Head Tolerances

NOTE: These tolerances will apply to austenitic (300 series) material only. Any tolerances for special or non-standard material should be discussed with your sales representative. When products are designed as ASME, the configurations and tolerances set forth in Division 1, Section VIII shall take precedence over all other tolerances.

Straight Flange

Both straight flange and finished inside depth cannot be held simultaneously; therefore, heads will be trimmed to comply with overall depth tolerances as long as minimum straight flange is held as follows:

Head Thickness Standard Straight Flange Minimum Straight Flange
12 gauge or less 1" 1/2"
10 gauge or less 1 1/2" 1/2"

If the standard straight flange length must be held, please notify your sales representative of the requirement in advance of fabrication and Paul Mueller Company will apply a tolerance of ± 1/8" and allow the depth to become a reference dimension. The maximum straight flange that can be offered is 3.0" and is offered as special order only.

The tolerance for toe-out or toe-in for typical flanged and dished heads will be ± 1/16" as measured at 90° from machined edge. All heads and cones with a knuckle radius under 2" and of any material thickness 10 gauge and thicker (12 gauge and thinner cannot be flanged with a 2" straight flange using a small knuckle radius), there shall be a maximum of 2" straight flange. A tolerance of 3/32" on the toe out and 1/16" on the toe-in shall have applied to all heads with less than a 2" knuckle radius as described above.

Circumference and Finished Inside Depth

The following tolerances apply to all typical flanged and dished heads for tank components (for specialized head type tolerances, please consult with your sales representative):

Head Diameter Circumference Finished Inside Depth
35" or less ± 1/8" + 1/2" / – 1/8"
36" through 96" ± 1/8" + 1/2" / – 1/8"
97" through 144" ± 1/8" + 3/4" / – 1/8"
145" and above ± 1/8" + 1" / – 1/8"

Out of round shall not exceed 1% of the outside diameter.

If the finished inside depth must be held, please notify your sales representative of the requirement in advance of fabrication and Mueller will apply a tolerance of ± 1/8" on the depth and there will not be any tolerance, except minimum, held on the straight flange.

All tori-conical heads have a circumference tolerance of ± 1/8". Cones that are not flanged do not have a circumference tolerance and will require trim and fit at installation by the customer. All cones have a finished inside depth (FID) tolerance of ±1". (Cones that are swaged at the bottom end may have an additional height tolerance of – 0"/+ 1/2" above the typical tolerance.)

Minimum Thickness
Forming Allowances

Minimum thickness of material after forming but not including polishing for typical flanged and dished heads:

ASME Flanged and Dished

Diameter 1/2" Thick or Less Greater Than 1/2"
16" to 300” Add .03125" Add .0625"


Diameter 1/2" Thick or Less Greater Than 1/2" Thick
20" to 220” Add .0625" Add 15%

2:1 Elliptical

Diameter 1/2" Thick or Less Greater Than 1/2" Thick
20" to 168” Add .0625" Add 15%

For example:
A 3/8" thick, ASME F & D tank head, with an as is / as is material finish and #2 / #2 weld finish = .375" – .03125" forming allowance to equal .3437" total minimum thickness after forming but before polishing.

Non-code heads with minimum thickness requirements must be special ordered and noted in advance of fabrication for assurance and verification. For custom F & D, tori-conical, or other designs with special order geometry, please contact your sales representative for minimum thickness after forming.

Grinding Allowances

Due to the custom nature of fabricating components, Paul Mueller Company recommends that you contact your sales representative to review your specific application and assess an agreed upon final minimum thickness with your quotation.

Reverse Dish

Typical dished and flanged heads will have a tolerance for reversed condition as follows:

Head Diameter Maximum Reverse
0" thru 100" 1/8"
101 thru 144" 3/16"
145" and above 1/4"

Measurement of reverse will be accomplished by the placement of a 12" straight edge from the knuckle to dish tangent toward the center hole and measuring the gap between the straight edge and the outer surface of the head. For specialized head types (specifically tori-conical heads), contact your sales representative for additional tolerance information.


The head (squared or beveled edge) when laid on a flat surface will not exceed a maximum gap of 1/4" across a 48" distance and will not have an abrupt change greater than 1/16" over a 12" distance along the surface. This tolerance does not apply to flanged only heads (specifically with welded seams) or specialized head types. For additional clarification, please consult your sales representative.

Dish Radius (Crown Radius)

The dish radius (crown radius) tolerance for dished heads will be in compliance with ASME, Section VIII, Div 1, UG-81(a) unless otherwise stated on the order. All heads ordered for ASME compliance or to meet UG-81 will comply with UG-81(a) unless specifically stated in the order that the head must meet UG-81(b) for external pressure designed heads.

Flared and Dished Heads

Flared and dished heads shall have the following tolerances:

Diameter Outside Diameter *Inside Diameter Out-of-Round
All + 1/2" / – 0" ± 1/4" Not to exceed 1% of OD

*Inside diameter tolerance is for reference only.

Dished-Only Heads

Dished-only heads shall have the following tolerances:

Diameter Circumference Diameter Tolerance Out-of-Round
All N/A + 1/2" / – 0" Not to exceed 1% of OD

Dished only heads will be sold on the basis of outside diameter only.

Flanged-Only Heads

Flanged Only heads shall have a circumference tolerance of ±1/8". Some warpage of the flat portion may be expected depending on diameter, thickness of material, and the knuckle radius. Any manual pressure to obtain flatness is acceptable.Flanged only head flatness tolerances do not apply to heads with weld seams.

Head Diameter Flatness Tolerance
60" or less +/– 3/16"
61" thru 95" +/– 1/4"
96" thru 120" +/– 1/2"