Session: Plenary Keynote - Luis San Andrés

Paper Number: 164088

164088 - Wet Annular Seals in Multiphase Pumps: Leakage and Rotordynamic Force Coefficients and a Method to Promote Seal Direct Stiffness 

Abstract: 

In the subsea oil and gas industry, multiphase pumps enable a long-distance tie back system and eliminate topside oil and gas separation stations. A persistent challenge to operate (vertical) centrifugal pumps handling (gas in liquid) mixtures is their poor reliability due to persistent sub synchronous vibrations (SSV). The gas volume fraction (GVF), changing over the life of the well, affects the dynamic forced performance of annular clearance seals, and which may lead to an increase in both lateral and axial rotor vibrations. The lecture presents measurements of leakage and dynamic force coefficients for a grooved seal and a wavy-clearance seal. The seals, short in axial length (L=0.342D), are typical as interstage bushing or impeller front wear ring seals. A mixture of air in ISO VG 10 oil with inlet gas volume fraction (GVF) ranging from 0 (just oil) to 0.8 (mostly air) lubricates the seals. The operating shaft speed equals 3.5 krpm (surface speed = 76.4 ft/s (23.3 m/s)) and the pressure ratio (inlet/exit) = 2.5 for the wavy seal and 2.9 for the grooved seal.  Dynamic loads exerted on the seal housing with a single frequency (max. 140 Hz) serve to identify the frequency dependent rotordynamic force coefficients for each seal. Large vertical turbines/pumps have very low natural frequencies and often show subsynchronous vibrations. Local injection of air into the seals alleviates the issue as it reduces the amplitude of rotor motions. The lecture shows the outcome of measurements with local gas injection (GVF~0→10%) to demonstrate a uniform clearance annular seal recovers a positive dynamic stiffness, hence promoting rotor stability. The results validate a well-known practice used to stabilize large vertical pump systems.

Presenting Author: Luis San Andrés Texas A&M University

Presenting Author Biography:  Luis San Andrés, former Mast-Childs Chair Professor of Mechanical Engineering at Texas A&M University (1991-2023), conducted experimental and analytical research on the rotordynamics of pump seals for rocket engine turbopumps and electrical submersible pumps and compressor seals for oil and gas applications. Luis is a Life Fellow of ASME, STLE, GPPS, and a member of the Industrial Advisory Committees for the Texas A&M Turbomachinery and Pump Symposia. Dr. San Andrés and graduate students published over 200 journal papers, several recognized as best in various international conferences.

ASME distinguished Dr. San Andrés with the 2022 Aircraft Engine Technology Award (International Gas Turbine Institute), the 2023 Mayo D. Hersey Award (Tribology Division), and the 2025 Henry R. Worthington Medal for his contributions to pump rotordynamics.