GROWTH – DEDICATED CALL – 7/99
TOPIC I.11
Design of GRP flanges and associated test(s) for verification purposes
This topic of this is directly related to the R & D activity Methodologies in support of European standardisation (R & D) under the Competitive and Sustainable Growth Programme (1.1.3). It falls under the generic activity 1.1.3-6 Measurement and Testing. Specifically, it is related to that part of the Objective 1.1.3-6.2 Methodologies for Measurement and Testing for which expressions of interest have been called.
Design, glass-reinforced plastic, flange, test, verification, quality control
It is estimated that the European flange market is worth 25 million Euro per year and there are several hundred thousand composite flanges in operation. In contrast to the fervent provision of specifications for pipes under the Construction Products Directive (CPD; 89/106/EEC) and the Pressure Equipment Directive (PED; 97/23/EEC) there exists no national or European standards for the design and adjudged performance requirements for flanged joints. Typically, the issue of flange performance is treated naively in the pipe system standards preferring to make the assumption that the flanged joint will be manufactured with a "strength equal to that of the pipes". Whether this occurs in practice is open to question since there are no product performance or material tests for flanges given in the pipe system standard to verify their capability.
It is expected as a result of the research programme that an increase in the reliability of flanged joints will contribute to a significant reduction in the number of process shutdowns for maintenance or repairs. In the case of the chemical industry, which handles dangerous and environmentally hazardous products, there will be an increase in the safety of the operating system and a reduction in the incidence of system failures and leakage resulting in environmental pollution. The benefits of the work will be farther reaching than the industries it will serve.
The results of this research will provide information and advice on the use of materials, laminate construction and design of flanges for specific product performance requirements. The work will also provide product performance tests and acceptability criteria for quality control and type tests for inclusion in the pipe system standards.
Realizing the lack of acceptable standards for GRP piping systems CEN/TC 155 "Plastics Piping Systems and Ducting Systems" set up in 1989 its working group WG 14 "GRP Piping Systems" giving it the responsibility for drafting standards in the fields of water supply, sewerage and industrial applications.
CEN/TC 155/WG 14 started their work in 1990 and priority has been given to draft three pipe system standards for water supply and sewerage. The standards on sewerage are already at formal vote stage even though do not refer to flange design or specify product testing for these components. At the time of drafting, there was very little appropriate documentation/information on flange design and performance characteristics.
The pipe system standard for industrial applications are currently being drafted and it is hoped that the results of this research programme can be incorporated. Additionally, it is intended that at the first revision stage (5 years hence) the findings of the research programme will also be incorporated into the water and sewerage system standards.
CEN/TC 74 was given the task to draft design rules for flanges made from various materials including those made from thermosetting resins. As there was little expertise with respect to thermosetting materials in the Technical Committee contact was made with CEN/TC 155/WG 14 for assistance. CEN/TC 74 and WG 14 agreed that the latter shall take over the task to draft design rules for GRP flanges bearing in mind the mating dimensions provided by TC 74.
CEN/TC 155/WG 14 accepted the work and formed a task group, TG 4 in November 1991. However, it was very quickly realised that the available information in this area was very limited and there was a lack of performance and design data. To this end, it was felt a research programme was needed to investigate the influence of material properties and anisotropy effects on flange design, with the results forming the basis of a design code for GRP flanges.
A list of the standards prepared by CEN/TC 155/WG 14 and to be used in the prosecution of this work are as follows:
System Standards:
prEN 1115 Plastics piping systems for underground drainage and sewerage under pressure - Glass-reinforced thermosetting plastics (GRP) based on unsaturated polyester resin (UP) - 7 Parts
prEN 1636 Plastics piping systems for non-pressure drainage and sewerage - Glass-reinforced thermosetting plastics (GRP) based on unsaturated polyester resin (UP) - 7 Parts
prEN 1796 Plastics piping systems for water supply - Glass-reinforced thermosetting plastics (GRP) based on polyester resin (UP) - 3 Parts
155wi032 Plastics piping systems for industrial applications - Glass-reinforced thermosetting plastics (GRP) based on unsaturated polyester resin (UP) - Above and below ground assembled from standard components - 7 Parts
155wi179 Plastics piping systems for industrial applications - Glass-reinforced thermosetting plastics (GRP) based on various types of resin - Above and below ground assembled from custom made components - 7 Parts
Test Standards:
EN 705 Plastics piping systems - Glass-reinforced thermosetting plastics (GRP) pipes and fittings - Methods for regression analyses and their use
155wi203 Plastics piping systems - Glass-reinforced thermosetting plastics (GRP) loose flanges - Determination of the mechanical strength
155wi206 Plastics piping systems - Glass-reinforced thermosetting plastics (GRP) flanges - Test method to verify the design
At the present time, manufacturers are not at liberty to modify the structural design code for metal flanges to suit the needs of flanges manufactured from composite materials. Although current practice means GRP constructions use the same design methodology as metallic flanges there is no European specification covering these products and as such the performance and quality may well be highly variable.
