asme-asme-2010A revised ASME PCC-1 has recently been published and includes several new appendices. Among these is a new Appendix M “Washer Usage Guidance and Purchase Specification for Through-Hardened Washers”, which outlines a purchase specification for the manufacture of through-hardened washers for use on pressure boundary bolted flanged connections. This paper outlines the background as to why the new appendix was considered necessary. It also details the logic behind the selected materials and the operational limits placed on those materials

1. BACKGROUND ON THE NEW ASME PCC-1–2010 APPENDIX M “WASHER USAGE GUIDANCE
AND PURCHASE SPECIFICATION FOR THROUGH-HARDENED WASHERS”
Joseph Barron
Northrop Grumman Shipbuilding
Newport News, Virginia, USA
b.j.barron@ngc.com
ABSTRACT
A revised ASME PCC-1 has recently been published and
includes several new appendices. Among these is a new
Appendix M “Washer Usage Guidance and Purchase
Specification for Through-Hardened Washers”, which
outlines a purchase specification for the manufacture of
through-hardened washers for use on pressure boundary
bolted flanged connections. This paper outlines the
background as to why the new appendix was considered
necessary. It also details the logic behind the selected
materials and the operational limits placed on those
materials.
INTRODUCTION
The use of washers on metallic bolted flanged
connections is not mandated by the ASME Boiler and
Pressure Vessel Code [1], ASME B31.1 [2] for Power
Piping or ASME B31.3 [3] for Process Piping. Even
ASME PCC-1 [4] notes that the “Use of washers is
optional.” However, PCC-1 goes further to state that “it
is generally recognized that the use of through-hardened
steel washers will improve the translation of torque input
into residual bolt stretch.” Users acknowledge this
benefit and frequently employ washers to improve the
torque-tension relationship as well as to prevent/remediate
damage to flange and nut bearing surfaces. Appendix M
in PCC-1 was developed to assist users in procuring
washers suitable in terms of dimensions and materials for
use on bolted flanged connections.
NEED FOR THROUGH-HARDENED WASHERS
As noted above, some users have employed washers on
bolted flanged connections to improve the torque-tension
relationship. Sometimes, these washers are only surface-
hardened. This can lead to cupping and thinning of the
washer due to plastic deformation of the soft interior. The
resulting deformation can adversely affect the torque-
tension relationship and can lead to loss of preload.
Figure 1 shows how a surface-hardened washer can
become damaged during installation.
An additional reason for employing through-hardened
washers is to prevent damage to the flange to nut bearing
surface. The most prevalent flange material is forged
carbon steel per ASTM A105 [5]. This material has a
specified hardness of 187 HBW (90 HRB) maximum.
The most prevalent nut material is carbon steel per ASTM
A194 [6], Grade 2H. This material has a specified
hardness of 212-327 HBW (95 HRB - 35 HRC). When
the nut is brought into contact with the flange bearing
surface and rotated, probable damage can occur with
attending variation in the torque-tension relationship.
Figure 2 shows new, undamaged flange and nut bearing
surfaces. Figure 3 shows the same flange bolt hole after
the joint was assembled by torquing the nut. Note the
damage to the flange bearing surface. The nut has
penetrated deeply enough into the flange surface such that
the washer face is no longer the sole contact surface
between the nut and flange. The corners of the nut
outside the washer face diameter are now contacting the
flange surface as the nut is turned. This will increase
friction and decrease the tension produced for a given
tightening torque.
DIMENSIONAL REQUIREMENTS
There are several existing specifications defining washer
dimensions for inch product. These include ASME
B18.22.1 [7] and ASTM F436 [8]. For applications on
bolted flanged connections, washers in accordance with
the F436 standard are used most frequently since this
standard requires the washers to be through-hardened up
to and including 1-1/2 in. nominal size. However, these
specifications do not provide washers with dimensions
suitable for use on typical pressure boundary flanges such
Proceedings of the ASME 2010 Pressure Vessels & Piping Division / K-PVP Conference
PVP2010
July 18-22, 2010, Bellevue, Washington, USA
PVP2010-25774
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2. as those per ASME B16.5 [9] if the flanges are spotfaced
or backfaced. Figure 4 shows a 1-1/4 in. nominal ASTM
F436 washer aligned over the spotface of a 4 in. nominal
Class 1500 flange. The washer outside diameter is
approximately 0.125 in. (3.2 mm) larger than the spotface.
