Piping and Vessels Flushing and Cleaning Procedure

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Ammonia Plant Technology
Pre-Commissioning Best Practices
GBHE-APT-0101
Piping and Vessels Flushing and
Cleaning Procedure
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Ammonia Plant Technology
Pre-Commissioning Best Practices: Piping and Vessels Flushing
and Cleaning Procedure
CONTENTS
1 Scope
2 Aim/purpose
3 Responsibilities
4 Procedure
4.1 Main cleaning methods
4.1.1 Mechanical cleaning
4.1.2 Cleaning with air
4.1.3 Cleaning with steam (for steam networks only)
4.1.4 Cleaning with water
4.2 Choice of the cleaning method
4.3 Cleaning preparation
4.4 Protection of the devices included in the network
4.5 Protection of devices in the vicinity of the network
4.6 Water flushing procedure
4.6.1 Specific problems of water flushing
4.6.2 Preparation for water flushing
4.6.3 Performing a water flush
4.6.4 Cleanliness criteria
4.7 Air blowing procedure
4.7.1 Specific problems of air blowing
4.7.2 Preparation for air blowing
4.7.3 Performing air blowing
4.7.4 Cleanliness checks

4.8 Steam blowing procedure
4.8.1 Specific problems of steam blowing
4.8.2 Preparation for steam blowing
4.8.3 Performing steam blowing
4.9 Chemical cleaning procedure
4.9.1 Specific problems of cleaning with a chemical solution
4.9.2 Preparation for chemical cleaning
4.9.3 Performing a chemical cleaning
4.10 Re-assembly - general guideline
4.11 Preservation of flushed piping

1.0 Scope
This Process Engineering guide covers Best Practices in Ammonia Plant -
Pre-commissioning; Piping and vessels flushing and cleaning procedures,
and shall apply to all GBH Enterprises (GBHE) process engineers
worldwide.
2.0 Aim/purpose
This procedure applies generally to the cleaning and flushing of
underground and above ground pipelines, tanks and vessels which shall
be performed for process reasons during pre-commissioning. Special
instructions for the system will be fixed by a detail procedure.
The purpose of flushing and cleaning lines and vessels is to remove loose
foreign matter, production residues and surface protection substances
from the inside of line and vessels (welding rods, sand, earth, pebbles,
nuts and bolts, tools, rags, oil and greasy films, etc.) in order to avoid line
blockages, damage to sensitive components such as orifice plates,
turbine, compressors, pumps impellers, valve seats and so on.
3.0 Responsibilities
The responsibilities are given in the work instructions to the plant operator,
standard engineering procedures preparation of commissioning, working
step, network cleaning, flushing and purging.
4 Procedure
4.1 Main cleaning methods
4.1.1 Mechanical cleaning
When a system, or part of a system, can be entered, it may be possible to
carry out pipe wall or vessel wall cleaning manually using either rotary (i.e.
air driven) or hand held steel wire brushes. Rust, scale, and dirt that are
dislodged may be subsequently removed by the use of an industrial grade
vacuum cleaner, by air blowing, or a combination of these two methods.
In any event, stainless steel equipment is not likely to have significant
deposits of surface dirt or oxide, i.e. mechanical cleaning is normally not
applicable.

4.1.2 Cleaning with air
Two main methods may be used:
a) Continuous blowing of air
Air is continuously blown from a source (directly from air compressor or
via a large capacity vessel) at a high velocity through the lines (and
vessels) to carry away the loose material. Due to the high velocity of
the air, a light erosion of the walls generally occurs during the air blowing,
which is beneficial with regards to cleaning.
b) Quick decompression
A network is filled with compressed air up to the setting pressure of a
rupture disk. When the rupture disk blows out, the source of air is stopped
and the pressure inside the network decreases quickly.
This operation will preferably be done using a "quick opening valve" after
having pressurized the network to the desired level of pressure. The
existing valves of the network may not be used for this purpose, except for
special cases.
The quick decompression causes a high velocity of air in the pipes, thus
removing loose material and performing a light erosion on the walls which
eliminate rust and scale. During this operation the reaction forces affecting
the piping shall be considered.
4.1.3 Cleaning with steam
(for steam networks only)
Whenever steam is available, an excellent cleaning fluid is provided.
Steam can be used, like air, for continuous blowing, and preferably, for
intermittent blowing. The advantage of the latter is that between two
blowings the pipes (and possibly vessels) cool and contract causing
millscale and rust deposits to crack. These deposits are then easily
removed in subsequent blowings. Steam blowing shall be used only for
steam networks.

