ASME Heat Treatment by Eng. Ibrahim Eldesoky

Cairo Inspection Company Eng. Ibrahim Eldesoky ASNT –NDT-LEVEL III ASME AUTHORIZED INSPECTOR

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 internal atomic changes affecting their material properties. Cairo Inspection Company (CIC)

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UW-2 SERVICE RESTRICTIONS (a) When vessels are to contain lethal substances, either liquid or gaseous, all butt welded joints shall be fully radiographed, ……….. When fabricated of carbon or low alloy steel, such vessels shall be post weld heat treated.

When a vessel is to contain fluids of such a nature that a very small amount mixed or unmixed with air is dangerous to life when inhaled, it shall be the responsibility of the user and/or his designated agent to determine if it is lethal. Cairo Inspection Company (CIC)

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UW-10 Postweld Heat treatment Pressure vessels and pressure vessel parts shall be heat treated as 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.

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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 temp. variation. Cairo Inspection Company (CIC)

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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 to UCS-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 is permissible. (f) The term nominal thickness is the thickness (t) of the welded joint as follows.  For pressure vessels or parts being post weld heat treated in a furnace charge, t is the greatest weld thickness in any vessel or part which has not previously been post weld heat treated. Cairo Inspection Company (CIC)

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UW-40 Procedures of PWHT (f) Nominal Thickness

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UW-40 Procedures of PWHT (f) Nominal Thickness continued...

UW-49 Check of PWHT Practice The Inspector shall satisfy himself that all PWHT has been correctly performed and that the temperature readings conform to the requirements. Cairo Inspection Company (CIC)

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UCS-56(a) Requirements for PWHT Requires 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 austenitizing range.

UCS-56(b) Requirements for PWHT Holding 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. Cairo Inspection Company (CIC)

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UCS-56(c) Requirements for PWHT When 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.

UCS-56(d) Requirements for PWHT

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). During the heating period, there shall not be a variation in temperature greater than 250°F (120°C) throughout the vessel within any 15 foot (4.6 meter) interval of length. Holding times and temperatures per Table UCS-56orUCS56.1. Cairo Inspection Company (CIC)

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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 post weld heat treatment temperatures permitted only for P-No. 1 Gr. Nos. 1 and 2 materials. Cairo Inspection Company (CIC)

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UCS-56(d) Requirements for PWHT 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 on the vessel. Above 800°F (425°C), cooling shall be done 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. Cairo Inspection Company (CIC)

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