MSS SP-45-2020
Drain and Bypass
Connections
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: standards@msshq.org
www.msshq.org
MSS
STANDARD PRACTICE
SP-45
This MSS Standard Practice was developed under the consensus of the MSS Technical Committee 106, Cast
Iron Valves, and the MSS Coordinating Committee. The content of this Standard Practice is the resulting efforts
of knowledgeable and experienced industry 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 industry at large. It is the
responsibility of the user of this Standard Practice to establish appropriate safety and health practices and determine
the applicability of regulatory requirements prior to use. The existence 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, 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 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 A). This Standard Practice
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 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.
For all MSS Standard Practices, the term “shall” means “must” and “shall not” means “must not”.
In this Standard Practice, all text, notes, annexes, tables, figures, and references are construed to be
“normative” and essential to understand the standard’s message. All appendices, footnotes, or other
information denoted as “supplemental”, that may be included within this Standard Practice, DO NOT include
mandatory or normative requirements.
The U.S. customary units and SI (metric) units in this Standard Practice are regarded separately as the standard
and may not be technically equivalent; each should be used independently of the other. Combining or
converting values between the two systems may result in non-conformance with this Standard Practice. U.S.
customary units was the original system in this Standard Practice and should be taken into account in cases of
conflict or incongruity.
This Standard Practice has been substantively revised from the previous 2003 (R2008) edition. It is
suggested that if the user is interested in knowing what changes have been made, that a direct page
by page comparison should be made of this document and that of the previous edition.
Non-toleranced dimensions in the Standard Practice are nominal unless otherwise specified.
Excerpts of this Standard Practice may be quoted with written permission. Credit lines should read
‘Extracted from MSS SP-45-2020 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 unless written permission is granted by the
Manufacturers Standardization Society of the Valve and Fittings Industry Inc. All rights reserved.
Originally Approved: July 1953
Originally Published: 1953
Current Edition Approved: May 2019(January 2020)
Current Edition Published: February 2020
MSS is a registered trademark of Manufacturers Standardization Society of the Valve and Fittings Industry, Inc.
Copyright ©, 2020 by
Manufacturers Standardization Society
of the
Valve and Fittings Industry, Inc.
Printed in U.S.A.
i
MSS
STANDARD PRACTICE
SP-45
FOREWORD
The original 1953 edition of MSS SP-45-1953, Bypass and Drain Connection Standard, was a combination
of two former MSS Standard Practices: MSS SP-5-1944, By-Pass Size Standard, and MSS SP-28-1943,
Drain Tapping Standard. As the subject matter of these two Standard Practices was so closely related, they
were combined as a convenience to the user.
MSS SP-5 was originally adopted in 1924 and applied to steel gate valves only. Bosses on steel castings
of that period presented a more complex problem than castings of other metals and the diversification of
requests in regard to size, location, and number of bosses on the part of users prompted the MSS to initiate
a standardization program on the subject. The original Standard Practice established the number of bosses,
minimum O.D. of a boss, and the pipe thread size for steel gate valves in sizes 3 to 24 inch inclusive. The
bosses were intended to be used for both drain and bypass connections.
In 1937 a new edition of SP-5 was adopted. This edition was greatly expanded over the original and
included both cast iron and steel valves in the gate, globe and angle patterns. The subject matter was
confined to by-passes only and standard locations were established for the bypass on each type of valve.
Two sets of bypass sizes were established; one for the purpose of warming up main lines before opening
the main valve and one for the purpose of balancing the pressure on both sides of the main valve to facilitate
its operation. The edition has been reaffirmed periodically up to the promulgation of the new MSS SP-45.
MSS SP-28 was originally adopted in 1937 and was also prompted by the variety of user requests for
connections on valves and fittings at odd locations and varying sizes, with and without bosses. MSS SP28 established standard drain sizes for each size valve and fitting, standard maximum sizes for unbossed
tapping’s, and standard locations with standard symbols to designate the location. MSS SP-28 was revised
in 1945 at which time a standard method of designating openings of reducing fittings was added. This
Standard Practice was also periodically reaffirmed.