4.1.4 Cleaning with water
4.1.4.1 Cleaning of piping by circulation of water
Line flushing uses water from the normal supply network of the plant, if
available. Water supply could conceivably be from other sources, i.e. city
water lines, supply boat temporary pumps, etc. depending upon the
ongoing situation.
This type of flushing normally involves taking a section of piping and
flushing it from a "start-point" to an open end. A high velocity flow should
be achieved in order to be effective in removing loose debris and
rust from piping (or vessel) walls. In some circumstances additional
pumping capacity will be required.
4.1.4.2 Cleaning of piping by retro-jetting
In case retro-jetting will be considered as cleaning method, a
subcontracted specialist will be selected and all technical aspects will be
reviewed and shall be accepted before starting the work.
4.1.4.3 Fill and dump water flushing
Fill and dump flushing is often used for cleaning vessels. The method
being quite simple, the adequately vented vessel is filled to the desired
level with flush water and then dumped to grade, the flush water
dislodges loose debris and rust and carries it out of the equipment. Note
that some lines connected to the vessel can be flushed by dumping the
water through them. One major problem with this method is the disposal of
the large quantities of water involved which may overload the normal
drain systems.
4.1.4.4 Cleaning of vessel or equipment by water spray or high pressure
water
If there is only dust on the walls of a large vessel, a water spray from a
hose pipe might be sufficient.
High pressure water may be used to remove solid particles or foreign
matter from inside walls or inside parts of vessel or equipment, in
particular where access is a problem.

Attention has to be given to the potential corrosiveness of water (chloride
ions on stainless steel, sea water on carbon steel) and special water
quality may be necessary (demineralized water or inhibited water).
4.1.4.5 Cleaning with a chemical solution
Cleaning of piping and inside walls of vessels or equipment by circulation
of a chemical solution is only used for removing production residues and
surface protection substances (oil and greasy films, etc.) in case it should
disturb commissioning or start-up of the plant.
This type of cleaning is applicable subsequent to a.m. flushing methods. A
chemical solution will be circulated by means of a pump and finally
disposed to waste water treatment or special treatment. The cleaned
piping, vessel or equipment to be flushed with fresh water or
demineralized water to remove remaining chemical solution.
4.2 Choice of the cleaning method
The choice of the cleaning method shall depend upon:
a) The fluids available on the site: compressed air, steam, cooling
water, service water, potable water, demineralized water and so on.
b) The volume of the network: this determines the quantity of fluid to
be used and the time needed to fill the network to the desired
pressure (quick decompression method).
c) The piping diameter:
• Circulation of water, is usually selected for diameters up to
DN150, because of the large flow required.
• Water "retro-jetting" is effective up to large diameter lines but
necessitates a specialized subcontractor.
• Air blowing is acceptable for small diameter lines to be
calculated according to the possible air flow and an average
speed of 40 m/s.
• Air quick decompression method can be used on any pipe
diameter provided necessary precautions are taken (see
paragraph 4.7).
• Mechanical cleaning shall be used for vessels (manual
cleaning) but also for large diameter pipes (≥ DN 800) providing
safety rules are respected (vessel entry).

d) The design conditions of the system: some large diameter piping
used for gas service cannot withstand their own weight when they
are full of water. Some piping cannot withstand the expansion
caused by steam blowing.
e) The material specification: for stainless piping, air blowing is better
(if the other conditions allow it) than water cleaning, to avoid the
possibility of corrosion by chloride ions.
f) The process function of the system:
 Water lines are usually flushed with water. Process gas
lines, inert gas lines and air lines should be air blown.
 Low operating temperature lines shall be air blown.
 Hydraulic pipelines shall be air blown.
4.3 Cleaning preparation
The following principles shall apply:
• Whenever possible, the cleaning fluid shall flow from top to bottom.
• The diameter of the outlet pipe may be at least two thirds of the
diameter of the line to be cleaned, and at least as large as the inlet
pipe.
• Main headers shall be cleaned first (i.e., before their connecting lines).
• Large diameter pipes shall be cleaned before small diameter ones.
• Dead ends shall be avoided or, if not possible, cleaned separately.
• Fragile devices included in the network (all flanged valves, turbine-type
flowmeters, orifice restrictions, etc.) shall be removed (see section
4.4).
• Protection of the devices in the vicinity of the network shall be carefully
studied in particular near the water (or air) outlet in order not to
damage electric motors or instruments with water or dirty air (see
section 4.5).
• Existing block-valves on the lines to be cleaned shall not be used to
control an air flow as they could be damaged by erosion (due to the
high velocity of the fluid).
• A special care shall be taken for vessels designed only for an
atmospheric pressure service, in order not to create, during washing, a
high pressure due to a water head.

• Whenever a vessel full of water has to be emptied, a special note shall
be issued to state that a vent will have to be opened previously in order
not to create a vacuum in the vessel.
• The cleaning fluid shall not flow through a conventional exchanger
unless the pipes upstream of the flushing flow have been cleaned (use
the by-pass, if any, or "break" the line before the exchanger). It shall
never be flown through a plate exchanger.
• The cleaning fluid shall never flow through pumps or compressors
unless the upstream lines have been cleaned, the lines shall be
disconnected before the equipment or a "jumper" shall be installed.
• For large diameter pipes, some temporary supports, hangers, pads,
etc., may have to be added to withstand the weight when a line is
disconnected
• During flushing, the spring supports, spring hangers, etc., shall be
blocked according manufacturer’s instructions.
• When a couple of flanges has to be opened to allow the flow to flush
out, distance between the two flanges shall be at least 1/6 of the pipe
diameter.
4.4 Protection of the devices included in the network
During the flushing or the blowing of a line, some particles such as sand,
rust, etc. are carried away at high velocities and may either damage some
devices when an impact occurs, or clog small diameter pipes. Accordingly,
fragile devices have to be removed from the pipe before flushing/blowing.
Are considered as fragile devices:
o Control valves and check valves
o Safety valves
o Calibrated orifices
o Turbine type flowmeters
o Pitot tube flowmeters
o Venturies
o Rotameters
o In-line flowmeters except types without internals
o Nozzles of ejectors
o Traps
o Bellow valves
o Internals of filters and strainers
The list is not exhaustive and shall be revised according to local
necessities.

