Bursting Discs, Burst Indication, Static Mixers, Heat Exchanger.

Bubble size – The bubble size of a gas to be dissolved in a liquid affects the solubility of the same. The gas exchange area increases with decreasing bubble size which, in turn, increases the potential of dissolving a gas in liquid.

With the solution of gases in liquids, the term ‘solubility’ designates a coefficient indicating the amount of gas dissolved in the liquid in diffusion balance with the gas space in relation to the gas pressure. We differentiate between the ‘qualitative solubility’ (does the material dissolve in a certain solvent in a detectable quantity?) and the ‘quantitative solubility’ (which amount of substance can be dissolved in the unit volume of a particular solvent?).

With regard to the dissolution of gases in liquids (processing of drinking water, carbonisation of all types of beverages, etc.) STRIKO strives to realize the optimal dissolution of a gas in a liquid by using appropriate mixing elements, properly dimensioned mixing tubes and optimal dosing devices. This depends, in addition to the bubble size which should be in the µm range, also on the parameters of pressure and temperature and on the media themselves.

Burst tolerance – The burst tolerance refers to the range in which a bursting disc is allowed to react in deviation from the nominal bursting pressure. This is +/- 10 % as standard. A reduction for STRIKO bursting discs is possible if the interplay of diverse process parameters (nominal size, bursting pressure, temperature, etc.) permits this.

Bursting disc – A bursting disc unit is a pressure relief device which is typically made up of a bursting disc and a bursting disc holder. The bursting disc is designed to be pressure loaded and reacts to pressure increases. With our wide product range of metal or non-metal, corrosion-resistant materials we cover a comprehensive range of nominal sizes, bursting pressures and temperatures.

Bursting pressure – Differential pressure between inlet and outlet side of the bursting disc at which the bursting disc opens and frees the flow cross section. The bursting pressure is always subject to a bursting tolerance which is specified on the label of the disc. The bursting pressure is affected by the back pressure prevailing on the outlet side, a fact which has imperatively to be considered when when analyzing the disc’s location.

Bursting temperature – The bursting temperature is the temperature assigned to a bursting pressure corresponding to the expected temperature of the bursting disc at the time of reaction. It is important for designing the bursting disc as the bursting pressure (above all of metallic bursting discs) is heavily dependent on the temperature. In principle, the bursting pressure decreases as the temperature increases – and increases as the temperature drops, – a fact which may pose a corresponding safety risk for the system. For this reason, STRIKO always enquires about the prevailing parameters on the bursting disc at the expected time of reaction.

Composite bursting disc – Multilayer (stainless steel / PTFE / stainless steel) built up metal bursting disc for direct installation between flanges (without bursting disc holder). Composite bursting discs are mainly flat bursting discs used for low to medium / static pressures. Depending on the design, composite bursting discs can be vacuum-resistant or may safeguard different degrees of high pressures in excess and low pressure directions. As a supplement, flat composite bursting discs can be fitted with inductive burst monitoring.

Concave bursting disc – Forward acting, arched bursting disc with the pressure being directed against the concave side

Convex bursting disc – Pressure-loaded, arched bursting disc (also known as “reverse acting rupture disc”) with the pressure being directed against the convex side

Cross-sectional area – See opening cross-section

Design code – The design code refers to the design standard of pressure equipment. The pressure equipment from STRIKO process technology are manufactured in accordance with the applicable regulations and provisions. In Europe, these are the pressure equipment directive PED, German abbreviation DGRL 2014/68/EU with the policies AD 2000 and EN 13445 and in America and Asia the ASME Boiler and Pressure Vessel Code. The AD 2000 policy currently is the most frequently requested policy. With the introduction of the harmonised norm EN 13445 it will be found more and more frequently as it is intended to be the successor to the AD 2000. The ASME code can be divided into two categories: ASME Section VIII Division 1 for pressure vessels and ASME B31.3 for piping.

Design data – In the field of technology, this term refers to the preliminary information required in order to be able to build or design equipment or components in such a manner that they ultimately fulfil their specified purpose. Design data can refer to all aspects of the draft, design, manufacturing, operation or deployment. For the design of STRIKO bursting discs, data for instance such as the installation location, the medium to be protected, the working, burst and back pressure, the work temperature on the bursting disc or the type of load situation all play a role. For static mixers made by STRIKO on the other hand, parameters such as the medium applied, the fluid group, the steam pressure, volume flow, density and dynamic viscosity are just some of the design data initially required from the customer in order to be able to design the right type of mixer for the respective application. It is only after decisions about the layout, the materials to be used and the design have been made that geometrical quantities are defined as part of the calculations or the dimensioning.

