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MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
444.*.:
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H.C. S 1.60;MN_,50
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This paper was submitted for publication
in the open literature at least & Fonths
prior to the issuance date of this Micro-
card. Since the U.S.A.E.C. has no evi-
dence that it has been published, the pa-
per is being distributed in Microcard
form as a preprint.
THE NEW ASME SECTION III NUCLEAR PRESSURE VESSEL CODE
Pentru informati
e
opanowa Towar porno
indir T
reatment
JUN 24 1988
Presented at Joint Symposium on "Advanced Technology in Nuclear Reactor
als and Fabrication", of New York Sections of American Welding
Society and American Nuclear Society, New York, May 12, 1964.
by Edward C. Miller, Oak Ridge National Laboratory*, Oak Ridge, Tennessee
* Operated by Union Carbide Corporation for the U. S. Atomic Energy
Commission.
MASTER
-
-
-
Appreciation of the significance and limitations of the new ASME Section III
-
-
...
Nuclear Pressure Vessel Code requires some review of the history of the
Boller Code Itself. It had its inception almost half a century ago when an
alarming increase in the frequency and severity of explosions of power and
marine boilers accompanied by increases in operating temperatures and press
Porno,
sures, prompted the adoption of many different sets of boiler rules by
-
-
-
-
-
-
-
-
: various states, municipalities, and other jurisdictions. The situation be-
-
T.
-
-
-
?
-
-
-
came chaotic and the American Society of Mechanical Engineers was asked
-
--
-
-
.
3
to establish a uniform set of rules for construction of power boilers. An
A.S.M.E. Boiler Code Committee prepared a uniform Boller Code which was
widely adopted-both voluntarily and as a legal document and a remark-
21
We
.
able decrease in boiler failures resulted. Over the years, the Code has
LEGAL NOTICE
me MOLFOR PUBLIO REFERRED

.
FAX
..
arsim, o spalmam
This report mo prepared as an account of Govorament sponsored work. Neithor the United
States, nor the Commission, nor any person roting on behalf of the Commissions
A. Makos any warranty or representation, oxpressed or implied, with respect to the accu-
racy, completeness, or usofulnose of the information contained in this report, or that the use.
of any information, Apparatus, method, or process disclosed in this roport may pot infringe
privately owned rights, or
B. Assumos any llabilities with rospect to the use of, or for damages resulting from the
use of any information, apparatus, method, or procesu disclosed in this report.
As used in the above, "person soting on behalf of the Commission" includes way om-
ployce'or contractor of the Commission, or omployee of such contractor, to the extant that
such employee or contractor of the Commission, or employee of such contractor proparos,
disseminates, or provides acceso to, any information pursuant to his employment or contract
with the Commission, or blo employment with such contractor.
wered ECT CONTACTO
RELASYD FOR ANNOUNCERTANI)..
.
IN NUCLEAR SCIENCE ABSTRACTS
not, it and does not w.
.....
...
, iirise.Write monitoriza..iwi!:
prinsidonnaroon si
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... Santorini' son primis in his
-
2 -
ST
-
-
kept pace with the development of power boilers and has also been extended
to cover other types of pressure containment, including unfired pressure
vessels and, more recently, nuclear vessels.
The Code is widely accepted today as a standard for the safe construction
of pressure-containing equipment. It is, nevertheless, a set of minimum
rules, not a design manual, and it still requires the exercise of sound,
responsible professional engineering competence, integrity, and judgment
in the design, construction, and operation of pressure equipment-require-
SAL
-
ments which are not always apparent to the general public, the regulatory
J
authorities, and, in some cases, to engineers themselves. It does not
provide detailed rules for operation, maintenance, or periodic Inspection
and repair of vessels, leaving much of this to the operating and regulatory
agencies. It does not attempt to provide rules to insure against failures
due to service-induced deterioration, but it does provide some recom-
mendations for the consideration of environmental conditions.
..
