Flash Tank: The Ultimate FAQ Guide

I know you’d like to get high quality and reliable flash tank.

Or, you want to learn more about flash tanks.

Whichever the case, all information you’re looking for is right here – keep reading.

1. What is Flash Tank?

A flash tank is an assemblage system that contains several condensates drain lines.

This tank often collects high pressure condensate that is further exposed to a team source of low-pressure.

In the event that this activity takes place, a specific amount of condensate flashes to moisture at the lower pressure.

The interior of a Flash tank is black steel while the exterior is coated with a coat shop primer.

Flash tank

Flash tank

2. What Material is Flash Tank made of?

Flash tanks are made of the following materials due to their special properties of durable, strong, and high tensile strength:

  • Carbon Steel; the most common grade is A516-Grade 70
  • Stainless steel; S30403 grade
  • Low Alloys
  • Duplex Stainless; S32205.

3. What are the Parts of Flash Tank?

Below are the different parts of a Flash tank which are responsible for its overall performance:

  • Vent
  • Inlet
  • Outlet
  • Internal drop leg outlet
  • Hand hole
  • Sparge tubes
  • Condensate inlet
  • Stainless steel wear plate

Flash tank system

Flash tank system

4. How does Flash Tank Work?

A Flash tank basically is a space where all condensate drain lines are located as one big system.

The tank first receives high pressure condensate before they expose it to a source of low-pressure steam.

As a result of this, a specific amount of steam will convert into steam at the lower pressure.

What happens is due to a temperature drop.

The heat released from the system evaporates a significant portion of condensate thus producing flash steam.

You then discharge condensate, and this helps direct it to the sewer or return condensate back to the broiler.

As a result, it is important to isolate flash steam from the condensate.

Flash tanks vent steam to the air.

They can similarly vent flash steam passing it through a pipe than to a low pressure drain.

Simultaneously, it brings back the remainder condensate drain directly to the boiler instead of draining it.

Flash tanks have to be bigger to make sure the released steam is dry as well as to prevent carryover by the steam of water which occurs in droplet form.

5. What are the Limitations of Flash Tank?

Flash tanks have elevated pressures and temperatures. As such, there is a need for level measurement to control flash tank level.

Flash tanks may be costly seeing as one with less carrying capacity/volume costs more than $1,000.

For its efficient operation, you need some accessories for Flash vessel tank.

These accessories incur additional costs. Together with the maintenance costs, Flash tanks are costly.

6. Do Flash Tanks have a Warranty?

Absolutely, yes.

Flash tanks have a warranty of 1-or more than years depending on the manufacturer.

One can return their flash tank back to the manufacturer if it has some manufacturing defects.

7. What are the Standard Specifications for Flash Tanks?

There are material and technical specifications for Flash tanks.

These specifications give an overview of what a flash tank could look like.

Some of the technical specifications of a Flash tank include:

  • Outlet 1 1/2″ – 2″
  • Vent: 2 1/2″ – 8″
  • Inlet: 2″ – 8″
  • Pipe Thread A: 3/4″ – 2″
  • Maximum Flash Load: 500 – 4,000 lbs/hr
  • Pipe Thread B: 1/2″
  • Maximum Condensate Load: 2,000 – 30,000 lbs/hr
  • Diameter: 6 5/8″ – 20″
  • Overall Height: 39″ – 51″

Material specification is:

  • Steel that could be carbon or stainless steel

The standard volumes for Flash tanks range from 13 to 180 gallons.

The standard pressure is 150 PSIG

8. What is the Pressure Rating for Flash Tanks?

The standard pressure rating for Flash tanks is 150 PSI or rather around 10 bars.

There are however other pressure ratings which are available upon request.

These ratings are also dependent on the use it is intended for.

If the flash tank is intended for use in a larger plant then there would be a higher-pressure rating and vice-versa.

9. What are the Available Configurations for Flash Tanks?

The majority of the manufacturers offer Flash tanks in both vertical and horizontal configurations.

9.1 Horizontal Tanks

Horizontal flash tank

Horizontal flash tank

Horizontal tanks are function in such a way that it involves flashing.

Flashing that occurs mirror that which takes place from the surface of a pool of water.

For efficiency, surface flashing needs a bigger tank.

It reduces steam pressure before getting back to boilers, condensate tanks or drainage to sewer mains.

Horizontal tanks have a prime painted exterior together.

In addition, it is ASME code built and marked for 150 PSI working pressure of carbon steel.

9.2 Vertical Tanks

Vertical flash tank

Vertical flash tank

Vertical tanks tend to rely on a cyclone effect to separate the flash from the condensate.

Vertical flash tanks are often small in size allowing for a smaller footprint when needed.

High pressure condensate moves from the top of the tank to the bottom.

Some of the flash steam is re-evaporated via the stream-trap and then released.

What remains is separated from the other flash steam and drained through the stream trap at the end of the vessel.