The proposed research programme will aim to alleviate these shortcomings by providing a design methodology for GRP flanges, which could then be used as the basis of a European specification. In addition, the findings of the research work could be used by the GRP standards committee CEN/TC 155/WG 14 to help in the development of new standards or during the revision of existing standards.
All European composite flange manufacturers will benefit from this initiative by optimisation of the product's performance together with a specification, which will ensure product uniformity between customers. The production benefits of manufacturing products to a standard design will be reflected in a reduction in product cost.
Apart from the economic benefits, the research project will provide direct industrial benefits by reducing the number of process shutdowns for the repair of leaking joints or for maintenance purposes. Moreover, as GRP pipelines are often used for the transmission of pernicious and dangerous chemicals the improved reliability and performance of GRP flange joints will contribute to the overall safety of the operating system and reduce the probability of leakage resulting in environmental damage and pollution.
6.1 Main objectives and expected results for the research
The main objectives of the work programme are to draft a design code for the use of GRP flanges and incorporate these findings into a European Standard.
Currently, the design rules for GRP flanges are simple transpositions of the codes used for metallic flanges. Such rules are incorrect for composite materials and impose unnecessary cost penalties. These design rules are fundamentally incorrect as they do not take account of the properties of the material, in particular, their laminate nature.
It is envisaged that the results of the work will provide an understanding of the performance of current designs of GRP flanges and their failure mechanics under short-term overload conditions. The critical areas of the design where excessive strains are imposed on the product will be assessed by direct measurement and through finite element analysis techniques. The influence of laminate structure on product performance will also be defined. Given these findings, the flange design will be revised and subsequently manufactured and tested to failure. As well as the ultimate flange performance, the production process will be assessed in terms of its ease of production, efficiency of resources, productivity and cost. All associated technical difficulties arising from these modified designs will be monitored and reviewed.
The results of the work are to be applied in two areas:
b) by the proposers: To provide a detailed knowledge of the allowable service conditions and design methods which will enable further development of the product design and fabrication techniques.
6.2 State of the art and innovation
This research programme will assist in the technological development of the construction materials together with improvements in the efficiency and quality of the manufacturing and production process.
The availability of modern numerical tools such as finite element analysis will be used to exploit the properties of composite materials used in flanges in terms of heterogeneity, anisotropy and laminate construction. Given that flanges are in general, "thick" components, the types of elements used in the analysis will be used to determine their characteristic shear properties.
Significant technological improvements of the products may be obtained by the efficient use of filament reinforcement especially in multi-dimensional textile weaving. Such technologies reduce the inter-laminar shear effects and offer an optimised structure.
By starting with a precise definition of the service conditions for flanges, a design procedure will be developed. A complete test methodology will be developed that will consider the specificity of the particular resin/glass construction used to manufacture the flanges. This will consider joint performance for the predicted life of the piping system under both in-plane and out-of-plane loading conditions.
6.3 Methodology and Structure Proposed for The Project
The structure for the project should consider the following tasks:
a) design
An overview and review of the literature will be carried out to define more clearly the current design philosophies for flanges. The review will cover metallic and composite structures and shall consult current industrial design practices for all available flange designs.
b) product appraisal and testing
The mechanical performance of current flange designs shall be evaluated. For whole product integrity testing, a short-term test method shall be devised for prediction of long-term performance. The laboratory testing will be augmented and supported by field testing such products under typical installation and operating conditions. The overall performance of products will be classified in terms of their laminate structure.
This part of the project will be supported by all the partners and will involve "round robin" testing of existing products using an agreed testing programme.
c) product modifications and validation
Where appropriate, changes to the flange design shall be made to optimise performance. These changes may be purely dimensional although technological developments will be used to establish the effects of different reinforcement types and fabrication techniques on performance. Prototype fabricated products will be initially manufactured and their performance evaluated using an agreed test programme.
d) implementation
The findings of this work will be implemented by manufacturers to produce performance optimised products, which will be fully supported by a design code of practice or standard for GRP flanges. In addition, the viability of translating the various fabrication processes to an automatic continuous process will be reviewed together with any refinements that can be made to the production process.
The above stages of research will proceed in parallel using an interactive approach between partners and the work will link all partners where there is mutual expertise.
The results and findings of the work will be exploited through European standardisation and used to form the basis of a design standard for GRP flanges.
The implication of a common design procedure will be reflected in greater competition within the European community for the supply of flanges for piping. The enhanced performance characteristics of any flange product that is developed will be used to compete on an economic basis with other flange materials and products.
Any new products developed as a direct result of this work will be actively promoted through scientific journals, publications and brochures for circulation at conferences and exhibitions. The work will be aimed at pipeline designers, end-users and inspection bodies.
A period of 4 years is envisaged for the whole project. However, throughout the course of the project, interim report will have to be provided to report on progress and findings of the project.
The results of each task are required as separate reports for processing by CEN/TC 155. The reports will clearly present the proposals of the new design approach and its related validation as previously specified. All experimental data generated during the research shall be included.