Design pressure – The pressure equipment directive (PED, German abbreviation DGRL) classifies pressure equipment into various categories depending on the pressure equipment volume V respectively the nominal size DN for piping and the maximum permissible pressure PS. Here, the maximum permissible operating pressure PS according to art. 1 para. 2 no. 2.3 PED (resp. German DGRL) is defined as “the highest pressure specified by the manufacturer for which the pressure equipment is designed”. As a manufacturer of pressure equipment STRIKO process technology is also obligated to specify the design pressure of its pressure equipment on the nameplate.

Design standard – STRIKO process technology provides new and existing customers with special forms for inquiry specification in which the customer, alongside the general information, also specifies the design data and the design standard for the STRIKO product requested. The design standards the client can choose from include the pressure equipment directive (PED, German abbreviation DGRL, AD 2000), a certification in accordance with the ASME Code (leading technical guideline for the construction, manufacturing and testing of pressure equipment and pressure-bearing components of the ‘American Society of Mechanical Engineers’) or others as for instance DIN EN 13445.

Documentation, technical – A technical documentation, structured logically and clearly, includes all documents describing a technical product. It is also referred to as product documentation. All relevant information is included here systematically and clearly allocated to the documented product usually using name and number systems. The objectives of a technical documentation among other things are to provide information and instructions to a defined target group but also to protect the liability of the manufacturer. It usually draws attention to all aspects of the product from the development right up to its disposal. Technical documentations use a product-specific nomenclature and often a highly specialised vocabulary. For all STRIKO pressure equipment a technical documentation is compiled. It consists of the declaration of conformity, the technical drawing, material certificates and operating instructions, along with any relevant inspection and test certificates.

Final acceptance – Is carried out before delivery to the customer depending on the classification of the pressure equipment. Here, pressure equipment is to be subjected to the acceptance process as described below.

a) Final inspection
Pressure equipment must be subjected to a final inspection, where a visual inspection and test of the related documentation is to be carried out in order to check that the requirements of this guideline are fulfilled. In doing so, inspections carried out during manufacturing may be taken into account. If required for safety reasons, the final inspection of the inside and outside of all parts of the equipment must be carried out during the manufacturing process (e.g. if testing during final inspection is no longer possible).

b) Pressure test
The acceptance of the pressure equipment must also include a pressure strength test which is normally carried out in terms of a hydrostatic pressure test where the pressure for this is clearly specified.  For equipment of the category I manufactured in series this inspection can be carried out on a statistical basis. If the hydrostatic pressure test is disadvantageous or infeasible, other tests can be carried out which have proven effective. For tests other than the hydrostatic pressure test, additional measures such as non-destructive tests and other equivalent procedures must be used first.

c) Testing safety equipment
For components, the acceptance must also comprise a test of the equipment parts with a safety function, whereby it must be tested that the requirements have been fully satisfied.

Flow cross-section – When reacting, a bursting disc frees a cross-sectional area for discharging the medium. The required free cross-section partly depends on the medium, the particular construction of the bursting disc, the bursting pressure, the temperature and the volume to be discharged and is determined on an individual basis for each specific application. Considering all these parameters, the minimum nominal size of the bursting device can be determined for each single application.

Flow rate – The flow rate (or flow velocity) is a physical size and defines the speed in a flow, in a directed movement of particles or in continuous bodies (liquids).
Flow velocity=(Volume flow )/(Area of pipe cross-section)

The flow rates of the individual particles are differentiated from the medium flow rate using a vector line element, a surface element, a volume element or a time interval. The flow rate is the spatial change of a single point along its trajectory. Medium flow rates can be determined for instance via the flow cross-section, the flow rate or a flow line. In literature, the flow rate is specified in a variety of ways. It is known under the symbols ω (small Omega), ν and c.
Alongside the viscosity the flow rate is an important factor influencing pressure loss and thus flows into the calculations for static mixers and heat exchangers.

Forward acting rupture disc – Bursting discs are pressure relief devices protecting a vessel or a system from damaging high or low pressure by making a disposable membrane burst. Bursting discs consequently act as a type of predetermined breaking point. STRIKO process technology disposes of a comprehensive range of bursting discs and differentiates for instance between forward acting and reverse acting rupture discs. STRIKO forward acting rupture discs are aligned with the concave side to the process medium, i.e. the bulge of the bursting disc points away from the process. If the process pressure exceeds the permitted operating pressure the tensile strength of the material is reached; the disc bursts. In the production of forward acting rupture discs, STRIKO process technology also uses ultra-modern, laser-based production technology. Forward acting rupture discs made of metal of the STRIKO series SZ-X are installed in the standard holder SHZ or in the pre-loaded holder SHZ Pro between flanges. They are particularly suitable for safeguarding medium to high working pressures, can be used as sole pressure safety protection or in combination with a safety valve, dispose of a fragment-free opening behaviour, are suitable for gases, steams and liquids and are available in various materials such as high-grade steels, nickels and special materials such as Hastelloy® or Tantal. Alongside a multitude of design options the forward acting rupture discs made by STRIKO can also be combined with an optional burst indicator installed on the discharge side.

