1、MSS SP-86-2014 Guidelines for Metric Data in Standards for Valves, Flanges, Fittings, and Actuators 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
2、: (703) 281-6671 E-mail: standardsmss-hq.org www.mss-hq.org MSS STANDARD PRACTICE SP-86i This MSS Standard Practice was developed under the consensus of the MSS Technical Committee 302 and the MSS Coordinating Committee. The content of this Standard Practice is the resulting efforts of competent and
3、 experienced volunteers to provide an effective, clear, and 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
4、of an MSS Standard Practice does not in itself preclude the 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,
5、 as applicable. MSS has no power, nor does it undertake, to 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
6、 of the statement. “Unless indicated otherwise within this 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 B). This Standard Practi
7、ce shall remain silent on the validity of those other standards 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
8、 in connection therewith. MSS shall not be held responsible 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, f
9、igures, and references are construed to be essential to the 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 doe
10、s not include mandatory requirements. The SI (metric) units and U.S. customary units in this Standard Practice are regarded separately as the standard; each should be used independently of the other. Combining or converting values between the two systems may result in non-conformance with this and o
11、ther Standard Practices. This Standard Practice has been substantially revised from the previous 2009 edition. It is suggested that if the user is interested in knowing what changes have been made, that direct page by page comparison should be made of this document. Excerpts of this Standard Practic
12、e may be quoted with permission. Credit lines should read Extracted from MSS SP-86-2014 with permission of the publisher, Manufacturers Standardization Society of the Valve and Fittings Industry. Reproduction and/or electronic transmission or dissemination is prohibited under copyright convention un
13、less written permission is granted by the Manufacturers Standardization Society of the Valve and Fittings Industry Inc. All rights reserved. Originally Approved: February 1977 Originally Published: July 1977 Current Edition Approved: August 2014 Current Edition Published: December 2014 MSS is a regi
14、stered trademark of the Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. Copyright , 2014 by Manufacturers Standardization Society of the Valve and Fittings Industry, Inc. Printed in U.S.A. MSS STANDARD PRACTICE SP-86ii TABLE OF CONTENTS SECTION PAGE PURPOSE . 1 1 SCOPE
15、 1 2 RECOMMENDED CONVERSION FACTORS 2 3 STYLE AND USAGE 2 TABLE 1 Size Correlation between DN and NPS 4 A1 Considerations in Rounding 7 A2 Considerations in Precision . 7 ANNEX A Detailed Guidelines for Dimensional Conversions . 5 B Referenced Standards and Applicable Dates . 8 MSS STANDARD PRACTICE
16、 SP-861 PURPOSE This Standard Practice provides recommended rules and guidelines to be followed by MSS Technical Committees while developing or revising Standard Practices or other documents in which there is a need to use both U.S. Customary and metric units. This Standard Practice may also benefit
17、 end-users of MSS standards and other interested parties. Where both units are included, the standards developing group determines the order in which they are presented. When used, the alternate units shall be either: a) In textual references, immediately following the preferred unit in the text and
18、 be separated by parentheses or; b) In tabular references, included in separate columns or presented at the end of the document in the form of an annex. 1. SCOPE This Standard Practice establishes recommended rules and guidelines for determining metric units and numbers, when needed, for use in MSS
19、valve, flange, fitting, and actuator Standard Practices. 2. RECOMMENDED CONVERSION FACTORS 2.1 Nominal Size NPS, followed by a dimensionless number (without an indicator of the unit of measure), is the designation for nominal pipe size (e.g., NPS 2) in ASME standards and documents by other standards
20、 developing organizations. NPS designations are related to nominal diameter (DN) designations used in international standards. Table 1 shows the common nominal sizes in customary (inch) designations and the corresponding metric designations. 2.2 Nominal Pressure Class, followed by a dimensionless nu
