- Steam Theory
- 1. Basics of Steam
- 2. Steam Heating
- 3. Basics of Steam Traps
- 4. Steam Trap Selection
- Steam Trap Selection: How Application Affects Selection
- Steam Trap Selection: Understanding Specifications
- Steam Trap Selection: Safety Factor and Life Cycle Cost
- Traps and Orifices Part 1
- Traps and Orifices Part 2
- Casting vs. Forging
- Applications of Different Types of Steam Traps
- Don't Get Steamed : Selecting Steam Trap Design
- Understanding Steam Traps
- Compare Two Fixed Orifice Venturi Products to a Variable Orifice Free Float Steam Trap
- 5. Steam Trap Problems
- 6. Steam Trap Management
- 7. Water Hammer
- Water Hammer: What is it?
- Water Hammer: The Mechanism
- Water Hammer: Cause and Location
- Water Hammer: In Steam Distribution Lines
- Water Hammer: In Equipment
- Water Hammer: In Condensate Transport Piping
- Identifying Water Hammer Using a Thermal Camera
- Mitigation of Water Hammer in Vertical Flashing Condensate Transport Piping
- Stop Knocking Your Condensate Return
- Steam Trap Management: Do Something; Anything. Please!
- 8. Risk Mitigation
- 9. Steam Quality
- 10. Steam Distribution
- 11. Condensate Recovery
- Introduction to Condensate Recovery
- Returning Condensate and When to Use Condensate Pumps
- Condensate Recovery: Vented vs. Pressurized Systems
- Condensate Recovery Piping
- What is Stall?
- Methods of Preventing Stall
- Cavitation in Condensate Pumps
- Steam Heat Exchangers are Underworked and Over-Surfaced
- Allocate New Plant Focus to Steam System Design—Part 2
- Optimize Reboiler Performance via Effective Condensate Drainage
- Vent Away Condensate Pump Frustrations in a Flash
- 12. Energy Efficiency
- Tips to improve steam plant efficiency
- Advice on Winter Preparation for Steam Systems
- Insulating Traps
- Steam Compressors
- Why Save Energy?
- Management Strategies for Conserving Energy
- Recovering Steam Clouds and Waste Heat
- Waste Heat Recovery
- Boiler Energy Saving Tips
- Steam Line Energy Saving Tips
- Steam-Using Equipment Energy Saving Tips
- Preventing Steam Leaks
- Handle Steam More Intelligently
- Optimize the Entire Steam System
- Use Available Data to Lower System Cost
- 13. Compressed Air / Gas
- 14. Other Valves
Condensate Recovery Piping
Contents:
Condensate that is discharged from steam traps is handled in one of two ways. It is either drained out of the system to sewer, which can result in wasted heat energy and water, or it flows into piping to be transported elsewhere, ideally for recovery.
Piping for Two-Phase Flow
The piping used to transport condensate is typically called “condensate recovery piping” or “condensate return piping”. The design sizing of such piping requires significant specialization because condensate recovery piping collecting from steam traps must be designed for two-phase flow. The design should not be based on calculations for piping that transports only water because these are not valid for two-phase flow.
Two-phase flow refers to flow in which vapor such as steam (either flash steam, live steam, or a mix of both) flows through piping together with liquid condensate. Although flowing together, this does not necessarily mean that the liquid and vapor are flowing in distinct separate layers. The flow pattern within the piping can also be mixed, as illustrated in the below animation.
Piping Considerations for Flow Patterns of Two-Phase Flow

Why is Steam Present in Condensate Recovery Piping?
Considering steam vapor when designing condensate recovery piping may at first seem counterintuitive, but is in fact necessary.
This is due to a phenomenon known as flash evaporation, which occurs when high temperature condensate formed at a high pressure is suddenly introduced into a low pressure system such as a condensate recovery line on the outlet side of a steam trap. Upon discharging through a steam trap, the high temperature condensate from the inlet is now subjected to a lower pressure and therefore contains too much heat energy to remain in the liquid phase. This excess sensible heat causes part of the condensate to instantly evaporate or “flash” back into steam. The term “flash steam” simply describes the way the steam was created; it is otherwise no different from “live steam.”
For more on flash steam evaporation, please read the article:
How Flash Steam Amount Influences Pipe Size

At lower recovery line pressures, the specific volume of saturated steam can be more than 1,000 times that of saturated condensate. In many instances, this volumetric ratio can be more than 90 to 1. The volumetric proportion of steam to condensate will therefore vary depending on the amount of flash steam created or “flashing rate”, and this in turn can greatly affect pipe sizing design requirements.
If no flash steam occurs, the piping design velocity and pressure drop calculations can be similar to those for single-phase water transport piping. However, a “no flash” situation can only occur if the condensate is significantly subcooled to a temperature less than the saturated water temperature associated with the recovery line pressure. If the amount of flash steam is large, the required piping size becomes almost identical to that of steam piping. As such, designing condensate recovery piping first requires calculating the amount of flash steam and then sizing the pipe to accommodate the specific volume ratios for both water and steam flow, with their respective required velocity and pressure drop design parameters.
Example of Condensate Recovery Piping

Example of Condensate Recovered Using a Flash Tank

There are multiple benefits to installing a flash tank. The flash steam can be used to supply low pressure equipment or be used for pre-heating, while the hot, non-flashing liquid condensate can be returned to the boiler where its heat is reused, increasing overall efficiency.
High energy condensate can be used either at the boiler or some other point along the transportation line. If the flash steam energy can be used locally, the system designer can weigh the relative benefits of either a) returning condensate to the boiler, using smaller size piping but requiring a pumping system, or b) using larger piping to return the condensate without a localized flash system. Transporting flashing condensate over large distances requires certain design constraints for gravity return to mitigate the introduction of water hammer.
For more information, read:
- Water Hammer: In Condensate Transport Piping
- Mitigation of Water Hammer in Vertical Flashing Condensate Transport Piping
Design Methods for Condensate Recovery Piping
As previously stated, TLV recommends sizing condensate recovery piping based on the amount of flash steam and liquid condensate that can be present in a return piping system.
We recommend using specific volumes of each phase to determine volume ratios of condensate and steam at a given pressure and then calculating a maximum allowable flow velocity. You should then size piping based on the allowable velocity and pressure drop parameters.
Other factors that may be considered when sizing condensate recovery piping are:
- The presence of live steam in the piping from leaks or bypassed traps
- The long term effects of corrosion or mud in the system, possibly reducing the internal cross-section piping area
Both of these may have the effect of increasing velocity, pressure drop, and system back pressure. For a more detailed explanation of the calculation for sizing condensate recovery piping, readers can refer to TLV’s technical handbooks entitled “Condensate Drainage and Recovery” and “Efficient Use of Process Steam”.
Condensate Recovery: Vented vs. Pressurized Systems | What is Stall? |