Fouling – Refers to general contaminants / impurities. In relation to the heat exchanger, fouling may occur in the jacket area (heating medium) and in the product tubing. Particularly when tempering viscous media (e.g. cooling silicon), fouling may occur as the dynamic viscosity (flowability) of the medium to be tempered increases exponentially as the temperature drops. Fouling inside the product tubing of heat exchangers can be counteracted by using the patented STRIKO S-Helical technology. Fouling reduces the heat transfer and in turn the efficiency of heat exchangers.

Fragmentation – The term fragmentation refers to the area characteristic of a bursting disc upon reaching the burst pressure. Depending on various factors, bursting discs may open with or without fragmentation. Due to the material, STRIKO graphite bursting discs e.g. always open with fragmentation. For multilayer STRIKO metal bursting discs, the area characteristic depends on the pressure and temperature at which the discs are used.

Gas cushion (with reverse acting rupture discs) – When using reverse acting rupture discs it must be ensured that there is always a gas cushion between the bursting disc and the medium to be secured. Gases are compressible when pressurised whereby they store a certain energy. This energy is required in order to ensure a perfect opening of the bursting disc. Reverse acting rupture discs are torn open by the impulse generated when the burst membrane turns. The energy of the impulse is taken from the compressed gas. For pure liquid applications this results in the burst membrane being turned (or deformed); however, this does not ensure opening. If the burst membrane of a reverse acting rupture disc turns but does not open the bursting pressure of this (damaged) reverse acting rupture disc will increase significantly. As a consequence, the safety function of the bursting disc device is definitively no longer available. Therefore it must be accurately checked during each single installation whether there is a gas cushion – or not.

Gas exchange area – Gas exchange is a physical process whereby gases (sometimes separated by a permeable membrane, sometimes by openings or pores) are spatially redistributed between two compartments, ideally until the same concentration is everywhere. Gas exchange is also referred to for gases which are physically dissolved in liquids. As large a membrane surface as possible favours gas exchange. For static mixers from STRIKO process technology this means that the bubble size of gases has a not insignificant influence on the solubility in liquids. The bubble size of a gas to be dissolved in a liquid affects the solubility of the same. The gas exchange area increases with decreasing bubble size which, in turn, increases the potential of dissolving a gas in a liquid.

Goodness of mixture – The goodness of mixture is a measure of the homogeneity or uniformity of a mix and is calculated from statistic base items. The coefficient of variation is the most commonly used measure. The closer this value approximates 0 the more uniform the mix. For visualisation, it is subtracted from 1 and specified in percent. Thus, 100 percent goodness of mixture (or coefficient of variation = 0) refers to the best goodness of mixture possible which, however, is practically not achievable.

The theory
From a mathematical perspective, the coefficient of variation is the quotient from the standard deviation of the chemical composition of samples from the mixing chamber, the arithmetic mean of the samples. With static mixers, the mixing chamber is the cross-section of the mixing tube with an infinitesimally small length. The value can thus be interpreted through the mixer cross-section as relative error of the target composition. At a goodness of mixture of 95 percent (coefficient of variation = 0.05; often referred to as technical homogeneity) – as known from stochastics – approximately 68 percent of all samples would lie in a range of +/- 5 percent of the target composition. Already 96 percent would lie in the range of +/- 10 percent. This is generally applicable for all normally distributed random experiments.

The chief task in designing a static mixer appropriate for the requirements consists in determining the number of mixing elements of a particular type that must be arranged in sequence to achieve the desired goodness of mixture at an acceptable pressure loss. The goodness of mixture to be aimed at for a particular application may greatly vary. Only a few elements are often already sufficient to reach a very good homogeneity for simple mixing applications where, for example, low-viscosity components, such as water, readily dissolve. Other scenarios require 20 or more elements to achieve acceptable results.

Graphite bursting disc – The advantages of bursting discs made of graphite are their high resistance to corrosion, a good price-performance ratio and an easy assembly. Furthermore, they are available from stock in the common nominal sizes and burst pressures. STRIKO safety bursting discs of the G2 and LPG2 (LP = low pressure) ranges are flat graphite bursting discs for low to medium reaction pressures. The G3A range which is also fitted directly between the flanges is made up of a graphite bursting disc integrated into a steel ring made of stainless steel. The steel ring absorbs increased axial forces during fitting which may occur due to misalignment of the flanges. A special holder is not required. STRIKO graphite bursting discs always open with fragmentation.

