Liquid SO2 - Storage Tanks
June 4, 2006

Introduction Codes and Standards Design Temperature and Pressure Materials of Construction Corrosion Allowance Typical Storage Tank

Associated Links Properties of Liquid SO2

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Introduction

Liquid SO2 is generally store at ambient temperatures in carbon steel pressure vessels.

Codes and Standards

As a vessel containing a liquid under pressure, a liquid SO2 storage tank must be designed to the ASME Boiler and Pressure Vessel Code, Section VIII, Division 1 or equivalent.

Welding procedures must be qualified in accordance to Sectin IX of the ASME Code or equivalent.

The design calculations, welding procedures and qualifications must be submitted to the appropriate agency or approval and registration.

Design Temperature and Pressure

The design temperature must take into account the typical ambient temperatures since this affects the vapour pressure of liquid SO2.   A typical maximum operating temperature is 50°C.  The mechanical design temperature can be conservative set at 100°C.

The design pressure must be set higher than the vapour pressure at the maximum operating temperature.  A typical design temperature for a storage vessel is 1448 kPa(g) (210 psig).  Relief valves should be set at 1379 kPa(g) (200 psig), which is 5% lower than the design pressure.

Materials of Construction

All materials should conform the ASME/ASTM standards. Typically, ASTM A516 Gr. 70 carbon steel will be used for all pressure containing parts.   When cold product or ambient temperatures are involved, all material must be impacted tested using Charpy 'V' notch specimens at -46°C (-50°F).  No specimen must be less than 15 ft. lbs.

In addition to impact testing, all material shall be normalized.

Corrosion Allowance

Even though anhydrous liquid SO2 is not corrosive to carbon steel, any moisture entering the tank when in contact with liquid SO2 will be corrosive.  A typical corrosion allowance will be 3 mm (1/8").

Typical Storage Tank

A typical storage tank will be a horizontal cylindrical vessel.  A vessel designed to hold 260 tonnes of liquid SO2 will be 12'-0" diameter by 70'-0" long.