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NONMANDATORY APPENDIX R
PREHEATING
INTRODUCTION
Preheating may be employed during welding to assist
in completion of the welded joint. The need for and
temperature of preheat are dependent on a number of
factors, such as the chemical analysis, degree of restraint
of the parts being joined, elevated physical properties,
and heavy thicknesses. Mandatory rules for preheating
are, therefore, not given in this Division except as
required
in the footnotes that provide for exemptions to postweld
heat treatment in Tables UCS-56 and UHA-32. Some
practices used for preheating are given below as a general
guide for the materials listed by P-Numbers in Section
IX. It is cautioned that the preheating temperatures listed
below do not necessarily insuresatisfactorycompletion of
the welded joint and requirements for individual materials
within the P-Number listing may have preheating more
or less restrictive than this general guide. The procedure
specification for the material being welded specifies the
minimum preheating requirements under Section IX weld
procedure qualification requirements.
The heat of welding may assist in maintaining
preheattemperatures after the start of welding and for
inspection
purposes, temperature checks can be made near the weld.
The method or extent of application of preheat is not
therefore, specifically given. Normally when materials of
two different P-Number groups are joined by welding,
the preheat used will be that of the material with the
higher preheat specified on the procedure specified on
the procedure specification.
R-1 P-NO. 1 GROUP NOS. 1, 2, AND 3
(a) 175F (79C) for material which has both a speci-
fied maximum carbon content in excess of 0.30% and athickness at
the joint in excess of 1 in. (25 mm);
(b) 50F (10C) for all other materials in this P-
Number.
R-2 P-NO. 3 GROUP NOS. 1, 2, AND 3
(a) 175F (79C) for material which has either a speci-
fied minimum tensile strength in excess of 70,000 psi
588
(480 MPa) or a thickness at the joint in excess of 58 in.
(16 mm);
(b) 50F (10C) for all other materials in this P-
Number.
R-3 P-NO. 4 GROUP NOS. 1 AND 2
(a) 250F (121C) for material which has either a
specified minimum tensile strength in excess of 60,000
psi (410 MPa) or a thickness at the joint in excess of 12in. (13
mm);
(b) 50F (10C) for all other materials in this P-
Number.
R-4 P-NOS. 5A AND 5B GROUP NO. 1
(a) 400F (204C) for material which has either a
specified minimum tensilestrength in excessof 60,000 psi
(410 MPa), or has both a specified minimum chromium
content above 6.0% and a thickness at the joint in excess
of 12 in. (13 mm);(b) 300F (149C) for all other materials in
these P-
Numbers.
R-5 P-NO. 6 GROUP NOS. 1, 2, AND 3
400F (204C)
R-6 P-NO. 7 GROUP NOS. 1 AND 2
None
R-7 P-NO. 8 GROUP NOS. 1 AND 2
None
R-8 P-NO. 9 GROUPS
250F (121C) for P-No. 9A Group No. 1 materials
300F (149C) for P-No. 9B Group No. 1 materials
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R-9 NONMANDATORY APPENDIX R R-10
R-9 P-NO. 10 GROUP
175F (79C) for P-No. 10A Group No. 1 materials
250F (121C) for P-No. 10B Group No. 2 materials
175F (79C) for P-No. 10C Group No. 3 materials
250F (121C) for P-No. 10F Group No. 6 materials
For P-No. 10C Group No. 3 materials, preheat is neither
required nor prohibited, and consideration shall be given
to the limitation of interpass temperature for various
thicknesses to avoid detrimental effects on the mechanical
properties of heat treated material.
For P-No. 10D Group No. 4 and P-No. 10I Group No.
1 materials, 300F (149C) with interpass temperature
maintained between 350F and 450F (177C and 232C)
R-10 P-NO. 11 GROUP
(a) P-No. 11A Group
Group No. 1 None (see Note)
589
Group No. 2 Same as for P-No. 5 (see Note)
Group No. 3 Same as for P-No. 5 (see Note)
Group No. 4 250F (121C)
(b) P-No. 11B Group
Group No. 1 Same as for P-No. 3 (see Note)
Group No. 2 Same as for P-No. 3 (see Note)
Group No. 3 Same as for P-No. 3 (see Note)
Group No. 4 Same as for P-No. 3 (see Note)
Group No. 5 Same as for P-No. 3 (see Note)
Group No. 6 Same as for P-No. 5 (see Note)
Group No. 7 Same as for P-No. 5 (see Note)
NOTE: Consideration shall be given to the limitation of
interpass
temperature for various thicknesses to avoid detrimental effects
on the
mechanical properties of heat treated materials.
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