GLOBE VALVES OS & Y - FORGED - ISO 15761/API 602/B16.34
Australian Pipeline Valve - Installation, Operation and Maintenance Manual
10
Special trim options and body materials such as valves with PTFE packing/soft seat/
special seals/ and gaskets that have maximum temperature limits less than the
valve, may require special welding and heat treatment considerations which are not
included herein.
FIGURE 2
INCORRECT
Arcing can occur across
close tolerance areas of valve
due to ground strap location.
Ground Strap
Ground Strap
Welding
CORRECT
Ground strap is
positioned before the valve.
Welding
WELD SET UP
1.3.6 Post Weld Heat Treatment (PWHT)
The recommended method of PWHT is via local ceramic resistance heaters, individually monitored with
thermocouples. Thermocouples are attached to the weld or welds. Properly sized ceramic heaters are
wrapped around the weld area, extending approximately 6.35mm (1/4”) past the weld on the valve side.
Do not wrap the valve body with a heating element. See Figure 1 for details. Wrap flexible insulation
around valve ends, extending approximately 12.5mm (1/2”) past the valve on the valves side. It is not
recommended to wrap the entire valve body with insulation. Prior to heat input close the valve
completely, then open the valve approximately 1.58mm (1/16”) of a turn after the handwheel slack is run
out. This very slight opening will allow the trim components to expand during the thermal cycle.
Following PWHT, inspect the valve for smooth operation by cycling open and closed. If possible, perform a
seat closure pressure test prior to service operation.
FIGURE 3
4
3
2
1
ITEM DESCRIPTION
1
THERMOCOUPLE
2
VALVE
3
FIBRE INSULATION
4
CERAMIC HEATERS
POST WELD HEAT TREATMENT
