pre heating cs condenser wall

[jerryb722]

we are cutting out and repairing our condenser wall. the thickness is 5/8. is there a need to preheat before welding
thanks

 

[metengr]

For a condenser shell that is probably fabricated of low to medium carbon steel plate (A 36 or A 5I6 Gr 70) is there a need (Code or Standard wise) no; is it beneficial yes, yes, and yes. All you need is to apply a local preheat of 150 deg F to assure removal of moisture. This is easy to do and will avoid problems.

By the way, I would use a flush patch plate to repair the condenser wall. This requires a full penetration weld. Don't forget to perform NDT (wet fluorescent MT) after the weld repair.

 

[Ubbe]

One method of examining the need for elevated working temperature is using the European standard 1011-2:2001.
Calculate the carbon equivalents (CET).
CET = C + (Mn + Mo)/10 + (Cr + Cu)/10 + Ni/40 (%).

It applies to the following range of concentrations (percentage by weight):
- Carbon 0,05 to 0,32
- Silicon max. 0,8
- Manganese 0,5 to 1,9
- Chromium max. 1,5
- Copper max. 0,7
- Molybdenum max. 0,75
- Niobium max. 0,06
- Nickel max. 2,5
- Titanium max. 0,12
- Vanadium max. 0,18
- Boron max. 0,005

You have to know the hydrogen content of your filler material (HD).
This is normally given by the manufacturer on the casing (here applicable in the range1 mg/100 g weld material to 20 mg/100 g weld material).

Working temperature, Tp is calculated as:

Tp = 697xCET + 160 tanh (d/35) + 62xHD^0,35 + (53xCET-32)xQ –328 (°C)
Plate thickness = d (mm)
Q = heat input I kJ/mm

Q may be calculated as follows:

Q = k (( U x I)/v)x 1E-3 (kJ/mm)
U = Volt
I = Current in Ampere
v = welding speed

k-factor below:
121 Submerged arc welding with wire electrode 1,0
111 Metal-arc welding with covered electrode 0,8
131 MIG welding 0,8
135 MAG welding 0,8
114 Flux-cored wire metal-arc welding without gas shield 0,8
136 Flux-cored wire metal-arc welding with active gas shield 0,8
137 Flux-cored wire metal-arc welding with inert gas shield 0,8
138 Metal-cored wire metal-arc welding with active gas shield 0,8
139 Metal -cored wire metal-arc welding with inert gas shield 0,8
141 TIG welding 0,6