Ships and marine technology -- Hydraulic oil systems -- Guidance for grades of cleanliness and flushing

ISO 28521:2009 specifies pipe cleaning and cleaning levels of hydraulic oil pipe systems. The cleaning of pipes and components in hydraulic oil pipe systems is essential for the trouble-free operation of hydraulic systems. It indicates methods and equipment for the practical execution of the cleaning of specific parts of hydraulic systems with appurtenant components. The purpose of the cleaning process is to remove installation dirt and to check that the piping and hydraulic system have been adequately cleaned. The cleaning process of a system is considered a “washing through” process when the Reynolds number,Re, u 3 000, and a flushing process when Re W 3 000. The Reynolds number is an indicator of whether a fluid flow is considered laminar or turbulent. ISO 28521:2009 presupposes that the pipe sections of the hydraulic system have been cleaned partly by pickling and partly by mechanical cleaning. It is furthermore assumed that both dynamic and static components from system suppliers are adequately clean when delivered. The specifications given in ISO 28521:2009 are supplementary to, and not a replacement for, the guidelines specified by the various manufacturers. The manufacturer's guidelines, where available, take precedence.

Navires et technologie maritime -- Circuits d'huile hydrauliques -- Guide relatif aux degrés de propreté et de rinçage

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Status
Published
Publication Date
25-May-2009
Current Stage
6060 - International Standard published
Start Date
14-May-2009
Completion Date
26-May-2009
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INTERNATIONAL ISO
STANDARD 28521
First edition
2009-06-01
Ships and marine technology —
Hydraulic oil systems — Guidance for
grades of cleanliness and flushing
Navires et technologie maritime — Circuits d'huile hydrauliques —
Guide relatif aux degrés de propreté et de rinçage
Reference number
ISO 28521:2009(E)
ISO 2009
---------------------- Page: 1 ----------------------
ISO 28521:2009(E)
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© ISO 2009

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ii © ISO 2009 – All rights reserved
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ISO 28521:2009(E)
Contents Page

Foreword ............................................................................................................................................................iv

1 Scope ......................................................................................................................................................1

2 Normative references............................................................................................................................1

3 Symbols..................................................................................................................................................2

4 Recommended pipe cleaning levels....................................................................................................2

4.1 Pipe cleaning levels during/after prefabrication ................................................................................2

4.2 Surface treatment ..................................................................................................................................3

4.3 Storage of prefabricated pipes and fittings ........................................................................................3

5 Level of cleanliness...............................................................................................................................3

6 Assembly and installation of pipe system..........................................................................................3

7 Blow-through/pull-through of the system...........................................................................................3

8 Description of coupling ........................................................................................................................4

8.1 Design phase .........................................................................................................................................4

8.2 Other considerations ............................................................................................................................4

9 Leakage test...........................................................................................................................................4

10 Filling with oil.........................................................................................................................................5

11 Shock testing/pressure testing............................................................................................................5

12 Flushing of yard-installed pipe system...............................................................................................5

12.1 Connection.............................................................................................................................................5

12.2 Special pump units................................................................................................................................5

12.3 Flushing filters.......................................................................................................................................5

12.4 Flushing oil.............................................................................................................................................9

12.5 Flushing times .....................................................................................................................................11

12.6 Methods for checking the cleanliness level .....................................................................................12

12.7 Leakage testing....................................................................................................................................13

13 Start-up of system ...............................................................................................................................13

Annex A (informative) Example of particle counting.....................................................................................14

Bibliography......................................................................................................................................................15

© ISO 2009 – All rights reserved iii
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ISO 28521:2009(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies

(ISO member bodies). The work of preparing International Standards is normally carried out through ISO

technical committees. Each member body interested in a subject for which a technical committee has been

established has the right to be represented on that committee. International organizations, governmental and

non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the

International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards

adopted by the technical committees are circulated to the member bodies for voting. Publication as an

International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 28521 was prepared by Technical Committee ISO/TC 8, Ships and marine technology, Subcommittee

SC 3, Piping and machinery.
iv © ISO 2009 – All rights reserved
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INTERNATIONAL STANDARD ISO 28521:2009(E)
Ships and marine technology — Hydraulic oil systems —
Guidance for grades of cleanliness and flushing
1 Scope

This International Standard specifies pipe cleaning and cleaning levels of hydraulic oil pipe systems. The

cleaning of pipes and components in hydraulic oil pipe systems is essential for the trouble-free operation of

hydraulic systems.

It indicates methods and equipment for the practical execution of the cleaning of specific parts of hydraulic

systems with appurtenant components.

The purpose of the cleaning process is to remove installation dirt and to check that the piping and hydraulic

system have been adequately cleaned.

The cleaning process of a system is considered a “washing through” process when the Reynolds number, R ,

u 3 000, and a flushing process when R W 3 000. The Reynolds number is an indicator of whether a fluid flow

is considered laminar or turbulent.

This International Standard presupposes that the pipe sections of the hydraulic system have been cleaned

partly by pickling and partly by mechanical cleaning. It is furthermore assumed that both dynamic and static

components from system suppliers are adequately clean when delivered (see Clause 5).

