Full Penetration Holes
considered a repair. However, if you cut a hole in a
watertight bulkhead and install a watertight door that
Full penetration holes are those holes that extend
modifies the ship's structure, it is an alteration. All
through the base material, as shown in figure 13-51.
repairs and alterations must be performed according to
Before welding up the hole, it must be opened up to a
the appropriate specifications and authorizations.
minimum of l/2 inch and a maximum of 2 l/2 inches at
Some of the problems encountered when making
the bottom. The sides are tapered with a 20-degree
repairs and alterations, such as avoiding notches in
minimum bevel to prevent slag entrapment and allow
plate, cutting holes in plate, stopping cracks in plate,
for rod manipulation.
correcting distortion and other problems associated
The hole may be welded using a backing strap or
with plate, are discussed in the following paragraphs.
left open. If a backing strap is used, it may be permanent
or removable depending on the fabrication
AVOIDING NOTCHES IN PLATE
requirements. If a permanent backing strap is used, it
must be of the same material as the base metal. If the
When repairs and alterations are being made, you
removable backing strap is used, remove it by
must take care to avoid introducing notches
mechanical means such as a cutting torch or grinder.
(geometrical discontinuities) in the ship's structure.
Most welders use a brass or copper backing strap
These points of stress concentration form the starting
clamped in place during the welding process. Since the
points for fractures. Serious notches are often caused
brass backing strap will not fuse with the welding
by striking arcs on plating adjacent to a weld or by
material, it will normally fall off with a light tap of a
leaving rough burned edges on the structure. Corners
hammer. After the backing strap is removed the hole
of doublers, insert plates, chips, and pads must lx
must be back gouged to 1/3T (where T equals material
rounded to eliminate the notch effect. Discontinuities,
thickness) or 3/8 inch depth, whichever is less, and the
such as slag inclusions, incomplete fusion, and undercut
back gouge is welded up. The reason for backgouging
in a weld, can also become the starting point for
the repair is to remove impurities that are drawn into the
fractures. You must be careful in your workmanship
weld metal from the brass plate. The hole is welded up
and inspections to prevent the introduction of such
using a filler metal compatible to the base material and
notches into the structure.
the weld procedure being used.
HOLE REPAIRS
MAKING CLOSURES WITH PLATE
PATCHES
You will be called upon to make repairs to all types
of holes in ship and submarine structures as well as
Sometimes it is necessary to cut temporary
equipment. A major source of hole repair is the repair
holes in shell plating, bulkheads, and decks to
of stripped out bolt holes in accesses and covers
remove and install machinery. You will have to
exposed to the weather. Generally, a hole must be 2 l/2
measure, cut, and prepare the patch for insertion.
inches or less in diameter. Holes greater than 2 l/2
All work must carefully be done so no unnecessary
inches must be replaced with a patch. We will look at
damage occurs. We will look at cutting new access
partial penetration holes and full penetration holes, as
h o l e s and cutting access holes involving
shown in figure 13-5 1.
previously made holes.
Partial Penetration Holes
Cutting New Access Holes
Partial penetration holes are those holes that do not
Cutting new access holes involves making cuts
extend through the base material more than
where no previously made cut existed. Before you
three-fourths of the thickness of the plate, as shown in
make an access cut you must determine the
figure 13-51. Before welding up the hole, it must be
location and configuration of the access cut.
opened up to a minimum of l/2 inch and a maximum of
Figures 13-52 and 13-53 demonstrate some of the
2 l/2 inches at the bottom. The sides are tapered with
requirements for determining access cuts and weld
a 20-degree minimum bevel to prevent slag entrapment
preparations.
and allow for rod manipulation. The hole is welded up
using a filler metal compatible to the base material and
DETERMINING LOCATION.--Before making
the weld procedure being used.
an access cut, you should consult the ship's plans for the
13-44
