1、 MSS SP-92-2012 MSS Valve User Guide Standard Practice Developed and Approved by the Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. 127 Park Street, NE Vienna, Virginia 22180-4602 Phone: (703) 281-6613 Fax: (703) 281-6671 E-mail: standardsmss-hq.org www.mss-hq.org MSS
2、 MSS STANDARD PRACTICE SP-92 i This MSS Standard Practice was developed under the consensus of the MSS Technical Committee 306 and the MSS Coordinating Committee. The content of this Standard Practice is the resulting efforts of competent and experienced volunteers to provide an effective, clear, an
3、d non-exclusive standard that will benefit the industry as a whole. This MSS Standard Practice describes minimal requirements and is intended as a basis for common practice by the manufacturer, the user, and the general public. The existence of an MSS Standard Practice does not in itself preclude th
4、e manufacture, sale, or use of products not conforming to the Standard Practice. Mandatory conformance to this Standard Practice is established only by reference in other documents such as a code, specification, sales contract, or public law, as applicable. MSS has no power, nor does it undertake, t
5、o enforce or certify compliance with this document. Any certification or other statement of compliance with the requirements of this Standard Practice shall not be attributable to MSS and is solely the responsibility of the certifier or maker of the statement. “Unless indicated otherwise within this
6、 MSS Standard Practice, other standards documents referenced to herein are identified by the date of issue that was applicable to this Standard Practice at the date of approval of this MSS Standard Practice (see Annex A). This Standard Practice shall remain silent on the validity of those other stan
7、dards of prior or subsequent dates of issue even though applicable provisions may not have changed.” By publication of this Standard Practice, no position is taken with respect to the validity of any potential claim(s) or of any patent rights in connection therewith. MSS shall not be held responsibl
8、e for identifying any patent rights. Users are expressly advised that determination of patent rights and the risk of infringement of such rights are entirely their responsibility. In this Standard Practice, all text, notes, annexes, tables, figures, and references are construed to be essential to th
9、e understanding of the message of the standard, and are considered normative unless indicated as “supplemental”. All appendices, if included, that appear in this document are construed as “supplemental”. Note that supplemental information does not include mandatory requirements. Substantive changes
10、in this 2012 edition are “flagged” by parallel bars as shown on the margins of this paragraph. The specific detail of the change may be determined by comparing the material flagged with that in the previous edition. U.S. Customary units in this Standard Practice are the standard; (SI) metric units a
11、re for reference only. Non-toleranced dimensions in this Standard Practice are nominal and, unless otherwise specified, shall be considered “for reference only.” Excerpts of this Standard Practice may be quoted with permission. Credit lines should read Extracted from MSS SP-92-2012 with permission o
12、f the publisher, Manufacturers Standardization Society of the Valves and Fittings Industry, Inc. Reproduction and/or electronic transmission or dissemination is prohibited under copyright convention unless written permission is granted by the Manufacturers Standardization Society of the Valve and Fi
13、ttings Industry, Inc. All rights reserved. Originally Published: February 1980 Current Edition Approved: August 2011 Current Edition Published: March 2012 MSS is a registered trademark of Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. Copyright , 2012 by Manufacturers
14、 Standardization Society of the Valve and Fittings Industry, Inc. Printed in U.S.A. MSS STANDARD PRACTICE SP-92 ii FOREWORD When a complex product is used for a variety of applications and in various operating environments, it is reasonable to expect that the performance of such a product will refle
15、ct upon its suitability for the specific service as well as its proper installation and maintenance. Recognizing that operating problems involving industrial valves frequently involve the use of valves not properly selected for the intended service, or adversely affected by improper handling, instal
16、lation, operation, or maintenance, the Manufacturers Standardization Society has prepared this Valve User Guide. The Society or its members, jointly or severally, make no guarantee and assume no liability or responsibility regarding the contents of this document. It has not been possible to include
17、every consideration related to the satisfactory use of valves, and, especially in abnormal or unusual circumstances, the possible need for other considerations and precautions should be recognized. MSS STANDARD PRACTICE SP-92 iii TABLE OF CONTENTS SECTION PAGE 1 SCOPE . 1 2 REFERENCES 1 3 SELECTION