• Process impulse lines for instruments shall be isolated by means of the
block valve on the impulse pipe itself and, whenever possible, shall be
disconnected. This operation shall be made by an instrument specialist
• Thermowells may remain installed.
• When a couple of flanges has to be opened to allow the flow to flush
out, it shall be checked that this operation does not create any stress
on a pump, turboexpander, compressor flange upstream or
downstream.
• The flushing is generally not carried out through columns or drums. But
if it is necessary to go through such equipment, or if the vessel is used
as an air reservoir, the removable internals have to be dismantled prior
to starting the flushing, in order not to damage them.
• Any column or drum to be used as an air reservoir must have its
associated relief valve(s) in normal operation before pressurizing starts
(except it is ensured that the source for pressurizing the column/ drum
will not deliver a higher pressure than the design pressure of the
equipment).
4.5 Protection of devices in the vicinity of the network
During flushing and blowing operations, large quantities of dirty water and
dirty air are spread out in the units. This water or air generally contains
sand, particles of rust, etc., and might damage other equipment (for
example: breaking the glass of a pressure gauge). Additionally, the water
itself may damage the insulation materials, the electrical motors, etc.
Accordingly, the following actions shall be taken where necessary:
• to put a tarpaulin on motors, insulation, instruments near the flow
outlet.
• to direct the outlet flow towards a place where there is no (fragile)
equipment.
• to change the direction of the flow by rotating an elbow.
• to connect a hose pipe at the outlet to drive the flow to a desired
location (for water flushing only).
• to add a dummy spool to extend the outlet further.
• to install and fix properly, a sheet of metal (insulation cover sheet
for example) perpendicularly to the flow, in order to break the flow
impact.
• drains, which are not designed for such large flows, should not be
used to evacuate water, as they might be flooded.

4.6 Water flushing procedure
4.6.1 Specific problems of water flushing
- Slow velocity:
The water velocity through the pipe is normally only about 3 to 4
m/s, seldom higher, which is much lower than air blowing velocity.
- Dirty water disposal:
As the drains are generally not designed for high water flow rates,
additional temporary piping and connection, might be required
- Weight of water:
For lines designed for gas service, the weight of pipes full of water
may be too heavy for the hangers, supports (this has to be checked
prior to any water flushing).
- Corrosion factor:
Water can cause corrosion due to its chloride content.
- Carbon steel pipes and vessels:
Cooling water, fire-fighting water and service water can be used for
the first wash but the final rinsing may be carried out with inhibited
water, if necessary.
- Stainless alloy pipes or vessels:
Demineralized water with a chloride content specified for
hydrostatic pressure test may be used. However, in some cases
deviations are possible if they are agreed with the department
concerned. In any case the final rinsing must be carried out with
low chloride containing water.
4.6.2 Preparation for water flushing
Note: Before the detailed preparation work starts, a meeting shall
organized with GBHE and the customer commissioning representatives to
finalize the detailed procedures based on the present general procedures,
taking into account the site restrictions and possibilities.
Commissioning will advise the operators during the preparation.

4.6.2.1 Definition of the network to be cleaned
A first selection shall be made according to construction progress and
geographical or functional criteria (i.e. drains, hot oil network, etc.). Then it
shall be adapted to suit the site requirements, the devices to be removed,
the configuration of the lines (low points, high points, lengths,
heights, etc.).
4.6.2.2 Calculation of the necessary flow
During cleaning operation, the water velocity shall be as follows:
- In liquid process lines and water lines, the velocity shall be the
lowest figure between 3 to 4 m/s and the velocity obtained with 1.3
times the maximum process or water flow. The minimum velocity
shall be 2 m/s.
- Gas process lines are generally blown, if they have to be flushed,
use 3 m/s, ensure that water filled lines are adequately supported.
4.6.2.3 Determination of the network pressure and maximum allowable
pressure
Estimate the maximum head loss. With the velocity calculated as above,
estimate the head loss for a flow going through the principal piping and
add the static head (if any).
If the flow and the head loss are compatible with the pumps available on
the site, go ahead, otherwise air blowing has to be considered.
If several pumps are available, a combination of pumps in parallel or in
series has to be studied to meet the flow or head loss requirements.
The pressure shall be carefully studied and specified in order that the
maximum allowable pressure in the system is never exceeded.
4.6.2.4 Sketch of the network to be cleaned
A sketch of the network to be cleaned shall be specially drawn for the
cleaning operation (P&ID’s will be used for this purpose).

