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WET WELDING
SIGNIFICANT ADVANCES IN QUALITY
By
Michael A Pett
HYDROWELD
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Wet welding is one of the most under rated, abused and
misunderstood welding processes in regular use today. Its poor reputation, developed over
the years, has fuelled critics' arguments that wet welding produces poor quality, hard,
low ductile welds, which are prone to cracking. But is this really the case? In 1999
Hydroweld, acknowledged leaders and an authority in the field of wet welding, shifted the
boundaries by producing the first ever, surface quality wet welds in accordance with the
AWS D3.6M-99 Class A welds.
Unfortunately, critics of wet welding can often justify their condemnation as the process
is regularly abused, particularly in the inshore civil engineering industry, where
weldment are made that rarely meet any welding standard or specification. This abuse is
mainly born out of ignorance, often on both sides of the contract, with the client having
very little understanding of the process and relying on the diving contractor whom may
have very little understanding of wet welding himself. Understandably the contractor, not
wanting to turn work away, will often bid for work on the basis that one or two of his
divers are conventional welders and should be able to weld underwater.
This general lack of knowledge often results in projects being awarded to companies who
have no wet welding procedures in place, welders with no formal or very little wet welder
training and using inappropriate welding electrodes. The results are predictable with
weldment's having significant weld defects such as slag, gas inclusions, lack of fusion,
and sometimes cracking. But not all wet welding projects are the same. Wet welding
projects, which often involve a third party, like a classification society, take on a
completely different approach with a much higher level of quality assurance (QA).
In the offshore oil and gas and to a lesser degree the shipping and civil engineering
industries, permanent structural wet welded repairs and modifications are becoming common
place. In these industries most of the wet welding project are subjected to the same
degree of QA applied to conventional dry surface welding projects. Production welding is
preceded by the qualification of wet welding procedures and welder qualifications to prove
the weldability of the materials, the performance of the welding consumable and the
capabilities of the welder. These procedures and qualifications are usually completed to
the 'AWS D3.6 Specification for Underwater Welding' which takes into consideration factors
associated with the underwater environment not included in surface specifications such as
water depth and or pressure.
The AWS D3.6 Specification for Underwater Welding was first published in 1983 to establish
a standard reflecting state of the art technology relative to underwater welding and to
provide those with a requirement for underwater welding a choice of weld quality, on a
fitness for purpose basis. The specification, which is revised roughly every 5 years to
keep up with modern technology, sets out four classes of welds identified as class A, B, C
or O. These classes are broadly defined as: class 'A' welds which are intended to be
comparable with above water welds by virtue of specifying comparable properties and
testing requirements. Class 'B' welds, which are intended for less critical applications
where lower ductility, greater porosity and larger discontinuities can be tolerated. Class
'C' welds, which are intended for applications where load bearing is not a primary
consideration and satisfy lesser requirements than class A, B and O. And finally class 'O'
welds which must also meet the requirements of another code or specification.
The AWS D3.6 details a list of essential variables, which are addressed and recorded
during the development of the welding procedures. These variables take into consideration
the joint configuration, base metal, filler metal, position, weldment temperature,
electrical characteristics, technique and environment. The specification also details the
non-destructive and destructive testing criterion for each class of weld. Whilst class 'B'
and 'C' welds are easily achieved with the wet welding process, the production of class
'A' welds has not, until recently, been an option because of the difficulties in meeting
all of the mechanical and visual property requirements detailed in the specification.
Essential to the production of these class 'A', surface quality welds, is the welding
consumable. However, many diving contractors carry out wet welding using ‘off the
shelf’ welding electrodes originally designed for surface welding. These electrodes
are either taped up or dipped in paint, varnish or other such coatings, in an attempt to
insulate and waterproof them. Whilst these electrodes may perform well on the surface,
when used underwater the environmental conditions can significantly alter the welding
characteristics and the mechanical properties of the competed weld.
Welds produced underwater are subjected to increased cooling rates and the process itself
breaks down water into its component elements thus producing high levels of hydrogen and
oxygen both of which are detrimental to the mechanical properties of the weld. Flux
formulations and filler metal composition used for conventional surface electrodes may not
cope with these inherent factors encountered underwater. The resultant welds frequently
exhibit unacceptable weld defects lack ductility and are likely suffer from hydrogen
embrittlement which can induce toe and under-bead cracking. These cracks could,
potentially, propagate into the parent metal thus causing more server damage than the
repair was intended to resolve. Even some of the electrodes commercially marketed today as
wet welding electrodes are conventional surface electrodes covered in some sort of
waterproofing and often sold as a 'cheap and cheerful' option! So it is not surprising
that even commercially available wet welding electrodes can not meet the all of the as
welded mechanical properties required by the specification. Whilst many may claim they
meet certain class 'A' test criterion like radiography, the overall mechanical properties
of the weld are still below that required.