21、mber (without an indicator of the unit of measure), is the designation for pressure-temperature ratings (e.g., Class 150) in ASME standards and documents by other standards developing organizations. Class designations are specific to the standard in which they are defined and are therefore not relat
22、able to nominal pressure (PN) designations used in international standards. 2.3 Linear Dimensions Care must be exercised to ensure that both the customary (inch) dimension and the converted (mm) dimension have the desired degree of precision and are consistent with each other and with the precision
23、of the applicable tolerances. CONVERSION FACTORS: 1 inch = 25.4 mm (exact) 1 mm = 4.251inches 0.03937 inches For additional information and recommendations on rounding for critical and nominal dimensions, refer to Annex A. 2.4 Pressure and Stress 2.4.1 Fluid Pressure The basic metric unit for pressu
24、re is the pascal, derived from the direct relationship between the basic unit of force (newton) and the unit of area (square meter). The pascal is very small, and it is most frequently expressed in bars (105pascals) or used with prefixes: kPa (103pascals) for fluid pressure and MPa (106pascals) for
25、stress. CONVERSION FACTORS: 1 bar = 100 kPa = 14.50377 psi 1 psi = 6.89476 kPa = 0.0689476 bar Fluid pressure should generally be stated using a maximum of three significant digits in both customary and metric units with no more than one decimal place. GUIDELINES FOR METRIC DATA IN STANDARDS FOR VAL
26、VES, FLANGES, FITTINGS, AND ACTUATORS MSS STANDARD PRACTICE SP-862 2.4.2 Stress For tensile strength and yield strength, the recognized metric unit is the megapascal (MPa), and should generally be stated using a maximum of 3 significant digits. (The term N/mm2is equal to MPa and may also be used). C
27、ONVERSION FACTORS: 1 psi = 0.0068948 MPa 1 MPa = 1 N/mm2= 145.04 psi 2.5 Force The metric unit of force is the newton, which is a force of about 3.6 ounces. Force numbers should generally be rounded to two or three significant figures, consistent with the precision of the customary figures. CONVERSI
28、ON FACTORS: 1 lbf = 4.448 N 1 N = 0.2248 lbf 2.6 Torque (a)The metric unit of torque is the newton-meter, abbreviated N-m. Torque numbers should generally be rounded to two or three significant figures, consistent with the precision of the customary figures. CONVERSION FACTORS: 1 lbf-ft = 1.356 N-m
29、1 lbf-in = 0.113 N-m 1 N-m = 0.7376 lbf-ft 2.7 Temperature Conversion Generally, metric temperatures stated in degrees Celsius should be rounded to whole degrees. CONVERSION FACTORS: 8.132FCF = 1.8 C + 32 where C = degree Celsius F = degree Fahrenheit The absolute temperature for the kelvin (K) and
30、Rankine (R) scales are determined as follows: K = C + 273.15 R = F + 459.67 2.8 Flow Coefficient A common U.S. Customary measure of incompressible flow efficiency for valves and fittings is Cvwhich is the volume (in U.S. gallons) of water at 60 F that will flow per minute through a device with a pre
31、ssure drop of 1 psi. The equivalent metric flow coefficient is Kvwhich is the volume (in cubic meters) of water at 4 C that will flow per hour through a device with a pressure drop of 1 bar. CONVERSION FACTORS: Cv= 1.1566 KvKv= 0.8646 Cv3. STYLE AND USAGE 3.1 Symbols The symbols for metric units and
32、 the conventions that govern their use must be strictly followed. To avoid errors, care should be taken to use the correct case for symbols, units, and multiples. The following list of rules provides guidance for metric symbols used in MSS Standard Practices: a) Print unit names in lower case (meter
33、, kilogram, second, kelvin, newton, pascal). b) Print unit symbols in upright (non-italic) type and in lower case except for liter (L) or unless the unit name is derived from a proper name (m, kg, s, K, N, Pa). c) Print decimal prefixes in lower case for each magnitude of 103and lower (k, m, , and n
34、) and print the prefixes in upper case for magnitudes 106and higher (M and G). d) Leave a space between a numeral and a symbol (45 kg or 37 C, not 45kg or 37C). e) Do not use a degree mark () with kelvin temperature (write K, not K). f) Do not leave a space between a unit symbol and its decimal pref
35、ix (write kg, not k g) and do not use the plural of unit symbols, but do use the plural of written unit names. g) Do not mix names and symbols (write N-m or newton meter, not N-meter). h) Do not use a period after a symbol (write 12 g, not 12g.). Supplementary Information Note: (a) The unit of Pound