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- 3 -
The adoption of the Atomic Energy Act of 1954 promised a much greater
participation by private industry in the atomic energy program, particularly
in nuclear power production, and it became apparent that this would in-
volve the use of nuclear-related pressure-containing equipment in situations
paralleling the non-nuclear applications traditionally covered by the Boiler
and Pressure Vessel Code. The ASME Code Committee appointed a task
group to study and recommend its proper participation in this field, which
resulted in the formation in March of 1955, of a Special Committee on
Nuclear Power-now the Subcommittee on Nuclear Power. Initially, this
group did not attempt to write a separate Nuclear Code Section; rather, it
provided for the construction of nuclear vessels by formulating Code "Case
Interpretations" which provided additional rules permitting nuclear vessels
to be built to the general requirements of either Section I, Power Boilers,
or Section VIII, Unfired Pressure Vessels. The Cases were revised
frequently, which provided flexibility and permitted the rules to keep pace
- 4 -
with the rapid developments and practical applications of nuclear technology.
As experience with the Case Interpretation method accumulated, the ASME
Code Committee decided to prepare a separate Code Section for nuclear
vessels. This went through some three or four draft revisions in two or three
years, and the 1963 edition of Section III was finally issued in early 1964.
Some of the differences in philosophy between the Nuclear Section III of
-
the Code and the conventional Sections I and VIII, should be mentioned.
The special rules in Section III which apply to materials, fabrication, and
Inspection of nuclear equipment result largely from differences in design
concepts and design criteria. A basic requirement ce Sections I and VIII
is that the wall thickness of a vessel should be such that the hoop stress
does not exceed the allowable stress, although it is recognized that higher
localized and secondary bending stresses generally exist in other parts of
a vessel, so Sections I and VIII allow a fairly generous safety factor and
impose some general design restrictions, thereby avoiding the requirement
- 5
-
of detailed stress analysis. In some cases this approach is overly con-
servative, but it may not be adequate in the event of extremely severe
thermal, cyclic stress, or design configurations. By way of contrast, a
principal objective in Section III has been a change in design rules to
permit the use of higher allowable stresses without reducing basic safety
levels. This is accomplished by requiring detailed stress analyses of the
vessels and by basing allowable stresses on different categories of stress.
Section III employs the maximum shear stress theory rather than the maximum
stress basis of Sections I and VIII. The maximum shear stress at a given
point is one-half the algebraic difference between the largest and smallest
of the three principal stresses at that point. The theory states that yielding
.
in a component occurs when this maximum shear stress value equals the
maximum shear stress which would occur at the yield point in a tensile test.
To simplify the calculations, Section III adopts a term, "stress Intensity",
which is defined as twice the maximum shear stress, and is directly com-
one per rinn.
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parable to the stress values found from tensile tests.
The Nuclear Code Section divides different types of stresses into: (1)
primary stresses, including general and local primary membrane stress and
primary bending stress; (2) secondary stresses; and (3) peak stresses
(see Table I). For the temperature ranges up to 700 or 890°F, presently
covered by Section III, the principal, or general primary membrane stress
intensity, Pm (somewhat analagous to maximum design or permissible hoop
stress in other Code Sections) is limited to a stress intensity limit, Sme
which is 2/3 the yield strength or 1/3 of the ultimate strength, whichever
.
is less. This contrasts the lesser of 5/8 the minimum yield strength or
.
.
1/4 the minimum ultimate strength used for ferrous materials in the Unfired
Pressure Vessel Code. It has been established analytically and experi-
mentally that the local primary membrane stress Intensity (P1) may be safely
limited to 1.5 times the design stress intensity limit (1.5 Sml, as can the
sum of the primary membrane and bending stress intensities (Pm + Pb or P, +P).
-
.
-
-
-
-
-
.
-
7
-
Also, the sum of the primary and secondary stress intensities (Pm + Pb+Q
or Py + Pb+Q) may be safely limited to 3 times the stress intensity limit
(35m). Section III provides means for considering fluctuating stress-
low cycle fatigue-on the basis of a modified Goodman diagram. Creep and
stress rupture are not involved as design stress criteria in the current
edition of Section III, but Code Case 1331, "Nuclear Vessels in High
Temperature Service", does permit the design of nuclear vessels to Section
III for operation at higher temperatures.