The main area's in which these electrodes falter and which appeases the critics, is in the
hardness and the lack of ductility. Vickers hardness testing commonly reveals harnesses of
well over 400 even on materials with a relatively low carbon equivalent CE. Typically most
electrodes deliver elongation figures of between 6% and 9% where as the class 'A'
specification requires a minimum of 14%. Hydroweld FS™ electrodes, which have rapidly
become the industry standard for wet welding, comfortably fall below the maximum
macro-hardness value of 325 HV10 and exceeds the elongation
requirements for class 'A' welds with recorded elongation of between 16% and 18% which is
comparable to conventional above water welds. Hydroweld FS™ Charpy impact results also
prove to be comparable with conventional surface welding with figures of with recorded
results of 45J @ -20oC and 32J @ -30oC, room temperature results gave 56J @ 20oC. Visually
it is almost impossible to distinguish between welds produced with Hydroweld FS™ wet
welding electrodes underwater and a good conventional weld produced on surface.
Although Hydroweld FS™ wet welding electrodes have outstanding user friendly properties,
and produces consistently good results it is imperative that well trained, skilled welder
divers are used to complete the weldment. Whilst the principle and equipment used for wet
welding is similar to conventional MMA welding there are some differences in the
techniques applied to wet welding and the choice, type and quality of the equipment used
also has a bearing on the final results.
In 1996 The Welding Institute (TWI), in response to demand from industry, joined forces
with Hydroweld to develop the first quality wet welding course of its kind. Until then
there were no quality welding courses available, in the UK, other than a basic
introductory course often attached to the end of commercial diving courses.
The TWI / Hydroweld wet welding course provides unrivalled wet welder modular training
courses world-wide and as such have become internationally recognised. The TWI / Hydroweld
wet welder-training courses are run at various locations throughout the world including
the UK and Thailand with courses planed in Canada later this year. These intensive 10-day,
predominantly practical, wet welding courses are scheduled to run several times a year and
provide students with in-depth knowledge of wet welding and successful students with an
opportunity to complete a welder performance qualification (WPQ) to AWS D3.6-93 class 'B'
welds. These welder performance qualifications are witnessed by Lloyds Register of
Shipping, as is the testing. Certification issued on successful completion of the
course includes a welder performance qualification certificate issued by Lloyds Register
of Shipping and a certificate of attendance issued by TWI's School of Welding
Technology.
To cater for students with a limited command of English the theoretical element of the wet
welding courses is clearly delivered using a significant amount of pictorial illustrations
and practical demonstration. The practical side of the course is also designed to be as
student friendly as possible with the wet welding instructor taking an active, in water,
role to guide the student through the finer techniques required to produce high quality
wet welds.
The TWI/Hydroweld wet welding courses are run in the United Kingdom at TWI North at their
hi-tech underwater centre in Middlesbrough. This centre includes one of the largest
purpose built in-door commercial diver training tanks in Europe being 6.5 metres deep and
8 metres in diameter. The Tank is heated and continually filtered to maintain exceptional
underwater water visibility. Using modern and well maintained diving and wet welding
equipment, students can enjoy an unequalled training opportunity. Students progress is
monitored by hat mounted and tank mounted underwater CCTV which, is viewed in the dive
control area. The theoretical element of the courses is completed in one of the centres
outstanding classroom facilities.
TWI / Hydroweld wet welding course are also run in the Kingdom of Thailand at Mermaid
Maritime Ltd's state of the art training facilities in Laem Chabang, Thailand. The
underwater training centre there provides outstanding and cost effective training and
examination opportunities for divers throughout the region and beyond. It comprises, among
other facilities, an indoor 5.5 metre deep by 3.5 metre diameter training tank, air
conditioned dive control where the diver training can be monitored via underwater CCTV,
dedicated toilet and shower facilities and superb modern air conditioned classrooms.
With development of new welding electrodes, modern welding equipment and significant
improvements in welder training, production of surface quality wet welding has at last
become a reality. The process, which is used in all sectors of the industry, has been
steadily gaining credibility and wider acceptance resulting in increasing work load and
demand for skilled welder divers with recognised certification.
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