Heat Treatments

Section VIII, Division 1

Heat Treatment Terms

Post weld Heat Treatment

■ Any heat treatment subsequent to welding.

Normalizing

■ A process in which a ferrous metal is heated to a suitable

temperature above the transformation range and is subsequently

cooled to below the transformation range.Stress Relieving■ Uniform heating of a structure or portion thereof to a sufficient

temperature to relieve the major portion of the residual stresses,followed by uniform cooling.

Transformation Range■ A temperature range in which ferrous materials undergo internalatomic changes affecting their material properties.

Transformation TemperatureSamples

UW-10 Postweld Heat treatment

Pressure vessels and pressure vessel parts shall be heat treatedas prescribed in UW-40 when PWHT is required in the applicablepart of Subsection C.

UW-40 Procedures of PWHT

(a) In the procedures that follow, the minimum soak band shallcontain the weld (W), heat affected zone (HAZ) and a portion of thebase metal adjacent to the weld being heat treated.

UW-40 Methods of PWHT

(b) The temperatures and rates of heating and cooling to be used aregiven in UCS-56, UHT-56, UNF-56 and UHA-32.

(c) The minimum PWHT temperatures shall be the minimumtemperature of the plate material of the shell or head (furnace gastemperature measurement alone is not considered sufficientlyaccurate).■ Where more than one pressure vessel or part are treated in onefurnace charge, thermocouples shall be placed in the bottom, centerand top of the charge, or in other zones of possible temperaturevariation.

UW-40 Procedures of PWHT

(d) When pressure parts of two different P-Number Groups arejoined by welding, the PWHT shall be that specified according toUCS-56 or UHA-32, for the material requiring the higher PWHTtemperature.

(e) PWHT, when required, shall be done before the hydrostatic testand after any welded repairs except as permitted by UCS56(f).■ A preliminary hydrostatic test to reveal leaks prior to PWHT ispermissible.

(f) The term nominal thickness is the thickness (t) of the weldedjoint as follows.■ For pressure vessels or parts being postweld heat treated in afurnace charge, t is the greatest weld thickness in any vessel orpart which has not previously been postweld heat treated.

(f) Nominal Thickness

UW-40 Procedures of PWHT

(f) Nominal Thickness continued...

UW-40 Procedures of PWHT

UW-49 Check of PWHT PracticeThe Inspector shall satisfy himself that all PWHT has beencorrectly performed and that the temperature readingsconform to the requirements.

HOW?

UCS-56(a) Requirements for PWHT

Requires WPS qualification per Section IX.Everything requires PWHT unless exempted by Tables UCS-56 orUCS-56.1.Exemptions to PWHT do not apply when:■ PWHT is a service requirement (UCS-68),■ joining material of certain P-Numbers and thicknesses welded

with either the electron beam, inertia and continuous drive friction,electroslag or electrogas welding processes.Heating and cooling rates do not apply for P-No. 1 weldedmaterials heat treated in the austenitizingrange.

UCS-56(b) Requirements for PWHTHolding times and temperatures may exceed stated values unlessprohibited by Table UCS-56.Intermediate PWHT need not conform to Table UCS-56.Heat treatment may be performed in multiple PWHT cycles.

UCS-56(c) Requirements for PWHT

When welding pressure parts of different P-Numbers, use thetable with the higher PWHT temperature.When welding non-pressure parts to pressure parts, the PWHTtemperature for the pressure part shall govern.Furnace temp, shall not exceed 800°F (425°C) at the time thevessel or part is placed in it.

During the heating period, there shall not be a variation intemperature greater than 250°F (139°C) throughout the vesselwithin any 15 foot (4.6 meter) interval of length.Holding times and temperatures per Table UCS-56orUCS56.1.

Above 800°F (425°C), the heat up rate shall not exceed 400°F perhour (222°C) divided by the maximum metal thickness of the shellor head in inches, but in no case more than 400°F per hour(222°C).