They reduce steam pressure before getting to boilers, condensate tanks or drainage into sewer pipes.

10. What are the ASME Standards for Flash Tanks?

Below are the ASME Standards for Flash tanks:

  • Flash tanks are designed and built to an ASME Section VIII, Div. 1 standards Code requirements
  • It is developed for a 150-working pressure
  • Flash tank must have a 316 stainless steel wear plate
  • The drop-leg and sparge designs must meet the stated design conditions
  • Engineering Design focusing on Compress/Solid Works 2018
  • National Board Certificate R (Repair)
  • 4 Pressure Piping
  • Welders certification

11. What is the Cost of Flash Tank?

The price of a Flash tank depends on the carrying capacity, and weight/shipping cost.

A sample price list for different models of Flash Tanks is shown below:

Model              Price     Tank Volume (Gallons)        Shipping/Weight in (Lbs)

FT-013-HRZ     $3,151             13                                            65

FT-015-HRZ     $3,271             15                                            70

FT-018-HRZ     $3,367             18                                            75

FT-024-HRZ     $3,606             24                                            80

FT-030-HRZ     $3,830             30                                            85

FT-048-HRZ     $3,973             48                                            115

FT-080-HRZ     $4,845             80                                            150

FT-125-HRZ     $6,250             125                                          255

FT-006-VRT     $3,460             4                                              78

FT-008-VRT     $3,889             7                                              110

FT-012-VRT     $5,555             17                                            167

FT-016-VRT     $8,872             37                                            220

The overall cost also includes the costs incurred in the design, manufacture and quality testing of the Flash tanks.

Generally, they are sold at competitive prices in the market.

12. How does Flash Tank and Air Storage Tank compare?

Some of the main differences are:

12.1 Air Storage Tank

An Air storage tank is an efficient system that is a continuation of your compressed air system enhancing the performance of the other system’s components.

It functions as a reservoir for compressed air that you can easily use during high-peak demands.

Air storage tank

Air storage tank

12.2 Flash Tank

Flash tank, on the other hand is a system that aids in bursting of high-pressure condensate into steam as well as low pressure heating supply mains.

Flash tank also aids in lowering steam pressure before returning to boilers, flash condensate tanks or release into sewer mains.

It helps mainly in carbon steel construction.

Both Flash and Air storage tanks have low maintenance costs.

13. How do you Size Flash Tanks?

Typically, when sizing Flash tanks you have to emphasize the capacity, expected blowdown rate and pressure.

Incase you are using a horizontal flash tank, the required area for the tanks is through

13.1 A Multiplication of the Length of the Flash Tank with the Diameter.

The result of measures the Flash tank’s ability to hold condensate.

The exact formula = (Flash Tank in square feet) = Length of Horizontal X Diameter

An example

If you vent a Flash tank to the atmosphere, what is the actual size of the flash tank needed with a team pressure of 12 PSIG, assuming the absorption machine condenses 12,000lb. of steam/hr. you may need a Flash tank of 2 ft. by 4.5 ft.

13.2 Sizing Vent Lines

There has to be properly sized vent lines if a Flash tank is to discharge steam into the air.

To find the right size of the Flash vent, first determine the area of the Flash tank.

For instance, calculate the Flash tank vent size of one which is 4 ft. by 9 ft. or 36 sq. ft.

Use a psychometric table when determining the size of the vent.

From this tool, 36 is in the 27 – 36 line which means that a vent size of 3 ½ is needed for the Flash tank.

13.3 Estimating Temperature

You have to determine the temperature to which condensate has to be cooled.

Dewpoints depend on factors such as temperature and humidity.

You first have to calculate the temperature to which the tank will be exposed.

Take ventilation into account when estimating humidity.

Estimate the cooling water quantity needed.

You then determine the size of temperature regulator valve and pipe size required.

There has to be a self-contained regulator having a typically closed valve to widely open when a rise in temperature is required.

Assuming you have these data what size of Flash tank would you require:

Steam pressure = 100 PSIG

Condensate gets into the flash tank at 1,550 lb./hr. at 335°F

The space into which the vent discharges must have an Ambient temperature of 75°F

A cold water temperature of 50°F

Using a psychometric chart, the dewpoint of the tank will be 64.5°F, and this is if the ventilation at this temperature is adequate to have over 70% relative humidity.

To ensure 1°F for safety, you have to cool the condensate from 338°F to 63.5°F.

Once the installation is complete, you can continue adjusting the device through resettling the regulator.

The total amount of heat that you extract from the condensate equals:

1,500 lb./hr. x (338–63.5)° F = 410,000 BTUH

The volume of cooling water needed:

410,000 BTUH (63.5 –50)°F = 30,500 lb./hr. or 3,670 GPH = 61 GPM

Based on this data, I recommend a 1.5-in. pipe and a 1.25-in. temperature regulator for this use.

