1、 TECHNICAL REPORT ANSI/ISA-TR96.05.01-2008 A Technical Report prepared by ISA and registered with ANSI Partial Stroke Testing of Automated Block Valves Approved 4 May 2008 ANSI/ISA-TR96.05.01 Partial Stroke Testing of Automated Block Valves ISBN: 978-1-934394-70-0 Copyright 2008 by ISA. All rights r
2、eserved. Not for resale. Printed in the United States of America. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic mechanical, photocopying, recording, or otherwise), without the prior written permission of the Publis
3、her. ISA 67 Alexander Drive P.O. Box 12277 Research Triangle Park, North Carolina 27709 - 3 - ANSI/ISA-TR96.05.01-2008 Preface This preface, as well as all footnotes and annexes, is included for information purposes and is not part of ANSI/ISA-TR96.05.01. This document has been prepared as part of t
4、he service of ISA towards a goal of uniformity in the field of instrumentation. To be of real value, this document should not be static but should be subject to periodic review. Toward this end, the Society welcomes all comments and criticisms and asks that they be addressed to the Secretary, Standa
5、rds and Practices Board; ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709; Telephone (919) 549-8411; Fax (919) 549-8288; E-mail: standardsisa.org. The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general,
6、 and the International System of Units (SI) in particular, in the preparation of instrumentation standards. The Department is further aware of the benefits to USA users of ISA standards of incorporating suitable references to the SI (and the metric system) in their business and professional dealings
7、 with other countries. Toward this end, this Department will endeavor to introduce SI-acceptable metric units in all new and revised standards, recommended practices, and technical reports to the greatest extent possible. Standard for Use of the International System of Units (SI): The Modern Metric
8、System, published by the American Society for Testing designers who identify automated block valve applications whose potential failure rate in the operating environment indicates the need for more frequent proof testing than supported by the operability and maintainability requirements; and operati
9、ons and maintenance personnel who need to understand how partial stroke testing is performed and what it indicates about the mechanical integrity of an automated block valve. The user of this document should be familiar with the operation of automated block valves and with the quantitative analysis
10、of its average probability of failure on demand (PFDAVG). The quantitative analysis is discussed in ISA-TR84.00.02 (ref. 2.3) and in CCPS/AIChE Guidelines for Safe and Reliable Instrumented Protective Systems (ref. 2.1). THE EXAMPLES OF PARTIAL STROKE TESTING REPRESENT POSSIBLE SYSTEM CONFIGURATIONS
11、 AND ARE PROVIDED FOR ILLUSTRATION PURPOSES ONLY. THE DIAGNOSTIC COVERAGE FACTORS ILLUSTRATED SHOULD NOT BE INTERPRETED AS THE ONLY ACCEPTABLE VALUES OR AS RECOMMENDATIONS. THE PERFORMANCE OBTAINED IN ACTUAL APPLICATIONS IS SPECIFIC TO THE OPERATING ENVIRONMENT IN WHICH THE AUTOMATED BLOCK VALVE IS
12、USED. AS SUCH, NO GENERAL RECOMMENDATIONS CAN BE PROVIDED THAT WOULD BE APPLICABLE IN ALL SITUATIONS. THE USER IS CAUTIONED TO CLEARLY UNDERSTAND HOW PARTIAL STROKE TESTING PROVIDES EARLY DETECTION OF VALVE ACTUATION PROBLEMS AND THE SPECIFIC ASSUMPTIONS RELATED TO ANY MANUFACTURERS CLAIMS. Publicat
13、ion of this technical report that has been registered with ANSI has been approved by ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709. This document is registered as a technical report according to the Procedures for the Registration of Technical Reports with ANSI. This doc
14、ument is not an American National Standard and the material contained herein is not normative in nature. Comments on the content of this document should be sent to ISA; 67 Alexander Drive; P. O. Box 12277; Research Triangle Park, NC 27709. This page intentionally left blank. - 11 - ANSI/ISA-TR96.05.
