4 Heat Treatment

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 Temperature Samples

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 applicable part of Subsection C.

UW-40 Procedures of PWHT(a) In the procedures that follow, the minimum soak band shall contain the weld (W), heat affected zone (HAZ) and a portion of the base 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 are given in UCS-56, UHT-56, UNF-56 and UHA-32.(c) The minimum PWHT temperatures shall be the minimum temperature of the plate material of the shell or head (furnace gas temperature measurement alone is not considered sufficiently accurate).■ Where more than one pressure vessel or part are treated in one furnace charge, thermocouples shall be placed in the bottom, center and 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 are joined by welding, the PWHT shall be that specified according toUCS-56 or UHA-32, for the material requiring the higher PWHT temperature.

(e) PWHT, when required, shall be done before the hydrostatic test and 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 welded joint as follows.■ For pressure vessels or parts being postweld heat treated in a furnace charge, t is the greatest weld thickness in any vessel or part which has not previously been postweld heat treated.

(f) Nominal ThicknessUW-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 been correctly performed and that the temperature readings conform to the requirements.

HOW?

UCS-56(a) Requirements for PWHTRequires WPS qualification per Section IX.Everything requires PWHT unless exempted by Tables UCS-56 or UCS-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 welded materials heat treated in the austenitizingrange.

UCS-56(b) Requirements for PWHTHolding times and temperatures may exceed stated values unless prohibited 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 PWHTWhen welding pressure parts of different P-Numbers, use the table with the higher PWHT temperature.When welding non-pressure parts to pressure parts, the PWHT temperature for the pressure part shall govern.Furnace temp, shall not exceed 800°F (425°C) at the time the vessel or part is placed in it.

During the heating period, there shall not be a variation in temperature greater than 250°F (139°C) throughout the vessel within 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 per hour (222°C) divided by the maximum metal thickness of the shell or head in inches, but in no case more than 400°F per hour (222°C).

UCS-56(d) Requirements for PWHT

TABLE UCS-56.1ALTERNATIVE POSTWELD HEAT TREATMENT REQUIREMENTS

FOR CARBONAND LOW ALLOY STEELS Applicable Only When Permitted in

Table UCS-56

NOTES:(1) Minimum holding time for 1 in. (25 mm) thickness or less. Add

15 minutes per Inch (25 mm) of thickness for thicknesses greater than 1 In. (25 mm).

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

During the holding period, there shall not be a greater difference than 150°F (83°C) in temperature between the highest and lowest readings.During the heating and holding periods, the furnace atmosphere shall be so controlled as to avoid excessive oxidation of the vessel surface.The furnace shall be designed as to prevent flame impingement onthe vessel. Above 800°F (425°C), cooling shall be done in in a closed chamber 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 require the repaired area to be re-heat treated, except as permitted in UCS-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 metals used to join the above,

provided the repair is made before the final pressure test and provided PWHT was not a service requirement per UW(2)(a) or UCS-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 minor restorations of the material surface, such as those required after removal of construction fixtures, and provided that the surface is not exposed to the vessel contents.■ (1) The Manufacturer shall give prior notification to the user or his designated 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, 2 and 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 the electrode diameter,■ (b) maintain 200°F (95°C) minimum preheat and interpass for P-No. 1, Groups 1, 2, and 3 materials.


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

weld repair and weld temper bead reinforcement technique."


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

Step 2: Remove approximately one-half the thickness of the first layer by grinding.

Temper beadStep 3: Subsequent layers shall be reinforcementDeposited with welding electrodes no larger than 5/32 in. (4mm) Dia.Bead deposition shall be as shown to assure tempering of the prior weld beads and their HAZ's.

Layer

A final temper bead weld shall be applied to a level above the surface being repaired without contacting the base material but close enough to the underlying weld bead to assure tempering of the base material heat affected zone.


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

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

5) After the finished weld has reached ambient temperature, PT or MT examine the finished weld surface.■ If the material is P-No. 3,Group 3, the re-examination is performed after 48 hours 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.


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

(a) The following provisions apply in addition to, or as exceptions to the general rules for heat treatment given in UG-85(b) Heat treatments as used in this section shall include all thermal treatments 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 specimens which have been subjected to the same heat treatments above the lower transformation 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 the specified temperature within reasonable tolerances such as are normal in actual fabrication.The total time at temperature shall be at least 80% of the total time at temperature during actual heat treatment of the product and may be performed in a single cycle.


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

(e) An exception to the requirements of (c) above and UG-85 shall apply to standard 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.


(f) P-No. 1, Groups No. 1 and 2, and all carbon and low alloy steels used in the annealed condition as permitted by the material specification are exempted from the requirements of (c) above when the heat treatment during fabrication is limited to PWHT temperatures below the lower transformation temperature of the steel.

(g) P-No. 1, Group No. 3 and P-No. 3, Groups 1 and 2 material specimens that are subjected to the requirements of (c) above and Table UCS-56 need not be recertified if the material is subjected to the alternate PWHT conditions permitted by Table UCS-56.1.

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


4 Heat Treatment

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