process
Data Source
AI summary
Disclosed is a VIT apparatus for mitigating APB in a wellbore casing annulus of a HPHT deepwater well. The apparatus includes inner and outer tubes formed of 15Cr-135 martensitic stainless steel having a vacuum space therebetween and a weld formed of high yield strength alloy for joining the inner and outer tubes. A protective weld overlay formed of corrosion resistant alloy is placed over the weld. The weld and the weld overlay are formed so as not to extend into the inner bore. Also disclosed are a process for forming the apparatus, and a system and method for using the apparatus. Multiple apparatus are connected by threaded couplings to form an elongated device that can be placed within a casing within a wellbore to carry fluids from the deepwater well to a surface location. When exposed to HPHT well conditions, the vacuum in the VIT apparatus is not lost.