18、1 4 SHIPPING AND STORAGE 5 5 INSTALLATION 6 6 OPERATION AND MAINTENANCE . 10 ANNEX A Referenced Standards and Applicable Dates . 17 APPENDIX X1 Reference Documents 18 MSS STANDARD PRACTICE SP-92 1 1. SCOPE This Guide presents information which should be helpful to users desiring to avoid the most ob
19、vious causes of problems with valves. The material is divided into five main sections: “References”, “Selection”, “Shipping and Storage”, “Installation”, and “Operation and Maintenance”. 2. REFERENCES The following standard references are normative to this Standard Practice (see Annex A): a) API 607
20、 b) ASME B16.5 b) ISO 10497 The standards, specifications, and manuals listed in Appendix X1 of this Standard Practice are included as useful reference documents to help the user understand the various valve types and their operational limitations. Such an understanding is particularly important whe
21、n selecting equipment for a specific pressure/temperature/fluid application. This “informative” list is not all-inclusive. Note that Piping Codes are not listed; however, the user is cautioned that they may include requirements for valves in certain applications. 3. SELECTION 3.1 General 3.1.1 It is
22、 beyond the scope of this Standard Practice to make recommendations for specific applications because misapplication of a valve type could result in operating problems which adversely affect system safety and efficiency. However, observance of the considerations, recommendations and cautions offered
23、 herein will provide increased assurance of satisfactory valve performance. 3.1.2 The valve industry offers a wide variety of valve types and materials for use in industrial piping applications. There are usually several possible choices for a given requirement. Any one valve may offer significant a
24、dvantages and/or limitations compared to another valve. It is good practice to consult the manufacturer regarding specific requirements. The purchasing function includes the responsibility for securing the required valves at the lowest cost, but must also ensure that the valves purchased are in fact
25、 satisfactory for the intended service. The lowest total user (life cycle cost criteria should be used only in choosing between alternatives that are known to satisfy the service requirement. 3.2 Pressure-Temperature Rating 3.2.1 The pressure-temperature rating of the valve must be properly selected
26、 for the service requirement. If the service involves a temperature above 100 F (38 C), the valve pressure rating at the service temperature must be verified as meeting the requirements of the application. 3.2.2 If system testing will subject the valve to a pressure in excess of its working pressure
27、 rating, then the intended testing pressure and a statement explaining whether the test pressure is through the opened valve or a differential across the closed valve, should be included in the purchase specification. 3.3 Bending Strength 3.3.1 Piping systems are subject to mechanical constraints at
28、 fixed support points such as rigid nozzles, anchors, etc. Cold springing at assembly, system temperature changes, together with gravity, possible inertia loads, landslides, non-MSS VALVE USER GUIDE MSS STANDARD PRACTICE SP-92 2 uniform subsidence in buried lines, etc., all potentially affect the be
29、nding moment at various points in the piping. 3.3.2 Valves are also subjected to the bending moment occurring in the adjacent pipe which is in addition to the normal pressure loadings. Bending loads can cause deformation in valve bodies that can be detrimental to valve functional performance. It is
30、therefore a recommended design practice to avoid locating valves at points of large bending loads. 3.3.3 In many cases, normal valve design practice results in a body strength greater than the strength of the adjoining pipe thereby providing inherent protection against valve damage. In other cases,
31、piping conditions or systems designs may actually increase the possibility of harmful valve body deformation. The following are examples of possible problems: a) Basic “standard“ valves that are made into “venturi“ type valves by providing enlarged end connections on the smaller standard basic valve
32、s. b) Gray iron valves installed in steel piping. c) Any “standard“ valve installed in heavy wall “overweight“ piping where the extra thickness may cause the pipe to be stiffer and stronger than the valve. 3.3.4 Valve designs having a high body bending strength should be used if there is reason for
33、concern regarding possible high bending loads. 3.4 Fire Safety 3.4.1 The terms “Fire Safe“ or “Fire Tested“ are not definitive and should not be used without an accompanying specification of what is required. Such a specification may be provided in the form of a requirement for a defined test or for
