ARTICLE KF-4HEAT TREATMENT OF WELDMENTS

KF-400 HEAT TREATMENT OFWELDMENTS

This section gives requirements for heat treatmentof weldments. For additional heat treatment require-ments for quenched and tempered steels, see KF-630.

KF-401 Requirements for Preheating

The welding procedure specification for the materialbeing welded shall specify the minimum preheatingrequirements in accordance with the weld procedurequalification requirements of Section IX. The need forand temperature of preheat are dependent on a numberof factors, such as the chemical analysis, degree ofrestraint of the parts being joined, elevated temperaturephysical properties, and material thicknesses.

KF-402 Requirements for Postweld HeatTreatment1

Before applying the detailed requirements and exemp-tions in these paragraphs, satisfactory qualification ofthe welding procedures to be used shall be performedin accordance with Section IX and the restrictions listedbelow. Except for nonferrous materials and exceptas otherwise provided in Table KF-402.1 for ferrousmaterials, all welded pressure vessels or pressure vesselparts shall be given a postweld heat treatment at atemperature not less than that specified in Table KF-402.1 when the nominal thickness, including corrosionallowance, of any welded joint in the vessel or vesselparts exceeds the limits in Table KF-402.1. Materialsin Table KF-402.1 are listed by P-Number, which maybe found in QW-422 of Section IX and the tables ofstress values in Section II, Part D.

KF-402.1 When Holding Temperatures and TimesMay Be Exceeded.Except where prohibited in TableKF-402.1, holding temperatures and/or holding times

1 Additional postweld heat treatment requirements may result fromthe requirements of Article KT-2.

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exceeding the minimum values given in Table KF-402.1may be used (see KT-112 for additional requirements fortime at temperature). A time–temperature recording ofall postweld heat treatments shall be provided for reviewby the Inspector. The total holding time at temperaturespecified in Table KF-402.1 may be an accumulationof time of multiple postweld heat treat cycles.

KF-402.2 Heat Treatment of Pressure Parts WhenAttached to Different P-Number Groups and Non-pressure Parts. When pressure parts of two differentP-Number groups are joined by welding, the postweldheat treatment shall be that specified in Table KF-402.1 with applicable notes for the material requiringthe higher postweld heat treatment temperature. Whennonpressure parts are welded to pressure parts, thepostweld heat treatment temperature of the pressurepart shall control.

KF-402.3 Definition of Nominal Thickness Govern-ing Postweld Heat Treatment.The nominal thicknessin Table KF-402.1 and Table KF-630 is the thicknessof the welded joint as defined herein. For pressurevessels or parts of pressure vessels being postweld heattreated in a furnace charge, it is the greatest weldthickness in any vessel or vessel part which has notpreviously been postweld heat treated.

(a) When the welded joint connects parts of equalthickness, using a full-penetration butt weld, the nominalthickness is the total depth of the weld exclusive ofany permitted weld reinforcement.

(b) For groove welds, the nominal thickness is thedepth of the groove.

(c) For fillet welds, the nominal thickness is thethroat dimension. If a fillet weld is used in conjunctionwith a groove weld, the nominal thickness is the depthof the groove or the throat dimension, whichever isgreater.

(d) For stud welds, the nominal thickness shall bethe diameter of the stud.

(e) When a welded joint connects parts of unequalthicknesses, the nominal thickness shall be the fol-lowing:

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KF-402.3 2001 SECTION VIII — DIVISION 3 KF-402.3

TABLE KF-402.101

REQUIREMENTS FOR POSTWELD HEAT TREATMENT OF PRESSURE PARTS AND ATTACHMENTS

Nominal Minimum Holding Time at Normal Temperature for Nominal ThicknessHolding Tem- (See KF-402.1)perature, °F,

Material min. Up to 2 in. Over 2 to 5 in. Over 5 in.

P-No. 1 [Note (1)] 1,100°F 1 hr/in. 2 hr plus 15 min for 2 hr plus 15 min for(1 hr min.) each additional inch each additional inch

over 2 in. over 2 in.

P-No. 3 [Notes (2), (3)] 1,100°F 1 hr/in. 2 hr plus 15 min for 2 hr plus 15 min for(1 hr min.) each additional inch each additional inch

over 2 in. over 2 in.

P-No. 5A [Notes (2), (3)] 1,250°F 1 hr/in. 1 hr/in. 5 hr plus 15 min for(1 hr min.) each additional inch

over 5 in.

P-No. 8 [Note (4)] . . . . . . . . . . . .

P-No. 10A [Notes (3), (5)] 1,100°F 1 hr min. plus 1 hr min. plus 15 min 1 hr min. plus 15 min15 min for for each additional for each additionaleach addi- inch over 1 in. inch over 1 in.tional inchover 1 in.

P-No. 42 [Note (4)] . . . . . . . . . . . .