Now let me emphasize that this design concept is acceptable and validi
.
only if one has confidence in the physical integrity of the vessel, as
established by the quality of fabrication and inspection. The design
A.
criteria do not provide excess safety factor margins for unverified structural
discontinuities, fabrication errors, or material or weld defects. Confidence
in the knowledge of the maximum size and distribution of possible defects
is particularly important in cyclic operation and in regions of high thermal
stresses, as well as in radioactive services where periodic inspection is
--
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difficult or impossible. These place premiums on the quality of materials
and fabrication, on the verification of this quality through inspection, and
on design to facilitate this inspection.
.
-
-
Section III groups pressure vessels in nuclear service into three general
classes. Class A vessels include reactor vessels, calandria vessels,
vessels which contain primary coolant, and any other vessels where acces-
sibility for periodic examination is limited by radioactivity considerations
or where severe cyclic operations are encountered. Class B vessels are
those generally known as containment vessels, the Code does not require
that containment vessels be used, it simply provides rules for the con-
struction of steel containment vessels when they are used. Class C
vessels are nuclear-related vessels generally designed to the requirements:
of Section VIII, which do not fall in the categories of Classes A or B. This
paper is limited largely to requirements of Class A vessels.

Section III requires that a design specification be prepared for each Class
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A vessel, specifying the functions, design requirements, classification,
and operating conditions on which the design, construction, and inspection
requirements are to be based. This design specification is the responsibility
of the owner; and requires certification of compliance by a registered pro-
fessional engineer experienced in pressure vessel design. A stress report
is also required for each vessel to include the stress calculations and
pressure part design drawings necessary to establish compliance with the
design specification; this report also requires certification by a registered
professional engineer. A detailed manufacturer's data report is required,
including certification that the materials, fabrication methods, and in-
spection techniques are in accordance with the Code Section, the design
specifications, and the design drawings.
Materials authorized for use in Section III are presently limited to a re- .
latively small number of carbon steels, low alloy steels, and high alloy
steels most frequently used in nucleai vessel construction. More materials
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- 10 -
will be added as the need develops, but the task of accumulating-and
sometimes experimentally developing-the data needed to establish safe
design stress intensity and yield strength values over the desired range
of temperatures is a substantial one. Several additional materials, parti-
cularly nickel-base alloys and some special steels for which material
specifications are not yet available-have been incorporated into new Case
Interpretations permitting their use in Section III.
Other features of Section III include provisions for verification of material
quality by supplementary inspection and nondestructive testing. Test
coupons are generally required, subjected to the same cycle of heat treat-
ment which the fabrication itself will undergo, and tested to determine com-
pliance with Code and specification requirements.
Ultra sonic inspection is required for all plates for reactor vessels, for
plates 4 in. and thicker for other Class A vessels, and for the bond between
the cladding and the base plate of certain materials. The ultrasonic
.......
.........
145
****
- 11 -
standards reject defects which continue during movement of the transducer
2 in. in any direction. Repair of rejected plates by welding is permitted
under some circumstances.
Forgings and bars in similar applications are also subjected to similar
ultrasonic examination, and, in addition, ring, flange, and other hollow
forgings require ultrasonic examination by the shear wave technique, whose
reference standard is a groove 1 in. long and 3% of the nominal forging
thickness in depth. Forgings are also required to be examined on all sur-
faces by magnetic particle or liquid penetrant methods,
Castings require radiographic examination, and castings over 12 in. thick
must also be examined ultrasonically. Castings also require examination
by magnetic particle or liquid penetrant methods. Subject to certain
limitations, they may be repaired by welding.
Pipe, tubes, and fittings are classed into Group A which normally confines
reactor coolant during operation, and Group B which includes all other
h
.
.

.
- 12 -
.1
....
.
.
.
..
tubular products. Group B does not require supplementary nondestructive
.
examination, but Group A products require full-length examination by an
applicable method of radiographic, ultrasonic, magnetic particle, liquid
penetrant, or eddy current examination.
Charpy V-notch impact tests at stated temperatures are required for certain
carbon steel, alloy steel, and chromium alloy steel materials. Test re-
'
.
.
quirements are based on two considerations—the material specifications
and the temperature limits imposed by hydrostatic testing and service pres-
surization, using the NDT+ 60°F concept, with the NDT impact values
related to specification minimum yield strengths. A 15 ft-lb minimum
average is required for materials with specification yield strengths less
than 30,000 psi, 20 ft-lb for 35,000 to 45,000 psi yield strengths, 30 ft-lb
for 45,000 to 75,000 psi, and 35 ft-lb for bolting with yield strengths over
75,000 psi. This is under review, however, and will probably be modified
to be consistent with newer developments in the field.