36、 Force Inch (lbf-in) is used in publications to show actuator and motor torque. MSS STANDARD PRACTICE SP-863 3.2 Decimal Point The period (.) will continue to be used as the decimal place marker. Note that previous dual unit or metric unit practices often used a comma (,) as the decimal place marker
37、 for metric data. It has been generally agreed to discontinue the practice, except in some European countries and in international standards (q.v., ISO and IEC). 3.3 Number Grouping Large numbers in metric units should be divided into groups of three digits divided by a space. Such division is not d
38、esirable, however, for four digit numbers, except that in columns of numbers, if four digit numbers appear in columns having other numbers of five or more digits, the separation should also be made in the four digit numbers. Correct Correct Incorrect603 000 6030 603,00021 600 2160 21,600110 000 1100
39、 110,0006 700 6700 6,700900 900 3.4 Reference Guide Several examples have been shown only to illustrate typical cases where style and usage must be considered. Various recognized publications are available that provide detailed recommendations for style and usage, and standards developing groups are
40、 urged to use them for reference. One recommended reference guide is IEEE/ASTM SI 10. MSS STANDARD PRACTICE SP-864 TABLE 1 Size Correlation between NPS and DN NPS DN NPS DN 1/8 6 24 600 1/4 8 26 650 3/8 10 28 700 1/2 15 30 750 3/4 20 32 800 1 25 34 850 11/432 36 900 11/240 38 950 2 50 40 1000 21/265
41、 42 1050 3 80 44 1100 4 100 46 1150 5(a)125(a)48 1200 6 150 50 1250 7(a)175(a)54 1350 8 200 60 1500 9(a)225(a)66 1650 10 250 72 1800 12 300 78 1950 14 350 84 2100 16 400 90 2250 18 450 96 2400 20 500 102 2550 22 550 108 2700 GENERAL NOTE: DN = 25 x NPS for NPS 4 and greater. SUPPLEMENTARY INFORMATIO
42、N NOTE: (a) Use of these sizes should be avoided for new design and construction. MSS STANDARD PRACTICE SP-865 A1. General In the development of this document, it was intended that its use would produce metric numbers that would prove to be fully satisfactory for practical use. Where metrication inv
43、olves soft conversion, products produced in conformance to the metric dimensions should be functionally interchangeable with the corresponding products conforming to the inch dimensions from which they were derived. At the same time, due cognizance is given to the practical and economic importance o
44、f avoiding excessive implied precision in the determination of the number of decimal places and significant figures to be used. This Standard Practice, therefore, recognizes two basic categories of dimensions occurring in standards and prescribed methods of conversion appropriate to those categories
45、. A1.1 Critical Conversions If it is considered necessary to limit the variance between the maximum and minimum dimensions permitted by the existing tolerances and those permitted by the converted metric dimensions to essentially the precision of the existing dimension, such dimension is considered
46、“critical“. The conversion and rounding methods will produce metric dimensions that duplicate the absolute value of the inch dimensions within the precision of the measuring process. A1.2 Nominal Conversions If some shift of the absolute value of the maximum and minimum dimensions permitted by the i
47、nch dimensions and those provided by the converted metric dimensions will not unacceptably affect the functional or safety characteristics of the product, such dimensions may be considered “nominal“. The conversion and rounding methods within this Standard Practice will permit liberal rounding of su
48、ch dimensions in order to facilitate ease of visual measurement. A2. Fractional Numbers When converting fractions or mixed numbers to metric it is important to recognize that the intended precision of the dimension is represented by the fractional portion of the number. By strict interpretation, the
49、 fraction 1/2 standing alone may be considered as representing a quantity that is greater than 1/4 and smaller than 3/4 (the smallest digit shown is the numerator “1“, and that represents the nearest number of 1/2s the quantity could be rounded to). If, however, there are accompanying numbers that include other common fractions such as 3/8, 3/4, 1/8, and perhaps an occasional simple whole number, it can be reasonably concluded that the intended precision was at the level of 1/8s; thus, 3/8 represents a quantity greater than 5/16 and smaller than 7/