The following color code may be used:
- Blue: lines to be flushed
- Green: items to be removed
- Pink: flanges to be disconnected
- Orange: items to be isolated
Although blinds are seldom used for flushing operations, if they are
necessary they will be indicated and numbered with a red color.
Installation and removal of blinds shall be followed up by commissioning by the
mean of a blind list. Installed blinds shall be tagged and equipped with a visible
handle painted red.
4.6.2.5 Location of water inlets and outlets
A site review shall be done to determine the possible water inlets and
outlets, the water source, the pump(s) location, the additional pipes or
hose pipes layout from the source to the network. The water disposal
problem (flood risk) and the protection of the equipment and people nearly
shall be carefully studied.
4.6.2.6 Additional material and pieces of equipment required
The drawings for the additional pipes to be manufactured and erected may
be drawn if required. The required material (pipes, valves, gaskets, etc.)
and the means (monorails, cranes, pulleys blocks, etc.), tools, gaskets,
grease for bolts, nuts, etc. required to carry out the removal and
reassemble, the needs for the dummy spools (flanges, pipes, etc.) will be
determined.
4.6.2.7 Fragile devices to be removed
All "fragile" devices to be removed shall be identified. The removal
possibilities shall be investigated on site. The required dummy spools to
be fabricated shall be drawn on sketches.
Attention shall be mainly paid to:
• heavy devices (control and block valves, check-valves),
• supports, hangers, pads, spring supports, possible stresses on
pumps’ flanges.

4.6.2.8 Quality of water
Whenever possible, good quality water shall be used from the beginning
until the end. However, if the quantities involved are very large, and
except for stainless steel materials, it is allowed to carry out the first
flushing operations on a given network with raw water, and to perform the
last one (rinsing) of the same network with a good quality water.
The quality of the water shall comply with the specification for hydrostatic
test and the design basis for the plant respectively.
4.6.2.9 Safety
The safety rules and instructions must be strictly obeyed.
The following particular precautions shall be taken for flushing operations:
- Period of time for flushing:
Generally water flushing will take place during normal working hours.
- Restricted area:
An area of at least 5 meters around the outlet points will be roped off
during the release of water.
- Work permit:
Any water flushing operation shall be subject to specific work permits
according to the safety procedure.
- Space between flanges at the outlet:
When a couple of flanges has to be opened to allow the flow to flush out,
the distance between the two flanges shall be at least 1/6 of the pipe
diameter.
- Restraints:
Wherever necessary, the pipes at the water outlets shall be rigidly fixed to
avoid damage to the lines, equipment and people nearby.
- Environment protection:
Adequate protection of the devices in the vicinity of the water outlet has to
be installed in order not to damage electric motors or instruments with
water.

- Personal protection:
Protection of personnel carrying out the operation must be ensured by
suitable protective equipment, i.e. gloves, boots, coveralls, goggles, etc.
4.6.2.10 Preparation of documents and notice to commissioning
- A work permit shall be issued for each flushing operation according
to the safety procedures.
- Notice to the commissioning team shall be sent together with
colored P&ID(s).
4.6.3 Performing a water flush
Once all preparation works are completed the commissioning engineer
shall inspect the site and give the authorization to start the water flushing
operation.
To check the flow rate if no flowmeter is installed, a pressure gauge can
be installed at the inlet of the network to be flushed (downstream of the
inlet valve) and the flow then adjusted by acting on the inlet valve till the
head loss equals that calculated for the required velocity.
The flow / discharge pressure curve of the pump can also be used to
check the flow rate (make sure the pump runs at its normal speed).
When the main header of the network is deemed clean (see 4.6.4), stop
the water flow and prepare the network to flush the connections and
smaller diameter pipelines.
When the complete network has been flushed satisfactorily, the circuit
shall be rinsed if necessary.
Then the removed devices shall be reassembled and, if necessary, fill up
with inhibited water.

The duration of the flushing is the time needed for the outlet water to be as
clean as it is at the inlet (take two samples in glass bottles and compare),
and shall also be sufficient to open all the vents, drains, impulse lines
(when the instruments are disconnected) and to obtain clean water at
each of these points.
Commissioning engineer shall estimate when the cleanliness criterion has
been reached and give authorization to stop the flushing operation.
4.7 Air blowing procedure
4.7.1 Specific problems of air blowing
- Large volumes of air:
If the quick decompression method is used, large volumes of air are
required, and it may take a significant time to raise the pressure in the
network up to the desired value.
- Air blowing is a HAZARDOUS OPERATION:
Very high forces are generated at the air outlet. Therefore, specific safety
procedures must be closely adhered to; generally air blowing operations
will be undertaken when all other works have been stopped on site.
- Air quality:
For some operations, especially instrument air system, oil free air and/or
dry air might be needed (temporary drier and oil extractor may be
necessary).
4.7.2 Preparation for air blowing
Note: Before the detailed preparation work starts, a meeting shall be