The specifications given in this International Standard are supplementary to, and not a replacement for, the

guidelines specified by the various manufacturers. The manufacturer's guidelines, where available, take

precedence.
2 Normative references

The following referenced documents are indispensable for the application of this document. For dated

references, only the edition cited applies. For undated references, the latest edition of the referenced

document (including any amendments) applies.
ISO 3448, Industrial liquid lubricants — ISO viscosity classification

ISO 4406, Hydraulic fluid power — Fluids — Method for coding the level of contamination by solid particles

ISO 28523, Ships and marine technology — Lubricating and hydraulic oil systems — Guidance for sampling

to determine cleanliness and particle contamination
© ISO 2009 – All rights reserved 1
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ISO 28521:2009(E)
3 Symbols
The following symbols are used throughout this International Standard.
A (mm ) pipe cross-sectional area
βx (—) particle filtration ratio
d (mm) pipe diameter
∆p (bar) pressure drop
K (—) flushing-filter factor
R (—) Reynolds number
Q (l/min) flow rate of filter
Q (l/min) flow rate of system
v (cSt) viscocity
W (m/s) flow velocity
4 Recommended pipe cleaning levels
4.1 Pipe cleaning levels during/after prefabrication

4.1.1 Black-steel pipes and pipes of other material qualities showing oxide scale as a result of

heating or welding

These should be cleaned internally after welding together of prefabricated pipes and fittings using either

chemical cleaning (alkaline cleaning and pickling) or mechanical blow cleaning to achieve a cleanliness

corresponding to Sa 2½ as specified in ISO 8501-1.

Steel shot should not be used because of the risk of adhesion by magnetism and subsequent rust seizure;

copper (Cu) slag should be used instead. Sealing faces should be protected during the blow cleaning.

4.1.2 Precision-steel pipes and pipes of other material qualities, which are delivered, and remain,

free of oxide scale (no heating or welding)

After cutting and careful deburring, pipes and fittings that are joined without being subjected to prior heating or

welding processes, for example by means of clamping rings, should be cleaned by one of the following

methods:
⎯ chemically (using an alkaline cleaning process);
⎯ blown through with pressurized air;
⎯ by pulling through lint-free cloths.
2 © ISO 2009 – All rights reserved
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ISO 28521:2009(E)
4.2 Surface treatment

In order to maintain the afore-mentioned cleanliness of pipes and fittings until their mounting onboard, it is

recommended to treat internal and external surfaces at the ends of the pipes and fittings with a suitable oil

product. To prevent dust and sand entering the pipes and sticking to the surfaces, the pipe ends should be

blanked off.

The applied oil product should not change the properties of the flushing or system oil.

4.3 Storage of prefabricated pipes and fittings

Cleaned and surface-treated prefabricated pipes and fittings should be blanked off and stored in dry,

preferably controlled, conditions. If this is not possible, the pipes shall be protected against rain and venting

should be secured on all surfaces. Inadequate storage conditions might necessitate additional cleaning and

surface treatment.
5 Level of cleanliness
For pretested components and oils forming part of the system:

⎯ Component suppliers shall be able to specify the level of cleanliness of the components delivered. This

applies to suppliers of dynamic as well as static components.

⎯ ISO/TR 10949 and ISO 18413 indicate methods according to which evaluation and documentation of the

level of cleanliness can be carried out. In addition to information regarding the level of cleanliness at the

time of delivery, the yard and the system supplier should agree in advance on the necessary level of

cleanliness of the system oil and the cleaned system to achieve a long and reliable operation.

6 Assembly and installation of pipe system

It is important to avoid any welding, brazing, soldering or heating of the pipes (and production of oxide scales)

when assembling and installing pipes. If this cannot be avoided, then the pipes in question shall be cleaned

and protected again (repaired). In particular, it is important to remove soldering materials.

Protection covers should be removed as late in the installation process as possible. Preventing dirt (from the

installation process) from entering the pipe system is crucial. PTFE sealing fluids and tape should be applied

with great care.
7 Blow-through/pull-through of the system

Before connecting the pipe system to machines, panels, pump stations, etc., all pipes should be blown

through with dry pressurized air and/or nitrogen. If this is not possible (because of the pipe dimension) then

pulling through clean, lint-free cloths should clean the pipes.

The purpose of this is to remove loose dirt in the most efficient way and, at the same time, ensure that the

pipes are dry internally (nitrogen helps eliminate water that has condensed in the pipes).

© ISO 2009 – All rights reserved 3
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ISO 28521:2009(E)
8 Description of coupling
8.1 Design phase

During the design phase, i.e. at the structuring of the hydraulic diagram, it is important to consider carefully

how the complete system can be flushed in practical terms (including grouping).
When grouping off the pipe system, the following should be observed.

a) “Dead” areas are unacceptable during flushing (these can be avoided by changing the coupling points).

b) Circuits should always be connected in series.

c) Relevant coupling options should be considered (the objective being connection of uniform pipe

diameters in order to avoid large pressure losses).
8.2 Other considerations
The following shall also be taken into account.

a) Components that might hinder a high flow velocity, or which might be destroyed by a high flow velocity,

should be bypassed.
b) Built-in filter elements shall be removed before flushing.

c) Pump stations, assembled units and subcomponents that have not been pre-tested shall be flushed

separately in case they are not delivered in a cleaned condition.

