Premium Connection Testing
As Oil & Gas companies are drilling always deeper and in more
severe environments, OCTG products need to prove reliable
for use in these conditions.
Testing facility, Aulnoye-Aymeries (France).
HP/HT wells are now reaching up to 250°C and 20,000 psi reservoir pressure. Premium OCTG products are required to demonstrate their performance to be adapted to withstand the extreme load conditions. The threaded connection especially must remain gas tight in the well conditions, as well as keep the mechanical integrity of the string and allow for multiple assemblies (make-up and break-out, so-called M&B for Make & Break).
End-users have developed procedures to test connections, in conditions that are representative of the well conditions they experienced. In the 80’s, a first version of API RP 5C5 was issued by American Petroleum Institute, giving recommendations and test protocols for premium connections evaluation. Some customers also specified their own testing requirements (NAM TEO 3 by Shell, URC procedure by Exxon…).
Since 2002, API RP 5C5 rev3 / ISO 13679 1st edition has become the reference for premium connection testing Standard, defining four Connection Application Levels (CAL I to CAL IV) representative of the test severity, from CAL I (least severe) to CAL IV (most severe).
Post-Macondo regulations and lessons learnt emphasized the need to demonstrate the performances of all components of the well, including OCTG products. The worst case scenarios are determined to calculate the maximum load cases that the OCTG products will have to withstand. Tests are done accordingly.
Premium Connection testing
Process of connection testing consists in the following steps:
• Thread machining
• Surface treatment
• Static sealability tests and/or other tests (fatigue, failure, expansion…)
A / SAMPLES DESCRIPTION AND MACHINING
To guarantee the performance of any single joint that goes out from production mill, the first condition is to test the thread in the most critical design configurations: this is achieved by machining test samples in the extreme tolerances allowed by the product drawing, that are known to be the most critical for specific performances: worst sample configuration for M&B, other ones for Sealability, etc. ISO 13679(2002) defines the design configuration cases, specifying seal and thread interferences, as well as pin and box thread taper, to cover the extreme cases of the product drawing tolerances. To prepare the test samples, special care must be taken as the targeted dimensions are much narrowed compared to production tolerances (reduced to one tenth of the tolerance). Test samples are thus machined on dedicated CNC lathes, in R&D facilities, and require an accurate set-up for each piece.
B / SURFACE TREATMENT AND M&B TESTS
A first performance to be validated is the multiple assembly: tests consist in applying the surface treatment specified by the connection designer (e.g. raw surface, sand-blasting, phosphate, copper plating…) and to repeat make-up and break-out in the critical conditions of thread compound type and quantity, and torque values. The M&B tests evaluate the galling resistance of the threads, since the product should not be damaged during assembly, and connections may need to be disassembled many times on the rig (in case of work-overs, wrong initial assembly…). Vallourec testing facility has a complete range of tong to perform vertical or horizontal make up. We have developed also specific protocol to simulate specific condition: arctic or desert condition, misalignment make-up or hard stabbing. Cleanwell® and Cleanwell® Dry, that are innovating coating solutions applied on threads to replace storage and make-up thread compound have been extensively tested on different thread designs to guarantee the best M&B properties.
C / COMBINED LOADS SEALABILITY
Different loads, such as tension, compression, torsion and pressure, internally and externally, apply to the casing and tubing strings downhole. Depending on the drilling and production phases, as well as formation and reservoir conditions, loads are combined and will repeat over time.
To evaluate the mechanical and sealability performance of premium connection, ISO 13679 defines Series A, Series B and Series C load points cycles that will be applied on the limits of service load envelope for a given premium joint.
Example of ISO13679 load points, for the testing of VAM® 21: the loads applied on the sample
are based on the connection ratings vs. the pipe body yield strength (in the case of VAM® 21,
the connection is 100% as strong as the pipe, the ellipses match entirely).
These tests consist in applying pressure (gas or liquid, internally and externally) combined with tension or compression (Series A), doing tension and internal pressure cycles at elevated temperature (135°C up to 180°C, Series C) and bending (Series B), in static load frames. ISO 13679 also specifies the equipments for gas leak detection to be installed around the thread.
Failure tests are part of the product evaluation and defined in ISO 13679. They are performed with the same equipments. It consists in increasing the load value up to the mechanical limit (collapse, burst, internal pressure and tensile force until parting…).
D / SPECIFIC TESTS
For dedicated applications, other types of tests are done in Vallourec facilities:
• Solid expandable product expansion, up to 25% of outside diameter increase. Expansions of VAM® ET WISE samples are performed in the facility of Aulnoye (France), and the connection is tested after expansion in static frames for sealability performance.
• Resonant Fatigue tests, either for Riser products (VAM® TOP FE, VAM® TTR…) evaluation, or for OCTG products to simulate applications causing fatigue loads (Drilling with Casing, Shale gas frac. cycles and extended reach…). Fatigue tests have been performed on many VAM® connections, e.g. VAM® SG, VAM® TOP, DWC/CTM, VAM® SLIJ-II, VAM® 21, DINO VAM®).
• Rotating fatigue for Drill products (e.g. VAM® Express, VAM® EIS, VAM® CDS).
SOME MAJOR ACHIEVEMENTS
ON VAM® CONNECTION TESTING:
• More than 400 qualification test programs done for customers on VAM® connections. VAM® TOP products have been the most tested. This includes many isolated products tested for specific HP/HT projects, required by customers.
• Sealability combined load testing as per ISO13679 performed at 250°C for an extreme HP/HT project, with internal and external pressure. One of the main challenges was to develop innovative equipments to achieve external pressure test at this temperature (external pressure vessel design & seals, pressurizing media, heating and cooling methods, high-sensitivity leak detection).
• VAM® threads coated with Cleanwell® Dry have been made up at -30°C, to simulate arctic conditions.
• More than 35 VAM® connection product lines have been developed. Examples of recent test validation programs are: VAM® 21, VAM® SG (Shale Gas), VAM® BOLT, Cleanwell® Dry on VAM® TOP and VAM® 21…
• Tests as per new ISO13679/FDIS2011 CAL IV, successfully passed with VAM® 21 connection, on 100% Von Mises Envelope of the pipe.
• Gas-tight expandable products (VAM® ET family), tested after both hydraulic or mechanical process, in fixed-free, fixed-fixed and free-fixed conditions, up to 25% diameter increase. Samples are tested after expansion in combined loads frames.
• VAM® TTR and VAM® TOP FE are threaded and coupled premium connectors dedicated to riser and offshore applications. Both have been extensively tested in fatigue with more than 200 samples of various sizes and grades. VAM® TTR has a fatigue resistance better than SAF 1.5 and VAM® TOP FE fatigue resistance is rated better than 2.0 vs. DNV-B1 curve.
Conclusion and perspectives
Vallourec has always been the leader for premium connection testing, with VAM® connections being the most extensively tested OCTG products. These tests are done in compliance with relevant industry Standards and customer specifications, the reference today being ISO 13679(2002) / API RP 5C5.
Due to the growing demand for qualifications by customers, and due to the type of tests (see ISO13679/FDIS2011, around 70% longer than the previous protocols, and more severe), Vallourec dedicates a lot of R&D testing resources. This is a consequence of the more challenging E&P projects, and the request from customers to have demonstrated performances to mitigate the operational risks.
Vallourec is investing continuously in equipment upgrade and testing capacity to keep its technical leadership and innovation excellence in VAM® products and OCTG solutions.
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