1.General
1.1 Potential danger
Working with high pressures doesn’t have to be dangerous.
The pressure / liter product, i.e. the product of volume and pressure, is decisive for the potential risk of a pressure-bearing system. In addition, however, there is the compressibility of the fluid and the expansion of the pressure body and the dangerousness of the fluid — (flammable, caustic, poisonous). All gases and liquids are fluids.
Often the problems, especially with gas systems, tend to occur in the low-pressure range, since too little attention is often paid to this. Gas cylinders, for example, are often a greater source of danger than high pressure systems.
The dangers of a high pressure system are sometimes misjudged. Safety devices are installed out of place, are too weak or vice versa, or are created with excessive effort.
To ensure operational safety, always make sure that the system is in good condition and that regular tests are carried out.
1.2 Advice
People working with a high pressure system must be aware of the dangers that can arise. If in doubt, consult a specialist. Obtain written notification of which security measures he deems appropriate. When selecting the components, it should be ensured that they have the necessary capacity, pressure approval, corrosion resistance and other required functions so that they can be used for the intended purpose. We would be happy to advise you on the selection of the components, but the final decision and the responsibility to fulfill the task to the satisfaction rests with the user.
You can also call in a competent expert at any time, even if there is no obligation to accept the system. In Germany, experts for pressure vessels are Dekra, TÜV or DNV-GL.
For each larger high-pressure system or several together, there should be a safety officer who familiarizes himself with the matter and who is appropriately trained through appropriate courses and courses. The employees working with a high-pressure system should be informed at regular intervals, e.g. every three months, about the applicable accident prevention regulations and necessary safety and possibly also first aid measures. Any “near misses” should also be discussed. The safety officer should regularly check that the employees are following all safety instructions and that the necessary safety checks are carried out in accordance with the regulations.
1.3 Manufacture of plants
High-pressure systems may only be manufactured by competent specialists.
If you do not belong to this group of people, obtain a complete, properly manufactured system with the associated acceptance papers and safety devices.
Every printing system must comply with the Pressure Equipment Directive and / or the Machine Protection Act. Just as it is not permitted to drive an unauthorized motor vehicle, it is not permitted to work with an unapproved high-pressure system.
The Machinery Directive can be read under the following link:
https://eur-lex.europa.eu/legal-content/DE/TXT/?uri=CELEX%3A32006L0042
Compliance with the Machinery Directive is required by law. The Machinery Directive is quite extensive, essential parts are a matter of course for a machine manufacturer. It makes more sense to observe the Pressure Equipment Directive, which is part of the Machinery Directive.
The Pressure Equipment Directive can be found under the following link:
https://eur-lex.europa.eu/legal-content/DE/TXT/?uri=uriserv:OJ.L_.2014.189.01.0164.01.DEU
1.4 energies under pressure
Never underestimate the energies of a fluid under pressure. The compressibility of water at 1,000 bar pressure is approx. 5%, that of oil approx. 10%. In addition, there is the elastic tension energy of the component and possibly the chemical energy of the content. These forces are suddenly released. You can greatly accelerate a component and provide it with considerable penetrating power.
A possibly escaping liquid jet can lead to serious injuries, including cutting off parts of the body. A jet of liquid penetrating the body tissue usually leads to blood poisoning and must be treated immediately.
Gas systems are more dangerous than liquid systems, because
they accelerate any released components more strongly in the range below 1000 bar. When the gas has reached its own volume during compression, from around 1000 bar, the difference in compressibility between gases and liquids decreases until it is almost the same.
When working with high-pressure systems, it is advisable to wear hearing protection, as sudden changes in pressure, for example when a rupture disc safety device is triggered, can cause sudden noise and otherwise damage your hearing. Working behind a protective wall is generally recommended, as a pressure wave can also lead to injuries if a component fails.
1.5 Lifetime
Machine components can fail after some time due to unforeseen chemical and mechanical influences. On the other hand, experience has shown that employees become less carefree over time with accident-free operation.
