Using Non-Contact Anti-Corrosion Under Insulation Materials to Increase Efficiency of Acoustic Insulation for Pipes

Abstract Insulation for process pipework is required for thermal, acoustic and fire protection, either to maintain fluid temperature, reduce noise emissions or protect process systems from fire. However, corrosion under insulation is a key concern for plant operators. Moisture can penetrate the insulation cladding and some fibrous materials can allow that moisture to wick down to the pipe wall and allow corrosion to occur. Although there are insulation materials that perform well to prevent this wicking effect, there is a growing consensus for using non-contact insulation systems to either raise the insulation from the pipe wall and/or raise the external jacket from the insulation material. For thermal requirements, these non-contact systems have some benefits to help reduce the thickness of the overall system. However, there are significant benefits in the reduction of insulation system thickness for acoustic insulation systems. Acoustic insulation for pipes, valves and flanges is governed by ISO15665. The standard outlines a series of classifications for the acoustic insertion loss performance of insulation systems. These system classifications are often used in the design and operational requirements for industrial process plants. There is often a requirement for these plants to increase the lifetime of, and to reduce the thickness and weight of these insulation systems. A revision of the standard was implemented in 2023. Within the revision, emphasis was placed on selecting appropriate materials for an acoustic system where Corrosion Under Insulation (CUI) was a concern. The revision of the standard also emphasizes the requirement to test an acoustic insulation system to meet a defined acoustic insertion loss classification. Non-metallic standoff membranes offer a simple but highly effective method for providing non-contact options to reduce corrosion under insulation risk through removal of insulation from pipe walls and cladding respectively. Open and closed cell flexible elastomeric foams (FEF) and aerogel blanket insulation materials are installed in varying constructions to provide superior sound attenuation for pipework, valves and flanges. These insulation materials also provide inherent protection from liquid and vapor migration and are often used to provide corrosion under insulation protection for contact approved systems. Using PTFE or PVC non-contact systems with conjunction with the FEF and aerogel insulation materials, a range of non-contact, acoustic insulation systems were developed to meet the acoustic insertion loss classification requirements of ISO15665. Emphasis was made on minimizing the thickness of the systems. Acoustic insulation on pipework is required to reduce the passage of airborne sound through a combination of acoustic absorption and mass barrier effects. The insulation is also required to minimize the transfer of vibrational energy from the pipe wall to the external cladding through vibration isolation and damping. The combination of these material factors helps to define the sound attenuation that can be achieved by the acoustic insulation system at each frequency. Currently there is no recorded study emphasising the effect of acoustic performance of pipework acoustic insertion loss for standoff systems incorporated into acoustic insulation of pipes. It was however considered that the incorporation of the annular spaces provided by the non-contact standoffs could be advantageous for purposes of reducing sound propagation from the pipe wall through the insulation system. This paper presents a summary of the work done to enhance acoustic insulation systems for pipework to meet the classification requirements of ISO15665, with minimum possible thickness along with offering protection against CUI and stress corrosion cracking (SCC) that the standoff systems can provide. These hybrid systems meet the demanding acoustic, environmental and cost-effective solutions required by the industrial process industry.

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