Investigation Tactics for Prevention of Floating Roof Rim Seal Failures

Introduction

Minimizing costly disruptions caused by floating roof issues is critical for owner/operators looking to maximize tank performance and improve the operational reliability of their aboveground storage tanks. Of the many components impacting the performance of a floating roof, rim seals are often exposed to demanding environmental conditions as well as demanding operational envelopes. Given the challenges, rim seals are required to maintain consistent and problem-free performance. Tank owners expect rim seals to operate flawlessly throughout the maintenance cycle, and rim seals are frequently monitored and inspected for compliance with local and national regulations. Rim seals found to be out of compliance must be repaired, which can result in costly impacts on operations and the environment. It is important to highlight that the risk associated with rim seal failures is not just about downtime and operational costs; the primary purpose of rim seals and other emissions control products is to protect the environment by containing and preserving the product stored. 

Therefore, the failure of a floating roof rim seal is a critical problem in both midstream and downstream sectors. A calculated and thought-out investigation into aboveground storage tank floating roof rim seal failures is required to provide usable and relevant data to support sound risk mitigation decisions. Incorrect assumptions and conclusions can result in additional unexpected and expensive downtime. It is important to understand the key characteristics of seal failures and their potential causes. In this article, a thoughtful and logical approach to diagnosing rim seal failure modes, as well as case study examples, is provided. Tank owners, contractors, engineers, and inspectors will find this information a useful addition to their failure inspection analysis toolbox.

Rim Seal Failure Modes

The United States government defines the type of rim seals to be used in specific aboveground floating roof storage tanks through the Code of Federal Regulations 40 CFR Part 60, Subpart Kb in the current edition [1]. Rim seals are used to provide a barrier between the floating roof and the tank shell with the purpose of controlling emissions from the stored product. Rim seal designs differ in physical construction and how they perform the task of emission control, with certain floating roofs requiring specific designs. As such, external and internal floating roof tanks utilize different requirements for rim seals. Even though requirements differ, all rim seals for aboveground floating roof storage tanks are subjected to numerous physical and environmental forces. The variability in the design of rim seals requires a broad examination of factors that impact performance and may cause a rim seal failure.

Specifically, the modes of rim seal failure can be broken down into degradation, tolerancing, adhesion, and external forces. These failure modes can apply to certain designs of rim seals or can be all-encompassing. This article will break down these failure modes and how they are applied to floating roof rim seals.