ASME PCC PCC-1–2010 -1–2010
APPENDIX D GUIDELINES FOR ALLOWABLE GASKET CONTACT SURFACE FLATNESS AND DEFECT DEPTH D-1 FLANG FLANGEE FACE FACE FLAT FLATNESS NESS TOL TOLERANC ERANCES ES
that any waviness of the flange faces is complimentary, such that the seating surfaces follow the same pattern. This is found in multipass exchanger joints and is often caused by thermal distortion. In this case, it is conservative to calculate the overall gaps between the flanges at points around the circumference and utilize the singleflange tolerances as shown in Table D-1M and Table D-1 to determine acceptability of the gap.
Existing industry flatness tolerance limits 1 do not include an assessment of the ability of the gasket to tolerate imperfections. The below tolerances are dependent on the type of gasket employed and are categorized based on the initial compression of the gasket to the final assemb assembled led load. Soft Soft gaske gaskets, ts, such such as spiral spiral wound wound,, PTFE, PTF E, fib fiber er,, etc etc., ., ha have ve an ass assemb embly ly com compr press ession ion in exc excess ess of 1.0 mm (0.04 in.). Hard gaskets have less initial compression than this and, while this can help with improved assembly due to less bolt interaction, it generally means that they are more susceptible to flange flatness out-of-tolerance. It is not appropriate to classify by gasket type; for example, 1.5 mm (1 ⁄ 16 16 in.) thick PTFE or fiber gaskets do not have sufficient compression to be classified as soft gaskets. It is suggested that loadcompression test results for the gasket being used are obtaine obta ined d fro from m the gas gasket ket man manufa ufactu cture rerr in or order der to det deterermine which limits may be employed. It should be noted that the compression limit is measured perpendicular to the gasket surface and therefore gaskets such as the RTJ gasket type are to be regarded as hard gaskets. It is acceptable to gauge mating mati ng flanges that have only one possible alignment configuration and determine
D-2 FLANG FLANGEE FACE FACE IMPERFECT IMPERFECTION ION TOLER TOLERANCE ANCES S The tolerances shown in Table D-2M and Table D-2 are separated separated into two catego categories, ries, depending depending on the gasketbeingemplo gas ketbeingemployedin yedin thejoint thejoint.. Sof Soft-f t-face aced d gas gasket ketss ar aree gaskets that have sufficient soft filler (such as graphite, rubber, or PTFE) that both the gasket and flange surface finish will be filled and additional filler exists on the gasket such that any small imperfections will also be filled as the gasket is compr compresse essed d betwe between en the flange flanges. s. Care should be taken to ensure the correct tolerances are employed for the gasket being installed. It may not be acceptable to categorize by gasket type as extremely thin gaskets or gaskets without sufficient filler will not fill imperfections and therefore should be categorized as har hard d gas gasket kets. s. Meta Metal-f l-face aced d gas gasket kets, s, suc such h as RT RTJJ or double jacketed gaskets, are categorized as hard faced. It is important to note that the tolerances apply to the gasket seating surface (area where the gasket seats both initially initiall y and finall finally y after assembly). assembly).
1
For example: PIP VESV1002, Vessel Fabrication Specification, ASME Boiler and Pressure Vessel Code Section VIII, Divisions 1 and 2 (May 2009), para. 7.3.9; PIP VESST001, Shell and Tube Heat Exchange Excha nge Specification Specification (Ma (May y 2009 2009), ), para para.. 7.3. 7.3.8; 8; and API 660, 8th edition, Table 3.
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ASME PCC-1–2010
Table D-1M Flange Seating Face Flatness Tolerances (Metric) Measurement
Hard Gaskets
Soft Gaskets
Acceptable variation in circumferential flange seating surface flatness
T1
<
0.15 mm
T1
<
0.25 mm
Acceptable variation in radial (across surface) flange seating surface flatness
T2
<
0.15 mm
T2
<
0.25 mm
Maximum acceptable pass-partition surface height vs. flange face GENERAL NOTE:
−0.25 mm
< P <
0.0 mm
−0.5 mm
< P <
0.0 mm
See Figs. D-1 and D-2 for description of T1 and T 2 measurement methods.
Table D-1 Flange Seating Face Flatness Tolerances (U.S. Customary) Measurement
Hard Gaskets
Soft Gaskets
Acceptable variation in circumferential flange seating surface flatness
T1
<
0.006 in.
T1
<
0.01 in.
Acceptable variation in radial (across surface) flange seating surface flatness
T2
<
0.006 in.
T2
<
0.01 in.
Maximum acceptable pass-partition surface height vs. flange face GENERAL NOTE:
−0.010 in. < P < 0.0 in.
See Figs. D-1 and D-2 for description of T1 and T 2 measurement methods.
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−0.020 in.
< P <
0.0 in.
ASME PCC-1–2010
Fig. D-1 Flange Circumferential Variation Tolerance,
T1
Align the measurement tool and set the datum at four points around the circumference. Take measurements around the full circumference to compare to tolerance T1, increment out 6 mm (0.25 in.) and repeat measurement. Repeat until full gasket seating surface (grey region) has been measured.
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22.5 deg
High
Low
T1 =
the maximum acceptable difference between the highest and lowest measurement for each circumferential line of measurement. Must not occur in less than a 22.5 deg arc.
24
ASME PCC-1–2010
Fig. D-2 Flange Radial Variation Tolerance, T2 = the maximum acceptable difference across each radial line of measurement
T2
Align the measurement tool and set the datum at four points around the circumference on the inner edge of the seating surface. Take measurements along radial lines across the gasket seating surface (grey region) every 200 mm (8 in.) or less until the entire gasket seating surface has been measured.
<200
mm (8 in.)
P
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P =
distance from the inner edge of the flange seating surface to the pass partition plate seating surface
Table D-2M Allowable Defect Depth vs. Width Across Face (Metric) Measurement r d < w /4 w /4
< r d <
w /2
w /2
< r d <
3 w /4
r d > 3 w /4
GENERAL NOTE: measurement.
Hard-Faced Gaskets
Soft-Faced Gaskets
<
0.76 mm
<
1.27 mm
<
0.25 mm
<
0.76 mm
Not allowed
<
0.13 mm
Not allowed
Not allowed
See Figs. D-3 and D-4 for description of defect
Table D-2 Allowable Defect Depth vs. Width Across Face (U.S. Customary) Measurement r d < w /4 w /4
< r d <
w /2
w /2
< r d <
3 w /4
r d > 3 w /4
GENERAL NOTE: measurement.
Hard-Faced Gaskets
Soft-Faced Gaskets
<
0.030 in.
<
0.050 in.
<
0.010 in.
<
0.030 in.
Not allowed
<
0.005 in.
Not allowed
Not allowed
See Figs. D-3 and D-4 for description of defect
25
ASME PCC-1–2010
Fig. D-3 Flange Surface Damage Assessment: Pits and Dents Gasket seating surface
S r d i n g l e
Pits and dents
r d
Do not locally polish, grind, or buff seating surface (remove burrs only)
J o r d i n e d
r d =
projected radial distance across seating surface
r d d ≤ r di
r di
d =
radial measurement between defects
Scattered; r d = the sum of
r di
Fig. D-4 Flange Surface Damage Assessment: Scratches and Gouges
Scratches and gouges r d r d
Do not locally polish, grind, or buff seating surface (remove burrs only)
r d =
projected radial distance across seating surface
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r d r d