Heat capacity – The relationship between the heat supplied to a body and the temperature rise resulting thereof is called the heat capacity C of the body:

C = d Q / d T

The unit of the heat capacity is J/K.

The specific heat capacity c [J/m*K; J/m²*K; J/kg*K; …], often abbreviated to specific heat or also inaccurately referred to as heat capacity, is a thermodynamic chemical property. It measures the capacity of a material to store thermal energy.

To design a heat exchanger, the specific heat capacities both of the medium to be tempered and the tempering medium is of decisive importance as this allows, amongst others, to calculate the corresponding volume flows.

Heat exchanger – The transfer of thermal energy from one material flow to another takes place in a suitable appliance, the heat exchanger.

STRIKO heat exchangers are specially designed to temper viscous to highly viscous media – reliably and smoothly up to a viscosity range of 500,000 mPas. This is made possible thanks to the S-Helical technology patented by STRIKO, by means of which the medium to be tempered is kept in constant motion and rearranged from the centre of the tube to the tube wall and back, a procedure which prevents fouling and improves efficiency.

Holder (inlet and outlet part) – The use of bursting discs in bursting disc holders ensures the reliable functioning of the bursting discs. In the holder, the metallic sealing gasket between the bursting disc and the holder inlet part is established – either by using the screws of the flange connection (standard holder) or by the four high-strength screws integrated into the pre-loaded holder. The holders are usually designed in common high-grade steels like 1.4571 or in special materials like Hastelloy®. For graphite bursting discs, holders made of graphite, special materials or even stainless steel with PTFE-coating are used.

Integrated burst control – In order to reliably detect the reaction (opening) of bursting discs, burst indicators or leakage sensors can be used. These are usually installed between holder outlet part and flange instead of the sealing gasket. With the integrated burst control, the monitoring unit is integrated directly into the bursting disc which reduces the number of individual components whilst increasing the complexity of the bursting disc. Burst control can also be realised by using inductive proximity switches positioned in the holder outlet part which are reacted by a metal vane affixed to the bursting disc.

Leakage sensors – Leakage sensors are used in order to detect the smallest of leaks of bursting discs or safety valves. “Normal” burst indicators only react to the entire opening of bursting discs or safety valves if a large volume flow meets the burst indicator. Leakage sensors, on the other hand, are designed to be “tight”, meaning that even the smallest volume flows lead to bulging and in turn to the leakage sensor being triggered.

Mass flow – The term mass flow defines the fluid loading in kg/h being present in the gaseous phase intended to be separated.

Material – The term material refers in the broadest sense to a substance or a combination of substances out of which a material results. The term material is a synonym of substance. Depending on the product group, a wide range of materials are used at STRIKO. Those worth mentioning here include standard steel, high-grade steel, aluminium, also graphite and special materials such as Monel®, Hastelloy® and plastics such as PP, PE, PTFE and PVDF for STRIKO bursting discs.

Mounting of bursting discs (flanges/holders) – Depending on the individual type of bursting disc it may either be directly inserted between existing flanges on-site or in a corresponding holder provided by STRIKO. STRIKO flat metal bursting discs can be fitted directly between flanges. Arched bursting discs (forward acting or reverse acting rupture discs) however must be fitted in a holder in order to ensure correct functionality. For this, STRIKO offers standard holders (SHF / SHZ / SHU) and preloaded holders (SHF-Pro / SHZ-Pro / SHU-Pro). STRIKO also provides individual solutions for bursting discs with especially small nominal sizes and high pressures. For bursting discs made of graphite it is also possible to insert them directly between flanges (range G3) or in holders (range G2 with holder HG2).

Nominal diameter – Nominal diameter or also DN (derived from French for ‘diamètre nominal’, English: Inside diameter) for ‘passage standard’. The nominal diameter indicates the inner diameter of a tube or the connection dimension of a mounting part. In connection with the nominal pressure level and the material class the nominal diameter determines all dimensions of a tubing. It is often the case that steel is not explicitly referred to as a material but is nevertheless required. It is also important to note that the actual inner diameter and the specified nominal diameter often differ by a few millimetres, for instance because the wall thickness of some steel tubes grows inwards with increasing pressure stage – as a consequence, the free cross-section is reduced. Therefore, tubes from different manufacturers can only be combined with one another without any difficulty if the nominal diameter is specified referring to the same DIN standard. The outer diameter on the other hand – except in case of very thick-walled tubing for very high pressure and for tubing made of glass fibre reinforced plastic – remains constant whereby the same thread can be cut for virtually all tubes of one nominal diameter. Thus it is possible to use the same pipe sleeves, also known as fittings, for all pressure stages. The nominal diameter is introduced in accordance with EN ISO 6708 with the abbreviation DN followed by a dimensionless number roughly corresponding to the inner diameter in millimetres. In accordance with ANSI the nominal diameter is specified in NPS (Nominal Pipe Size) in inches. For STRIKO specifications of the nominal diameter play an essential role when it comes to finding the right product for the customer’s demands. In the area of bursting discs and burst indicators STRIKO process technology usually provides products with nominal diameters between DN 20 and DN 600.

