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Underwater Welding & Inspection Underwater Welding & Inspection

PresentationPresentation

Presented by:

Saiful Rizal Uayan

VID/QCU

Dec. 19, 2004

Purpose:

The purpose of this presentation is for general knowledge only on how “underwater welding” is carried out. Safety is also emphasized here as we are dealing with two types of activities, Diving and Welding.

One must remember that underwater welding is a different world, and so special precautions are adhered to for maximum safety of the welder/diver.

Outline:

• Introduction

• Uses

• The Welder/Diver

• Classification

• Principle of Operation

• Codes, Standards & Specifications

• Underwater Inspection

• Risk Involved

• Safety

• Developments

Introduction:

Underwater welding began during World War 1 when the British Navy used it to make temporary repairs on ships. These repairs consisted of welding around leaking rivets of ship hulls. Underwater welding was also restricted to salvage operations and emergency repair works only. In addition, it was limited to depths below the surface of not over 30 ft (10meters).

At first, underwater welding was just applied to weld a patch until a more thorough repair could be performed. But as soon as more experience was gained, ambitious individuals and companies joined forces to improve results and to establish achievable specifications.

Uses:

While underwater welding have been used for new construction & installation of offshore structures, subsea pipelines, & harbor facilities, it is most often used for maintenance and repair applications. These includes repair of damage caused by corrosion, fatigue, and accidents of offshore structures such us oil platforms, repair & replacement of damaged subsea pipeline sections, repairing holes in ship’s hulls or collision damage to harbor facilities.

Uses (cont’d)

Judging from the photographs shown below, it is obvious that these structures has to be repaired. And one of the tools of repair is underwater welding.

Sinking Offshore StructureDamaged Offshore Structure

The Welder/Diver:

Welder/diver – is a certified welder who is also a commercial diver, capable of performing tasks associated with commercial subsea work, weld setup and preparation, and who has the ability to weld in accordance with the AWS D3.6, Specification for Underwater Welding (wet or dry), and other related activities.

Welder/diver qualifications required for a given assignment vary from project to project. Most diving contractors would like their welder/diver to be “a jack of all trades”. This means that the welder/diver must know how to do underwater cutting, fitting and rigging, inspection and nondestructive testing, and underwater photography.

Welding

Cutting

Underwater welding is classified into two categories.

1. Welding in-the-wet environment = This was used primarily for emergency repairs and salvage operations in shallow waters due to poor quality welds.

2. Welding in-the-dry environment = This technique produces high-quality welds that meet X-ray and code requirements.

Classification:

As the name implies, underwater wet welding is done in an environment where the base metal and the arc are surrounded entirely by water. The electrode types used conform to AWS E6013 classification. These electrodes are waterproofed by wrapping them with waterproof tape or by dipping it into special sodium silicate mixes and allowing them to dry. The power source is a direct current machine rated at 300 or 400 amperes.

The power of the arc generates a bubble of a mixture of gasses which lets metal melting and joining occur more or less normal as shown on the above photo.

Welding in-the-wet environment

Welding in-the wet (cont’d):

Below is a typical underwater welding equipment set up.

Power Supply

work

Knife switch

electrode+ _

Waterproof Electrode

Holder

Welding in-the-dry environment

Welding in-the-dry environment is again divided into two:

• Hyperbaric welding, in which a chamber is sealed around the structure to be welded and is filled with breathable gas at the prevailing pressure.

• Cofferdam welding, which is carried out in the dry, in air, where a rigid steel structure to house the welders is sealed against the side of the structure to be welded, and is open to the atmosphere.

Welding in-the-dry Environment:

Hyperbaric welding is done with the use of a welding chamber or habitat. This method provides high quality weld joints that meet radiography and code requirements. The chamber is sealed into a structure or pipeline and filled with breathable mixture of helium and oxygen (90-95% helium and 5-10% oxygen).

Welding Chamber

Welding Chamber Internal

Welding in-the-dry (cont’d)

Cofferdam welding is also a type of dry welding where a rigid steel structure to house the welders is sealed against the side of the structure to be welded and is open to the atmosphere. It is normally used for harbor works or ship repair.

Dummy structure Actual structure

Welding in-the-dry (cont’d)

Photographs below are examples of Cofferdam

Welding.

Principle of Operation:

The sketch at right shows the general arrangement for underwater welding. Underwater welding should always be a direct current machine grounded to the ship. The welding circuit includes a knife switch that is operated on the surface by an assistant upon the signal of the welder/diver. The knife switch cuts off the welding current and is design this way for safety reasons. The electrode holder utilizes a twist type head for gripping the electrode. The work lead is attach within 3 ft. from the point of welding and is perfectly insulated to avoid leaks. The welding circuit should be direct current electrode negative.

Codes, Standards & Specifications:

Underwater welding is covered under:

• AWS D3.6 Specification for Underwater Welding.

• ASME N-516 Underwater Welding Section XI Div. 1

• BS EN ISO 15618-1:2002 Qualification Testing of welders for underwater welding.

• Saudi Aramco SAEP-1117 Welding Test Supplement S17 for SMAW, Wet Welding

AWS D3.6M 1999 Specification for Underwater Welding

Abstract

This specification covers the requirements for welding for welding structures or components under the surface of the water. It includes welding in both dry and wet environments. Sections 1 through 6 constitute the general requirements for underwater welding while sections 7 through 10 contain the special requirements applicable for four individual classes of weld:

Class A – Comparable to above-water welding.

Class B – For less critical applications.

Class C – Where load bearing is not a primary consideration.

Class O – To meet the requirements of another designated code or specification.

Case N-516-3 Underwater Welding ASME Section XI

• Scope and General Requirement – Requirements for wet and dry underwater welding.