The 1953 edition of MSS SP-45 combined these two Standard Practices so that the user has all information
pertaining to drain and bypass connections in a single document. In this edition the newer methods of
making attachments, such as butt welding were recognized.
The 1971 edition expanded the coverage of the document by including coverage of ball valves. In preparing
this edition, the entire Standard Practice was reviewed and up-dated to keep pace with the expanding
technology.
The 1976 edition expanded the coverage of the bypass sizes to include valves through NPS 48 and the
document was metricized.
The 1982 edition expanded the coverage of the document to include plug valves and included a minor
change in title to “By-Pass and Drain Connection Standard”.
The 1987 edition was a reaffirmation of the 1982 edition with no substantive change.
The 1992 edition changed the title to “Bypass and Drain Connections”, removed metric units, and made
several editorial changes.
The 1998 edition added metric units and made several editorial and format changes.
The 2003 edition was issued with only editorial changes.
The 2008 edition was a reaffirmation of the 2003 edition with one editorial correction in Annex A.
This 2020 edition revised the title to “Drain and Bypass Connections”, added additional drain sizes, revised
Sections 1 through 6, revised Table 1, Table 2 (including Notes), Table 3, and Table 4, updated Figures 1
and 2 (including Notes), updated Annex A references, in addition to other editorial, clarifying, and format
related changes.
ii
MSS
STANDARD PRACTICE
SP-45
TABLE OF CONTENTS
SECTION
1
2
3
4
5
6
7
8
SCOPE ........................................................................................................................................ 1
STANDARD SYMBOLS, LOCATIONS, AND DEFINITIONS .............................................. 1
STANDARD DRAIN SIZES ..................................................................................................... 1
STANDARD BYPASS SIZES ................................................................................................... 2
BYPASS LOCATIONS .............................................................................................................. 3
DRAIN AND BYPASS CONNECTION DIMENSIONS .......................................................... 4
BOSSES ...................................................................................................................................... 5
REDUCING FITTINGS ............................................................................................................. 6
TABLE
1
2
3
Standard Drain Sizes ................................................................................................................... 1
Bypass Sizes ............................................................................................................................... 2
Connection Dimensions .............................................................................................................. 4
FIGURE
1
2
3
4
5
6
Minimum Pipe Thread Length .................................................................................................... 4
Welding Socket Dimensions ....................................................................................................... 4
Butt Welds .................................................................................................................................. 5
Boss Diameters ........................................................................................................................... 5
Method of Designating Location of Opening for Drains and Bypasses ..................................... 7
Method of Designating Location of Opening for Drains ............................................................ 8
ANNEX
A
Referenced Standards and Applicable Dates ............................................................................. 9
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MSS
STANDARD PRACTICE
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Manufacturers Standardization Society of the Valve and Fittings Industry
iv
SP-45
MSS
STANDARD PRACTICE
SP-45
DRAIN AND BYPASS CONNECTIONS
1. SCOPE
1.1 This Standard Practice establishes requirements for connections to valves and fittings to
accommodate drains and bypasses in all pressure classes.
1.2 Specific requirements contained in this Standard Practice include:
a) Standard symbols and locations of openings for drains and bypasses
b) Standard sizes of drain and bypass openings
c) Minimum pipe thread lengths in drain and bypass tapping’s
d) Minimum diameter and depth of socketweld connection for drains and bypasses
e) Butt-welding connections for drains and bypasses
f) Bosses for drain and bypass connections
g) Method for designating outlets of reducing fittings
2. STANDARD SYMBOLS, LOCATIONS, AND DEFINITIONS
2.1 Figures 5 and 6 illustrate the application of standard symbols for the locations of openings for drain
and bypass connections recognized as standard. These symbols should be regularly employed on
drawings, specifications, requisitions, and other documents, as they pertain to these types of connections.
2.2 When a tap is required at some other location, it is recommended that the manufacturer be consulted
as to its practicability, and both the inquiry and the order should be accompanied by a sketch indicating
the location upon the valve or fitting.
2.3 Standardized definitions for terms contained in this Standard Practice may be found in MSS SP-96.
3. STANDARD DRAIN SIZES
3.1 When valves and fittings require drain openings, they are regularly furnished with the size shown in
Table 1 unless otherwise specified by purchaser.