P-No. 43 [Note (4)] . . . . . . . . . . . .

P-No. 44 [Note (4)] . . . . . . . . . . . .

P-No. 45 [Note (4)] . . . . . . . . . . . .

NOTES:(1) Postweld heat treatment is mandatory under the following conditions:

(a) for materials over 11⁄4 in. nominal thickness;(b) on material over 5⁄8 in. nominal thickness for pressure parts subject to direct firing.

(2) If during the holding period of postweld heat treatment, the maximum time or temperature of any vessel component exceeds the provisionsof KT-112, additional test coupons shall be made and tested.

(3) Postweld heat treatment is mandatory under the following conditions:(a) for all materials over 3⁄8 in. nominal thickness;(b) on materials of all thicknesses intended for pressure parts subject to direct firing.

(4) Postweld heat treatment is neither required nor prohibited for joints between materials of P-Nos. 8, 42, 43, 44, or 45, or any combinationthereof.

(5) Consideration should be given for possible embrittlement of materials containing up to 0.15% vanadium when postweld heat treating atminimum temperatures.

(1) the thinner of two adjacent butt welded partsincluding head-to-shell connections;

(2) the thickness of the shell in connections totubesheets, flat heads, covers, flanges, or similar con-structions;

(3) in Figs. KD-700, KD-1112, KD-1121, KD-1122, KD-1130, and KD-1131, the thickness of theweld across the nozzle neck, shell, head, or attachmentfillet weld, whichever is greater;

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(4) the thickness of the nozzle neck at the jointin nozzle neck-to-flange connections;

(5) the thickness of the weld at the point ofattachment when a nonpressure part is welded to apressure part;

(6) the thickness of the weld in tube-to-tubesheetconnections.

(f) For repairs, the nominal thickness is the depthof the repair weld.

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KF-410 PART KF — FABRICATION REQUIREMENTS KF-411.6

KF-410 HEATING PROCEDURES FORPOSTWELD HEAT TREATMENT

KF-411 Methods of Heating

The postweld heat treatment shall be performed inaccordance with one of the procedures of this paragraph.In the procedures that follow, the soak band is definedas the volume of metal required to meet or exceed theminimum PWHT temperatures listed in Table KF-402.1.As a minimum, the soak band shall contain the weld,heat-affected zone, and a portion of base metal adjacentto the weld being heat treated. The minimum widthof this volume is the widest width of weld plus 1t or2 in. (51 mm), whichever is less, on each side or endof the weld. The termt is the nominal thickness asdefined in KF-402.3.

KF-411.1 Heating Entire Vessel.Heating the vesselas a whole in a closed furnace is preferred and shouldbe used whenever practical.

KF-411.2 Heating Vessel Portions.Heating the ves-sel in more than one heat in a furnace is permitted,provided the overlap of the heated sections of thevessel is at least 5 ft (1.5 m). When this procedure isused, the portion outside of the furnace shall be shieldedso that the temperature gradient is not harmful (seeKF-412). The cross section where the vessel projectsfrom the furnace shall not intersect a nozzle or otherstructural discontinuity.

KF-411.3 Heating Components and Circumferen-tial Welds

(a) It is permissible to heat shell sections, heads,and other components of vessels, for postweld heattreatment of longitudinal joints or complicated weldeddetails, before joining any sections to make the com-pleted vessel. Circumferential joints not previously post-weld heat treated may be locally postweld heat treatedby heating a circumferential band that includes suchjoints.

(b) This procedure may also be used for local heattreatment of circumferential joints in pipe, tubing, ornozzle necks. In the latter case, proximity to the shellincreases thermal restraint, and the designer shouldprovide adequate length to permit heat treatment withoutharmful gradients at the nozzle attachments. If this isnot practical, see KF-411.5.

(c) The width of the heated band on each side ofthe greatest width of the finished weld shall be notless than two times the shell thickness. The portionoutside the heating device shall be protected so thatthe temperature gradient is not harmful. For such localheating, the soak band shall extend around the full

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circumference. The portion outside the soak band shallbe protected so that the temperature gradient is notharmful. This procedure may also be used to postweldheat treat portions of new vessels after repairs.

KF-411.4 Heating Vessel Internally. The vesselmay be heated internally by any appropriate meanswhen adequate temperature indicating and recordingdevices are utilized to aid in the control and maintenanceof a uniform distribution of temperature in the vesselwall. The vessel shall be fully insulated where requiredprior to heating so the temperature requirements ofKF-413 are met.

KF-411.5 Local Heating of Nozzles and ExternalAttachments on Vessels

(a) Heating a circumferential band containing nozzlesor other welded attachments that require postweld heattreatment in such a manner that the entire band shallbe brought up uniformly to the required temperature(see KF-413) and held for the specified time. Exceptas modified in KF-411.5(b), the soak band shall extendaround the entire vessel, and shall include the nozzleor welded attachment. The portion of the vessel outsideof the circumferential soak band shall be protected sothat the temperature gradient is not harmful.