15、01-2008 Introduction Significant investments have been made in mechanical reliability and preventive maintenance programs for fixed equipment. These programs yielded significant performance improvements, demonstrating that it was acceptable to run the fixed equipment for longer periods between maint
16、enance intervals (or turnarounds). The improvements have extended the maintenance interval to the point where, in some market sectors, the fixed equipment is no longer the weakest link for reliable process operation. Attention is now shifting to standby devices, such as automated block valves, which
17、 operate in a demand mode. Standby devices are used in many critical applications, such as instrumented protective systems, safety instrumented systems, life safety systems, emergency shutdown systems, and fire and gas systems (see ref. 3.1). As critical equipment, reliability is important, since fa
18、ilure may result in significant process impact. A reliable standby device operates as intended when required, does not require frequent repair and maintenance, and does not cause an inadvertent process disruption or shutdown. An important aspect of reliability is the capability to detect device fail
19、ure, e.g., incipient, degraded, safe and dangerous failures, so that identified failures can be corrected, rendering the standby device in the “good as new” condition. For automated block valves, complete on-line proof testing is limited in many applications. The extension of fixed equipment mainten
20、ance intervals (unit outages) has resulted in reduced off-line proof test opportunities. Yet, the automated block valve must meet the required reliability in the operating environment. Partial stroke testing can be used to identify certain failure modes associated with automated block valves. Partia
21、l stroke testing can be performed on-line with a wide variety of equipment and can be executed either manually or automatically. This technical report addresses the applications when partial stroke testing may be useful, the various methods used for partial stroke testing, and the advantages and dis
22、advantages of each technology. Partial stroke testing identifies failure modes associated with the block valve actuator and a limited number of failure modes associated with the valve body or internals (e.g., valve stem damage and stem to valve connection). Rising stem and rotary actuators operate d
23、ifferently, so they have a different distribution of failures across common failure modes and some unique failure modes. Consequently, the percentage of the overall valve failures detected is different for rising stem and rotary actuators. None of the partial stroke testing methods presented in this
24、 report detects failures associated with the valve seat, e.g., leak tightness. This page intentionally left blank. - 13 - ANSI/ISA-TR96.05.01-2008 1 Scope ANSI/ISA-TR96.05.01 is informative and does not contain any mandatory requirements. ANSI/ISA-TR96.05.01 is limited to automated valves normally o
25、perating in either a full open or full closed position. The boundary of the automated valve includes the following: a) Limit switches and other monitoring devices b) Air regulation and filtration system c) Actuated valves whose fail position is specified as spring-return fail closed, spring-return f
26、ail open, or double acting d) Valve body specified to meet the functional requirements for its application ANSI/ISA-TR96.05.01 does not address automated valves used for regulatory control applications. Guidance is provided on the following: a) Identifying when partial stroke testing may be useful b
27、) Various criteria to consider when selecting the partial stroke method, e.g., automated versus manual test execution, spurious trip potential, and on-line maintainability c) The advantages and disadvantages of three basic types of partial stroke test methods: mechanical limiting, positioners, and s
28、olenoid operated valves d) The use of diagnostic coverage factors in the performance calculations for an automated block valve being partial stroke tested periodically 2 References Guidelines for Safe and Reliable Instrumented Protective Systems, Center for Chemical Process Safety, American Institut
29、e of Chemical Engineers, New York, NY 10017, 2006. Offshore Reliability Data, OREDA, 3rd edition, ISBN: 82-14-00438-1, Det Norske Veritas, Veritasveien 1, N-1322 Hvik, Norway, 1997. ANSI/ISA-TR84.00.02, “Safety Instrumented Systems (SIS) Safety Integrity Level (SIL) Evaluation Techniques”, ISA, Rese
30、arch Triangle Park, NC, 2002. 3 Abbreviations DC diagnostic coverage ISA Instrumentation, Systems, and Automation Society D dangerous failure rate MTTR mean time to repair ANSI/ISA-TR96.05.01-2008 - 14 - PFDAVG average probability of failure on demand TI Test Interval 4 Definitions 4.1 bypass: an ac
31、tion taken to override, defeat, disable, or inhibit equipment operation. These actions prevent equipment from operating as required. 4.2 dangerous failure: failure affecting equipment in a system that has the potential to put the system in a fail-to-function state or to cause the process to be put i
32、n a hazardous state. 4.3 diagnostic coverage: fractional decrease in the probability of dangerous failure resulting from automated diagnostics that report faults to the operator and take a specified action on fault detection. 4.4 failure: termination of the ability of equipment to function as specif
