Our clients were in the final stages of developing their range of Premium Connectors and they wanted to gain confidence in the design before they committed to final qualification testing. Global, local and functional criteria relating to the strength and sealing performance needed to be assessed against the ISO/FDIS 13679 International Standard. The output of our analyses had to give them a definitive ‘Pass’ or ‘Fail’ conclusion. We verified product compliance to the ISO/FDIS 13679 International Standard, provided 99.9% certainty of the final qualification testing outcome and through the use of our Automation Tools, delivered the analysis and the qualification report in 50% of the predicted time.
Premium connectors are used in drill pipe, casing and tubular applications throughout the Oil Country Tubular Goods (OCTG) industry. Due to the criticality of their nature, premium connectors need to comply with a number of design codes (e.g. ISO/FDIS 13679, API 5CT, API RP 5C5, ISO 13628-7, API 17G etc.) and they must undergo final qualification product testing to ensure they have the strength to withstand the onerous combination of pressure, elevated temperature, tensile and bending loads that they will see in practise. Testing is essential to prove the premium connectors are fit for purpose, but testing is also time-consuming and expensive. When a company is developing a premium connector, it is essential that they have a high degree of confidence that the connector will work before they commit to final qualification testing. Several design codes now mandate the use of finite element analysis as part of the connector qualification process, but they stop short of prescribing how the finite element analysis should be performed. Due to the complex nature of the thread forms involved, the various loading scenarios that need to be considered and the way the ultimate assessment needs to be done against the design code allowables, such analyses need to be undertaken by a competent and experienced engineer.
Our client’s vision is ‘to be the leading manufacturer of seamless pipes’. They were in the final stages of developing their range of Premium Connectors and they wanted to gain confidence in the connector design before they committed to final qualification testing of the entire product range at the Oil States Industries (OSI) state of the art test facility in Aberdeen. Global, local and functional criteria relating to the strength and sealing performance needed to be assessed against the ISO/FDIS 13679 International Standard and in the case of two of the connector sizes, the effects of internal pressure and elevated temperatures (356°F/180°C) also needed to be taken into consideration. The output of our analyses had to give our client a definitive ‘Pass’ or ‘Fail’ conclusion as to whether or not the range of connectors would pass the final qualification testing.
The first deliverable was the Analysis Plan. The Analysis Plan is a comprehensive document which clearly states what will be done and how. It fully defines the analysis procedure, i.e. the units, geometry to be analysed, element types and mesh details to be employed, material data, boundary conditions, contact type definitions and loads. It also fully defines the applicable code, the design code allowables that the results will be compared against and how the analysis results will be post-processed and presented in their final form. The Analysis Plan provides certainty from the outset that the analysis itself will answer the right ‘exam question’ and it provides certainty that the analysis will give the client the key information that they need. The Analysis Plan for the connector range was duly approved by our client, subject matter experts and the analysis itself got underway. The nominal connection geometries were created in ANSYS Mechanical using the ANSYS Parametric Design Language (APDL), or ‘classic’ interface, and they were analysed as 2D axisymmetric models. Additional geometry variations accounting for manufacturing tolerances were also considered to examine their effect on the overall performance for one of the connections. Each model was created in such a way that the definition of the complete external torque vs. preload curve for each connection could be defined by altering the relevant pin and box positions and by the modification of the box thread, a specified preload could be introduced. Automation Tools were created for the generation of the appropriate meshes, as well as for the definition of the load steps and solution settings for all of the connector geometries. Material and geometrical nonlinearities were accounted for by using elastic-plastic material behaviour definitions and large deformation effects were considered. A number of analyses were completed which accounted for different levels of initial torque/preload being applied to each connection. In addition to the preload, a combination of axial tension/compression loads and internal/external pressure loads were applied and capacity curves were derived in accordance with the ISO/FDIS 13679 – 2011 standard. The analysis results were post-processed against the global and local failure criteria with respect to the structural and operational performance of each connector. All three connectors passed the assessment criteria and all three connectors passed the final qualification testing at OSI without any issue. Correlation between the predicted capacity derived from our analysis and the actual capacity determined during final qualification testing at OSI was excellent.
- Independently verified product compliance to the ISO/FDIS 13679 International Standard.
- Provided 99.9% certainty of the final qualification testing outcome.
- Reduced the total product development time by 24 weeks (50% reduction).