A first selection shall be made according to construction progress, and
geographical or functional criteria (i.e. compressor suction line, main
transfer line, air service system, etc.). Then, it shall be revised to suit the
site requirements, depending in particular, of the facilities available on site,
the devices to be removed, the configuration of the lines, etc..
During cleaning operation, the air velocity shall be as follows:
- In the gas process lines, the velocity shall be the lowest figure
between 60 m/s and the velocity obtained at 1.3 time the maximum
process flow rate. The minimum velocity shall be 30 m/s.
- In liquid process lines, a velocity between 30 m/s and 60 m/s shall
be used. If the quick decompression method is used, the pressure
in the network could be raised up to 6 bars.
The total volume of the network shall be estimated and the time required
to raise the pressure up to 6 bars with the compressor(s) shall be
calculated.
Mechanical design pressure limits are to be considered.
pressure
If the quick decompression method is used, the air pressure in the network
shall never exceed 6 bars. It should also be checked that all pipes and
vessels of the network are designed to withstand a pressure of 6 bars.
If the network cannot withstand a pressure of 6 bars, the pressure shall be
carefully studied and specified in order that the maximum allowable
pressure in the system is never exceeded.
If a rupture disk is to be installed on a large diameter pipe, the set
pressure of the disk shall be carefully calculated in order to limit the
energy released when bursting occurs to an acceptable level (in particular
with regard to recoil effect).

For pipes above DN 250 especially the first blowing will take place with the
network pressurized at only 2-3 bars.
Identical to 4.6.2.4 only the lines to be flushed will be colored yellow.
4.7.2.5 Location of air inlets and outlets
A site review shall be made to determine the possible air inlets, the
possible outlets, and the necessary temporary pipes (avoid hose pipes
when possible). Detailed drawings shall be prepared if necessary,
and the required equipment to be supplied and installed (pipes, valves,
gaskets) shall be determined.
4.7.2.6 Opening means
Where the quick decompression method has been selected, the pressure
release can be obtained by:
- a quick opening valve,
- a rupture disk.
In the first case, the flow rate may be roughly adjusted, if necessary, and
the valve may be closed in case of emergency; in the second case, no
control is possible.
Due to the high velocity involved, the quick opening valve might be eroded
if it is used in an intermediate state (i.e. not completely opened).
Therefore, whenever possible, the valve shall be completely open.
Same as for water flushing (see item 4.4 und 4.6.2.7).
Attention shall be paid to tray manholes and other internals of the vessels
used as air capacities (quick decompression method).
4.7.2.8 Quality of air
The quality of air shall comply with the design basis.

4.7.2.9 Safety
Due to the high forces generated at the air outlet, the following particular
precautions shall be taken for blowing operations:
- Period of time for blowing:
Generally air blowing will take place after normal working hours.
- Restricted area:
An area of at least 30 meters around the outlet points will be roped off
during the release of air.
- Work permit:
Any air blowing operation shall be subject to specific work permits
- Space between flanges at the outlet:
To obtain the desired space without hammering, spacers (pieces of tube
of a diameter slightly larger than the bolts), or pile of washers, may be
installed on bolts fixed by two nuts between the two flanges in two holes
diametrically opposed (see figure below). Other fixing systems are also
possible.

- Restraints:
The flanges(s) at the air outlet shall be fixed by means of shackles and
cables or slings. For diameters larger than DN100, at least four cables
shall be used. The second end of the cable shall be fixed rigidly to the
structures (see figure below).

- Clamps, tie bars, rigid struts, shims, U-bolts, etc.:
Wherever necessary, the pipes shall be rigidly fixed with clamps, tie bars,
rigid struts, U-bolts, etc., to avoid damage to the lines, equipment, and
people nearby.

- Blanks:
Blanks shall be rigidly fixed to the flanges by bolts and nuts in order
to prevent them flying off when opening the quick opening valve or
when the rupture disk blows out.
The large quantities of dirty air released during the flushing carries
particles of sand, rust. welding rods, .etc. which could damage
nearby equipment. Therefore adequate protection has to be
installed.
- Personnel protection:
Protection of personnel carrying out the operation must be ensured
by suitable protective equipment, i.e. ear protection, gloves,
coveralls, goggles as a minimum.
Identical to 4.6.2.10.
4.7.3 Performing air blowing
Once all preparation work is completed the commissioning engineer shall
inspect, the site (and check specially that all protections are installed: pipe
restraints, clamps, supports, protection of equipment in the vicinity of air
jets) and obtain the clearance of the safety engineer. Once satisfied he
shall give the authorization to start the air blowing operation.
4.7.3.1 Continuous blowing method
- Start the compressor (see particular procedure and vendor
requirements).
- Open the valves on the main header to be air flushed.
- Allow the air flow to enter the network up to the calculated flow rate
(check by difference at the outlet of the compressor, before and after).

