My task is to perform PWHT on a pressure vessel working with H2S after repair by welding of cavities appeared after corrosion and erosion. Defects were repaired by welding plating temper bead welding method .
dimensions are 68 m high, 5m diameter, wall thickness between 65 and 70 mm, low alloy steel.
Local PWHT shall be performed by the method of heating with electrical heaters in each circular band containing the defects repaired.
My question is: what is the minimum surface repaired which is not mandatory to be PWHT?
For example, a cavity repaired with dimensions 100mm long x 300mm wide x 15mm deep ; this means 0.03m square
This requires PWHT ?

The pressure vessel is located in a plant in Romania.
I am the contractor for heat treatment and I have done PWHT in the past on similar vessels here.
For repairs performed two years ago, project engineer requires PWHT for repaired areas exceeding 0.064m square, but now he asks for all areas regardless of the surface. He says there is a stipulation in ASME that require PWHT for all repairs to pressure vessels working with H2S.
NDT inspections , Destructive Testing , NACE tests in Germany and UK , all were made ; finite element method calculations are made to establish the size of soak band and more .

Igor Gradinarescu steel heating services