TABLE 1
Standard Drain Sizes
Valve or Fitting
Drain
NPS
DN
NPS
DN
2–4
50 – 100
1/2
15
5–8
125 – 200
3/4
20
10 – 24
250 – 600
1
25
30 – 36
750 – 900
2
50
42 – 48
1050 – 1200
21∕2
65
1
MSS
STANDARD PRACTICE
SP-45
4. STANDARD BYPASS SIZES
4.1 When valves are ordered with a bypass attached, the size of bypass shall be as shown in Table 2,
except where unusual service conditions warrant consideration of a special oversized bypass.
TABLE 2
Bypass Sizes
Main Valve
NPS
2–4
DN
50 – 100
5
125
6
8
150
200
Bypass
(a)
Series A
NPS
DN
1/2
15
3/4
3/4
3/4
Series B(b) (c)
NPS
DN
1
25
20
11∕4
32
20
1
1 ∕4
32
20
1
1 ∕2
40
1
10
250
1
25
1 ∕2
40
12
300
1
25
2
50
14
350
1
25
3
80
16
400
1
25
3
80
18
450
1
25
3
80
20
500
1
25
3
80
24
600
1
25
4
100
30
750
1
25
4
100
36
900
1
25
6
150
42
1050
1
25
6
150
48
1200
1
25
8
200
NOTES:
(a) Series A is for preheating the piping system (normally with steam) before opening
main valve and for balancing pressures where lines are of limited volume.
(b) Series B is primarily for lines conveying gases or liquids where bypassing
may facilitate the operation of the main valve by balancing the pressure on
both sides of the closure member. The larger bypass sizes, specifically NPS
3 (DN 80) and greater, are typically used for metal-seated valves, where
differential pressures can be more of a concern. These larger bypass sizes
may be of the bolted-on type.
(c) Bypass requirements for Resilient-Seated (RS) Gate Valves can vary
significantly depending on the valve size, design, type of bypass, and
application. Most RS Gate Valve installations do not require a
bypass. However, if the purchaser does require the use of a bypass, the
purchaser should verify availability with the manufacturer and ensure the
purchase documents reflect those requirements.
2
MSS
STANDARD PRACTICE
SP-45
5. BYPASS LOCATIONS
5.1 Gate Valves When gate valves, which are to be installed in a vertical orientation, are ordered with
a bypass attached, it shall be standard practice to attach the bypass on the side of the main valve with
the stems of both valves pointing vertically upward.
When gate valves are to be installed in a horizontal orientation, and are ordered with a bypass attached,
it shall be standard practice to attach the bypass on the center of the flow line, at the bottom of the main
valve (see Figure 5, locations C and D), with the stem of the bypass valve at a right angle to the main
valve stem. This is designated as the “bottom attachment”, or “bypass at the bottom”.
When any other “special attached location” or other position of the bypass valve is desired, a sketch
should be sent to the manufacturer.
5.2 Globe Valves When globe valves are ordered with a bypass attached, it shall be standard practice
to attach the bypass on the right-hand side of the main valve (see Figure 5), locations E and F), with the
stems of both valves parallel and pointing vertically upward.
When a bypass is “specially” required to be attached on the left-hand side (see Figure 5, locations A and
B), the designation shall be “left-hand attachment”. The right-hand side of a globe valve is the side at
the right, when facing the flow port, which leads to the underside of the disc.
5.3 Angle Valves When angle valves are ordered with a bypass attached, it shall be standard practice
to attach the bypass at the back of the main valve (see Figure 5, locations E and F), with the stems of
both valves parallel and pointing vertically upward.
When a bypass is “specially” required to be attached on the right-hand or left-hand side (see Figure 5
locations C and D, and locations A and B, respectively), the designation shall be “right-hand attachment”
or “left-hand attachment” accordingly. The right-hand side of an angle valve is at the right, when facing
the back of the valve.
5.4 Check Valves When check valves are ordered with a bypass attached, it is standard practice to
attach the bypass on the side of the check valve so that the bypass valve stem and the check valve cover
both point vertically upward.
