What is Steam blowing?
Steam blowing is a technique for cleaning pipe systems in which pollutants are eliminated from the piping network using the force and speed of Steam. Due to the pipe’s expansion and contraction, the mill scale is removed by steam blowing using the temperature differential.
The pressurized Steam used to clean pipes is produced by firing a boiler, unlike the pressurized air-blowing technique, which is similar to the steam-blowing method. Several specialized quick-opening valves with a thorough procedure, a carefully planned temporary network, steam quenching devices, silencers, and debris-containing equipment are employed to carry out this operation.
Terms Related to steam Blowing
- Cold Re-Heat Line (CRH Line): Steam that has lost its heat and pressure might have an impact during the steam-blowing process. This directs Steam to the steam generator’s inlet.
- The decreased pressure steam directed toward the condenser is referred to as HRH Line: Hot Re-heat.
- A superheater.
- RH: Re-warm
- High pressure:
- Low pressure (LP)
- Cleaning force ratio (CFR)
- MCR, or maximum continuous rating, refers to a steam boiler or generator’s ability to readily and continuously create the appropriate amount of Steam without experiencing any adverse side effects.
- Steam conditioning services use the PRDS (Pressure Reducing and DeSuperheating System) to lower the pressure and temperature of the Steam.
- To remove the scale, the inside surface of the pipe being purged is subjected to a heat shock during the puffing process.
Why is Steam blowing required?
An oxide coating forms on the interior surface of pipes during the fabrication process during hot working days. Before the line is charged with the service, the mill scale layer must be removed from the system.
Cleaning is done mainly for steam piping networks using Steam blowing due to the issue with steam condensation or condensate draining. It is possible that debris from the building phase could break off and go downstream during the startup of any facility. These particles can harm the piping network’s instruments and other crucial parts.
Steam blowing at boiler pressure results in a dynamic pressure in the pipes that is at least 20% higher than under typical operating conditions. Any potentially harmful particle inside the pipe could blow out the piping system during plant operation.
Methods of Steam blowing
There are two efficient methods for performing Steam blowing for internal pipe cleaning:
- Cycling high-pressure Steam blowing
- Continuous low-pressure Steam blowing
High-Pressure Cyclic steam blowing
This steam blowing involves gradually pressuring the steam-blowing piping arrangement until a specific pressure is reached. The steam-blowing system’s valve is swiftly opened to release Steam after the necessary pressure has been reached.
In the pipe system that needs to be cleaned, pressurized confined Steam is quickly released, creating a transonic phase with a high mass flow rate. The temporary pipe needs to be carefully built, and stress analysis must be completed before using the cyclic blow.
The same steam pressure and mass flow rate are used each time until the cleanliness of the pipe system cannot be verified. To ensure that the piping system is adequately cooled, no more than one cycle can typically be conducted per day.
Advantage of discontinuous steam blowing
- There is more thermal expansion in the primary piping system with this approach because of the higher pressure and temperature.
- No significant diameter gradients are needed from the steam-blowing line to the silencer.
- There is no need for an additional procedure or water injection system.
The disadvantage of discontinuous steam blowing
- The necessary K-factor is attained, but only for a very brief time.
- Rapid changes in temperature and pressure cause a significant rise in load.
- The system’s design parameters are not followed when steam blowing is done.
- DM water is used in large quantities instead of continuous steam blowing.
- Because temporary steam-blowing systems must be composed of alloy steam, they are more expensive.
- It is necessary to use a temporary blowout valve, which adds to the expense.
- Before succeeding cycles may begin, the steam generator must be restarted.
Low-Pressure continuous steam blowing
It is common to practice constantly injecting low-pressure Steam for cleaning most steam piping systems throughout the pre-commissioning process. The use of steam generators that continuously produce and burn Steam is necessary for this form of steam blowing.
In this instance, the steam generator’s generated velocity is greater than the Steam’s actual operating velocity in the plant. An orifice plate is put at the piping system’s inlet to control the Steam’s predetermined and necessary velocity. Low-pressure Steam is constantly blown through the system until an acceptable degree of cleaning is attained.
Recommended Parameter for Continuous steam blowing
For continuous steam blowing, the following conditional parameters are normal and most effective:
- 3.5 MPa is the dynamic steam pressure.
- MS temp is 420 °C (not to exceed)
- Hot Re-Heat Line Temperature = 480°C (not to exceed)
- The flow of steam = 845 TPH (Tonn per hour)
- According to Drum pr. (Kg force/cm2) = 40 Ksc
- 39% furnace load
Advantage of Low-pressure continuous steam blowing
- During steam-blowing cycles, the required K-factor is maintained for a more extended amount of time.
- The system is under less burden as a result of the pressure and temperature gradually and uniformly rising.
- Within the constraints of the design, Steam is blown.
- less DM water is needed compared to the discontinuous approach.
- The more affordable CS pipe can create a temporary steam-blowing piping system.
- No emergency blowout valve is necessary.
The disadvantage of Low-pressure continuous steam blowing
- Temporary plumbing connecting the steam blow line to the water injection system needs to be more prominent in diameter.
- In comparison to the continuous technique, the water injection system requires additional steps or water.
- Temporary plumbing that is larger and grades to larger diameters is needed to connect the water injection system to the steam blow line;
- Compared to the discontinuous technique, the water injection system requires more processing and drinking water.
Principle of Steam blowing
The piping network should be blown with enough steam pressure during Steam blowing to provide adequate cleaning force for removing debris, corrosion, and scale. The force of Steam during the steam blow should typically be at least 20% greater than it would be under normal operating conditions.