High-pressure components are often designed in such a way that they do not have an infinite service life!
The resistance to load changes, and thus the service life of many components, especially when they are under high pressure, is limited. In addition, it is very difficult to calculate and is often misjudged.
An error in the selection of the material, in the material, in the construction or in the production can also have effects that allow a component to bear its load only for a limited period of time.
A short pressure test or an approval by an expert is no guarantee that a pressure-bearing component will have a permanent service life.
You should therefore always work with your printing system in such a way that a failure of a component cannot injure anyone!
If it is unavoidable to work directly on pressurized parts, always wear protective goggles, a hard hat, safety shoes and protective clothing. Wear earmuffs if you expect loud noises.
Anyone who works unprotected on pressurized systems is not acting courageously, but irresponsibly!
2 Protocol
If you operate components that are subject to acceptance in accordance with the Pressure Equipment Directive, the AD 2000 Directive stipulates that a record must be kept. The AD 2000 set of rules dominates in Germany, but is increasingly being replaced by DIN EN 13445.
2.1 Protocol content
Work on a high-pressure system should generally be recorded.
Normal occurrences such as pressure and temperature loads, their periods of time, job descriptions, extensions, repairs and irregularities should be recorded in the log.
One person should never work alone with a high-pressure system. The people who work with the high-pressure system must be recorded in the protocol. If systems have to work unsupervised, it must be recorded in the log who is responsible for the running system, where the responsible person can be found, and how the system is to be handled in the event of a fault.
3 Conditions
3.1 General
In order to prevent premature fatigue and inattentiveness of the staff, the workplace must correspond to a normal workplace in terms of lighting, temperature control, ventilation and noise pollution.
In general, the installation site should be well ventilated, especially when working with flammable or toxic substances. A suitable system for the safe removal of any substances that may escape through safety devices must be guaranteed.
The workplace must at least be equipped with a fire extinguisher, first aid kit and a telephone.
Suitable tools must be available for service or repair work.
3.2 Gas systems
When working with gas systems, depending on the size of the pressurized volume, it may be necessary to provide a blow-out wall, automatically opening flaps or similar relief options.
When working with flammable gases, a suitable, regulation-compliant exhaust system must be provided. When working with liquids whose temperature is higher than the self-ignition temperature of the liquid, the apparatus must be placed in a container filled with nitrogen.
3.3 Protective walls
Although it is possible to calculate the required strength of protective walls, this is unlikely to make much sense in practice; it should be determined by experienced specialists.
The walls should be multilayered. For larger systems, a combination of a 10mm polycarbonate sheet, a 2mm sheet steel and a sharp-edged wood layer adapted to the application has proven to be very effective. A 2mm sheet steel should be attached to the outside.
The protective walls must be well secured so that people are not endangered by falling over after an impact.
A simple concrete wall is not well suited to larger systems. Although the impacting body does not penetrate the wall, as we have already experienced, a part on the back can loosen and fly on.
3.4 Burst protection container
Burst protection containers are often safer and cheaper than protective walls.
3.5 walls and ceilings
Never rely on the protective effect of the adjoining walls and ceilings, it is usually less than is generally assumed.
3.6 Windows
If you place your system in front of a glass window, make sure you are aware of the consequences of any broken glass.
The view of a high pressure system enables:
Polycarbonate offers limited protection that is mostly overrated. Single-walled polycarbonate, e.g. 10mm thick, does not offer any protection worth mentioning. Two-layer polycarbonate offers better protection up to approx. 3 kbar. Stable frames are very important.
We carried out several shot attempts with polycarbonate windows. The results were sobering. Let us advise you personally.
“Plexiglas” should not be used under any circumstances. “Armored glass” offers the best protection for high-pressure systems (see also https://de.wikipedia.org/wiki/Panzerglas).
TV cameras are also an alternative on occasion.