If the location of a bypass is important, its location should be specified according to Figure 5.
5.5 Plug Valves When plug valves are ordered with a bypass attached, it shall be standard practice to
attach the bypass on the side of the main valve with the stems of both valves pointing vertically upward.
If the main valve should have a handwheel on the side of the valve, the bypass, where possible, should
be located on the handwheel side.
If any other location is required, the position should be specified according to Figure 5.
5.6 Ball Valves When ball valves are ordered with a bypass attached, it shall be standard practice to
attach the bypass on the side of the main valve with the stems of both valves pointing vertically upward.
If the location of bypass is important, its location should be specified according to Figure 5.
3
MSS
STANDARD PRACTICE
SP-45
6. DRAIN AND BYPASS CONNECTION DIMENSIONS
6.1 Pipe Threads Pipe threads shall be tapered pipe threads in accordance with ASME B1.20.1. Metal
thickness shall be sufficient to allow the effective thread length specified in Table 3. These lengths are
equal to the effective thread lengths of tapered external pipe thread found in ASME B1.20.1.
Where wall thickness is insufficient or the tapped hole needs reinforcement, a boss is required.
6.2 Sockets Sockets (socket-welding) may be provided in the wall of a fitting or valve if the metal
thickness is sufficient to allow the depth of socket specified in Table 3.
Where the wall thickness is insufficient, or the size of socket requires opening reinforcement, a boss
is required.
FIGURE 1
Minimum Pipe Thread Length
FIGURE 2
Welding Socket Dimensions
NOTE: Dimension L in Figure 1 is equal to the effective thread length of ASME B1.20.1 External Pipe Threads.
TABLE 3
Connection Dimensions
Connection Size
Welding Socket
(See Figure 2)
Diameter
Depth
A, Min.
B, Min.
Pipe Thread Length
L, Min.
(See Figure 1)
NPS
DN
in.
mm
in.
mm
in.
mm
3/8
1/2
3/4
1
1 1∕4
1 1∕2
2
2 1∕2
10
15
20
25
32
40
50
65
0.41
0.54
0.55
0.69
0.71
0.73
0.76
1.14
10.4
13.6
13.9
17.4
18.0
18.4
19.3
28.9
0.690
0.855
1.065
1.330
1.675
1.915
2.406
2.906
17.53
21.72
27.05
33.78
42.55
48.64
61.11
73.81
0.19
0.19
0.25
0.25
0.25
0.25
0.31
0.31
4.8
4.8
6.4
6.4
6.4
6.4
7.9
7.9
INFORMATIONAL NOTE: SI (metric) dimensions within this table are not necessarily equivalent to U.S.
customary units; the SI (metric) dimensions were aligned with associated external standards.
4
MSS
STANDARD PRACTICE
SP-45
6.3 Butt Welds Connections may be made by butt welding directly to the wall of the fitting or valve.
See Figure 3.
FIGURE 3
Butt Welds
7. BOSSES
7.1 When a boss is required to meet the thicknesses in Table 3, the diameter shall be not less than those
shown in Figure 4.
NPS
DN
Boss Diameter
J
in.
mm
3/8
10
1.25
31.8
1/2
15
1.50
38.1
3/4
20
1.75
44.5
1
25
2.13
54.1
1
1 ∕4
32
2.50
63.5
1
1 ∕2
40
2.75
69.9
2
50
3.38
85.9
1
65
4.00
101.6
Connection Size
2 ∕2
FIGURE 4
Boss Diameters
5
MSS
STANDARD PRACTICE
SP-45
8. REDUCING FITTINGS
8.1 When a drain opening is required on the side of a reducing fitting whose side is tapered, the axis of
the drain opening should be at right angles to the centerline of the fitting.
8.2 The size of the drain opening on a reducing fitting shall be governed by the size of the adjacent outlet.
8.3 When a tap is required on a reducing fitting at a point centrally located, such as “G” on a reducer, its
size shall be governed by the average of the drain openings which would be used for the largest and smallest
outlet, using the drain opening size which is standard, or the next smaller size as shown in Table 1.