UCS-56(d) Requirements for PWHT

TABLE UCS-56.1

ALTERNATIVE POSTWELD HEAT TREATMENT REQUIREMENTS

FOR CARBON

AND LOW ALLOY STEELS Applicable Only When Permitted in

Table UCS-56

NOTES:

(1) Minimum holding time for 1 in. (25 mm) thickness or less. Add15 minutes per Inch (25 mm) of thickness for thicknessesgreater than 1 In. (25 mm).

(2) These lower postweld heat treatment temperatures permittedonly for P-No. 1 Gr. Nos. 1 and 2 materials.

During the holding period, there shall not be a greater difference than150°F (83°C) in temperature between the highest and lowestreadings.During the heating and holding periods, the furnace atmosphere shallbe so controlled as to avoid excessive oxidation of the vesselsurface.The furnace shall be designed as to prevent flame impingement onthe vessel. Above 800°F (425°C), cooling shall be done in in a closedchamber or cooling chamber.Cooling rates above 800°F (425°C) shall not exceed 500°F per hour(278°C) divided by the maximum shell or head thickness in inches,but in no case more than 500°F per hour (278°C).From 800°F (425°C) the vessel may be cooled in still air.

UCS-56(d) Requirements for PWHT

UCS-56(e) Requirements for PWHTRepairs to vessels in the postweld heat treated condition requirethe repaired area to be re-heat treated, except as permitted inUCS-56(f).

UCS-56(f) Requirements for PWHT,Alternatives & Exemptions

Exemptions to re-heat treating repaired areas are as follows:■ P-No. 1, Group No's, 1, 2 and 3 materials,■ P-No. 3, Group No's. 1, 2 and 3 materials, and the weld metalsused to join the above,

provided the repair is made before the final pressure test andprovided PWHT was not a service requirement per UW(2)(a) orUCS-68. The exemptions of Table UCS-56 apply.■ The welded repairs shall meet the requirements of (1) through (6)below.

■ These requirements do not apply when the welded repairs are minorrestorations of the material surface, such as those required after removal ofconstruction fixtures, and provided that the surface is not exposed to thevessel contents.■ (1) The Manufacturer shall give prior notification to the user or hisdesignated agent and shall not proceed until acceptance has been obtained.Such repairs shall be recorded on the Data Report.■ (2) Repair depth shall not exceed 1 lA in. (38mm) for P-No. 1, Groups 1, 2and 3 materials and 5/8 inch (16mm) for P-No. 3, Group 1, 2 and 3 materials.The total depth is measured from both sides of a weld at a given location.■(3) MT or PT examine the excavated area per Appendix 6 or 8 respectively.■ (4) Use Section IX qualified groove weld procedure and :■ (a) use the manual SMAW process with low hydrogen electrodes,conditioned per SFA 5.5. The maximum bead width shall be 4 times theelectrode diameter,■ (b) maintain 200°F (95°C) minimum preheat and interpass for P-No. 1,Groups 1, 2, and 3 materials.

UCS-56(f) Requirements for PWHT,Alternatives & Exemptions

■ (4) continued..■ (c) maintain a 350°F (175°C) minimum preheat and interpass, andmaximum interpass temperature of 450°F (230°C) for P-No. 3, Groups 1, 2and 3 materials,■ For P-No. 3 materials, the welding technique is limited to the "half bead

weld repair and weld temper bead reinforcement technique."

UCS-56(f) Requirements for PWHT,Alternatives & Exemptions

Step 1: The initial layer of weldmetal shall be deposited over theentire area using 1/8 in. (3mm)maximum diameter electrodes.

Step 2: Remove approximatelyone-half the thickness of the firstlayer by grinding.