34、 limitations on the valve failure mode. Examples of such limitations are: a) Destruction of elastomeric or polymeric materials in the valve shall not result in gross valve pressure boundary leakage. b) Destruction of elastomeric or polymeric materials in the valve shall not result in leakage greater
35、 than a specified rate when the valve is closed. c) External heating of the valve shall not cause uncontrolled buildup of pressure in the body cavity of a double seated valve. 3.4.2 Requirements related to after-fire operability and seat tightness are difficult to define other than by actual testing
36、 using standardized procedures. Valve post-fire operability simulation “Fire Testing“ is covered by such standards as API 607 (e.g., soft-seated valves) and ISO 10497 (e.g., metal-seated valves). See Appendix X1 for other “Fire Test” related standards that may be useful. 3.5 Pressure Surge 3.5.1 Clo
37、sure of a valve in a flowing fluid line causes the velocity of the fluid to be reduced to zero. If the fluid is a relatively incompressible liquid, the inertia of an upstream column produces a pressure surge at the valve whose magnitude is inversely proportional to the time required for closure. The
38、 surge pressure is also proportional to the length of the upstream fluid column and the fluid velocity prior to closure initiation. If the application involves a long upstream line, a long downstream line, high velocity, and/or rapid closure, singly or in any combination, the possibility of an unacc
39、eptable pressure surge should be investigated. 3.5.2 Also to be considered are condensation induced pressure surges which occur when a fluid velocity change is caused by rapid condensation or when a slug of water is accelerated by contact with steam. An example would be when condensate collects on o
40、ne side of a closed valve that has steam on MSS STANDARD PRACTICE SP-92 3 the other side, then opening the valve will cause collapsing steam voids, sharp pressure surges and acceleration of condensate slugs. Condensation induced pressure waves can result in pressure pulses that are significantly hig
41、her than those produced by a sudden valve closure. In such events, non-shock rated gray iron valves installed in steel piping systems are particularly vulnerable to catastrophic failure. Traps are required to prevent condensate accumulation and “blow-off“ valves located at the low point in the syste
42、m are needed to ensure condensate drainage. Operation and maintenance personnel must be aware of the function of these devices in relationship to the “shut-off“ valve operation and the necessity for their being in proper working order. 3.5.3 The flowing media should be considered as being “stopped“
43、instantaneously in the case of a check valve closure on a flow reversal. Consequently, the pressure surge may be very high depending on the velocity of the reverse flow at the instant of closure and the length of the fluid column. Applications of check valves in liquid lines should always be evaluat
44、ed for possible pressure surge (water hammer) problems. 3.6 Check Valve Application 3.6.1 Check valves are actuated by the flow or pressure of the line fluid. Problems involving excessive wear of internal parts or noisy operation can result from the use of check valves which are not fully opened by
45、the normally sustained flow. 3.6.2 A check valve should not be used as a primary “shut-off“ valve for any application, including energy source isolation. Check valves should be applied as containment devices to prevent gross backflow. For example, to restrict backflow into equipment such as boilers
46、and pumps operating off a common header. 3.6.3 Piston and ball check valves that are designed with close diametrical clearances between the moving parts are sensitive to a “sticking operation“ when used in a service where internal rust or other solids may develop. It is recommended that check valves
47、 selected for use in this type service be tolerant of a rust buildup in the valve. 3.6.4 Applications involving gas or steam flow may be complicated by an energy transfer phenomenon which can cause valve cycling even under steady flow conditions. Such cycling may cause rapid wear and premature valve
48、 failure or malfunction. Valve closure element cycling may also be a problem when the flow is cycling as it would be at the discharge of a reciprocating pump. 3.6.5 The preferred sizing of a check valve is such that at normal sustained flow, the valve closure element will be held against its stop in
49、 the full open position. Applications in gas or steam lines, or in liquid lines with low or unsteady flow, should be described fully in the purchase specification so that the manufacturer can evaluate the suitability of the valve design as some check valves require a minimum flow rate for stable operation. 3.6.6 Check valves should not be located close to upstream flow disturbances such as control valves, elbows and tees. Turbulence in the flowing fluid entering the valve may cause disc motion and excessive wear. It is recommended that check valves be located at least five pipe d