Consequently, the cleaning force necessary for steam blow should be 1.2, or CFR 1.2. This force is necessary to ensure that any potentially harmful particles are blown out of the piping system before commissioning and plant operation.
Steam blowing flow calculation formula
With the aid of the following formula, the force necessary for steam cleaning operations is determined:
CFR= (Qc2 x Vc) / (Qo2 x Vo)
- Cleaning Force Required (CFR)
- Qc: Required steam mass flow rate for cleaning
- Qo: Steam mass flow rate at normal conditions
- Vc: Specific volume of Steam during cleaning
- Vo: Specific steam volume under normal operation
Pre-cleaning Procedure for steam blowing
Some checkpoints need to attain before proceeding with steam blowing. The pre-cleaning Procedure for steam blowing is as follows:
- Check for all piping supports, namely guides and anchors, as well as temporary support for the layout of the steam-blowing system.
- Make sure that every line has undergone a thorough inspection and is hydrated.
- Check if the pipe system still has any control valves, desuperheaters, flow monitoring devices, thermowells, or other crucial piping components attached.
- Verify that the temporary steam-blowing pipe system has an adequate drain.
- Verify that these drains are directed to a secure area.
- Install a temporary pressure gauge to track system pressure buildup and log pressure readings.
- Create a suitable communication channel between the operator at the shutdown valve and the controlling station. If auditory communication is not as audible in loud environments, look for visual communication facilities such as yellow flags.
- Make sure that employees’ movement is restricted while Steam is being blown.
- During steam blowing, ensure the area surrounding the vent pipe is free of anyone.
- To protect hearing from loud noise, appropriate garments must be used.
- Steam Blowing Procedure
- Once all areas have been cleaned in preparation for steam blowing. With the approval of the determining authority in the control room, the actual steam-blowing Procedure begins. To be observed when steam bowing is:
- Start the steam generator, then gradually raise the boiler pressure until it reaches the desired level and firing rate.
- To test the stability of the system’s temporary and permanent supports, the first blow must be delivered at low pressure.
- To blow Steam through the superheater, the main steam pipe, and the temporary pipes, a temporary valve must be opened.
- With a targeted plate, do the first few steam blows until the Steam becomes clean.
- Once the Steam is clear, target plates must be positioned to catch any particles carried by the Steam from the leading pipe network.
- Fire is put out while blowing, and pressure is reduced to ensure the correct temperature differential is present to move any material.
- Steam blowing must stop, and the boiler is restarted to build pressure.
- Cleanliness should be periodically examined until a sufficient level is attained.
- Stop the steam generator and close the steam blowing valve once the requisite cleanliness standard has been met and all pressure buildup in the generator has reached zero.
- All other networks must be cleaned similarly after the mainline is cleaned using steam blowing.
Noise reduction during steam blowing
Too much noise and fog are created when the steam generator releases Steam into the atmosphere. This much noise may interfere with surrounding activity. Steam must be cooled by condensate to bring the noise level down to a tolerable level.
Two techniques exist to lessen noise:
Installing a conventional silencer that functions as an expander is the first step. This broadens the surface area and facilitates steam cooling. This noise reduction method is used for continuous Steam blowing at high pressure.
The second method, quenching, operates by a water injection system. With this technique, Steam loses heat and condenses, with the condensate later being partially recovered for use when blowing Steam. For low-pressure continuous steam blowing, this approach of noise reduction is employed.
How to determine cleanliness after steam blowing?
After the steam blowing is tested with “Targeted plates,” the piping system must be checked, and its cleanliness must be determined. These plates are constructed of copper or aluminum. The following three steps are used to determine it:
When Steam is blown, targeted plates must be placed at the primary piping system’s exit point. The influence on the Targeted plate will also be examined during steam blowing.
When two successive targeted plates show less than two pits per square inch with a maximum diameter of 0.3mm, cleaning by Steam blowing may be an option.
Steam traps and other equipment removed before steam blowing must be installed again after steam blowing is finished.
After completing all three phases, the piping system can warm and charge according to operating needs.
Target plate Selection Criteria
Following are some factors to consider when choosing a targeted plate to evaluate for cleanliness while Steam blowing:
- The target’s dimensions Steam vent width and length should be 8% of ID and ID, respectively.
- Less than 90 should be the Brinell hardness number.
- No 0.8 mm diameter or larger indentation
- Not more than two indentations per 1000 mm2 of the target plate surface should be more significant than 0.4 mm in diameter.
- More than 0.2 mm deep indentations should not exceed 10 per 1000 mm2 of the target plate surface.
- Indentations less than 0.2 mm in diameter should be evenly distributed and exhibit little to no concentration.
Steam blowing is a forced cleaning method for the internal surface cleaning of the piping network. Steam blowing is used to remove scale, welding grit, and another material from a pipe’s inside surface. The following statements can be used to summarise this topic quickly:
- It prevents important pipe network components from being harmed by foreign objects.
- There are two ways to blow Steam:
- Either cyclic Steam blowing at high-pressure Puffing
- Continuous low-pressure steam blowing
- When Steam is blowing continuously, too much noise is made. Therefore, silencer installation is required to lower noise levels.
- The force of Steam applied during a steam blow should be 20% greater than the force of Steam under normal operating conditions.
- As mentioned in the preceding paragraphs, a few checkpoints must be accomplished before Steam may be released.
- A “Targeted plate” made of copper or aluminum is placed at the steam exit point to test the cleanliness of the piping system. The cleaning is acceptable if two consecutive Targate plates measure two grits per inch2.
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