14. What Problems do Flash Tanks Exhibit?

Some of the problems Flash Tanks exhibit include:

  • A Flash tank vibrates excessively due to vessel not being secure, condensate lines being undersized or a water hammer.
  • Flash tanks have excessive flash steam as it is important to make adjustments to pressure thereby lowering back or valve pressure regulator
  • Differential settings from PRV to BPR may occur
  • Stream trap failure
  • Failure of the pump trap on discharge line. Alternatively, there could be a discharge check valve failure.
  • The standard point of the valve could be very low as such, the safety relief valve blows off

When you experience these above problems with your flash tanks, you should take them for repair, replace the faulty parts or contact the factory that manufactured them.

The best way of identifying these problems is through regular maintenance of the flash tanks.

15. How do you Install Flash Tank?

Below is the step-by-step process of installing a Flash tank:

Prior to installation, you have to check that the flash tank is suitable for the intended use.

Check aspects such as materials and temperature/pressure ratings.

Remove the plastic covers on the connections then begin the process.

First, visually inspect the Flash tank for possible damages which may have occurred during shipment.

In the event that there are damages, one should contact their supplier.

Second, install the Flash tank in piping system with the use of an inlet connection as its inlet.

The low side connection will be the outlet.

In addition, you can include a drain valve at the bottom of the tank for the periodic clean out and blow down.

You discharge the condensate via the bottom of the Flash tank.

Discharge the condensate directly to a return line, especially when draining flash steam via a pipe directly into a low-pressure steam line.

The most important thing is that the flash tank’s condensate has adequate pressure differential to prevail over back pressure from the return line.

Also, you have to place a flash tank before a steam trap to avoid blast of steam.

Further, you can include an inverted bucket trap if a steam strap is essential.

The sizing of the trap must be with a 3:1 safety factor.

Proper drainage is key, in the event that back pressure exceeds tank pressure it may be better to use a pumping trap and reservoir.

However, if you hold a flash tank at atmospheric pressure you do not necessarily need a steam trap on the discharge line.

It is because the flash steam is already being released out into the atmosphere.

Next, you drain the condensate via gravity directly to a vented receiver.

This component is often positioned under the flash tank level.

A flash tank is located below any steam or equipment.

The condensate return lines have to be positioned facing the flash tank.

Flash tank has to be well attached to the surface on which the tank sits.

As it should be, outlet and inlet piping should be properly supported.

If you have several return lines forward them directly into the flash tank.

That is, examine the valves to ensure that they are attached to each line to avoid condensate reversal flow and last flash steam.

You have to insulate the flash tank, condensate lines and low-pressure steam line to prevent flash waste in the form of radiation.

When you pipe the flash steam to a low-pressure stream line, especially in applications within a plant you have to accurately control the flash tank pressure.

For control, you can connect a back-pressure regulator into the low-pressure stream line.

Note: when seeking a safety relief valve do not use a BPR.

For high pressure stream line, you can connect a pressure reducing valve.

Note: you should install a well-sized safety relief valve directly to the flash tank.

16. What is Flash Tank used for?

A Flash tank is mainly used in the release of steam from a condensate high in temperature before releasing directly into low pressure low-pressure lines.

You can similarly use a Flash tank to condensate and then direct back to the particular condensate tank’s boiler.

Prior to this, you use a flash tank to cool and reduce to low-pressure steam.

17. Is Flash Tank and Flash Vessel the same?

Of course, no.

A Flash vessel separates steam from water removing it through bursts of flash steam.

This equipment is designed to provide low velocity flash steam with limited/no water carryover.

It is considered to be the major component in a flash recovery system, and its steam is used in heating equipment as well as in low pressure process.

A flash vessel is applicable in plants using steam for their operations.

In steam plants, high-pressure condensate is changed to lower pressure.

Flash tank, on the other hand, is designed to enable high pressure condensate to flash as well as reduce pressure steam.

Overall, a flash tank is a collection system while a flash vessel mirrors a separation system.

It is however important to understand that sometimes flash tanks are refereed to as flash vessels.

18. How do you Test Quality of Flash Tank?

To ensure that a Flash tank is high quality and thus safe for use, it has to undergo a number of quality tests.

Some of these quality tests include:

  • Corrosion testing is done to determine if the material used to make a flash tank is suitable for its intended use
  • Material control test
  • Water fill testing
  • Radiography test
  • Liquid Penetrant Testing
  • Ferrite test
  • Leakage test
  • UT Thickness material measurement

19. What are the Safety Features of Flash Tank?

Flash tank system

Flash tank system

Some of the safety features of a Flash tank are:

  • Safety relief valve; it used to limit or control the pressure in a flash tank. If not controlled, pressure may build up creating a process upset or the tank’s component failure
  • Pressure gauge; monitor the flash tank so that everything is working well
  • Exterior Gray Alkyd Shop Primer; protects the outer surface of the Flash tank from external conditions

With the information in this guide, am sure you can get the right flash tank for your specific applications.

In case you have any question or inquiry, contact FilSon Filters now for assistance.

Scroll to Top