High pressure metrology for industrial applications

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Publishable JRP Summary Report for IND03 HighPRES
High pressure metrology for industrial applications

New high pressure technologies such as autofrettage, hydroforming and isostatic pressing are being widely developed and used in the car industry, diesel engineering, vessel production for the petrochemical and pharmaceutical industry, manufacturing water cutting machines, new material fabrication and, recently, for food sterilisation. With these new technologies the quality and lifetime of products and efficiency of processes can be increased, material and energy resources saved, and the emission of pollutants reduced. New transducers for measuring pressures up to 1.5 GPa have recently been used in new high pressure applications. Several European consultancy groups predict high pressure sensing will grow from the current 1 % up to 5 % of the total pressure measurement market (which reached 2 billion US $ in 2007) in the near future. However, no adequate standards for pressures higher than 1 GPa are currently available in the EU with which the modern pressure transducers could be adequately calibrated. Without a calibration service provided for companies using high-pressure technologies, their quality assurance and safety requirements cannot be fulfilled, which hinders any expected technology improvements if the process pressure increases.
This JRP will create a primary pressure standard for the range of 1.6 GPa. It will be realised as two pressure-measuring multipliers each consisting of a low and a high pressure piston-cylinder assembly. Stress-strain finite element analysis (FEA) will be performed to design the multipliers and a pressure generation system. With FEA, the pressure distortion coefficient – the main parameter of high pressure balances - will be determined. Dimensional properties of the piston-cylinder assemblies, elastic constants of their materials and pressure-dependent density and viscosity liquids to be used as a pressure-transmitting medium – the data required for the design of the pressure multipliers and their FEA analysis - will be measured. Metrological characterisation of the new pressure standards and validation of the theoretical results will be performed by cross-float experiments. Transfer pressure standards up to 1.5 GPa to be used in JRP-Partner pressure comparisons or on-site calibrations will be developed on the basis of modern 1.5 GPa pressure transducers. To this purpose, different types of high pressure transducers will be tested concerning their drift, hysteresis, sensitivity, repeatability, long-term stability and load cycling effects. The results of this study will be provided to transducers’ manufacturers and to enable the optimisation of the transducers.
The JRP’s scientific and/or technological methodology is a sound concept because of former examples of pressure-measuring multipliers, special realisations up to 2.5 GPa and commercially produced instruments up to 1 GPa. Thermal shrinking technology and jacket pressure techniques are available and have been applied which will enable manufacture and operation of high pressure piston-cylinders and other components for pressures up to 1.6 GPa and higher. The thermal shrinking is reached by assembling two precisely machined cylinders with the outer having a higher temperature than the inner one, with the following temperatures equalisation leading to a compressive stress in the inner cylinder. A jacket pressure is generated and applied to the outer surface of the outer cylinder and, thus, produces an additional support of the inner cylinder. An FEA based methodology for analysis of pressure balances up to 1 GPa has already been developed and applied in 2 EURAMET projects 256 “Calculation of the elastic distortion of piston cylinder assemblies in pressure balances and hydraulic amplifiers in force machines” and 463 “Calculation of elastic distortion and associated uncertainty in piston cylinders operating up to 1 GPa”. A new strain gauge and resonant ultrasound spectroscopy techniques have also recently been established at JRP-Partners LNE and PTB for accurate measurement of pressure balances’ elastic constants. A unique capability for measurement of viscosity and compressibility of liquids up to 1.5 GPa is available at JRP-Partner Technical University Clausthal (TUC). Furthermore, there are good examples of high pressure transducers’ used in precise cross-float measurements and in international comparisons (e.g. APMP.M.P-S8).
This JRP goes beyond the state of the art by creation of a primary pressure standard for pressures up to 1.6 GPa with a relative expanded uncertainty as low as 0.0005, development of transfer standards and calibration methods for the range 0.1 to 1.5 GPa based on high pressure transducers.
All this will allow the JRP to provide an internationally recognised, routinely available and affordable pressure calibration service up to 1.5 GPa.

Key achievements

FEM software was developed and validated to perform stress-strain, elastic-plastic deformation and contact process analysis of the high pressure components of pressure balances, to calculate the pressure distortion coefficient and to predict the piston fall rate. FEM modelling of the high pressure (HP) and low pressure (LP) piston-cylinder assemblies (PCAs) was performed. Fluid flow models were developed and applied to the piston-cylinder gap of constant width. Piston fall rates were calculated and target mean gap widths defined. Using this, optimal design of the 1.6 GPa high pressure piston-cylinder assemblies (PCAs) was developed, commercially available high pressure tubing was studied on its suitability for 1.6 GPa and sealing properties of the high pressure connections predicted.
Strain gauge measurements on commercial high pressure tubing, connectors and valves at pressures up to 1.6 GPa were performed. Samples of tungsten carbides and steels for measuring elastic constants and hardness were prepared. Elastic constants of tungsten carbides were measured by resonant ultrasound spectroscopy (RUS). Hardness of high pressure components was determined and effect of thermal treatment of the sealing lenses investigated.
Samples of potential pressure-transmitting liquids were prepared for measurement their density and viscosity at ambient and high pressure. Density and viscosity were measured at atmospheric pressure and temperatures near the room temperature. Stability of the liquids after pressurising them up to 1.6 GPa was investigated. A high pressure viscometer was modified, taken in operation and evaluated.
Design of HP PCAs was specified, technical drawings of the pressure measuring multipliers prepared, production of the LP and HP PCAs as well as of pressure multipliers’ parts started. Development, design, manufacture and testing of 1.6 GPa pressure generation and control systems, including a 2 GPa pressure intensifier, were continued and a first principal design of the pressure generation system prepared. Tests of performance of commercial HP components at pressures up to 1.6 GPa were finished. The concept of the HP generation system was finished and preparation of technical drawings was started. Investigation of the 1.5 GPa pressure transducers was prepared. All high pressure transducers were delivered and preloaded. Design of the transfer standards was developed. Parts to manufacture the high pressure transfer standards were ordered and manufacture of the transfer standard hardware was started.

JRP impact

A brief review of JRP-Partners’ past experience of calibrations and unfulfilled calibration demands for high pressure instruments was carried out and published on the JRP website. With this information, traceability of high-pressure measurements can be monitored and the application fields of calibrated high-pressure transducers and the needs of end users better understood.
A 1-day workshop "High Pressure Metrology for Industry" was organised and held at CMI, Brno, on 14 June 2012.
JRP was also presented at two high pressure related conferences: XX IMEKO World Congress, Korea, Busan, September 9 – 14, 2012, http://imeko2012.kriss.re.kr/ and 50th European High Pressure Research Group (EHPRG) Meeting, Greece, Thessaloniki, September 16 – 21, 2012, http://www.ehprg.org/meetings/.
A JRP homepage was established at CMI, http://emrp-highpres.cmi.cz, where the outputs appropriate for public access are available for download and where the possible beneficiaries of this JRP can initiate their communication with the JRP-Consortium.