NOTE This also applies to pipe systems where space conditions on board do not allow flushing of the pipe

systems installed.

d) It is important that sampling of oil during the actual flushing be carried out in a way that ensures a

representative sample. Reference should be made to ISO 28523 and ISO 4021, which describe sampling

from a dynamic system.
9 Leakage test

Before filling with flushing oil, the leak-tightness of the system can be checked in the following ways:

a) Connect the pipe system (bypass/blank off components), then pressurize in accordance with the

directions of national standards, using clean, dry air or nitrogen, and perform external testing with soapy

water or monitoring for pressure drop during a certain time.

b) After filling with the flushing oil, the leak-tightness of the system can be tested by means of shock or

pressure testing (see Clause 11).
4 © ISO 2009 – All rights reserved
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ISO 28521:2009(E)
10 Filling with oil
For the choice of oil type and quality, see 12.3.
The filling procedure is as follows.
a) Connect the pipe system (bypass components).

b) Clean the tank in the portable pump-station and the power pack to a cleanliness level corresponding to

the cleaning level of the components supplied to the system (see Clause 5).
c) Fill the system by pumping the oil through a filter until the tank is full.

The filter shall be capable of filtering the oil to a minimum of two ISO-codes below the cleanliness specified for

the system, in accordance with ISO 4406. Care should be taken that air bubbles do not enter the system

during the filling operation; if necessary, the system should be topped up and vented.

11 Shock testing/pressure testing

a) Connect the pipe system (bypass components). Ensure that it is completely filled.

b) Pressurize the pipe system up to the relevant testing pressure and relieve it again by opening the relief

valve on the pump station. Repeat this procedure a minimum of 25 times, unless otherwise specified.

12 Flushing of yard-installed pipe system
12.1 Connection

Connect the pipe system (bypass/blank off components). Ideally, the use of a vibrating unit will be over a

broad frequency range. It is appropriate to change the flow direction more than once during the flushing

period.
12.2 Special pump units

Experience shows that very good results can be achieved when cleaning pipes using a hydraulic accumulator

and a pulsation valve sending pressure/flow pulsations through the pipes.

In a pipe system with a small internal diameter, in which a turbulent flow can be difficult to achieve because of

a large pressure drop, special gas/oil units can be used that fill the entire pipe system with gas and oil loads

which are subsequently compressed; when these loads are released, the gas pockets expand, resulting in a

turbulent oil flow.
12.3 Flushing filters
12.3.1 Filter capacity

The permanent filters of the systems should not be used for cleaning of flushing oil; instead, special flushing

filters designed to increase the filter capacity to a predetermined extent during flushing may be used together

with the portable pump station.

It is advisable to place filters on both the pressure line and the return line in order to reduce the total flushing

time.

The choice of filter capacity should be made with the aim of achieving an acceptable service life for the filter

element.
© ISO 2009 – All rights reserved 5
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ISO 28521:2009(E)

The service life is, all other things being equal, determined by the filter’s contamination capacity.

It is difficult to determine the desired contamination capacity and to obtain information on the relevant

contamination capacity from the manufacturers. For this reason, the flow capacity of the filter (expressed in

l/min) is often used as the basis for achieving an acceptable service-lifetime.

The filter flow capacity, Q , is calculated by multiplying the flow capacity of the system, Q , by a factor of K ,

1 2 1

which normally varies between 2,5 to 3,5 for flushing filters. A high K value is chosen for high-pressure

systems and a low value is chosen for low-pressure systems.
is given in 12.3.3, and an example of its use given in Table 2.
The method of calculation for Q

A filter element which in a cleaned condition is capable of handling a flow rate of Q at a pressure drop, ∆p, of

0,3 bar, should be chosen according to the manufacturer's specifications.

Flushing filter elements shall be exchanged when the maximum ∆p for a contaminated filter is reached during

flushing (this is read from a pressure gauge or from a contamination indicator, if fitted).

The contamination indicator shall be of a type that gives a signal before the bypass valve opens. As it is

impossible to calculate and obtain different filter capacities for varying flushing operations, in practice, the

individual yards are encouraged, on the above basis and their own parameters, to calculate and use one or

more “standard filters” that can be used within specific limits.
The following equation is proposed for calculation of choice of filter:
Q = Q × K
1 2 1
where
= W A
and
W = R /1 000 × v/d
A = π (d /4)

The values of Q , W, R , v, and d are explained in 12.3.2. Q is also given in Table 2.

2 e 2

Since R can be fixed at, for example, 3 000, and v can also be kept constant by using flushing oil of a

stadardized quality at a fixed temperature, only d and K are variables.
Where pipes are of a relatively small diameter, K is largest (high pressur
...

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