- If the valve between the compressor and the network to be flushed is a
globe valve, and if the compressor allows for quick increases of flow rates,
changes of flow rates in the line may be made, thus changing the velocity
and removing more quickly the rust and scale encrusted on the surfaces
(this method may be attempted if the amount of encrustation is large and /
or if the pipe has to be very well cleaned).
For normal dirtiness, a continuous blowing at a constant speed should be
sufficient.
Instead of a compressor a large capacity vessel (column or drum) can be
pressurized by a smaller compressor (to approx. 6 bar, depending on the
mechanical design pressure), then the content of this vessel can be
depressurized into the system to be cleaned as described above.
4.7.3.2 Quick decompression method
Check that the network is isolated.
- If a quick opening valve is used, allow the air to enter the network and
carefully check that pressure in the system never exceeds the maximum
allowable pressure. When the required pressure is reached, check that all
safety measures have been adhered to, and open the valve. If necessary,
this operation shall be repeated several times (see cleanliness criteria in
paragraph 4.7.4).
- If a rupture disk is used, after having checked that safety measures have
been taken, allow the air to enter the network; check continuously the
pressure rise, and when the rupture disk blows out, stop the air inlet in the
network. The operation shall be repeated several times (see cleanliness
criteria in paragraph 4.7.4).
These depend upon the ongoing requirements. For instance a compressor
suction line will need to be much more thoroughly cleaned than a drain
line.

Principal checks are:
- Color of the air at the exit point. This will roughly indicate whether or not
rust and dirt remain in the piping. This is usually sufficient for the majority
of process and utilities piping.
- Inspection by having a close look at the line system.
Commissioning engineer shall be responsible to estimate that the desired
cleanliness has been reached and shall then give the authorization to stop the
flushing operation.
4.8 Steam blowing procedure
4.8.1 Specific problems of steam blowing
- The principle differences between air blowing and steam blowing are:
a) the temperature, which creates dilation stresses. Therefore
steam blowing shall be performed only for steam networks.
b) the vacuum hazard created when steam condenses in a closed
system. This can cause vessels and large diameter piping to
collapse.
- The main advantage of steam over air is the embrittlement of pipe wall
deposits, especially millscale, caused by temperature changes between
blowings and the subsequent contraction of the piping or equipment
causing a cracking effect on pipe wall deposits.
- Steam blowing is a HAZARDOUS OPERATION:
Very high forces are generated at the steam outlet. Therefore, specific
safety procedures must be closely adhered to; generally steam blowing
operations shall be done when most of the other works in the area have
been stopped, personnel which will stay in the area should be
informed/warned before blowing, hearing protection is mandatory.
4.8.2 Preparation for steam blowing

A first selection shall be made according to construction progress, and
geographical or functional criteria (i.e. steam inlet line, main transfer line,
etc.). Then, it shall be revised to suit the site requirements, depending in
particular, of the facilities available on site, the devices to be removed, the
configuration of the lines, etc..
During cleaning operation, the steam velocity shall be the lowest figure
between 60 m/s and the velocity obtained at 1.3 time the maximum
process flow rate. The minimum velocity shall be 30 m/s.
pressure
The pressure and temperature shall be carefully studied and specified in
order that maximum allowable pressure and temperature in the system
are never exceeded. For steam blowing the maximum working pressure
shall be limited to 9 bar.
Identical to 4.6.2.4 only the lines to be flushed will be colored red.
4.8.2.5 Location of steam outlets
A site review shall be made to determine the possible steam outlets and
the necessary temporary pipes and devices. Detailed drawings shall be
prepared if necessary, and the required equipment to be supplied and
installed (pipes, valves, gaskets) shall be determined.

determined.
Same as for water flushing (see 4.4 und 4.6.2.7).
4.8.2.8 Quality of steam
The quality of steam shall comply with the design basis.
4.8.2.9 Safety
Steam is potentially very dangerous and can cause severe burns.
About two thirds of the total heat in steam is taken up in the change of state from
boiling water to steam, and hence when steam condenses, two thirds of its total
heat is given up to the body on which it condenses. This is what makes steam
such an effective heating fluid, and this is also what makes it very dangerous if it
condenses on the human body. Hence to get a part of the body in a jet of steam
is many times worse than in a corresponding flow of hot air at the same
temperature .
The following precautions should be observed:
- When blowing steam lines make sure that everyone is clear of the area.
- Follow the guidelines laid down for air blowing operations (see paragraph
4.7.2.9).
- Personnel must always be adequately clothed when working in the
proximity of steam lines. Shorts and tee-shirts are forbidden.
- Close liaison with boiler house personnel is required.
Identical to 4.6.2.10.