This washer cannot be used on this particular flange due
to the gap introduced. Table 1 lists the minimum spotface
diameter from MSS SP-9 [10] along with the maximum
outside diameters for F436 and B18.22.1 washers. Note
that neither washer standard provides all necessary
nominal sizes. Therefore, the outside diameters,
including tolerance, of the washers in Appendix M were
selected to enable the washers to fit on the minimum size
spotface specified in SP-9.
The inside diameters of the washers defined in Appendix
M were dimensioned to allow them to fit relatively
closely to the stud or bolt threads. When studs are used,
they can be installed under whichever nut is turned during
tightening. However, when bolts are used, these washers
must be installed under the nut. Installation under the bolt
head may lead to interference between the bolt shank or
under head fillet and the inside diameter of the washers.
The benefit of the smaller inside diameter is that it
maximizes the contact area between the nut and washer.
The thicknesses of the washers in Appendix M were
selected to be equal to one quarter of the nominal
diameter with a maximum value of 0.250 in. The values
were based on a review of F436 and current
manufacturing methods. Thicker washers are more
effective in distributing load across the flange surface.
However, cost efficient manufacturing concerns impose
limits on greater thicknesses.
The washers defined in Appendix M cover nominal sizes
from ½ in. through 4 in. Appendix M also provides
washer dimensions for metric applications from 14 mm to
100 mm nominal size. Dimensions for the metric washers
were selected in the same manner as for the inch washers.
Tables were developed in Appendix M defining the
various washer dimensions and associated tolerances.
MATERIAL REQUIREMENTS
In order for a washer to provide a low friction bearing
surface, it must have sufficient hardness to resist galling
and indentation. Additionally, since many bolted flanged
connections operate at elevated temperatures, the washer
material needs to be commensurate with the flange
bolting material. Based on the successful use of ASTM
F436 washer material on bolted flanged connections at
assembly, the same hardness value of 38-45 HRC (353-
421 HBW) was selected for Appendix M washers. In
regard to material, again based on the successful use of
F436 washers in lower service temperature bolted flanged
connections, the same carbon steel material was selected
for Appendix M. However, F436 washers were
developed for use on structural steel joints which do not
see elevated temperatures. Therefore, a low alloy steel
material, either UNS G41300 or G41400, was included in
Appendix M in order to have a material which would
retain its hardness at a higher service temperature. Since
austenitic steel bolting is widespread in certain
applications, a suitable washer material was needed for
this application. However, since austenitic steel would
not produce the required hardness, a martensitic steel,
UNS S4100, was selected. This alloy is available in sheet
form and is readily heat treated to the required hardness.
Acknowledging that the UNS S41000 martensitic steel
has reduced corrosion resistance compared to the
austenitic steel bolting, a precipitation hardening steel,
S171400, was added. The S17400 alloy has improved
corrosion resistance compared to S41000. It cannot
achieve the same hardness as the other materials so a
slightly reduced value of 33-42 HRC (311-390 HBW)
was specified. Therefore, Appendix M has the option for
four types of materials for various applications.
In order to guide users in selecting the appropriate washer
material, a table of service temperature limits for the four
types of materials was developed. This is reproduced as
Table 2. The table includes two service temperature
limits for each material. The reuse temperature is based
on preventing exposure to a temperature in excess of the
tempering temperature for that material. Thus, the
material should not soften while in service. The single
use temperature is much higher and is based on
replacement of the washer whenever the joint is
disassembled and the washer has been exposed to a
temperature in excess of the reuse limit.
Appendix M notes that the service temperature of the
washers is based on the actual temperature of the bolting,
not the process fluid temperature. This is acknowledged
in B31.3 which considers the flange bolting temperature
to be 80% of the process fluid temperature for un-
insulated flanges.
PURCHASE SPECIFICATION
Since no standard currently exists, Appendix M contains
information for the procurement of through-hardened
washers. The information is patterned after ASTM F436.
