Table 2. MSS SP-70 Grey Iron Gate Valves—
Non-shock Pressure Temperature Ratings
“classes” such as those listed in ASME
B16.34 for valves (i.e. 300, 600, 1500,
etc.) The fitting classes are the pressure
ratings of the fittings at ambient temperature.
Aside from the common tees, elbows
and couplings, many other fitting types
are in use today; some of these smaller
diameter steel fitting types are listed in
Table 1.
The olet-type fittings are great time
and money savers for the pipe fabrication industry. The technical name for the
“olet” type fittings is “integrally reinforced forged branch outlet fitting,” and
their design and dimensions are covered
in MSS SP-97. Olet fittings are sometimes welded onto valves to attach auxiliary piping or drains when there are no
bosses, or thickness of the valve body is
insufficient to allow for sockets or
threads.
Unions are very useful fittings in any
piping system where future disassembly
might be required. Unions are made in
various classes such as 150 and 300, but
they also are made in fitting classes
3000 and 6000. The union is basically
two machined seating surfaces held
together with an externally threaded col-
lar. The union’s purpose is to enable a
piping section to be easily altered or
repaired without having to unthread sec-
tions of pipe or remove welded fittings
from the system. Just like the seating
surfaces on valves, the seats of a union
must be kept clean and free of scratches.
Table 2 lists the piping component
classes for a hypothetical application.
Table 1. Small-diameter Steel Fitting Types
Name Usage & notes
Olet For attaching threaded or socket weld pipe to a larger diameter
pipe without the use of a tee
Cross Connects four pipes together at 90-degree angles in the
horizontal plane
Reducer For connecting dissimilar pipe sizes
Lateral A tee-like connector branching at a 45-degree angle from
the main pipeline
Bushing An externally and internally threaded fitting for connecting
dissimilar-sized threaded end pipe
Plugs Dead-end fittings designed to thread inside female pipe threads
and seal the end of a pipe
Caps Dead-end fittings designed to thread onto the outside of
threaded pipe components and seal the pipe
Union An adjustable piping component that allows pipe or piping
components to be easily removed for alteration or maintenance
dardization Society in 1964 (MSS SP-
66). The data in the MSS document
would be utilized by the writers of the
ASME B16.34 document a few years
later. The initial publication of ASME
B16.34 in 1973 finally put all the pres-sure-temperature rating and class material into one document, where it still
resides today.
USING THE TABLES
Table 1 is a portion of Table VII- 2-1. 1
excerpted from the current edition of
ASME B16.34. This table includes the
common carbon steel materials ASTM
A216 grade WCB and ASTM A105.
Looking at the table, we see temperatures in the left column. The temperatures actually go to 1000° F (538° C),
but the two materials referenced are not
recommended for continuous use at
temperatures above 800° F (427° C), so
the higher temperatures have been
omitted from this table. The top row
lists the pressure classes from 150
through 4500. Determining the working
pressure of WCB or A105 material at a
specific pressure class, requires just
glancing over to the appropriate column
and looking down to match the temperature. However, the table is most often
used to select the proper pressure class
when the temperature and pressure are
known.
For example, what pressure class
should be chosen for a steam valve operating at 1100 psi at 650° F (343° C)?
In looking at the table and reading up,
we see the class is 600.
Other valve types use different pressure ratings. For example, cast iron
valves built in accordance with MSS
SP-70 Grey Iron Gate Valves use their own
class ratings as listed in Table 2. Valves
built to different standards, including
the American Water Works Association
(AWWA), also have their own rating
systems.
Rating systems are vitally important
in the valve industry. Because of the
many types of valves and sectors of the
industry, there are several rating systems. As for the industrial refining,
petrochemical, chemical and power
industries, the class rating is by far the
most common. But all rating systems
serve a niche, so it is a good idea to
become familiar with those rating sys-
tems that are used in your particular
industry. VM
Temperature NPS NPS degrees F 2-12 14-24
(degrees C)
- 20 to 150 200 150 (- 29 to 66)
200 (93) 190 135
225 (107) 180 130
250 (121) 175 125
275 (135) 170 120
300 (149) 165 110
325 (163) 155 105
350 (177) 150 100
375 (191) 145
400 (204) 140
425 (218) 130
450 (232) 125
Note: all pressures are non-shock working pressures
CONTINUED FROM PAGE 24
Table 2. Piping Component
Classes
Pipe size ¾-inch
Working pressure of line 2400 psi
Working temperature
of line Ambient
Valve pressure class 1500
Flange class 1500
Minimum pipe schedule 80
Fitting class 3000
LARGE-DIAMETER FLANGES
Large-diameter fittings such as tees and
elbows are available in virtually every
pipe size. Oftentimes, the elbows are
actually manufactured by bending pipe
under high pressure and at high temperatures. For large-diameter tees and laterals, these are often fabricated by
welding components together. The most
common design standards for these
types of fittings are ASME B16.9,
“Factory Made Wrought Buttwelding
GREG JOHNSON is a contributing editor to Valve
Magazine and president of United Valve
( www.unitedvalve.com), Houston, TX. Reach him
at greg1950@unitedvalve.com.
NPS NPS NPS
30-48 2-12 14-24
150 500 300
115 460 280
100 440 270
85 415 260
65 395 250
50 375 240
355 230
335 220
315 210
290 200
270
250
U.S. ALLOYS, INC
Since 1976, Round Bar Supplier for Valve & Fitting Manufacturers
of
Petrochemical / Power Generation / Nuclear / Aerospace
Round Bar Stock
GRADES:
(Domestic and Import)
A105
A350 LF2
SA105
A675 GR 70
A696 GR C
SIZES:
304/304L
316/316L
317/317L
321/321H
347/347H
F- 11
7/8” to 24”
Cut to length 7/8” – 24” OD
ASTM/ASME/(Latest editions)
NACE MR01-75/NACE MR0103
DIN 3. 1.B/EN 10204
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