6
MSS
STANDARD PRACTICE
FIGURE 5
Method of Designating Location of Openings for Drains and Bypasses
7
SP-45
MSS
STANDARD PRACTICE
SP-45
NOTE: The illustrations above show two views of the same fitting and represent fittings with symmetrical shapes,
except for the Side Outlet Elbow and the Side Outlet Tee (Straight Sizes).
FIGURE 6
Method of Designating Location of Openings for Drains
8
MSS
STANDARD PRACTICE
SP-45
ANNEX A
Referenced Standards and Applicable Dates
This Annex is an integral part of this Standard Practice and is placed after the main text for convenience.
Standard Name
Description
ASME, ANSI/ASME
B1.20.1-2013(R2018)
Pipe Threads, General Purpose (Inch)
MSS: ANSI/MSS
SP-96-2017
Terminology for Valves, Fittings, and Their Related Components
The following organizations appear in the above list:
ANSI
American National Standards Institute, Inc.
25 West 43rd Street, Fourth Floor
New York, NY 10036-7406
ASME
American Society of Mechanical Engineers (ASME International)
Two Park Avenue
New York, NY 10016-5990
MSS
Manufacturers Standardization Society of the Valves and Fittings Industry
127 Park Street, NE
Vienna, VA 22180-4602
9
MSS
STANDARD PRACTICE
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Manufacturers Standardization Society of the Valve and Fittings Industry
10
SP-45
MSS
STANDARD PRACTICE
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11
SP-45
MSS
STANDARD PRACTICE
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Manufacturers Standardization Society of the Valve and Fittings Industry
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SP-45
Purchase or View a Full Listing of MSS Standards at:
http://msshq.org/Store/PriceList.cfm
MSS Standard Practices (SPs) related to or referenced in this publication:
ANSI/MSS SP-25
ANSI/MSS SP-96
Standard Marking System for Valves, Fittings, Flanges, and Unions
Terminology for Valves, Fittings, and Their Related Components
–––––––––––
American National Standards Published by MSS, an ANSI-accredited Standards Developer:
ANSI/MSS SP-25
ANSI/MSS SP-44
ANSI/MSS SP-55
ANSI/MSS SP-58
ANSI/MSS SP-96
ANSI/MSS SP-114
ANSI/MSS SP-122
ANSI/MSS SP-134
ANSI/MSS SP-135
ANSI/MSS SP-138
ANSI/MSS SP-144
Standard Marking System for Valves, Fittings, Flanges, and Unions
Steel Pipeline Flanges
Quality Standard for Steel Castings for Valves, Flanges, Fittings, and Other Piping Components
– Visual Method for Evaluation of Surface Irregularities
Pipe Hangers and Supports – Materials, Design, Manufacture, Selection, Application, and Installation
Terminology for Valves, Fittings, and Their Related Components
Corrosion Resistant Pipe Fittings Threaded and Socket Welding Class 150 and 1000
Plastic Industrial Ball Valves
Valves for Cryogenic Service, including Requirements for Body/Bonnet Extensions
High Pressure Knife Gate Valves
Quality Standard Practice for Oxygen Cleaning of Valves and Fittings
Pressure Seal Bonnet Valves
–––––––––––
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All Standard Practices are officially available only from MSS and through our authorized distributors:
About MSS
The Manufacturers Standardization Society (MSS) of the Valve and Fittings Industry is a non-profit technical association organized
for development and improvement of industry, national and international codes and standards for Valves, Valve Actuators, Valve
Modifications, Pipe Fittings, Flanges, Pipe Hangers and Supports, and Associated Seals. Since its establishment in 1924, MSS has
been dedicated to developing standards for national and global applications, in cooperation with other standardizing bodies and
regulatory authorities. MSS is an American National Standards Institute (ANSI)-accredited standards developer.
For more information on membership and eligibility requirements, visit: http://msshq.org/Store/Membership.cfm
Manufacturers Standardization Society of the Valve and Fittings Industry, Inc.
127 Park Street, NE, Vienna, VA 22180-4620 • Phone (703) 281-6613 • Fax (703) 281-6671
“The Technical Voice of the Industry”
IHS-MSS SP-45-2020