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- 13 -
To facilitate the design and inspection of welded joints, the weld joint
categories of Fig. 1 have been adopted. Category A Includes longitudinal
welded joints, welded joints in a sphere or a formed flat head or surface,
and certain circumferential welded joints; Category B Joints include most
other circumferential welded joints; Category C welded joints are largely
flange connections; and Category D joints are nozzle-type joints.
Category A joints require full-penetration, double-welded or equivalent,
butt joints and also require full radiography. Category B joints require
XTHN1 SAYLI
full penetration and full radiography. Plates or elements which do not
lie in the same plane are limited to an offset angle of 30%. Category C
joints, Illustrated in Fig. 2, are designed for full radiography, bụt may
OGLASI
sometimes require special radiographic techniques and, in some cases,
partial ultrasonic inspection. Category D joints, Fig. 3, require full-
penetration welds, radiography-sometimes with special techniques, and,
in some cases, ultrasonic examination.
- 14 -
Special fabrication requirements of Section III include certification of
materials by the vessel manufacturer if he is required to perform tests after
fabrication and heat treatment, complete and accurate identification of
materials in all stages of fabrication, and examination of edges of
material shapes as fabrication progresses, sometimes by magnetic
particle or liquid penetrant examination.
Welding requirements are similar to those of other sections of the Code,
except that essentially all welds are required to be completely radio-
graphed. Section III contains some supplementary welding procedure
qualifications, and some additional essential variables for certain types
of welding such as tube sheet joints and weld overlay cladding. Special
certifications are required to establish that the additional tests and
examinations of materials have been made.
The duties of the inspector in verification of material quality, dimensional
.
checks, heat treatment practice, hydrostatic tests, and post-weld heat
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- 15 -
treatment, are spelled out in some detail, as are the requirements for the
Inspection of welds and checking the welding procedure and welding operator
performance qualifications. The term Inspection is used to designate the
responsibilities of the authorized inspector; examination covers the actions
performed by nondestructive testing operators.
Requirements for radiographic examination of welded joints are similar to
those of Sections I and VIII; all three sections have recently adopted a new
type of penetrameter which provides improved equivalent sensitivity for
weld thicknesses over 1-1/2 in., and for wall thicknesses less than 1/2 in.,
the penetrameter sensitivity is based on a slit 1/4 in. long by 0.010 in.
wide. Ultrasonic examination is required for certain materials, certain
Category C and D joints, and in conjuncion with the recently accepted
electroslag welding techniques; but, in most other cases it is not yet
mandatory or a permissible alternate to radiography. Magnetic particle
and liquid penstrant examinations, where required, follow ASTM procedures:
- 16-
with minor Code modifications. Acceptance standards call for the removal
of cracks and linear defects, and place restrictions on the size and fre-
quency of aligned inclusions and nonlinear defects
.
Use of a new document such as the Section III Nuclear Pressure Vessel
Code will certainly reveal shortcomings, inadequacies, and errors in it.
The Subcommittee is already considering a number of possible changes,
..
additions, and interpretations. To improve the Code still further, will
require a considerable feed-back from users, who are urged to relay their
experiences, problems, and suggestions in writing to the Secretary of the
ASME Boiler and Pressure Vessel Code Committee.
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TABLE
BASIC STRESS INTENSITY LIMITS

Categories
Tabulated
Sy value
Stress Intensity Limit in terms of
Yielu Strongsh
Ulrimato Tonsile
Strongth (S)
(Sy)
:
Cenoral primary membrane
stress inlcnsity,
<
Local primary membrado
stress igicosity,
1.5 Sam
ES,
< su
Ppi
.
.
.
..
---- ..
2.5 m
.-.
Primary membrane plus
bending stress intensity,
[Pm (or Pi) + Pol
Primary plus secondary
slrcos intensily,
Pom (or P.) + PA+
.and
3 SON
< 2 Sy
e su
..................

....
..
.
Fig. 1. Welded Joint Categories:
... in Schematic Pressure Vessel
.
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12
12
5 / 23 / 66
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