IPE-TM-600 Instruments
Push Pull Gas Blanketing System
IPE-TM-600-10
1. Purpose
This procedure identifies the equations and data required to calculate the maximum gas blanketing rate for a pressurized surge drum.
2. General
Engineers preparing Instrument Schedule “A” Project Specifications (600 series specifications) shall use this procedure to maintain a consistency of design practice for determining the maximum gas blanketing rate for a pressurized surge drum.
3. Diagram
4. Procedure
Determine the maximum blanketing gas flow rate on the basis of the pump RATED capacity, converted to gas volume units at Standard Conditions using the vessel operating temperature and pressure. For design purposes, assume that the vent gas flow rate is equal to the blanketing gas flow rate.
Use the spreadsheet “T-616-01 Drum Blanket Rate.xls”, located on the Server at .
Example Equations:
= cfh @ Vessel Temp & Press
5. Considerations
5.1 The Cv requirements for the blanketing and vent gas control valves are determined on the basis of the calculated blanketing gas flow rate, and system hydraulics at the vessel NORMAL operating pressure.
Use the gas supply temperature for the blanketing gas valve Cv calculation.
Use the vessel operating temperature for the vent gas valve Cv calculation.
5.2 The blanket gas supply pressure and the vent gas system pressure are determined by the Design Engineer, and are generally available from the hydraulic tabulations.
5.3 Use the vessel pressure for both the blanket gas valve outlet pressure and for the vent gas valve inlet pressure.
DO NOT USE ELECTRONIC “I” FILE DATA FOR CONTROL VALVE SIZING.
5.4 Only a MAXIMUM Cv is calculated for both the blanket gas and vent gas control valves.
5.5 Select a valve Cv equal to or slightly larger than the calculated Cv. The valve trim must be single ported and the plug characteristic should be equal percentage, if possible. There is no requirement for “tight shutoff”.
5.6 Use this calculation method for vessels operating at moderate temperatures (< 550 °F) and pressures (< 100 psig) that have an open loop circulation with net system liquid into and out of the drum).
Do not use this procedure for vessels in a closed loop circulation system such as a Hot Oil Surge Drum.
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Disclaimer. This material is provided for informational and educational purposes only and does not constitute professional engineering advice. Calculations, reference data, and methodologies are based on published standards and accepted engineering practice but are not a substitute for engineering judgment, site-specific analysis, or review by a licensed Professional Engineer. Inflection Point Engineering, LLC makes no warranties, express or implied, regarding the accuracy, completeness, or fitness for a particular purpose of any content presented here, and shall not be liable for any direct, indirect, incidental, or consequential damages arising from its use. Users assume all risk associated with applying this content to real-world design, operations, or decisions.
© 2026 Inflection Point Engineering, LLC. All rights reserved.