• Additional variables for dry underwater welding – Procedure and Performance qualification.

• Additional variables for wet underwater welding – Procedure and Performance qualification.

• Filler metal qualification – Each filler metal is tested in accordance with applicable SFA specification.

• Alternative procedure qualification requirements – By Charpy V-notch.

• Examination – By NDE.

Saudi Aramco Engineering Procedure:

SAEP – 1117 Welding Test Supplement S17 for SMAW, Wet Welding

Scope:

This test supplement governs the testing of welders with the Shielded Metal Arc Welding (SMAW) process, welding progression vertical down, for wet welding carbon steel base metals. This supplement shall be used to test the ability of certified contract welders hired by Saudi Aramco to perform underwater (wet) welding on Saudi Aramco offshore facilities.

Underwater Inspection:Underwater inspection also includes visual and photographic examination of underwater structures and repairs, and NDE such as MT, UT, and RT.

Photo at left shows a typical underwater Inspector equipped with lights and camera.

Photo at right shows an underwater

structure showing signs of corrosion.

Underwater Inspection (cont’d)

Non-destructive Testing like UT, RT and MT can also be done underwater.

The photograph at right shows an underwater NDT technician using Magnetic Particle Testing on underwater structural supports.

Books are also available in

the market for reference like;

• Non-destructive Examination of Underwater Welded Steel

Structures.

• Underwater Wet Welding and Cutting.

• Underwater Repair Technology.

• Professional Diver’s Manual on wet Welding.

Underwater Inspection (cont’d)

Visual, video and photographic examination can also be carried out during maintenance inspection on any underwater structures as shown below.

In order to carry out a

proper visual and NDT

check, blast cleaning has

to be carried out to remove

all seawater organisms

that grows on the

underwater structure

as shown on this

photograph.

Underwater Inspection (cont’d)

Latest development in underwater inspection is the use of ROV’s.

These are machines operated by an ROV pilot.

ROV Pilot

ROV machine Submarine Rescue Machine

Underwater Inspection (cont’d)

TWI World Center for Materials Joining Technology

Courses Offered:

• Underwater Inspection – Underwater Training and Examinations

• CSWIP 3.1U – NDT Inspection Diver

• CSWIP 3.2U – NDT Inspection Diver

• CSWIP 3.3U – ROV Inspector

• CSWIP 3.4U – Underwater Inspection Controller

• CSWIP General Visual Inspectors for Offshore Facilities and Structures

Risk Involved:Below are some risks involve in underwater welding:

• Electric shock – there is a possibility of electric shock when the equipment is not properly insulated, or when the power supply is not shut off immediately when the welder terminates the arc during welding.

• Explosion – arc welding produces hydrogen and oxygen. Pockets of gasses can build up and are potentially explosive.

• Nitrogen Narcosis – a health hazard normally experienced by divers during the diving activities when safety stops at certain level is not adhered to. Curiously, the risk of drowning is not listed with the hazards of underwater welding.

• For welded structures, inspection of welds after welding maybe more difficult than welds made above water. There is a risk of defects that may remain undetected and may cause failure in the long run.

Safety:

OSHA Standard 1915.6 – Commercial Diving

OSHA Standard 1910.424 – SCUBA Diving

Volume IV, Issue 3, 3rd Quarter 2002

Occupational Health Newsletter – Commercial

Diving Medical Emergencies in Saudi Aramco

Safety: (cont’d)

Annex D of AWS D3.6 - Recommended Guidelines for Safety in Underwater Welding

Scope is limited to recommended safe practices specifically related to underwater welding and associated work activities performed in either a dry (hyperbaric) or a wet environment.

Annex D comprises safe practices, underwater communication, electrical equipment, hand-held power tools, preparation for work, performance of work, and inspections and examinations.

Welding:

Necessary precautions should be carried out such as:

• Follow employers safety practices.

• Fumes and gasses can be hazardous to your health.

• Arc rays can injure eyes and skin.

• Use adequate ventilation while welding.

• Wear suitable eye protection and protective clothing.

• Do not touch live electrical parts.

• Wear rubber gloves.

• Only change the electrode when cold.

Safety (cont’d)

Developments:With the latest development in construction of offshore oil platforms, there has been an increased demand for underwater welding. The use of hyperbaric chambers to produce code-quality weld is very expensive to operate.

Sea Grant Researcher Dr. Chon Tsai, has developed a new welding electrode for wet welding nickname “Black Beauty” for the black appearance of its waterproof coating. The electrode exhibits excellent visual appearance and profile, micro-cracking of weld has been eliminated, operating characteristics are superior to other commercially available electrodes, and the electrode produces suitable results when used in any position.

Developments (cont’d)

Wet-Dry welding – Dry hyperbaric chambers or habitats are extremely expensive. This is because it must be built for special applications such as repairing or making tie-ins on horizontally laid pipes. Recent improvements allowed GMAW (Gas Metal Arc Welding) process to be used in underwater welding with the use of special nozzles, domes or miniature chambers. In using this type of apparatus the welder/diver is in the water but the nozzle of the welding gun and material to be welded is in the dry atmosphere. These localized dry gas environment chambers are inexpensive, small and lightweight. It is made of transparent material or has sufficient number of windows so that the welder can see the inside to properly manipulate and direct the welding gun. This process can be utilized for welding up to 125 ft. (35m) below the water surface.

References:• TWI Knowledge Summary – Underwater

Welding

• Underwater Magazine – Commercial Diving

• Divers Academy International

• Atlantic Welding & Fabrication Centre

• Special Applications of Welding – Underwater Welding

• Saudi Aramco Intranet - Wet Welding

Two Types:a). Recreational Diving – diving for funb). Commercial Diving – diving for money