33、ied. 4.5 failure mode: a symptom, condition, or effect by which a failure is observed. Failure modes are often divided into three categories: critical, degraded, and incipient. 4.6 failure rate: limit when t goes to 0 of the expected rate at which equipment failures occur in the time interval t to t
34、+t given that no failures have occurred until time t. 4.7 mean time to repair: average time required for equipment to be repaired and returned to normal operation after its failure is detected. 4.8 normal operation: operation of the process within the design envelope. Normal operation includes any p
35、lanned operational mode, such as steady-state, reduced rates, maintenance, testing, start-up, and shutdown. 4.9 off-line: process equipment is not operational (i.e., shutdown). 4.10 on-line: process equipment is operational (i.e., running, producing product). 4.11 operating environment: where equipm
36、ent is intended to be used, such as external environmental conditions, process operating conditions, communication robustness, process and system interconnections, and support system quality. 4.12 probability of failure as a function of time (PFD (t): probability of a device failing such that it can
37、not respond to a process demand during a specific time period. The average probability of a system failing to respond to a demand in a specified proof test interval is the average probability of failure on demand, (PFDAVG). 4.13 process safety time: time period between a failure occurring in the pro
38、cess or its control system and the occurrence of the hazardous event. - 15 - ANSI/ISA-TR96.05.01-2008 4.14 proof test: a documented test, or series of tests, performed to detect failures in equipment so that, if necessary, the equipment can be restored to its “as good as new” functionality. This per
39、iodic activity validates equipment operation for those functions covered by the specific proof test. 4.15 reliability: related to the probability that the equipment operates according to its specification for a specified period of time under all relevant conditions. 4.16 review: an inspection of the
40、 process equipment, drawings, procedures, emergency plans, and/or management systems, etc., usually by an on-site team and usually problem-solving in nature. 4.17 risk: a measure of human injury, environmental damage, or economic loss in terms of the event frequency of occurrence and the severity of
41、 the injury, damage or loss. 4.18 safe state: a state of the process where a hazardous event cannot occur. 4.19 spurious trip: refers to a process shutdown, or disruption, due to the spurious operation of a protective function. Other used terms include nuisance trip and false shutdown. 4.20 test int
42、erval: time period between two successive proof tests. 5 Automated block valve testing In conventional applications, off-line proof testing is used to demonstrate that the block valve can achieve the specified safe state when a process demand occurs. Over the last twenty years, off-line maintenance
43、intervals have become longer, as plant reliability programs have demonstrated that fixed equipment can run longer between maintenance intervals. The requirements for proof testing, however, have remained unchanged. The proof test should demonstrate that the automated block valve can operate as requi
44、red, such as achieving the safe state position, speed of response, and leak tightness. This technical report does not address testing of valve leak tightness. It addresses the use of manual and automated means of testing the block valves capability to move toward its specified safe state position. A
45、utomated means can be implemented to determine whether the block valve is under-stroking (moving too slow) or over-stroking (moving too fast). Block valves can be full stroke tested while the process is on-line by placing the block valve in bypass for the duration of the test. When a bypass line is
46、used, the block valve is not available to operate when required. The test can also be executed without bypass, if a hazard analysis team approves the test. The team should assess the hazards of performing a full stroke test on an in-service block valve and the hazards if the valve does not return to
47、 its normal operational state when the test is completed. The test should be conducted according to a written procedure. Verification of test execution should be included in the procedure, as necessary. A full-stroke test of an automated block valve is conducted in a fixed sequence. Work permits may
48、 be required for certain applications. Prior to implementing the bypass, the automated block valve assembly and its connections to the process piping should be examined externally, noting any damage or leakage. The pneumatic source should be examined from the connection to the valve actuator to the
49、air exhaust. For example, inspect the instrument air tubing, air filter, and solenoid operated valve vent port. Electrical connections to the equipment should also be examined and any identified deviation from acceptable installation practice should be corrected. ANSI/ISA-TR96.05.01-2008 - 16 - If visual inspection does not reveal any problems that would make the test potentially unsafe, the full-stroke test is executed. The speed of response is important in many applications, since the automated block valve is a major contributor to overall system response time. A va
