Modernization of Steam Turbine Diaphragms for the Saudi Aramco Gas Plants
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Date
2013
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Turbomachinery Laboratory, Texas A&M Engineering Experiment Station
Abstract
The critical components of the Saudi Aramco Uthmaniyah and Shedgum gas plants are eight trains of turbomachinery, 4 trains per plant. Each train consists of a steam turbine and a centrifugal compressor. At the time of their design and manufacture, these steam turbines were at their chronological level of technology. They operated reliably and effectively for their original design. However, during their 35+ years of operation,
some of the diaphragms developed problems as the gas plants production gradually increased. With increased gas production, the mechanical strength of the heavily loaded diaphragms became marginal. As a result of the increased loading, these diaphragms deflected more than they did originally and caused axial rubs with serious diaphragm and rotor damage.
Over the years as the operating conditions changed, Saudi Aramco personnel made several requests for the manufacture of “spare” diaphragms. Even though the operating conditions changed, the basic Saudi Aramco requirements did not. Specifically:
-The diaphragms had to have adequate increased mechanical strength to withstand the increased loads.
-They had to be more efficient.
-They had to be a “drop-in” design which could be installed into the existing turbine without any rework of the case and rotor.
At each request, diaphragm design changes were made to produce diaphragms that met Saudi Aramco’s requirements. Each design step exemplified the latest technology available at the times of their design and manufacture.
This paper describes the design and manufacturing evolution leading to the current diaphragm design. The advanced analytical tools (FEA for defining stresses and deflections) were used for evaluating the mechanical integrity of the various diaphragm designs. Design improvements (vane profile, tangential vane lean, tip and new shaft seals), and manufacturing improvements (electron beam welding, laser and water jet cutting, electric discharge machine wire cutting), which have led to substantial gains in mechanical strength, efficiency and reliability will be described in detail
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