3 BFPA/P100 – GUIDELINES FOR THE PROOF AND BURST PRESSURE TESTING OF FLUID POWER COMPONENTS Due to the wide diversity and application of fluid power components these notes cannot be applied to all scenarios but do set down some general guidelines that have been applied successfully by contributors over many years. The importance of observing additional guidance and reference to specific component standards, test Foreword requirements cannot, however, be overstated, such as those listed in the Normative References section of this document. It should also be noted that these guidelines do not cover the fatigue pressure testing of components, which is now covered by BS ISO 10771-1: 2015. In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure within an enclosed circuit. During operation the components in the circuit may be subject to a variety of loads, including those arising from internal pressure, gravity, inertia, thermal variations and external forces. The nature of these loads can vary from a single static application, to continuously varying amplitudes including repetitive loadings and shocks. Whilst it is important to know how well a particular component can withstand such loads, these guidance notes address only the loading due to internal hydrostatic pressure. Two commonly encountered tests which play a vital part in the determination of a safe working pressure for fluid power components are those to verify proof pressure and burst pressure (see section 1). There are a number of standards already in existence which address the pressure rating of some particular types of fluid power component, examples being gas-loaded accumulators, hydraulic connectors, hoses and cylinders. These guidance notes are not intended to displace such Introduction standards. There are, however, many other fluid power components which are not adequately catered for by existing standards and for which some general guidance will be useful. Original equipment manufacturers and system builders of fluid power equipment need to be able to demonstrate that auditable test procedures have been adopted at appropriate points in the equipment supply chain. Manufacturers are effectively obliged to either undertake adequate testing of any fluid power components incorporated into the machine, or to obtain documentation to show that the component suppliers have carried out sufficient testing to assure product safety. In hydraulic systems, attention will inevitably turn towards pressure integrity. These notes, therefore, are intended to provide the fluid power industry with guidance on carrying out proof and burst pressure tests on fluid power components in a safe, traceable and technically sound manner, in situations where existing standards are judged to be either inadequate or inapplicable. 5 BFPA/P100 – GUIDELINES FOR THE PROOF AND BURST PRESSURE TESTING OF FLUID POWER COMP 1. DEFINITIONS 1.1 Maximum Rated Pressure A pressure confirmed through testing at which a component or assembly is designed to operate for a number of repetitions sufficient to ensure adequate service life. 1.2 Proof Pressure A test pressure applied after assembly in excess of the maximum rated pressure of the component that causes no damage to or subsequent malfunction of the component or assembly. 1.3 Burst Pressure A test pressure at which a component or, piping, fails and fluid begins to escape. 2. TEST SAFETY Please refer to HSE GS 4 (fourth edition) Safety in pressure testing for guidance. 3. TEST SPECIMENS 3.1 For burst or proof testing of fluid power components the minimum acceptable number of test specimens is three. In order that the results are statistically meaningful; more specimens would enable a greater degree of confidence to be placed on the test results. 3.2 The specimens should ideally be standard production items selected at random from a production batch and should conform to manufacturing drawings and specifications. It is possible that specimens will have to be selected for test from a pre-production batch; in such cases any subsequent change to the component design, materials or method of manufacture may invalidate the proof or burst test, unless it can be demonstrated irrefutably that such changes do not affect the pressure retaining capability of the component. Material conformity for test specimens should be demonstrable through receipt notes, goods receiving inspection, material batch test results, supplier conformance certification etc. 3.3 It is good practice to subject burst test specimens to the proof test before undertaking the burst test. It should however first be confirmed by inspection that the proof test has not changed the test component in any way. 4. TEST FLUID 4.1 A common test fluid for proof and burst pressure testing is a mineral oil having a kinematic viscosity not greater than 32cSt at the test temperature. Other fluids may be used if necessary, although it is essential that any candidate fluid is compatible with the specimen, particularly the seal materials. Testing should be carried out at normal room temperature but within the range 10°C to 30°C. 4.2 After testing, certain components may retain small quantities of the test fluid. It is important that the fluid with which the component is subsequently used is compatible with the test fluid and hence keeping a record of the test fluid specification is vital. 5. PROOF PRESSURE RATING 5.1 The proof pressure rating could, in theory, be any pressure between the maximum rated pressure and the burst pressure. If the component however is either used or capable of being used after proof testing, then it is important that the proof pressure applied should not be sufficient to cause yielding in any point of the material. Since this is difficult to determine it is essential that the Design Authority for the component is consulted and approves the intended test pressure prior to testing. A factor of 1.5 – 2 times the maximum rated pressure is used for proof testing many fluid power components. For pressure equipment designed and manufactured in accordance with The Pressure Equipment (Safety) Regulations 2016, the proof pressure or hydrostatic test pressure referred to within Clause 27 (and defined within Clause 40) must be no less than: That corresponding to the maximum loading, to which the pressure equipment may be subject in service taking into account its maximum allowable pressure and its maximum allowable temperature multiplied by the coefficient 1.25 or The maximum allowable pressure multiplied by the coefficient 1,43 whichever is the greater. 5.2 When determining the proof test pressure, it should be noted that some materials such as stainless steel, exhibit low yield strength when compared to carbon steel. UPDATES UPDATES FROM: Contact the BFPA at Tel: +44 (0)1608 647900 • enquiries@bfpa.co.uk • www.bfpa.co.uk BFPA Technical Update Dr Neal Milne Retires as Chair from BFPA Technical Committee TC 16 Hydraulic Fluids The British Fluid Power Association (BFPA) would like to extend a sincere thank you to Dr Neal Milne for his hard work and commitment as Chair of the TC 16 Hydraulic Fluids Committee. Neal has stepped down from the Committee ahead of his retirement this spring. The BFPA wishes Neal a happy and healthy retirement. A successful meeting was held on 5 March, during which the committee discussed key topics including biodegradability tests for lubricants (BS EN 16807 is currently under revision), fire testing, and BFPA publication P104 Hydraulic Fluids – A Practical Guide. The BFPA is pleased to announce that the new Chair of the Hydraulic Fluids Technical Committee will be Katy Gibson of Shell Research Ltd BFPA Technical Publications The BFPA has a library of useful technical publications, including guides on a range of topics, many of which are free for members to download. Non-members pay a small fee for BFPA publications. Please visit the BFPA website www.bfpa.co.uk/publications/ to browse a selection of technical guidelines, reference manuals and position papers, covering: fluids, hose and fittings, safety, seals, systems, testing, waste, contamination control. Other publications available include: BFPA D8 Quality Control Procedures and Certification Requirements for the manufacture of flexible hose assemblies for fluid power, BFPA training reference manuals and fluid power salary surveys. BRITISH FLUID POWER ASSOCIATION BFPA/P100 GUIDELINES FOR THE PROOF AND BURST PRESSURE TESTING OF FLUID POWER COMPONENTS Featured update: P100 Guidelines for the proof and burst pressure testing of fluid power components BFPA Guidelines for the proof and burst pressure testing of fluid power components has recently been updated by the BFPA’s TC 9 (Systems and Accumulators) and is free for members to download from the BFPA’s website www. bfpa.co.uk/publications/. This guide covers the topics of test safety, test equipment and specimens, test fluids, proof pressure rating, and procedures for both proof and burst testing. For more information on the BFPA Technical Committees (including the Hydraulic Fluids Committee), and publications contact Kelly Webster-Garvey on kelly@bfpa.co.uk.
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