Paul Hughes, Global Subsea Market
Leader at Hydratight,
organisations have an obligation
to maintain their aging pipelines
and how they can best go about
achieving leak free pipelines, in
the env i ronmentally sensitive
subsea environment. A Chartered
Engineer with 10 years experience
in the subsea engineering field,
Paul discusses the advantages of
using mechanical connectors for
There is no escaping the fact that many of the
subsea pipelines around the world are reaching
the end of their natural life. Indeed, some are
probably already working beyond this point. The
majority were brought in to service in the 1970s
in places like Europe’s North Sea and the ‘Mumbai
High’ fields in India, and as such will need more
rigorous maintenance in the coming years.
The Nor th Sea, and more recently ‘Mumbai
High’, have seen a rapid expansion of oil and gas
extraction activities, due mainly to demand for
oil and gas having risen significantly as consumer
habits altered and the incomes of the world’s
population rose. It is estimated that around 25 per
cent of subsea pipelines are now operating beyond
their intended lifespan.
This createsa number of problems for the
industry. Firstly, there will become an increasing
need for a larger propor tion of budgets to be
spent on maintenance, which naturally cuts
into bottom lines.
Secondly, in light of a number of high profile
incidents, political and environmental pressure
has grown on organisations to ensure that they
maintain pipelines and joint integrity.
The industry needs to ensure that incidents like
this don’t happen again, in order to repair its
badly tarnished image in some quarters of the
Finally, it is worth noting the cost implications of an
unscheduled shutdown. These can run into millions
of dollars in lost production time per day if a platform
is taken out of action for any period of time, meaning
that a leaking pipeline cannot be ignored until
routine maintenance checks are carried out.
It is likely therefore that at sites across the world
many pipeline repairs will have to take place in the
coming years. But, the big question is; how should
these repairs be done?
As a rule it would normally be suggested that in
shallow water welding would be the way to go
when tackling a repair. This is not always the case,
with some people within the industry subscribing
to the view that pipelines can be wrapped with
repair clamps, composites and epoxy materials. In
our experience though, this kind of repair should
be limited to smaller, more localised repair jobs.
Surprisingly to me, welding still remains the
principal method used by most organisations for
repairs in deeper water. At depths of up to a couple
of hundred meters it is usually relatively simple to
arrange for divers to come and carry out work, but
beyond this problems start to arise.
However beyond that the equation suddenly
becomes significantly more complex. The need
for hyperbaric chambers, specialised rigs and
the fact that due to a number of factors repairs
rarely have the longevity of the original fitting,
mean that financial and speed advantages of
welding suddenly don’t seem so great. So what
is the solution?
We believe that now, and in the future, more and
more pipeline repair work will be done using
mechanical connectors. Indeed, since Mumbai
High has been actively explored, mechanical
connectors have become an increasingly popular
Mechanical connectors are by no means a new
technology. They have been in use since the 1920s,
however for a number of reasons, ranging from
sealing problems and issues with materials, which
included inflammable elements, they were largely
obsolete by the 1970s.
However since the end of the 1980s the situation
has changed significantly and much work has been
done to improve both systems and sealing materials,
making connectors a real alternative to traditional
Organisations such as our own, have led the field
in graphite sealing systems, which overcome many
of the fire-safe and shelf-life disadvantages of the
polymer and elastomeric seals previously used.
Indeed there has been almost a development of
an industr y within an industry, specialising in
Even up until the turn of the last century many
engineering papers were dismissive of the use of
mechanical connectors. Often citing a belief that
they weren’t as durable as welds, and that the
mechanical systems used for installation were not
accurate enough to ensure that further damage
wasn’t done whilst installing them, many in the
industry were rather mistrusting of the technology.
Welding seemed to be the ‘chosen son’ in terms of
method of repair, and although attitudes are gradually
shifting, there are still elements within the industry
that seem unwilling to shift from this paradigm.
In reality, many connector systems, through well
over 15 years of painstaking research now offer a
number of benefits, that welding cannot; particularly
in deep-water exploration sites. Systems available
now offer strength and safety benefits, above those
offered by welding and in every case less damaging
to the metal structure of the joint, and which are far
Modern diverless connection methods for welding or
mechanical connection use the same highly-accurate
systems. These were not available 15 years ago,
and have given rise to increased confidence in the
application of connectors. It is not in the interest of
anyone in the industry to jeopardise safety, and as
an organisation we know this from our conversations
with other businesses working in the field.
But is it possible for mechanical systems do the work
of typical welded ones?
Yes. In our own experience and through rigorous
product testing of our own range, it is certified in
place of welds (DNV, Lloyds, API, ABS, ROK) on pipes
up to 42 inches in diameter and on pressure ratings
up to ANSI Class 2500. We have also shown that we
can create a joint at least as strong as a weld.
We can only speak about our own product, but its
designed connection life is at least 30 years. Over
the years we have installed approaching 2,500
connectors around the world in the past 2 decades,
many of them diverless, and they have a 100 per
cent leak-free record.
Do mechanical connector soffer advantages
In many instances they do. The benefits of welding
are only really apparent at lower depths. Mechanical
connectors require no welding, which means no
specially trained divers; they cannot introduce the
common problems of welds, including contamination
and the requirement for pre and post weld treatments
and inspection. Indeed, pressure testing is made
significantly easier by using connectors, with all
of our connectors having pressure-test facilities
Other major advantages include the negation of the
need for specialised machining and preparation tools
or careful shaping of the joint, and most importantly,
complex requirements such as hyperbaric chambers
are not required to install them.
Mechanical connectors, fitted diverless on largediamete
rlines, do admitte d l y re q u i re heav y
placement and alignment rigs, but this would be
the same when using welding as a method too.
In practical terms, it could be argued a weld rig
requires greater accuracy, as the need for bringing
pipes together within a millimeter of each other is
apparent, and they must be held in this position
until the weld has cooled. Mechanical connectors
have much wider installation tolerance and as
soon as the system is tensioned, the connection
is at full strength.
Mechanical connector systems offer a range of
elements - pipe-to-pipe connectors, pipe-to-flange
connectors, riser connectors, subsea and topside
connectors, end caps and special tees amongst many
more, to cater for all manner of emergencies and
repairs that may arise.
A number of organisations also now routinely hold
mechanical connectors in storage, for use as and
when emergencies occur. Connectors can also be
used on lines that need to be connected and then
disconnected, which is another advantage of using
them, as they can be reused a number of times.
There has been a lot of talk within the industry
about the usage of mechanical connectors to tie longer welded lines together, by staging them
at intervals along sections of pipeline. Our own
experience suggests that the usage of connectors
is particularly cost effective when fields are over
100km out to sea. This is due to the complexities
associated with organising manpower and the
sheer logistical nightmare that such a welding
operation can involve.
An example of what is achievable from our own
operations with modern connectors comes from
using one of our products on a Nor th Sea gas
platform. The estimated welding time for four twoinch
flange adaptors was 50 hours, added to around
240 estimated hours for another five 12in couplings
and one flange adaptor. Whilst a very experienced
welding team may have been able to reduce this
time, by using connectors the work was completed in 70 hours, and with fewer personnel. Each hour that
a platform is down costs money, and by reducing the
down time, connectors helped the organisation in
question limit their losses.
Whilst welding will invariably still play a significant
role in the future of the pipeline repair industry,
undoubtedly the case for the use of mechanical
connectors is growing ever stronger as operators
look to improve profitability and more importantly
safety on platforms.