BRIDGE AND PALLET CRACK DEFORMATION INSPECTION AND REPAIR (Contd)
a. Welding of Aluminum Alloy EN AW 7020 used in fabrication of bridge quarters is only to be
carried out by approved welders under supervision of a person who is an international welding
specialist using metal insert gas (MIG), shielding gas (Argon), and 0.047 in. (1.2 mm) wire.
Welds may be repaired up to a maximum of four times. This
number must NOT be exceeded under any circumstances. Failure
to comply may result in equipment damage.
b. Field repair is only permitted for crack lengths that do not exceed the length given in tables 2
and 3 under unserviceable.
Personnel must observe all relevant safety precautions to prevent
inhaling toxic fumes or dust when cleaning or welding around
epoxy paints used on bridge quarters. Failure to comply may result
in injury or death to personnel.
Removal of damaged welded-on-parts from bridge must be carried
out using grinding or milling equipment. Welded-on-parts must
not be broken off using a hammer or lever as this will lead to
development of cracks.
When carrying out any pre-heating procedures, temperatures
must be limited to below 248 F (120 C). Higher temperatures
will weaken the joined materials.
In order to determine extent of damage, careful visual examination aided by x 10 magnification
and dye penetrant testing procedures should be used.
d. The surfaces of damaged areas must be thoroughly cleaned prior to welding. Oxides, dirt, paint,
and other foreign substances must be removed from approximately 1.181 in. (30 mm) beyond
the limits of repair area.
Welding must not be carried out at ambient temperature below
41 F (5 C).
At aluminum temperatures below 59 F (15 C) the welding area must be preheated using
suitable means, pre-heating mats to a maximum of 248 F (120 C). Pre-heating by naked flame
is also permitted.
After each welding pass, clean weld, check temperature weld area should be cooled to below
266 F (130 C) before the next pass is made.
Component of 0.390.79 in. (1020 mm) thickness are to be pre-heated to between 212248 F
(100120 C) using heat equipment. Temperature control should be checked using temperature
To compensate for post weld shrinkage in a larger inserted plate
over 9.843 x 11.811 in. (250 x 300 mm) the insert should have an
additional 0.079 in. (2 mm) added to dimension of each weld seam
in direction of load. The plate should be bowed to accomodate this
allowance, to enable it to be fitted into repair hole accurately.
h. Tack welds should be approximately 1.97 in. (50 mm) in length and spaced along seam so as to
maintain components to be joined in their correct relative positions before welding.
All welding repairs carried out on bridge should be post weld heat treated. Inspection of heat
affected area for cracks, inclusions, and flaws must be carried out.