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API TR 6AF1 Document Information:
Title
Technical Report on Temperature Derating on API Flanges under Combination of Loading
American Petroleum Institute
Publication Date:
Nov 1, 1998
Scope:
1 Scope
This report is a continuation to the report on the capabilities of
flanges under combined loadings (PRAC 86-21) which resulted in the
publication of API Bulletin 6AF. Included herein is an in-depth look
into the effect of elevated temperatures on API flanges.
The results in this report are analytical and assume a temperature
gradient across the flange as stated in this report. When the flange is
insulated on the outside surface, the allowable loads will be higher.
Additional finite element models of five new flanges in
API6A, Sixteenth Edition, 1989, which were not in the 1986 Fifteenth
Edition, used as a basis for the earlier work, were developed for the
combined loading of bolt makeup, internal pressure, tension and bending
moment. The API materials were then grouped into four material
categories. A thermal analysis was performed (using all 63 axisymmetric
finite element models of PRAC 86-21 and the 5 new models) to determine
the temperature gradient and resulting thermal stresses at steady state
for all four material types at design bore temperatures of350°F and
650°F.
The post-processor program of PRAC 86-21 (calculating the maximum
moment capacity for various levels of pressure and tension based on
superposition) was partly modified to include thermal effects and
produce separate rating curves on the same chart, based on the leak or
loss of preload (on the ring joint) criterion and the stress criteria.
The stress criteria used were of two types: a) ASME Section VIII,
Division 2, allowable stress categories for the flange with the basic
membrane stress allowable established by API, and b) allowable bolt
stresses as established by API. The results of this post-processing are
presented in plots of pressure vs. allowable moment for various tension
levels. These new rating charts were developed at two elevated
temperatures for all four material categories in Appendices A, B, C,
and D respectively.
See Section 4 for details of the axisymmetric analysis and
Section 5 for details of the load capacity calculations.
As in the previous report PRAC 86-21, this report does not address the
actual gasket contact loads required to make a seal. This report
utilizes the leak or loss of preload (on the ring joint) criterion as in
Bull 6AF (PRAC 86-21) and Bull 6AF2 (PRAC 88-21) and not the leakage
criteria in report PN 90-21.
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