DIN Standards Committee Water Practice
DIN 19901
Installations for separation for light liquids and greases - Verification of structural stability and steadiness
Abscheideranlagen für Leichtflüssigkeiten und Fette - Nachweis der Tragfähigkeit und Gebrauchstauglichkeit
Overview
Different conceptions exist in the member states regarding static testing of installations for separation of light liquids according to DIN EN 858-1 and DIN 1999-100 and of greases according to DIN EN 1825-1 and DIN 4040-100. Due to the lack of uniform European specifications for static verifications, they were represented by references to national regulations in the first generation of harmonized European standards for separator systems. For the purposes of the Construction Products Regulation, the mandates given to CEN by the European Commission and the European Free Trade Association will be modified according to the new conditions. It is currently not clear in which time frame and to what extent the affected harmonized European standards for construction products - meaning separator systems as well - need to be revised as a consequence. In any case statements will then need to be given on static verifications for these systems; reference to national regulations will no longer be permitted. Germany has now dealt with this task since so far the European partners have shown no interest which is also due to the lack of European regulations within CEN/TC 165/WG 8 "Separators". A subcommittee formed within the structure of Working Committee NA 119-05-05 AA "Abscheider" ("Separators") and exclusively appointed for this task in which the available expertise could be pooled had ventured into this new territory in the field of wastewater engineering. During very intensive work in the past it was possible to complete the standard on this topic. It is of course required to supplement the European standards for separator systems accordingly with the specifications stipulated in the standard, taking into account the requirements from the series DIN EN 1990. Future consultations of CEN/TC 65/WG 8 will reveal whether and how this German venture will be used in European standardization. It was intended to prepare this standard to align the still different methods available in the market for statistical interpretation of separator systems and to establish a uniform basis for static calculations. It takes into account different materials, shapes of containers and installation types of separator systems and will allow comparison of the various combinations. This standard will supplement the statements made in the European and national standards on verification of structural stability and steadiness of installations for separation of light liquids and greases. From a procedural point of view a separator system can consist of several structures. Every individual structure can thus be considered in a statically separate manner provided it does not act structurally and statically as a unit with other structures. The explanation of the term "structure" seemed therefore necessary. Due to the necessary set of formulae all symbols and abbreviations were explained. The installation situation of structures for separator systems determines the classification into various installation types. Every installation type is determined by the influences prevailing in this situation. This leads to design loads which shall be taken into account in static calculations under consideration of the intended installation conditions and conditions of use. Basically, distinction is made between above ground and buried systems. Depending on the installation type considered, the structure is subjected to specific influences. Constant influences include dead load, soil pressure, external and internal water pressures and buoyancy. Fluctuating influences include live loads, temperature, transport influences, installation, maintenance and leak testing, media influences, wind, snow and ice loads and UV-radiation. Every one of these influences is described as detailed as possible with respect to verification. It was clear to all parties involved from the very beginning that this is the problem area of theory versus practice and that it will be necessary to establish conventions for specific boundary conditions, even though clear and transparent regulations exist, in order to minimize the scope of interpretation as much as possible. Regarding material parameters the situation was exacerbated by the fact that at least in Germany there is a lack of experience concerning the use of particular materials, for example GRP. Structural stability and steadiness are calculated from the combination of the influences on installation conditions and material specifications. The ultimate limit states are determined by means of verification against structural failure due to breakage, stability failure and material fatigue. Partial safety factors were assigned to various influences for various installation types. Verification itself was provided depending on the relevant material. The limit state of stability is determined by verification of safety against buoyancy using restraining dead loads as well as against flooding. In this process, distinction is made between the consideration of exclusive effects of structural dead load and constant load and the influence of gravity. The connection to the requirements specified in the standards for separator systems is established during the evaluation of steadiness. This case concerns in particular such material-related requirements like reliability, deformation, water tightness and crack width. Particular importance is attributed to the static calculation report. It shall be complete, thorough, legible and clearly structured; assessment and testing by a third party shall be ensured. It was not the intention of the committee's work to establish new rules, but rather to adapt existing rules for separator systems. The committee's view is that this standard can also be applied to comparable wastewater systems, for example starch separators, sedimentation systems, abstraction basins and pump shafts under consideration of the special operating conditions.
