Bulk liquid storage terminals are a critical component in the energy industry supply chain between production and distribution. Floating roof tanks are commonly used to avoid having a vapor space or ullage between the liquid level and roof found in fixed-roof tanks.
A Storage Terminals magazine article, Staying on the Radar, shared some thoughts from Emerson’s Christoffer Hoffmann on avoiding abnormal and overfill conditions in these tanks. The article’s author opens highlighting some catastrophic accident that have occurred over the years from dated overfill prevention systems, noting that a reason:
…is that there are still considerable numbers of old and not adequately maintained storage tanks in service with non-existing, non-functioning or obsolete overfill prevention equipment.
While floating roofs remove the vapor space when functioning properly, they can have abnormal conditions.
A sinking, tilting, leaking or collapsing roof can cause significant mechanical damage and create overfills and the release of explosive hydrocarbon vapour.
The article highlights a PEMY Consulting whitepaper, Floating Roof Tanks in Petroleum Storage, that shows that most failure conditions can be foreseen.
These failure conditions can include:
…that the roof is stuck due to damaged or wrongly mounted rim seals. Leaking pontoons, overfills, strong winds and inadequate draining during heavy rain or snowfall can also dangerously affect buoyancy and roof position.
Continuous monitoring can identify roof tilt conditions [I added hyperlinks below].
Emerson’s Rosemount 3308 Wireless Guided Wave Radar and Rosemount 5900C Non-Contacting Radar both monitor roof position and tilt with the devices mounted on the tank top or the floating roof.
Preventing overfills is safety function.
Dual radar-based tank gauging enables the tank terminal to reach a higher level of safety than with traditional mechanical overfill prevention methods.
A Rosemount Tank Gauging system:
…includes radar level gauges, multiple spot precision temperature measurements, pressure transmitters, inventory management software and wireless connection capabilities. The available measurement devices range from SIL 2 to SIL 3 depending on configuration, with the Rosemount 5900S 2-in-1 being the only single-housing device in the world to achieve SIL 3.
Read the article for more on how these radar measurement devices achieve the necessary separation required in the global safety standards, how proof testing is performed, and how this continuous monitoring is part of an overall strategy to improve safe and reliable operations.
Visit the Tank Gauging and Level Measurement sections on Emerson.com for more on these technologies. You can also connect and interact with other tank management experts in the Measurement Instrumentation group in the Emerson Exchange 365 community.