2015 IR&D Annual Report

Testing and Analysis of Acoustically-Induced Vibration Stresses in Piping Systems, 18-R8478

Principal Investigators
Tim Allison
Brandon Ridens
Nicholas Niemiec
Jeffrey Bennett

Inclusive Dates: 07/01/14 – Current

Background — Acoustically induced vibration (AIV) is the phenomenon of high-frequency piping vibration downstream of a high-amplitude noise source, potentially leading to fatigue failure of the piping at a branch or welded support. Although AIV has long been a concern in high-capacity gas piping systems, recent capacity increases to aging systems and debottlenecking operations, as well as the development of new higher-capacity systems, have led to renewed interest in AIV mitigation strategies. Existing methods of AIV analysis used to predict if a weld failure is likely to occur are based on an incomplete historical dataset that does not properly address the fundamental physics of AIV, the high flow rates and pressure ratios encountered in modern blowdown systems, or the increasingly larger pipe sizes that are being implemented. In many cases, these methods are considered to be overly conservative and costly. Furthermore, AIV mitigation options are limited for existing systems that are predicted to fail. Therefore, a physics-based approach that is calibrated to physical measurements is needed for improving the accuracy of AIV failure predictions as well as accurate performance modeling of AIV mitigation strategies.

Figure 1: Experimental setup
Figure 1: Experimental setup
Figure 2. Test header configurations
Figure 2: Test header configurations

Approach — The objective of this project is to gather experimental AIV data during blowdown testing of several piping samples that span a wide range of diameter and wall thicknesses (Figure 1). Data from this testing, performed at SwRI's Gas Blowdown Facility (Figure 2), includes dynamic pressure and stress measurements to validate models of the noise source, internal piping acoustics, and piping stress response for several representative configurations of gas blowdown piping. Several AIV remedies including damping wrap, stiffening rings, and acoustic attenuators were also tested to quantify the stress reduction provided by each method.

Accomplishments — Test data for all piping configurations have been acquired and analyzed to quantify baseline AIV stresses and stress reduction performance of each AIV mitigation for the various piping geometries. Application of these experimentally obtained stress reductions to existing analysis methods enables SwRI to offer AIV analysis services with improved accuracy, and test data for various remedies increases the pool of available design and retrofit options. The test data are also analyzed to improve SwRI's capabilities for physics-based modeling of AIV. Detailed structural and acoustic finite element models were developed and analyzed for comparison with test data to determine combinations of acoustic and structural modes that lead to peak stress frequencies. An example comparison of test data with simulated mode shapes and frequencies is shown in Figure 3. Continued analysis of this data is in progress to determine possible methodologies for efficient physics-based AIV analysis.

Figure 3: Example AIV coincidence plot with experimental data overlay
Figure 3: Example AIV coincidence plot with experimental data overlay
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