Nondestructive testing – English abbreviation NDT, German abbreviation ZfP, also known as nondestructive examination (NDE). It is a procedure which tests components, materials and constructions before and during their operation for hidden faults and in doing so makes a big contribution towards PREVENTING accidents and catastrophes from happening. Since humans have been able to process materials and workpieces they have been driven by the desire to be able to test them without destroying them, i.e. testing them in a way that they can still be used after having been tested. As early as in primeval times humans have used nondestructive test procedures by critically eyeing manufactured objects, tapping them with their knuckles, feeling surfaces with their fingertips. But this technique only became an important economic factor much later when in the middle of the nineteenth century industry wanted to save material for the first time and simultaneously had to keep in line with the increased safety requirements. At this time, more specialised procedures of practical material inspection were being introduced which were occupied by the term ‘nondestructive material testing’. Nowadays, NDT has become an irreplaceable instrument for quality control and assurance in all branches of industry. Every security relevant part is inspected. In so doing, NDT uses physical measurement techniques – always on the condition that the introduced energy is not allowed to change the material to be tested. The methods applied are diverse in nature: Visual inspections, X-ray and ultra-sound procedures, thermographic heat flow testing procedures, computer tomography, video- and endoscopy, laser radiation, eddy-current test – depending on the particular test one will choose the form of energy which, according to the interaction energy, will result in a signal as high as possible. Being a manufacturer of pressure equipment STRIKO process technology of course satisfies the requirements of the applicable regulations. STRIKO heat exchangers and static mixers, all of them pass through the nondestructive testing according to the selected technical regulation.

Nozzle loads, additional – By additional nozzle loads, the loads or forces are being referred to which can be directed by external circumstances into an appliance or a piping device whose strength they significantly influence. This may be wind, snow or earthquake loads. However, most frequently it is loads which result from subsequent pipes.

Opening behaviour – The opening behaviour of bursting discs varies depending on the type of bursting disk in use. STRIKO bursting discs made of metal, for which the design specifies a defined opening, react fragment-free. Metal rupture discs open in an undefined manner. Parts of the bursting foil may be carried away here. STRIKO bursting discs made of graphite always open with fragmentation due to the material property. When calculating the necessary nominal sizes the opening behaviour directly influences the available flow cross-section of the bursting disc.

Opening cross-section – Describes the free cross-sectional area in mm² which a bursting disc provides after opening for the outlet of the medium to be protected. The required free flow cross-section is calculated in the design phase of a bursting disc depending on the individual application, resulting in the smallest usable nominal size for the specific range of application. (Depending on the pressure, it may be possible that the nominal size selected is greater than the area required, in order to be able to achieve a very low reaction pressure – the lower the reaction pressure, the greater the nominal size –> F=p*A)

Operating cubic metre – A counterpart to the standard cubic metre. The operating cubic metre refers to the volume of operating pressure and operating temperature and is a design parameter for STRIKO when it comes to static mixers and heat exchangers.

Packing specification – The term packing specification is also known as knitted fabric specification. The packing specification is made up of the packing density, the material and the wire diameter. At STRIKO for instance, it is specified in the following form: 9192-ss-0,28. The degree of separation, the diameter of the minimum droplet size, the density and viscosity of the liquids as well as the flow speed, they all have an impact on the specification and the dimensions of the knitted fabric. The decisive variables are the packing density and the wire diameter. Knitted fabrics with high packing density and low wire diameter exhibit a high separation efficiency but have a low flooding point. Via the continuity equation, the surface area of a knitted wire and the prevailing volume flow lead to an optimal surface area cross-section and in turn to an optimal flow speed. This results in the best-suited packing specification and an optimal surface area for each specific application. The height of the knitted fabric has a comparatively small influence both on the separation efficiency and the pressure loss. It serves much more as a reserve, for instance if any remaining solid content is not known or has not been precisely defined.

