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NIC uses modelling technique for composite pipe performance

Thu, 03 December, 2020

An innovative project is underway – within the framework of the Non-metallic Innovation Centre (NIC) and led by partners Saudi Aramco Technologies Company (SATC) and TWI Ltd – to develop a multi-scale modelling methodology for assessing the risk of electrostatic discharge occurring in non-metallic pipes.

The transport of natural gas and particulates through composite pipes can lead to the accumulation of static charge on the inner surface of the pipe, which due to the non-conductive nature of pipe walls is not dissipated.  This means there could be a significant risk of explosion with associated damage to assets and injury to personnel.  Moreover, if the charge built up across the pipe wall exceeds the dielectric strength of the polymer matrix, dielectric breakdown can occur.  This can cause holes in the pipe, a phenomenon known as pin-holing.  This risk of electrostatic discharge has to be quantified and mitigated in order to ensure safe utilisation of non-metallic pipes in natural gas service.

Current approaches to evaluating the risk of electrostatic discharge rely solely on determination of the flow regime (API/RP 2003 and NFPA 77), often using analytical approximations such as Baker and Mandhane charts.  These methods can be over-conservative.  In addition, mitigation methods to avoid a mist flow regime are difficult to implement.

Image (top) shows the electric potential along a pipe grounded at both ends, as built up by the flow of gas through the pipe

Mihalis Kazilas, NIC Programme Director at TWI explains “With this project, our team has developed a modelling approach combining heat transfer, computational fluid dynamics and electrostatics to provide a quantitative assessment of the risk of electrostatic charge build-up in composite pipes used in natural gas transportation.  The modelling approach will be validated in laboratory conditions and used in real-case field scenarios to demonstrate its efficacy.”

Abderrazak Traidia, NIC Technical Support Officer at Saudi Aramco Technologies Company adds “The electrostatic discharge (ESD) risk assessment methodology and simulation tools developed in this project will help the oil and gas industry gain more confidence in the reliability of composite pipes used in gas service. They will also provide a better understanding of the ESD mechanism, and insights on the key material and process parameters that govern the susceptibility to ESD. We believe that this tool is equally helpful for composite pipe manufacturers as it allows virtual assessment of different pipe designs and ESD mitigation techniques.”