3.7 Control elements
Of course, all controls must be outside of the print area.
3.8 Identification
The emergency regulations and measures for switching off the system in an emergency are clearly visible outside the danger area.
A high-pressure room must be marked accordingly from the outside.
4 Components
4.1 Material
When selecting the components, particular attention should be paid to the choice of materials. Each material has different physical and chemical properties. The user should also ask himself which by-products may arise in a reaction, under which boundary conditions (temperature, pressure, catalysts) and how this can be prevented. Nevertheless, the material must be suitable to safely guide these fluids.
4.2 Gas bottles
Special attention should be paid to standard gas cylinders, as they often store a very high energy potential.
Gas cylinders are not always in good condition and the prescribed test intervals are currently far too long.
The gas cylinders must not be set up in such a way that they can be damaged if a high-pressure component fails.
It is best to store gas cylinders outdoors, protected from the sun, locked and closed. See TRB 610.
It is not permitted to fill gas cylinders yourself. Serious accidents are not infrequently the result of violations.
4.3 Pressure gauges
With pulsating pressures, pressure gauges may only be used up to 2/3 of their display range. They should have an internal protective wall (special security / solid front). Only safety glass may be used as a front pane. A liquid filling is usually recommended. At pressures above 1000 bar, pressure gauges with a high pressure connection should be used.
Pressure transducers usually have a higher load capacity than pressure gauges. A safe construction should be ensured with regard to a failure of the membrane or the pressure pipe.
Manual valves are a very critical component, as the operator comes into direct contact with them.
The construction of many hand valves is unsafe. The gland nut can tear off or unscrew. Many locking plates, which are supposed to prevent the stuffing box nut from being unscrewed, are insufficient and only inadequately serve this purpose. Valves with an additional protective cap or a yoke over the stuffing box nut are better.
Pneumatically, electrically or hydraulically operated valves are safer than manual valves, as they do not have to be in the vicinity of the operator. In addition, they are often also cheaper, since less piping work has to be carried out and they often also have a longer service life.
4.4 High pressure connections
High pressure connections must have at least one relief hole.
In the event of a leak, the pressure loads the entire area of the thread of the pressure screw. In the case of a 10,000 bar M16x1.5 screw connection, the result is 100 times the load ((16𝑚𝑚) 2 (1.6𝑚𝑚) 2 = 100). Without a relief hole, the pressure screw would tear off and turn into a projectile.
The area of the relief bores should have at least 1/4 of the area of the nominal width, but at least a diameter of 2.5mm.
Example: Nominal size 8mm, two relief holes Diameter of the relief hole: √ (8𝑚𝑚) 24/2 = 2.8 mm.
The correct nominal diameter of the relief bore can easily be calculated using the nozzle formula, taking into account the maximum discharge volume.
4.5 High pressure pipes
High pressure pipes should be designed in accordance with DIN EN 13445.
If they transport toxic, flammable or caustic fluids, or if a certain pressure liter product is exceeded, they are subject to acceptance (see Pressure Equipment Directive).
Pipes should be fastened at intervals of 500 to 1000 mm. Otherwise, if the pipe ends fail, it could cause serious injury.
The bending radius must not be less than five times the pipe diameter. Cold-hardened pipes, which is currently most stainless high-pressure pipes, must not be hot-bent, welded or soldered, or heated to over 750 ° C, otherwise they will lose their work-hardening.
4.6 High pressure hoses
Working with high-pressure hoses that are operated at pressures of up to 4000 bar is very dangerous without additional protection. Particularly when operating hydroforming systems, high-pressure hoses are occasionally used in an irresponsible manner.
With regard to the acceptance regulations, hoses are to be treated like pipes.
Additional protective devices, such as protective hoses, can be supplied for high-pressure hoses. Different types of protective hoses are available: a clear PVC protective hose, which is primarily used as abrasion protection, and a burst protection hose, which is much more stable. Fireproof protective hoses can be used for higher temperatures. A simple, flexible one or two-layer hydraulic hose can be used as a burst protection hose. The protective hose ends can be made open or closed. When the ends are closed, there is the possibility of a controlled discharge of the fluid.