4.8.3 Performing steam blowing
Pipe work systems are to be prepared for steam blowing operations in
much the same way as for air blowing but it must be borne in mind that
much higher pressures, line, and escape velocities may be involved.
Obviously in these cases additional restraints and clamps will be required
to overcome reactive forces and avoid damage.
Special attention must be paid to system blinding and isolation.
Once all preparation work is completed the commissioning engineer shall
inspect, the site (and check specially that all protections are installed: pipe
restraints, clamps, supports, protection of equipment in the vicinity of steam jets)
and obtain the clearance of the safety engineer. Once satisfied he shall give
the authorization to start the steam blowing operation.
Initially steam should be slowly introduced into the system to allow a steady
temperature rise in the piping or equipment. Condensate must be drained from
all low points to avoid producing water slugs which could be propelled at high
velocity through the piping causing hydraulic shock and possible damage.
Following this warm-up period steam blowing may be started. In certain
applications, such as steam turbine HP steam inlet line blowing it may not be
possible to use a quick opening valve. In this case it is very important to use an
intermediate block-valve for controlling the steam flow. Always avoid using a
final stop valve in case its seat is damaged by erosion, this will cause future
problems when the steam supply needs to be isolated.
When steam blowing small diameter lines the normal block-valves may be used
for a limited time and should not be liable to damage.
When a steam blow has been completed, ensure the piping and equipment are
adequately vented to avoid pulling a vacuum during the cool down period. If
required, cool down can be accelerated by the injection of service air.
Cleanliness checks are to be carried out as explained in paragraph 4.7.4.
Additionally, target plates may be used if the steam line will feed a steam turbine.
- A polished aluminum or soft metal target plate is attached to the target plate
carrier on the tailpipe end (see the following figure)

- There is little point in using a target plate during the initial steam
blowings, these plates should be installed when the exhaust steam
appears to be clean.

Proceed as follows:
- If the exhaust steam appears to be clean install a target plate and steam
blow the system.
- Examine the plate at the end of the steam blowing.
- If the plate has became eroded and pitted, easily seen by a matt gray
appearance and surface pitting, continue steam blowing.
- Mark each plate and store in a safe place for comparison.
- The target plate surfaces will become brighter after each subsequent
blowing.
- When the plate surface remains bright it will be possible to count the
number of impact pits per blow caused by large dirt or rust particles.
- When the plate remains unmarked it may be assumed that the piping is
clean.
- If requested, submit the series of target plates to the equipment vendors
representative for his scrutiny and final approval.
- Ensure no dirt is re-introduced into piping during re-assembly following
steam blowing.
In the case that target plates will be used, note that wet steam may produce a
"matting" effect on a polished target plate which can be misleading. In this case
look for pitting marks as a general guideline.
When the equipment is considered to be clean, and / or meets the equipment
vendors representative requirements, etc., allow the piping to cool, drain
condensate from low points and, if necessary, carry out a drying procedure.
Reassemble the piping taking care not to reintroduce dirt into the equipment.
Commissioning engineer shall assess if the desired cleanliness has been
reached and give the authorization to stop the steam blowing operation.

4.9 Chemical cleaning procedure
4.9.1 Specific problems of cleaning with a chemical solution
- Field of application:
This procedure is applicable for removing production residues and
surface protection substances, i.e. oil and greasy films, in case it
should disturb commissioning or start-up of the plant. This
procedure is not applicable for special surface treatment, i.e.
"pickling and or passivation" - GBHE-APT-0102
- Degreasing:
A grease layer may have formed during transport or storage of the
equipment which may disturb further procedures. In this case, the
surfaces shall be degreased by means of a special lye
(components: carbonates, alkali-hydroxide phosphates and wetting
agent).
- Treatment:
A pre-treatment of the system using a method acc. to paragraphs
4.6 and 4.7 is necessary. The treatment itself will be carried out by
circulation of a chemical solution in a closed system. When the
equipment is degreased the solution has to be removed and
disposed to waste water treatment or special treatment. Finally the
system will be rinsed with fresh water or demineralized water to
remove the remaining chemical solution. After that the system may
be dried out by air or inert gas if necessary.
- Solution handling:
A separate vessel or drum may be necessary for preparation of the
chemical solution. Additional temporary pump, piping and
connection might be required. Precautions by handling chemicals
must be observed.

4.9.2 Preparation for chemical cleaning
organized with Uhde and the customer commissioning representatives to
define the systems to be treated and finalize the detailed procedures
based on the present general procedures, taking into account the site
restrictions and possibilities.
4.9.2.1 Definition of the system to be cleaned
A first selection shall be made according to process requirements for
commissioning and start-up of the plant, construction progress and
geographical or functional criteria (i.e. vessel, piping, etc.). Then it shall be
adapted to suit the site requirements, the devices to be removed, the
configuration of the lines (low points, high points, lengths, heights, etc.).
4.9.2.2 Calculation of the chemicals
Estimate the volume of the system to be cleaned and of the auxiliary
device. Determine the necessary chemicals for treatment and the required
concentration. Generally a concentration of 3 to 5 wt-% (Na-OH or KOH or
K2CO3 etc.) shall be used.
Calculate the amount of chemicals and water for treatment and rinsing.
Determine the air for drying out the system.
During cleaning operation, the chemical solution velocity shall not reach
the high figures as given in chapters 4.6 to 4.8 to avoid erosion. For
chemical cleaning it is important that all surfaces to be cleaned are in
good contact with the solution, the high velocities are here not so
important as for mechanical cleaning.
pressure
Estimate the maximum head loss. With the velocity actual, estimate the
head loss for a flow going through the principal piping and add the static
head (if any). If the flow and the head loss are compatible with the pumps
available on the site, go ahead, otherwise reduced flow or external pump
has to be considered.

