22-06-2012, 02:13 PM
UNDERWATER CUTTING and WELDING MANUAL
UNDERWATER CUTTING and WELDING MANUAL.pdf (Size: 3.3 MB / Downloads: 90)
INTRODUCTION
This manual is intended to provide information on the use of conventional techniques for cutting
and welding metals underwater. It is written for the U.S. Navy diver who specializes in ship salvage
and harbor clearance operations. It is not a procedural guide for certifiable welding used in
pre-planned underwater ship husbandry applications.
Divers who perform underwater cutting and welding must have greater skill and stamina than
those doing the same work topside. The success and speed of operations depend upon the conditions
under which the diver must work because the underwater environment imposes numerous
limitations and restrictions on the operator and equipment. The diver is often restricted to working
for only a short time on the bottom, particularly at deeper depths. The use of correct techniques
and equipment becomes extremely important in terms of work accomplished per hour. Diving
apparel, great depth, adverse currents, low temperature, lack of visibility and unstable footing are
all factors which make underwater cutting and welding difficult.
Whenever practical, cutting techniques are preferred over welding during ship salvage operations.
For example, when wrecking in place is the salvage technique, a chain reeved through two holes
cut in the hull and around a transverse frame is the preferred attachment method over a welded
padeye.
Only personnel trained and qualified in underwater cutting and welding may be assigned to use
the procedures and techniques described herein. Additionally, the procedures in this manual must
be carried out in conformance with the U.S. Navy Diving Manual (NAVSEA 0994-LP-001-9010)
and standard Navy safety practices. Appendix D covers safety in greater detail.
UNDERWATER CUTTING OVERVIEW
There are two underwater cutting processes currently approved for Navy use. They are:
• Oxygen-Arc cutting with exothermic electrodes, Steel-tubular electrodes and Kerie
Cable; and,
• Shielded metal-arc cutting.
Of these, oxygen-arc (oxy-arc) is preferred because of its ease of use.
Two types of electrodes (also called rods) are used for oxy-arc cutting: the exothermic and
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the steel-tubular electrode. Of these, the exothermic is preferred because it will burn independently
after an arc is struck and oxygen is flowing.
The second method of underwater cutting is the shielded metal-arc process in which the metal is
cut by the intense heat of the arc without the use of oxygen. This method is preferred over oxy-arc
when cutting metal of 1/4-inch or less in thickness or when cutting non-ferrous or corrosion-resistant
metal of any thickness.
Each underwater cutting method is covered in detail in Chapter 2.
UNDERWATER WELDING OVERVIEW
The installation of large patches, as well as the attachment of suitable pad-eyes presents a more
complicated problem to the diver than does underwater cutting. Considerable practice is necessary
to achieve a consistently good standard of underwater welding for salvage work. As a result,
the diver’s underwater welding techniques must conform to acceptable standards. Also, the ocean
acts as a large heat sink and draws off the heat of the electrode. This may cause blow holes and
possible loss of strength between the patch and hull. This is true because the gas cannot escape
from the molten pool of metal due to sudden cooling by the surrounding water. Despite the above
shortfalls, underwater welds of good strength that are acceptable for salvage work are possible.
Unless otherwise specified, the term “underwater welding” as used in this manual refers to the
wet welding technique where no mechanical barrier separates the welding arc from the surrounding
water.
The two types of welding to be covered in this manual are:
• wet welding and
• dry welding at the “splash zone.”
Shielded metal-arc welding is the most widely used process for wet welding. Specific welding
procedures for underwater maintenance work on ships is addressed in the Underwater Ship-Husbandry
Manual (NAVSEA S0600-AA-PRO-010) and the Naval Ship’s Technical Manual, Chapter
Wet welding is accomplished with both the diver and the work completely submerged. The
advantages and disadvantages will be discussed in detail in Chapter
Dry welding at the “splash zone” is generally conducted in a dry box or cofferdam at atmospheric
pressure. It is essentially conventional welding and is discussed in Chapter 3 to provide the salvor
with methods to exclude water from the weld area.
Before proceeding with any cutting or welding procedure described in this manual, all
personnel involved must thoroughly review and comprehend the applicable safety
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precautions, warnings and cautions. This information, which is based on knowledge and experience
gained through many years of Naval and commercial operations, is presented in Appendix
D and the Safety Summary. Strict adherence to the safety regulations is required. Before starting
any new job, a thorough inspection of the situation must be made to determine hazards to personnel,
equipment or ship that may exist. Appropriate action must be taken to eliminate or minimize
noted hazards.