Blowing Out Steam Piping
Contents
1. General
...............................................................................................................................
1.1 Safety and Noise Protection ................................................................................
2. Blowing-Out Circuits ............................................................................................................
3. Conditions
for Blowing Out
..................................................................................................
3.1 Dynamic
Pressure ..............................................................................................
3.2 Blow-Out Piping Design..................................................................................................
3.3 Blowing
Gate Valve
.............................................................................................................
4. Blowing
Out Operation
........................................................................................................
4.1 Duration
of Each Blow...............................................................................................................
4.2 Number
of Blows .................................................................................................................
4.3 Cooling Period ..................................................................................................
4.4 Blowing-Out Procedure..............................................................................................
5. Cleanliness Assessments ...................................................................................................
5.1 Blowing Mirrors......................................................... ............................................................................
5.2 Acceptance Criteria .................................................................................................................................................
1. General
This recommendation defines the blowing-out
requirements and cleanliness criteria specified by the manufacturer.
Blowing-out is carried out to remove rust,
scale, coatings, dirt, and foreign objects from steam piping. This prevents
blockage of the turbine inlet steam filter and damage to the turbine.
The turbine must never be started until the
boiler and all steam piping leading to the turbine have been properly cleaned.
If blowing-out is not performed in accordance with
this guideline, all risks are borne by the customer, and any
resulting damage is excluded from warranty.
The manufacturer reserves the right to inspect
the turbine before acceptance testing and, if necessary, to adjust
guarantee values based on its condition. Any additional costs resulting
from this inspection shall be borne by the customer.
If blowing-out is not carried out in accordance
with this guideline, the customer must be formally informed in writing
of the deviations and their consequences.
1.1 Safety
and Noise Protection
Before blowing-out begins:
- All steam lines must be insulated to prevent burns and fire
hazards.
- Danger areas must be clearly marked and
secured.
- Ensure no unauthorized personnel are present before each
blow.
- Noise protection measures are mandatory in
accordance with regulations.
Noise can be reduced by:
- Using a silencer, or
- Discharging steam under water
The boiler or piping supplier is responsible
for providing suitable noise-reduction measures.
2.
Blowing-Out Circuits
Blowing-out is required for:
- Boiler piping
- Main and secondary steam lines
- Bypass and pressure-reducing stations
- Seal steam systems
- Steam-jet air ejectors
Blowing-out is normally performed up to the
valve casing or as close as possible.
A temporary blow-out pipe is connected to
the steam pipe flange near the quick-action valve.
- If blowing-out is performed through a quick-action valve, it must
be removed.
- If removal is not possible and the valve is welded, blowing-out may
only be performed with manufacturer approval.
After completion, remove the temporary piping and
install the final steam piping under clean conditions.
Sensitive components (valve seats, shafts,
measuring orifices, etc.) should be removed from the blow-out circuit
whenever possible.
3.
Conditions for Blowing-Out
3.1 Dynamic
Pressure
Adequate dynamic pressure is the most
important factor for achieving high velocity of flow and, with these good
levels of steam piping cleaning by blowing out. When carrying out blowing out,
the dynamic pressure in the entire boiler and piping system must be greater
than the subsequent maximum in full-load operation.
Below, we will use index A for the maximum
through flow in full-load operation and index B for blowing out:
To ensure that the desired
parameters of the mass flow rate are achieved, you should carry out an
estimate
of the mass flow rate, if possible, by means of the operational measurement.
If
possible, you should measure the pressure and the temperature for the
calculation directly by the boiler outlet.
You
should aim to achieve high steam conditions, since experience has shown that
steam piping is not correctly cleaned until high temperatures have been
reached.
The following empirical values are used to
specify the pressure and temperature for blowing out:
- Pressure: ≥ 50% of rated pressure
- Temperature: At least 50 K superheat at rated pressure
3.2 Blow-Out
Piping Design
- Temporary blow-out piping should have a cross-section similar to
the final piping.
- Pipe supports must be designed for higher dynamic loads
during blowing-out.
- Permissible forces on turbine flanges must be respected.
The boiler or piping supplier is responsible
for the design, supply, installation, and safety of the blow-out piping.
3.3 Blowing
Gate Valve
A fast-opening blowing gate valve (opening
time ≤ 30 seconds) is mandatory.
- It must be installed upstream of the blow-out outlet
- It improves cleaning efficiency and reduces blow-out time
The boiler or piping supplier must provide this valve.
4.
Blowing-Out Operation
4.1 Duration
of Each Blow
Each blow should last 1–2 minutes, depending
on boiler capacity.
If the valve opening time exceeds 30 seconds, the
blow duration must be extended accordingly.
4.2 Number
of Blows
Blowing-out must continue until the required
cleanliness level is achieved (see Section 5).
4.3 Cooling
Period
After high-temperature blowing-out:
- Allow piping to cool to near ambient temperature
- Recommended cooling time: 5–6 hours (with insulation)
This prevents oxide layers from loosening after
cleaning.
4.4 Blowing-Out
Procedure
- Warm up piping and perform initial blows at moderate conditions
to detect faults.
- Increase boiler output to specified blowing-out conditions.
- Open the blowing gate valve for 1–2 minutes.
- Repeat blowing 2–3 times.
- Reduce pressure, drain and clean the boiler evaporator.
- Cool the boiler using fans.
- On the following day, perform blowing-out at full pressure and
temperature.
Steel mirrors are not installed during the first
blows due to heavy contamination.
5.
Cleanliness Assessment
5.1 Blowing
Mirrors
Cleanliness is checked using steel mirrors,
supplied by the boiler manufacturer.
- Mirrors are installed after the blowing gate valve
- A straight pipe section of at least 10 pipe diameters must be upstream
A mirror must be installed after each cooling
period.
5.2 Acceptance
Criteria
Cleanliness is acceptable when:
- Two consecutive blows show mirrors within limits
- After ≥12 hours cooling, two further consecutive blows also
meet limits
Assessment limits (per 2500 mm²):
- No strikes > 0.8 mm
- Max 2 strikes > 0.4 mm
- Max 10 strikes > 0.2 mm
- Strikes < 0.2 mm must be evenly distributed
CAUTION:
1. For the first blowing process it is not recommended to use target plate whereas for further cycles always the clean side of the target plate should be used.
2. The pipe lines which are not pre-cleaned are expected to take blowing cycles twice than the pre-cleaned pipe lines.
Comments
Post a Comment