It details not only dimensional and material requirements
but also workmanship, sampling, testing and marking
requirements.
The dimensional and material information contained in
Appendix M has been transferred into a draft ASTM
standard for through-hardened washers. This draft
standard is currently under review by the ASTM F16.02
Subcommittee on Steel Bolts. When issued, this ASTM
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3. standard is intended to replace Appendix M with respect
to a purchasing specification.
CONCLUSION
This paper documents the need for developing a washer
standard specifically tailored for use on bolted flanged
connections attaching piping and pressure vessels and
why existing washer specifications were not appropriate
for these applications. The paper also defines the process
by which the dimensions and materials for these washers
were selected.
ACKNOWLEDGEMENTS
The author notes that the development of Appendix M
was a collaborative effort of the entire ASME
Subcommittee on Flange Joint Assembly responsible for
the update of PCC-1–2010.
REFERENCES
[1] ASME Boiler and Pressure Vessel Code (2007)
[2] ASME B31.1 (2007), Power Piping
[3] ASME B31.3 (2008), Process Piping
[4] ASME PCC-1 (2010), Guidelines for Pressure
Boundary Bolted Joint Assembly
[5] ASTM A105 (2009), Standard Specification for
Carbon Steel Forgings for Piping Applications
[6] ASTM A194 (2009), Standard Specification for
Carbon and Alloy Steel Nuts for Bolts for High
Pressure or High Temperature Service, or Both
[7] ASME B18.22.1 (2008), Plain Washers
[8] ASTM F436 (2007), Standard Specification for
Hardened Steel Washers
[9] ASME B16.5 (2009), Pipe Flanges and Flanged
Fittings
[10] MSS SP-9 (2005), Spot Facing for Bronze, Iron and
Steel Flanges
Figure 1 - Damaged Surface-Hardened Washer
on Pressure Vessel Flange
Figure 2 - New, Undamaged Flange and Nut Surfaces
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4. Figure 3 - Damaged Flange Bearing Surface
Figure 4 - 1-1/4 Nom F436 Washer on
4 Nom Class 1500 Flange
Table 1
Comparison of Spotface Diameter to Washer OD
Nom.
Size
MSS SP-9
Min Spotface
Diameter
ASTM F436
Max OD
ASME B18.22.1
Type A Narrow
Max OD
(in.) (in.) (mm) (in.) (mm) (in.) (mm)
Yellow indicates
OD is larger than
Spotface
Yellow indicates
OD is larger than
Spotface
0.500 1.12 28.4 1.095 27.81 1.092 27.74
0.625 1.37 34.8 1.345 34.16 1.342 34.09
0.750 1.56 39.6 1.500 38.10 1.499 38.08
0.875 1.78 45.2 1.782 45.26 1.780 45.21
1.000 2.03 51.6 2.063 52.40 2.030 51.56
1.125 2.21 56.1 2.313 58.75 2.280 57.91
1.250 2.43 61.7 2.563 65.10 2.530 64.26
1.375 2.65 67.3 2.813 71.45 2.780 70.61
1.500 2.87 72.9 3.063 77.80 3.030 76.96
1.625 3.12 79.2 N/A N/A 3.795 96.39
1.750 3.31 84.1 3.438 87.33 4.045 102.74
1.875 3.50 88.9 N/A N/A 4.295 109.09
2.000 3.75 95.3 3.813 96.85 4.545 115.44
2.250 4.18 106.2 4.063 103.20 4.795 121.79
2.500 4.62 117.3 4.563 115.90 5.045 128.14
2.750 5.06 128.5 5.063 128.60 5.315 135.00
3.000 5.50 139.7 5.563 141.30 5.565 141.35
3.500 6.37 161.8 6.625 168.28 N/A N/A
Table 2
Service Temperature Limits
Washer Material Reuse Single Use
Carbon Steel 400°F (205°C) 800°F (425°C)
Low Alloy Steel 750°F (400°C) 1000°F (540°C)
Martensitic Steel 800°F (425°C) 1200°F (650°C)
Precipitation
Hardening Steel
1025°F (550°C) 1500°F (815°C)
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