Pre-loaded holder – STRIKO standard bursting disc holders in intermediate flange design only reach a fixed and dense clamping of the bursting device after tightening the flange screws. This means that after loosening the flange connection also the metallic seal between the bursting disc and the holder is removed. With STRIKO pre-loaded holders PRO for bursting discs of the series SZ and SU however, the required tightening torque for secure and dense installation of the bursting disc is already applied by the high-strength preloading screws when installing the bursting disc into the holder. Thus it is possible during machine downtime to loosen the flange connection and perform a visual inspection, to clean or even carry out the required replacement of the flange seals without the need to insert a new bursting disc. This shortens downtimes following a reaction of a bursting disc by up to 80%. The use of pre-loaded holders is particularly recommended for sensitive steel-enamel / glass and plastic pipes, polymerisation processes, in case of a tendency towards caking, unfavourable installation positions and frequent replacement of bursting discs.

Pressure equipment directive 2014/68/EU – The pressure equipment directive PED (German abbreviation DGRL) is a harmonisation guideline for aligning pressure equipment to the regulations of the EU member states specified by the European Parliament and Council in May 1997 according to article 95 of the EG treaty for the free movement of goods. It regulates the requirements for bringing pressure equipment onto the market within the European economic area and must be put by each and every member state into national legislation. The pressure equipment directive has been binding in the entire European Union since 2002. According to the directive, pressure equipment are to be classified in terms of pressure and volume (for piping in terms of nominal size DN) as well as fluid group and state of aggregation. On June 27th, 2014 the Official Journal of the EU L 189 published a new pressure equipment directive (German abbreviation DGRL). The directive 2014/68/EU replaces the old DGRL 97/23/EG. To a large extent, the fundamentals of the DGRL remain preserved. With regard to the scope and the conformity assessment diagrams there are just a few small changes. Existing certifications retain their validity. With respect to the updates two pieces of information are decisive: Parts of the new DGRL 2014/68/EU have already been effective since June 1st, 2015. Other points have been binding since July 19th, 2016. Since this reference date the use of the old directive is no longer permissible. Updates since June 1st, 2015: a) Alongside manufacturers, importers and distributors, the DGRL now also affects “representatives for manufacturers from third party countries”. b) The danger classification of the operating media takes place in accordance with the new DGRL and therefore the GHS/CLP regulation 1272/2008 and no longer in accordance with directive 67/548/EWG. c) The declaration of conformity must also be carried out in accordance with GHS/CLP regulation 1272/2008. Article 13 (classification of pressure equipment) is decisive. Updates since July 19th, 2016: a) The new directive has been adjusted to the legislative framework (New Legislative Framework – NLF). In front of this backdrop, manufacturers of pressure equipment must check their CE marking procedures and the documentation again after 2015 and adjust them to the new structure of the directive. b) Everyone bringing pressure equipment into circulation in Europe must be able to prove to the market supervisory authorities over a period of ten years from which company he/she has procured which pressure equipment or to whom he/she has supplied it. c) Manufacturers must conduct a risk assessment instead of a hazard analysis. d) New definition of several terms, module descriptions and contents. The detailed updates to the DGRL 2014/68/EU for manufacturers, distributors, representatives and importers as well as new participants, as well as updates to the obligatory documentation requirement can be found at netinform.de in the guide for the new DGRL 2014/68/EU.

Pressure loss – The pressure loss constitutes the pressure differential generated between two defined points through wall friction and internal friction in static mixers, pipes, moulded parts, fittings, etc. With static mixers, these points are the intake and outlet of the mixer. In engineering, a resistance coefficient ζ is used for elements installed in a pipe (mixing elements, valves, baffles, etc.) which can be taken from tables. The pressure loss generated by the wall friction is determined by the friction factor for pipes λ. In case of laminar flow the friction factor for pipes depends on the Reynolds number. The surface roughness plays a role especially with turbulent flows.

The theory
The equation for pressure losses in passed through flows with the prerequisite of a constant density is:

Druckverlust Formel

This is the Bernoulli’s energy equation, whereby the term of the static height is not taken into account because it does not represent a pressure loss.

Design criteria                                                                                                              ρ density in kg/m3
u medium flow velocity in m/s
λ friction factor for pipes
l length of the tubing in meters
d diameter of the tubing in meters
ζ resistance coefficient

Pulsation – Latin for “periodic fluctuation”. In technical systems such as pumps and compressors, as well as in tubes, pulsation is a pressure surge designating the dynamic pressure change of a liquid. Pulsating work pressures, if the wrong type of burst protection is chosen, can lead to premature failure of the bursting disc. This is an ideal application for the STRIKO reverse acting rupture disc as this is the most uncritical disc with respect to pulsating work pressures of medium to high strength.

