Why the ASTM D 5364 requirement for ovalling frequency of an FRP chimney liner may be misleading.

The American Standard, ASTM D 5364, “Standard Guide for Design, Fabrication and Erection of Fiberglass Reinforced Plastics Chimney Liners for Coal Fired Units” requires that the lowest ovalling frequency of a fiberglass reinforced plastic chimney liner shall not be less than 2Hz. From engineering practices and numerical experiments, the authors find that the frequency calculated in accordance with ASTM D 5364 deviates considerably from results using FEA. A modified equation has been proposed in this paper to better evaluate the lowest ovalling frequency for FRP chimney liners.

The major function of an FRP liner is to protect the outer shell from the thermal, chemical and abrasive environment of the hot boiler gases. One of the design concerns is to minimize the ovalling due to pressure fluctuations. Gas turbulence has been observed to cause liner ovalling on at least two occasions¹. However, the number of variables influencing modes of vibration and the unknowns associated with gas flow makes it extremely difficult to formulate a precise solution to ensure that ovalling will not occur. To avoid resonance when the frequency of gas turbulence matches the liner’s natural frequency of vibration², ASTM D 5364³ recommends a minimum criteria of 2 Hz for the lowest ovalling frequency. Meanwhile, it also provides two equations to calculate the lowest ovalling frequency for an unstiffened liner in Section 7.7.2.2, and a stiffened liner with ring stiffeners in Section 7.7.2.3. A review has been conducted using Finite Element Analysis (FEA) of 10 chimney liners similar to projects previously completed.

Ovalling due to gas turbulence is a design concern for FRP chimney liners. To avoid liner ovalling vibration which could lead to premature failure, ASTM D 5364 provides a lowest ovalling frequency requirement and two equations to predict the frequencies for unstiffened liners and stiffened liners. However, both equations are based on an idealized liner arrangement. The lowest ovalling frequency prediction in accordance with ASTM D 5364 considerably deviates from the FEA modal analysis results. The unstiffened liner frequency equation in ASTM D 5364 is applicable for liners with no circumferential restraints.

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1. ASCE, Design and Construction of Steel Chimney Liners. 1975, Fossil Power Committee, Power Division. American Society of Civil Engineers: New York, New York.
2. Dooms, D., et al., Wind induced vibrations of thin-walled cylindrical structures. 2008.
3. ASTM, Standard Guide for Design, Fabrication, and Erection of Fiberglass Reinforced (FRP) Plastic Chimney Liners with Coal-Fired Units, in D 5364. 2008, The American Society for Testing and Materials: West Conshohocken, PA.