Mechanically Attached Sour Environment Fitting
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In sour environments, carbon steel pipelines are prone to corrosion, cracking, and hydrogen-induced cracking due to the presence of H2S and CO2, which can lead to sulphide stress cracking (SSC) and hydrogen-induced cracking (HIC), making traditional welding methods risky and inefficient.
Innovation Solution
A mechanically attached fluid fitting using a coupling body and swage rings made of high-strength, low-alloy carbon steel, designed to replace welding, with predetermined interference ratios and sealing surfaces that minimize work hardening and meet NACE and ASME standards for burst and thermal expansion, reducing the risk of SSC and HIC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If welding is used to connect pipes in sour environments, then strong mechanical connection is achieved, but susceptibility to sulphide stress cracking and hydrogen induced cracking increases
Solution Approach 1:
The connection system is divided into separate components: a fitting body and a swage ring, which are assembled together mechanically rather than welded. This segmentation eliminates the heat-affected zone and welding-induced stress concentrations that make welded joints susceptible to SSC and HIC, while still achieving strong mechanical connection through the interference fit between components
Solution Approach 2:
The patent replaces the thermal welding process with a mechanical assembly system consisting of the fitting body and swage ring. The mechanical connection is achieved through interference fit and deformation of the swage ring onto the pipe, providing strong connection without the harmful effects of welding in sour environments
2Strength
If high-strength steel is used to increase connection strength, then mechanical strength is improved, but susceptibility to sulphide stress cracking increases
Solution Approach 1:
The patent specifies precise parameter ranges for the steel alloy composition (carbon content 0.28-0.50%, chromium 1.00-2.00%, molybdenum 0.15-0.50%, etc.) and mechanical properties (tensile strength 415-550 MPa, elongation ≥20%, reduction of area ≥40%). These controlled parameters achieve the required connection strength while maintaining resistance to SSC by avoiding excessive strength levels that increase cracking susceptibility
3Reliability
If mechanical attachment is used to avoid welding, then risk of SSC and HIC is reduced, but connection reliability may be compromised
Solution Approach 1:
The connection system uses a composite structure combining the fitting body material and swage ring material, both specified as NACE-compliant steel alloys with controlled composition ranges. This composite mechanical assembly achieves connection strength comparable to welding while maintaining resistance to SSC and HIC through the selection of appropriate materials and the mechanical (而非thermal) joining process
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 fitting provides a reliable, cost-effective, and safe connection for pipes in sour environments, reducing the risk of SSC and HIC, and avoiding the need for welding, while maintaining quality and safety standards.
Implementation Method 1
Longitudinally forcing the driver along the exterior surface of the sleeve causes deformation of the sleeve and concurrently of the tube section engaged within the sleeve such that the sleeve bites into the tube
Implementation Method 2
The predetermined interference ratios between the drive ring, body, and pipe along the length of a cylindrical contact area
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
A fitting 10 for coupling with a pipe 16 in a sour environment includes a coupling body 12, a ring 14 positioned to fit over an end 42 of the coupling body 12, a main seal 30 formed on an inner surface of the coupling body 12, a transition section 24, 26 positioned adjacent the main seal 30, an inboard seal 32 formed on an inner surface of the coupling body 12, and an outboard seal 34 formed on an inner surface of the coupling body 12. The transition section 24, 26 is formed as an indentation on the inner surface of the coupling body 12 and has a first portion with a first diameter and a second portion with a second diameter, with the first diameter being greater than the second diameter. When the ring 14 is fitted over the at least one end of the coupling body 12 via force, the ring 14 and coupling body 12 apply a coupling force to the main seal 30, the outboard seal 34 and the inboard seal 32 to connect the pipe 16 to the coupling body 12 in a non-leaking manner. The fitting 10 is made of a low alloy carbon steel material. The main seal 30 includes a first tooth 50, a second tooth 52, and a third tooth 54.