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1.0 SCOPE
This procedure covers the repair welding of unalloyed
carbon steel components. The appropriate base material specifications
are VIWI MS2 or equivalent.
2.0 DEFECT REMOVAL
The defect may be removed by carbon-arc, chipping,
grinding or machining. Carbon-arc is the most practical and flame-
cutting is not recommended. When carbon-arc is used the temperature of
the base metal should be at least 100°F (40°C).
It is imperative that the defect be completely removed
to sound metal, free from cracks, shrinkage and porosity. In critical
areas, the use of magnetic-particle or dye-penetrant inspection of the
weld cavity is strongly recommended.
3.0 PREHEAT TEMPERATURE
The minimum preheat temperature is 100° F (40°C).
Localized heating is permissible.
4.0 INTERPASS TEMPERATURE
The interpass temperature for electric-arc welding is
normally listed at 200° F (95°C) above the preheat temperature.
However, practical conditions dictate an interpass temperature of 600°
F (320°C) maximum.
5.0 WELDING PARAMETERS
The "shielded metal arc welding" process (SMAW)
should be used for all welding.
(A) Welding Current
Direct-Current, reverse-polarity (DCRP) is required
for the electrodes recommended. The voltage and amperage settings should
be based upon the recommendations of the electrode manufacturer. In the
absence of specific instructions, the following guide may be used:
Electrode Amperage Voltage Diameter Flat Position Flat
Position 1/8" (3mm) 120 22/26 5/32"(4mm) 160 23/27
3/16"(5mm) 240 24/29 1/4" (6mm) 320 25/30
NOTE: The use of smaller electrodes, and the
corresponding lower amperage is recommended.
(B) Electrode
A suitable electrode is the ATOM-ARC 7018 manufactured
by Alloy Rods. This is an AWS E-7018 electrode. Any major brand
electrode of this classification or AWS E-7015 or E- 7016 may be used.
6.0 TECHNIQUE
No special technique is required. The weld bead should
be the stringer type. The slag should be removed from the weld deposit
between each pass, by chipping, peening and wire- brushing.
7.0 POST-WELDING HEAT TREATMENT
In most cases, heat treatment after welding is not
necessary. In heavy sections of over 3" (8cm) thick, covering the
weld area with an insulating material, will retard the cooling rate and
reduce the welding stresses induced into the component. If
stress-relieving is necessary, it should be carried out in a
temperature-controlled furnace at 1100-1200° F (600-650°C). Holding
time at this temperature is 60 minutes/inch (25 minutes/cm). Cooling may
be carried out in the furnace or in still air. Localized
stress-relieving with gas torches is not recommended. |