(b) This procedure may also be used for local heattreatment of circumferential joints in pipe, tubing, ornozzle necks. In the latter case, proximity to the shellincreases thermal restraint, and the designer shouldprovide adequate length to permit heat treatment withoutharmful gradients — at the nozzle attachment, or heata full circumferential band around the shell, includingthe nozzle.

The circumferential soak band width may be variedaway from the nozzle or attachment weld requiringPWHT, provided the required soak band around thenozzle or attachment weld is heated to the requiredtemperature and held for the required time. As analternate to varying the soak band width, the temperaturewithin the circumferential band away from the nozzleor attachment may be varied and need not reach therequired temperature, provided the required soak bandaround the nozzle or attachment weld is heated to therequired temperature, held for the required time, andthe temperature gradient is not harmful throughout theheating and cooling cycle. The portion of the vesseloutside of the circumferential soak band shall be pro-tected so that the temperature gradient is not harmful.

(c) The procedure in KF-411.5(a) may also be usedto postweld heat treat portions of vessels after repairs.

KF-411.6 Local Area Heating of Double CurvatureHeads or Shells.Heating a local area around nozzles

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KF-411.6 2001 SECTION VIII — DIVISION 3 KF-420

or welded attachments in the larger radius sections ofa double curvature head or a spherical shell or headin such a manner that the area is brought up uniformlyto the required temperature (see KF-413) and held forthe specified time. The soak band shall include thenozzle or welded attachment. The soak band shallinclude a circle that extends beyond the edges of theattachment weld in all directions by a minimum oftor 2 in. (51 mm), whichever is less. The portion ofthe vessel outside of the soak band shall be protectedso that the temperature gradient is not harmful.

KF-411.7 Heating of Other Configurations. Localarea heating of other configurations not addressed inKF-411.1 through KF-411.6 is permitted, provided thatother measures (based upon sufficiently similar docu-mented experience or evaluation) are taken that considerthe effect of thermal gradients, all significant structuraldiscontinuities (such as nozzles, attachments, head toshell junctures) and any mechanical loads that may bepresent during PWHT. The portion of the vessel outsideof the soak band shall be protected so that the tempera-ture gradient is not harmful.

KF-412 Heat Treatment That May AffectVessel Stress Redistribution

The Manufacturer shall ensure, in accordance withKG-323(d), that any heat treatment given to a vesselor vessel part does not adversely affect the stressredistribution required by Articles KD-5, KD-8, KD-9, and KD-10. In addition, the Manufacturer shall meetthe requirements for heat treatment given in KF-830or KF-540(b), as applicable.

KF-413 Heating and Cooling Rates

Postweld heat treatment shall be carried out by oneof the methods given in KF-411 in accordance withthe following requirements.

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(a) The temperature of the furnace shall not exceed800°F (427°C) at the time the vessel or part is placedin it.

(b) Above 800°F (427°C), the rate of heating shallbe not more than 400°F/hr (222°C/hr) divided by themaximum metal thickness of the shell or head platein inches, but in no case more than 400°F/hr (222°C/hr) and in no case need it be less than 100°F/hr (56°C/hr). During the heating period, there shall not be agreater variation in temperature throughout the portionof the vessel being heated than 250°F (139°C) withinany 15 ft (4.6 m) interval of length.

(c) The vessel or vessel part shall be held at orabove the temperature specified in Table KF-402.1 forthe period of time specified. During the holding period,there shall not be a difference greater than 100°F (56°C)between the highest and lowest temperatures throughoutthe portion of the vessel being heated, except wherethe range is further limited in Table KF-402.1.

(d) During the heating and holding periods, the fur-nace atmosphere shall be so controlled as to avoidexcessive oxidation of the surface of the vessel. Thefurnace shall be of such design as to prevent directimpingement of the flame on the vessel.

(e) Unless modified by Article KF-6, above 800°F(427°C) cooling shall be done in a closed furnace orcooling chamber at a rate not greater than 500°F/hr(278°C/hr) divided by the maximum metal thicknessof the shell or head plate in inches, but in no caseneed it be less than 100°F/hr (56°C/hr). From 800°F(427°C), the vessel may be cooled in still air.

KF-420 POSTWELD HEAT TREATMENTAFTER REPAIRS

Vessels or parts of vessels that have been postweldheat treated in accordance with the requirements ofthis Article shall again be postweld heat treated afterrepairs have been made if the welds made in such repairsrequired postweld treatment under the requirements ofthis Article. The Manufacturer shall ensure that anyadditional heat treatments required shall not adverselyaffect the vessel material properties.

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