The hoses must be provided with a tear-off protection. This prevents the connection or hose from flying away if the crimping fails.
Instead of hoses, spiral-shaped pipes, the linear feed-throughs developed by us or pipes with rotary feed-throughs can often be used. These have a significantly higher level of safety, longer service life and larger nominal sizes.
4.7 Overpressure safety devices
4.7.1 Burst disc safety devices
The cross-section of burst disc safety devices is specified in AD 2000 regulations and the necessary rupture pressure of the burst discs must be at least 30% above the operating pressure.
The entire system must be designed for at least the bursting pressure of the burst discs or the opening pressure of an overpressure or safety valve.
A suitable discharge of the escaping fluid must be available.
Burst discs are subject to fatigue with a higher degree of utilization and pulsations. In such cases, premature bursting is to be expected.
Burst discs should primarily be used in systems in which a sudden increase in pressure is to be expected or which are difficult to seal. Otherwise, pressure relief valves are more recommended.
4.7.2 Pressure relief valves
Pressure relief valves, also known as pressure relief valves, which have been approved through a type test or individual acceptance by an expert, are called safety valves.
Pressure vessels or systems that are subject to acceptance must have a safety valve or an approved rupture disc safety device. There must be no shut-off facility between the pressure vessel and the safety device.
The opening pressure of the pressure relief valve may not exceed the operating pressure by more than 10%.
4.8 Pressure vessels
Pressure vessels with an operating pressure of over 0.5 bar are subject to acceptance by the manufacturer or an expert in accordance with the Pressure Equipment Directive. The corresponding set of rules is too extensive for its content to be reproduced in a few paragraphs, but can be looked up on the website linked above in the text.
A test book must be available for every pressure vessel that is subject to acceptance.
In this book, in the certificate for the preliminary test and in the acceptance test certificate, the permitted load changes, permitted operating pressure, permitted operating temperature and permitted fluid, as well as intervals for the repeat test and the other approval criteria are recorded.
Externally heated pressure vessels that are heated under pressure are subject to special regulations. Autoclaves are usually designed to be heated first, then pressurized. In the opposite case, a negative state of tension arises, i.e. the warm outer wall expands more than the cold inner wall. This can cause the container to fail.
In many cases, internal heaters are cheaper and react much faster. We supply internal heaters up to 10,000 bar pressure.
Particular care should be taken when opening pressure vessels that contain heated liquids, especially water. If the water is just below boiling point, pulling out the cap often creates a vacuum that can lead to a steam explosion. Serious scalds can result.
4.9 Machine components
Machine parts that have pressure-bearing components, e.g. B. Pumps and compressors, do not fall under the pressure equipment directive, but must be designed with a special safety.
This particular security consists in the fact that a safety factor of 3 instead of 1.5 should be used when the yield point is used. Since this is impossible with most high-pressure devices, these are, in the opinion of many experts, but not all, to be removed as an alternative to pressure vessels.
There are special acceptance regulations for pressure intensifiers.
4.10 Pressures
4.10.1 Static pressures
Components that are statically loaded and below the endurance limit theoretically have an infinitely long service life if they are properly constructed.
4.10.2 Dynamic pressures
An absolutely reliable mathematical design over the service life of machine components under high pressure and strong load changes is not possible. The dynamic pressures recommended by us are empirical values with a medium load.
5 Pressure systems
Pressure systems may only be operated if they comply with the applicable CE regulations.
This includes, among other things, that all applicable regulations are observed and that they have been produced by competent specialist personnel.
A proper operating manual must be available.
5.1 Dangerous high pressure systems
Special regulations apply to systems that contain toxic, flammable or caustic fluids and to a large number of special systems (see DIN EN 13445).