Temper beadStep 3: Subsequent layers shall bereinforcementDeposited with welding electrodes no largerthan 5/32 in. (4mm) Dia.Bead deposition shall be as shown toassure tempering of the prior weld beadsand their HAZ's.

lLayer

A final temper bead weld shall be applied to a level above the surfacebeing repaired without contacting the base material but close enough tothe underlying weld bead to assure tempering of the base material heataffected zone.

UCS-56(f) Requirements for PWHT,Alternatives & Exemptions

■ After completing all welding, the repair area shall be maintained at atemperature of 400°F-500°F (205°C-260°C) for a minimum period of 4hours.

■ The final temper bead reinforcement layer shall be removedsubstantially flush with the surface of the base material.

5) After the finished weld has reached ambient temperature, PT or MTexamine the finished weld surface.■ If the material is P-No. 3,Group 3, the re-examination is performed after 48hours to determine possible delayed cracking of the weld.■ If RT was required originally, and the depth of the repair exceeds 3/8 in.(10 mm), perform RT of the repaired area (per UW-51).6) Perform hydrostatic test after repair.

UCS-56(f) Requirements for PWHT,Alternatives & Exemptions

UG-85 Heat Treatment

When plate specification heat treatments are not performed by the materialmanufacturer, they shall performed by, or be under the control of thefabricator.■ The fabricator shall then place the letter "T" following the letter "G" in theMill plate markings (see SA-20) to indicate that the heat treatments requiredby the material specification have been performed.UCS-85, UHT-5(e) and UHT-81provide requirements for heat treatment oftest specimens.

(a) The following provisions apply in addition to, or as exceptions to thegeneral rules for heat treatment given in UG-85(b) Heat treatments as used in this section shall include all thermaltreatments of the material during fabrication exceeding 900°F (480°C),except as exempted below.(c) The material used in the vessel shall be represented by test specimenswhich have been subjected to the same heat treatments above the lowertransformation temperature and PWHT except as provided in (e), (f) (g), (h)and (i) below.■ The kind and number of tests and test results shall be as required by

the material specification.■ The vessel Manufacturer shall specify the temperature, time and

cooling rates to which the material will be subjected during fabrication[except per (h) below].

UCS-85 Heat Treatment of Test Specimens

(c) continued...Material from which the specimens are prepared shall be heated to thespecified temperature within reasonable tolerances such as are normal inactual fabrication.The total time at temperature shall be at least 80% of the total time attemperature during actual heat treatment of the product and may beperformed in a single cycle.

UCS-85 Heat Treatment of Test Specimens

(d) Thermal treatment of material is not intended to include such localheating as:■ thermal cutting,■ preheating,■ welding, or■ heating below the transformation temperature of tubing and pipe forbending or sizing.

(e) An exception to the requirements of (c) above and UG-85 shall apply tostandard items such as described in UG-1 l(a).■These may be subject to postweld heat treatment with the vessel or vessel

part without the same treatment being required of the test specimens.■This exception shall not apply to specially designed cast or wrought

fittings.

UCS-85 Heat Treatment of Test Specimens

(f) P-No. 1, Groups No. 1 and 2, and all carbon and low alloy steels used inthe annealed condition as permitted by the material specification areexempted from the requirements of (c) above when the heat treatmentduring fabrication is limited to PWHT temperatures below the lowertransformation temperature of the steel.

(g) P-No. 1, Group No. 3 and P-No. 3, Groups 1 and 2 material specimensthat are subjected to the requirements of (c) above and Table UCS-56 neednot be recertified if the material is subjected to the alternate PWHT conditionspermitted by Table UCS-56.1.

(h) The simulation of cooling rates for test specimens of non-impact testedmaterials 3 in. (75mm) and under in thickness is not required for heattreatments below the lower transformation temperature.(i) All thermal treatments which precede a thermal treatment that fullyaustenitizes the material need not be accounted for by the specimen heattreatments, providing the austenitizing temperature is as high as anypreceding thermal treatments.

UCS-85 Heat Treatment of Test Specimens