Pressure-shock-resistant construction
Definition
Pressure-shock-resistant design is a form of structural explosion protection for apparatus and vessels, in particular for mixers in which powders or hybrid mixtures are processed. A vessel is considered pressure-shock-resistant if it is designed to withstand the pressure shock generated by an internal explosion up to a specified maximum explosion overpressure without rupturing. Permanent deformation is permissible provided that the tightness and mechanical integrity of the vessel are maintained and no flames or explosive gases escape uncontrollably to the outside.
Typically, the apparatus is designed for a reduced explosion overpressure (pred) of approximately 0.5 to 10 bar – depending on the product, explosion parameters and the overall protection concept, for example in combination with pressure relief or explosion suppression.
Distinction from related designs
Design Description Condition after explosion
Pressure-resistant withstands the explosion pressure without permanent deformation fully functional, no deformation
Pressure-shock-resistant withstands the defined pressure shock; minor permanent deformation permitted, tearing not permitted functional, visible deformations may occur
Pressure-relief: pressure is controlled and vented via predetermined failure points such as burst discs or flaps; the load-bearing structure remains intact, the pressure-relief device must be replaced
The pressure-shock-resistant design is often combined with pressure-relief or explosion-suppression measures to reduce the peak pressure (pred) and limit the load on the structure.
Key features in mixing technology
Design pressure
Design of the mixing vessel to withstand the defined reduced explosion overpressure, typically 0.5 to 10 bar, in accordance with the determined substance data and the selected explosion protection concept.
Reinforced vessel geometry
Increased wall thicknesses and pressure-shock-resistant base and lid shapes, such as conical or Klöpper bases, to safely absorb local stress peaks.
Material selection
Use of tough, high-quality steels – typically stainless steels such as 1.4301, 1.4404 or 1.4571 – with defined strength and toughness properties, so that the explosion energy is absorbed primarily through plastic deformation rather than brittle fracture.
Specialised sealing systems
Shock-resistant shaft and casing seals, such as O-rings or inflatable seals, which prevent leaks even during an explosion and ensure the casing remains airtight.
Robust closure and connection mechanisms
Inspection and maintenance openings with reinforced locking mechanisms. All pipe connections, inlets and outlets, as well as shaft entries, are designed to be pressure-shock-resistant to prevent them from bursting open or being torn off in the event of an explosion.
Design and manufacture in accordance with standards
Designed in accordance with the relevant European and national directives and standards, in particular:
- DIN EN 14460 for the explosion resistance of equipment
- Directive 2014/34/EU for equipment manufacturers and the operator’s obligations under Directive 1999/92/EC
- Qualified weld execution in accordance with EN ISO 3834, as well as associated strength and material certificates
Certified equipment and documentation
The pressure-shock-resistant design is frequently combined with explosion-decoupling devices in the inlet and outlet lines, such as non-return valves or fire-extinguishing agent barriers. The scope of supply typically includes:
- Strength and stability analyses
- Material certificates, for example 3.1 in accordance with EN 10204
- Declaration of conformity and ATEX-relevant documentation
Explosion protection in mixers
Mixers frequently process combustible dusts, which can create an explosive atmosphere in the mixing chamber – typically Zone 20. Typical areas of application are:
- Food industry: milk powder, starch, sugar, cereal flours, cocoa
- Chemical industry: plastic granules, pigments, organic fine chemicals
- Pharmaceutical industry: active ingredients, lactose, cellulose derivatives
- Battery and metal powder industry: Aluminium, magnesium, graphite and other metal powders
- Construction and minerals industry: Dry mortar with combustible aggregates
The pressure-resistant design is particularly suitable where conventional pressure relief to the outside is structurally impossible or only possible to a limited extent, for example in multi-storey buildings, for indoor installation or in cleanrooms.
It is also the method of choice when flammable liquids, solvents or vapours are introduced into the process. In such hybrid mixtures, the minimum ignition energy decreases significantly, whilst the rate of pressure rise and maximum explosion pressure increase. The design pressure must then be determined on the basis of the characteristic values of the hybrid mixture, not on the basis of the dust characteristic values alone.
Specific advantages for mixers
Due to their design – often conical or cylindrical with a top-mounted drive – mixers have a drive and bearing area separated from the product chamber. In a pressure-shock-resistant design, this results in the following advantages:
Protection of people and the environment
In the event of an explosion, the plant remains sealed. This prevents flying debris and flames from escaping into the production area, whilst burning particles remain within the mixing chamber.
Protection of critical raw materials and processes
Suitable for the safe processing of explosive powders and hybrid mixtures without compromising product quality through additional safety measures in the process.
High plant availability
Unlike non-shock-resistant units, which are often destroyed in an explosion, a shock-resistant mixer can usually be returned to service after the event – depending on the extent of the deformation – following a visual inspection, the replacement of any seals and pressure relief devices where necessary, and a technical check.
Integration into explosion protection concepts
As the explosion risk remains contained within the mixing vessel, a more compact installation is often possible. Safety distances are reduced, the layout is simplified, and long pressure relief lines leading to the outside are not required.
Legal certainty and insurability
Design in accordance with the ATEX directives and the relevant standards facilitates compliance with statutory operator obligations and can have a positive impact on risk assessment and classification for property insurance.
Summary for practical application
The pressure-shock-resistant design is a technically sophisticated yet particularly reliable solution for controlling internal dust explosions in mixers and other powder-handling equipment. It combines:
- structural explosion protection through pressure-shock-resistant vessels and components
- high operational safety for personnel and buildings
- economic benefits through reduced damage and rapid return to service
- planning flexibility in plant layout, particularly indoors