5.1.1 Oxygen
Oxygen systems under high pressure are dangerous and are subject to special regulations (see “Handling oxygen”, leaflet M034, trade association for the chemical industry and UVV oxygen).
Oxygen systems must not be lubricated with normal oils or greases. There is a risk of explosion!
Oxygen must not be used in place of compressed air. Clothing soiled with oil or grease must not be worn when working with oxygen. Oxygen must not be blown into clothing! Avoid touching parts that come into contact with oxygen with greasy fingers. Oxygen may only be used in components that are intended for operation with oxygen.
Oxygen systems may only be cleaned with suitable solvents.
Leak tests may only be carried out by experts who have experience with leak tests and in dealing with oxygen.
Only plastics that have been tested and found to be suitable may be used. Pressure vessels that are subject to acceptance must be approved for oxygen. You have to be absolutely clean. There must be no chips or burrs in the system. Edges should be rounded.
Only pressure gauges (manometers) with the label “Oxygen! Keep oil and grease free ”should be used.
5.1.2 Hydrogen
Hydrogen is highly flammable and difficult to seal due to its low viscosity. In many steels, contact with hydrogen leads to immediate embrittlement and cracking. This usually results in bursting with accompanying ignition of the gas.
Only use materials suitable for hydrogen for operation with hydrogen!
5.1.3 Acetylene
Acetylene or ethylene systems must be free of copper and silver. This also applies to all individual parts, such as seals or valve glands.
There are precise regulations with regard to installation and operation.
There is TRAC 203 for operating regulations for acetylene compressors, and TRAC 204 for pipes carrying acetylene.
5.1.4 Nitrogen
Breathing in nitrogen without oxygen can lead to sudden death. Nitrogen can embrittle steels at higher temperatures. Argon should preferably be used at higher temperatures.
5.1.5 Liquids
In the case of liquids, their solidification point must be observed.
It is not uncommon for incidents to occur because the liquid has solidified, the pressure gauge shows no increase in pressure and the load on the system has increased further until it bursts.
Hydraulic oils solidify at 20 ° C at approx. 3000 bar, water at 20 ° C at approx. 7500 bar. In the case of narrow cross-sections, solidification begins considerably earlier than in the case of larger cross-sections.
You can obtain fluids suitable for high pressures from us.
5.2 Constellation test
If you have received components that are subject to acceptance and have been approved by an expert and these have been set up, an expert must carry out the installation test in accordance with DIN EN 13445. Only then may your system be operated for the permitted period.
5.3 Temperature monitoring
In the case of heatable systems, any subsequent pressure increase due to the greater expansion of the temperature-controlled fluid must be taken into account. A removed temperature limiting device must ensure that the intended operating temperature is maintained.
6 Service work
6.1 Procedure
As soon as service work is carried out on a system or device, the system must be switched off and the pressure released.
Check that all pressure gauges are not showing any pressure.
The drain valve must be open.
If the system is operating at an elevated temperature, wait until a normal temperature is reached.
Depending on the type of activity, the compressed air, the electrical voltage or the high-pressure connection should be disconnected.
6.2 High pressure screw connections
Do not loosen any high pressure screw connection that is under pressure.
Do not attempt to tighten a leaking high pressure fitting that is under pressure!
You can destroy the component in this case, as the mechanical load of your tightening torque is added to the pressure load.
Only use components that are designed for the operating pressure.
Use a suitable lubricant when assembling all high pressure fittings.
6.3 Leaks
All leaks must be repaired immediately. A permanent leak can be very dangerous. It is therefore forbidden for our personnel to pressurize a system if there is a leak.
Turn off the system, depressurise and repair the leak.
6.4 General safety information
Only repair components for which you have a usable and proper operating manual.
Do not try to make spare parts yourself.
Check whether your system still complies with the applicable safety regulations.
The recurring tests in accordance with the manufacturer’s information and the pressure equipment directive must be observed.
Call us in case of doubt!