The pressure shall be carefully studied and specified in order that the
maximum allowable pressure in the system is never exceeded.
A sketch of the network to be cleaned shall be specially drawn for the
cleaning operation (P&ID’s will be used for this purpose).
The following color code may be used:
- Blue with flags: lines to be chemical cleaned
- Green: items to be removed
- Pink: flanges to be disconnected
- Orange: items to be isolated
Blinds used for chemical cleaning operations, if they are necessary they
will be indicated and numbered with a red color. Installation and removal
of blinds shall be followed up by commissioning by the mean of a blind list.
Installed blinds shall be tagged and equipped with a visible handle painted
red.
4.9.2.5 Location of inlets and outlets
A site review shall be done to determine the possible solution and water
inlets and outlets, the water source, the pump(s) location, the additional
pipes or hose pipes layout from the source to the system.
The water disposal problem and the protection of the equipment and
people nearly shall be carefully studied.
determined.

All "fragile" devices to be removed shall be identified. The removal
possibilities shall be investigated on site. The required dummy spools to
be fabricated shall be drawn on sketches.
Attention shall be mainly paid to:
- heavy devices (control and block valves, check-valves),
- supports, hangers, pads, spring supports,
- possible stresses on pumps’ flanges.
4.9.2.8 Quality of water
Good quality of fresh water and or demineralized water shall be used from
the beginning until the end.
The quality of the water shall comply with the specification for hydrostatic
test and the design basis for the plant respectively.
4.9.2.9 Safety
The following particular precautions shall be taken for chemical cleaning
operations:
- Period of time for flushing:
Generally chemical cleaning operations will take place during normal
working hours.
- Restricted area:
An area of at least 5 meters around the system will be roped off or closed
off during the cleaning operation.
- Work permit:
Any chemical cleaning operation shall be subject to specific work permits

- Restraints:
Wherever necessary, the pipes shall be rigidly fixed to avoid damage to
the lines, equipment and people nearby.
Adequate protection of the devices in the vicinity of the system and water
outlet has to be installed in order not to damage equipment, electric
motors or instruments with chemical solution or water.
- Personal protection:
Protection of personnel carrying out the operation must be ensured by
suitable protective equipment, i.e. gloves, boots, coveralls, goggles, etc..
- A work permit shall be issued for each cleaning operation according to
the safety procedures.
- Notice to the commissioning team shall be sent together with colored
P&ID(s).
4.9.3 Performing a chemical cleaning
Once all preparation works are completed the commissioning engineer
shall inspect the site and give the authorization to start the chemical
cleaning operation.
Cleaning operation will be performed by circulating the chemical solution
for a predestined time.
To check the flow rate if no flowmeter is installed, a pressure gauge can
be installed at the inlet of the system to be cleaned (downstream of the
inlet valve) and the flow then adjusted by acting on the inlet valve till the
head loss equals that calculated for the required velocity.
The flow / discharge pressure curve of the pump can also be used to
check the flow rate (make sure the pump runs at its normal speed).
The temperature of the cleaning solution shall be approx. 50 to 70 °C.
When the complete system has been cleaned satisfactorily, the circuit
shall be emptied chemical solution.

After completion of chemical flushing the system shall be flushed with
clean water (quality depending on the operating systems). This step is to
remove the remaining chemicals from the system and may be repeated if
required.
Then the system may be dried out with air or inert gas, if necessary, and
the removed devices shall be reassembled.
The duration of the cleaning is the time needed for the reaction of the
chemicals with the oil and greasy material in the whole system expressed
as retention time plus an additional safety margin. Test on side may be
carried out if necessary.
Commissioning Engineer shall estimate when the cleanliness criterion has
been reached and give authorization to stop the cleaning operation.
4.10 Re-assembly – general guideline
After the cleaning operations, pipes, fragile devices, etc., have to be
reassembled. Great care is necessary in this operation.
The construction specifications have to be complied with, with particular
emphasis on the following points:
- Ring joints have to be carefully cleaned.
- New gaskets must be used on flanges broken for flushing purpose.
- Spring supports, sliding pads. etc., have to be installed according to the
drawings and released when the reassemble is completed.
- Threads shall be checked and wrapped with PTFE.
- Stuffing boxes and packing of valves shall be checked and changed if
necessary.
- Absence of stresses on pump and compressor flanges has to be
checked.
- The orientation of check valves, globe valves, etc., shall be checked
(according to their arrow) against the direction of flow.

- In-line instruments such as flow orifices, restriction orifices, rotameters,
shall be installed by instrument specialists.
- Expansion bellows shall be freed according to the vendor's instructions.
- Temporary blinds installed for cleaning purposes shall be removed.
4.11 Preservation of flushed piping
Following the flushing operations, if necessary, precautions for
preservation of the equipment shall be carried out, i.e. subsequent
commissioning is not practicable.

Piping and Vessels Flushing and Cleaning Procedure

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