Removability of the mixing elements – Static mixers from STRIKO guarantee a continuous operation in closed piping systems. They do not contain any moving parts but are fitted with mixing element chains, virtually all of which work wear-free. Mixing elements from STRIKO are also used in heat exchangers. Depending on the area of application various mixing elements are used. All mixer variants from STRIKO are maintenance-free and can be cleaned in-line. Furthermore, the static mixing elements from STRIKO can also be designed so that they are removable in order to be able to clean them better. Depending on the specific design this may require an additional stop ring, the design of which is determined over the course of the drawing release.

Metallic, convex bursting disc, where the pressure to be safeguarded acts against the bulge. Reverse acting rupture discs are fitted in the standard holder SHU or in the pre-loaded holder SHU Pro between flanges. They are particularly suitable for mid- to high-pulsating working pressures.

STRIKO offers the SU-R, SU-C and SU-X model ranges in various high-grade steels and special materials such as Inconel or Hastelloy®. STRIKO reverse acting rupture discs also dispose of a fragment-free area characteristic, they are vacuum-resistant, can be used in combination with safety valves and are typically fitted with a 3D-label.

Reynolds number – A dimensionless figure (symbol: Re) named after the physicist Osborne Reynolds. It is used in fluid mechanics and can be understood as the ratio between inertial and viscous forces. It has been shown that the turbulence characteristics of geometrically similar bodies are identical when the Reynolds number remains constant. This characteristic allows for instance realistic model tests in the wind and water channel.

The Reynolds number is defined by Re = ρ ⋅ v ⋅ d / η = v ⋅ d / ν

Where ρ is the density of the liquid, v the flow velocity of the liquid with respect to the body and d the characteristic length of the body. The characteristic length, also known as reference length, is defined or must be defined for each problem. For flow bodies, the length of the body in the direction of the flow is usually chosen. The kinematic viscosity v of the liquid is differentiated from the dynamic viscosity η = ν ⋅ ρ by the factor ρ.

If the Reynolds number exceeds a (problem-dependent) critical value Re crit, a so far laminar flow becomes prone to even the smallest disturbances. In accordance, for Re > Re crit, a change from laminar to turbulent flow must be calculated.

Shear rate – Shear rate is a term from kinematics. It describes the spatial change of the flow rate in liquids. As there are frictional forces in flowing media, various flow rates at various positions of a liquid also mean that a transmission of energy takes place. The shear rate is used in rheology to define the viscosity. It is the coefficient of proportionality between shear stress and shear velocity. The layered flow in laminary flowing media is observed here. The unit of measurement is s-1. This parameter also plays a big role in the design specification of static mixers as the characteristics of several media may change decisively at high shear rates.

Standard cubic metre – A question which often leads to incorrect calculation results is whether the volumes specified by the customer are standard or operating cubic metres.

The standard volume (particularly standard cubic metres, standard litres, etc.) is a volume unit common in pneumatic, process engineering and gas technology. It is used to compare gas volumes which are present in different pressures and temperatures (operating condition, operating volume). To do this, the gas volumes are converted to the respective standard condition, for instance by using the conversion factor.

As early as 1940, the following standard conditions were defined in DIN 1343 and have become established across the globe under the term “physical standard state”:

– standard pressure pn = 1013.25 hPa = 1.01325 bar
– standard temperature Tn = 273.15 K = 0 °C

The operating cubic metre describes the gas volume which is present under the actually prevailing operating conditions (operating pressure and operating temperature). Under operating conditions, important parameters like density and dynamic viscosity which have to be closely examinated, do change.

Static mixers – Static mixers from STRIKO guarantee continuous operation in closed piping systems. They do not have any movable parts and so are virtually wear-free. All mixer variants from STRIKO are maintenance-free, can be cleaned in-line, sterilised/steamed and slightly detached if required.

Sterile bursting discs – STRIKO sterile bursting discs made of metal are outstanding particularly due to their unique, minimal dead space design on the side in contact with the product – a feature customers from the pharmaceutical or food industry attach great importance to. Sterile bursting discs are usually inserted in Tri-Clamp®-connections. All available versions of sterile discs guarantee a fragment-free opening which is especially important for these types of applications. STRIKO sterile bursting discs are ideal for safeguarding gases, liquids or two-phase flows as well as media tending towards caking. STRIKO sterile bursting discs are available in a multitude of different designs, be it vacuum proof or with integrated burst indication, made of standard or special materials.

Surface roughness – Surface roughness is a term from surface physics and refers to the unevenness of the surface height. The quantitative characterisation of roughness can be determined by means of various calculation methods which take into account the specific properties of the surfaces. The surface roughness can for instance be changed by means of polishing, grinding, lapping, honing, pickling, sand blasting, bristle blasting, etching, vaporising or corrosion.

Temperature influence – The burst pressure of metal bursting discs is influenced by the prevailing temperature at the bursting disc when reacting. With increasing temperature the strength of the metallic material decreases which leads to a lower response pressure of the bursting disc. This will pose no problem with regard to the safety requirements as the bursting disc opens below the pressure critical for the facility to be protected. If, however, a bursting disc is designed for a higher temperature than the one actually prevailing at the bursting disc in operation, the bursting disc will react at a higher pressure than intended. The temperature influence depends on the material used but may range up to 18 per cent of the bursting pressure when deviating by 100 K from the design temperature, depending on the material and the type of bursting disc. This is why the correct temperature at which the bursting disc reacts is that crucial. For bursting discs made of graphite the influence is considerably smaller, if not completely negligible. Therefore graphite bursting discs are an excellent alternative to metal bursting discs whenever the temperature at which the bursting disc reacts cannot be foreseen.

Thermal conductivity – The thermal conductivity, also referred to as thermal conduction coefficient, relates to solid bodies, liquids or gases and is a material property for calculating the heat flow due to the heat conduction. Specified in the unit W/(m*K), designating the thermal conduction coefficient is essential in order to be able to perform the thermal design of a STRIKO heat exchanger.

Vacuum-soldered mixing elements
The manufacturing process of static mixers with gapless soldered mixing elements has been tested and developed over a period of several years. It starts by producing a special tube for the corresponding inner diameter. The mixing elements to be soldered are furnished with a longitudinal slot on the side where the solder is subsequently introduced. After this, the mixing element chain is inserted into the tube which is subsequently warmed up in the vacuum oven in specified temperature levels to over 1000°C. This is the melting phase. The solder is diffused during this process into the tube material and into the elements – a crystal transition takes place. In the crystallisation and maturing phase the gapless connection between mixing element and tube interior is created.

Each year, several hundred pieces of these gapless mixing tubes are integrated for instance into tube bundle heat exchangers in order to significantly improve the heat transfer and avoid caking. Other applications can be found for instance where dead spaces have to be avoided. This is a frequent demand in the pharmaceutical industry. For processes which generate large axial forces due to the product characteristics (very high viscosity), soldered mixing elements are also frequently used as this enables the forces to be fully delivered to the tube.

Gap clearance
By using measurement technology (e.g. X-ray, ultrasound) it is not yet possible to prove gap clearance. During specified test procedures the elements case confusing shadows, thus no definitive statement is possible. Up until now, only a visual assessment of the components has been possible.

Viscosity – The term viscosity relates back to the typically viscous juice from berries in the botanical systematics of mistletoes (viscum spp.) from which birdlime was gained. Viscosity is a physical value and gives information about the siziness of a liquid. Its reciprocal value is fluidity, measuring the flowability of a liquid. The larger the viscosity, the more viscous or the less fluid the medium is. We differentiate between dynamic and kinematic viscosity. Dynamic or absolute viscosity is measured in Pa.s or mPa.s and is usually determined with the aid of a rotation viscometer. The dynamic viscosity of most liquids reduces as the temperature increases. The kinematic viscosity is specified in m2/sec. It is the measurement for the internal friction of a liquid and describes the resistance of liquids against shear stress. Here, the term shear viscosity is used as opposed to bulk viscosity which results for instance from a consistent pressure to liquids. Kinematic viscosity can be calculated by dividing the dynamic viscosity by the density of a liquid. STRIKO process technology requires specifications on viscosity from its customers if for instance it is about choosing the right type of mixer in the static mixer product range for a special application. The more precisely the existing process parameters are known the more effectively a static mixer can be designed and produced.

Volume flow rate – The volume flow rate, less precisely referred to as flow rate, is a physical value from the field of fluid mechanics which indicates how much volume of a medium is transported through a defined cross-section in a defined time frame. For STRIKO it is an important parameter for designing heat exchangers and static mixers.

Work ratio – Ratio of working pressure (of a bursting disc) to bursting pressure (of a bursting disc) expressed as a percentage. The work ratio depends both on the material and on the construction of the bursting disc and ranges between 50 and 90 percent.

Working pressure (maximum) – Maximum pressure at which the bursting disc reaches its longest durability. The working pressure is calculated by multiplying the minimum bursting pressure by the work ratio. In case the maximum work pressure is exceeded, the bursting disc may suffer initial damages which can lead to a premature reacting / opening of the bursting disc.

X-shaped notched bursting disc – Bursting discs where the metallic bursting membrane has an X-shaped (crosswise) notch acting as the definition of the burst protection and as an opening aid. STRIKO has forward acting bursting discs (SZ-X) and reverse acting bursting discs (SU-X) with X-shaped notches as part of their range. These can be selected accordingly as required.