Taking the Plunge: Underwater Connections
By Lynda Nolen, Bishop & Associates Inc.
 For many of us, August
is the hottest month of the year. Temperatures soar into the 90s, and
even the 100s. In an effort to escape the oppressive heat, we head to
the water. Whether it is the ocean, the sea, a lake, or a swimming pool,
we appreciate the cooling and hydrating effect water has on us. But for
interconnects, repeated exposure or total submersion in water creates
one of the harshest environments an electrical or electronic connector
can encounter. Water, in any of it various forms—vapor, liquid or
solid—exposes these connections to a variety of environmental obstacles
that can affect the mechanical, electrical, and dimensional properties
of the part. To compound the problem, the type of water and level of
exposure each mandate a different level of protection, meaning there is
no one approach to protecting valuable electronic or electrical
connectors exposed or submerged in water.
Because each level of exposure dictates it own unique set of
environmental obstacles, connectors designed for use in or around water
are generally broken down into three categories:
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Connectors
designed for use in surface or shallow water
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Connectors
designed for use in deep water
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Connectors
designed for full ocean depth or sub-sea use
In addition to the level
or approach to protection, and of course the power or signal-carrying
capabilities of the connector, the category a connector falls within can
also dictate other conditions, such as resistance to pressure, extreme
temperatures, ergonomics, method of coupling, ability and ease of
installation, repair, and cost-effectiveness.
As in any application that carries signal or power, the ability to mate
or couple the connectors easily is vital. When dealing with connectors
designed for applications involving exposure or submersion in water,
this becomes even more significant. There are two basic methods of
coupling a connector that is exposed to water. With the dry-mate
approach, interconnects—either electrical, optical, or a combination of
the two—are mated or unmated in the air or in a dry environment prior to
being exposed to water. This type of coupling is common in applications
such as shipboard connections, oil or gas platform installations, and
meteorological measurement or broadcast systems. This type of coupling
is used frequently when equipment and cables can be brought to the
surface for repair. Interconnects that are actually mated or unmated
under water, at up to full ocean depths, are referred to as wet-mate
connectors. These types of connectors are used in sub-sea systems for
the oceanography, oil and gas, and defense industries. This choice of
coupling is chosen when surface retrieval is virtually impossible or
extremely cost prohibitive. Wet-mate connections generally on two
aspects of the connection—the front face of the connector, where the
active electrical or optical signals are joined, and the backend of the
connector, where the wires are terminated and the connector is sealed to
the cable.
Environmental Obstacles
Corrosion
Probably the
most crucial environmental obstacle a connector—used around or submerged
in water—must overcome, is based on the type of water to which it is
exposed. This is particularly important when discussing connectors
exposed to salt water or seawater. Salt water or seawater, which
represents 97 percent of all water on the earth, is made up of water (H2O)
with salt in it. These salts, which are composed of over 70 different
dissolved elements, decompose into electrically-charged atoms, or groups
of atoms, when placed in water. Of these 70 different elements, more
than 90 percent of the content is from these six elements:
sodium (Na+), chloride (Cl−),
magnesium (Mg+), potassium (K+), sulfate (SO4−), and calcium (Ca). These
six elements, in the presence of water, allow ions on dissimilar metals
to form, which slowly leach from the material in a galvanic reaction and
dissolve the plating. This galvanic corrosion can cause weakening
of the material and its properties, which can lead to reduced
current-carrying capacity and result in intermittent, and ultimately,
permanent failure of the connector. To overcome this, connector
manufacturers offer a variety of shell materials specifically designed
to withstand the corroding effects of exposure to these elements. These
materials include:
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- Stainless
Steel 316 & 316
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The choice of material
is normally based on the level of exposure, length of expected service,
operating temperature, composition of other components within the
system, and of course, cost.
Recognized for its excellent resistance to a wide range of organic and
inorganic liquids, high temperature rating, excellent tribological and
electrical properties and reasonable price, high-performance
thermoplastics, like PEEK, make a great choice for shallow or surface
water exposure. Connectors and backshells manufactured with
high-performance thermoplastics, such as Souriau’s UTS series, offer
discrete wire sealing with IP68/IP69K sealing when mated, optional
sealing caps for protection when not mated, and UV-and
salt-spray-resistance—ensuring rapid, secure mating. Available in three
shell sizes and nine contact arrangements, Souriau’s UTS series also
offers a variety of contact sizes and styles, including machined,
stamped, coaxial, and fiber optic. Because the contacts are crimped, all
four contact styles can be combined within the same connector. Also, the
connector can be field-terminated and easily repaired. The grommet,
which uses the backshell to maintain the pressure seal, is capable of
handling cable insulation diameters from 1.7 to 3mm. Each grommet cavity
has a membrane that is pierced only when a terminated wire is loaded,
therefore, no filler plugs are needed unless a cabling error or
modification has occurred.
Shells used on connectors designed for full ocean depth or sub-sea
environments are generally manufactured of high-grade metal alloy such
as nickel-aluminum-bronze, or one of the other metals previously
mentioned. These metals and metal alloys, which are used in a variety of
marine applications, are all recognized for their high strength and
excellent corrosion- and wear-resistance.
In addition to the corroding effects of saltwater or seawater, shear
stress must also be taken into consideration. As seawater moves over the
surface of a connector—particularly salt water that is heavily mixed
with sand—parallel stress is placed on any object perpendicular to the
movement of the water. Over time, metal shell connectors plated with a
protective coating can experience a shearing or a breaking down of this
coating as the velocity of the water increases. Overcoming this,
especially in applications where the connector will be placed in a
particular area for a lengthy period of time, proper selection of the
shell material at the onset of the connector selection is required.
Pressure
Pressure plays an important role in connectors used in applications
where water is involved. Pressure is particularly relevant for
connectors used in full ocean depth or sub-sea environments. Pressure,
which is defined as “force per unit area,” is all around us. When a
connector is used in a normal application, such as in a laptop or
printer, there is approximately 14.7 psi of air pressure also being
placed on the connector, in addition to any pressure placed on the
connector by the enclosure, PCB boards, or other components. This same
14.7 psi of air pressure is applied to a person standing in a room, but
humans are so accustomed to this pressure that they don’t actually feel
it. Water, being much heavier than air, adds approximately .445 psi per
foot of water, or approximately 1.46 psi per meter of water for a total
approximate pressure of 16.2 psi. This means that a connector used in a
sub-sea environment at approximately 2,000 meters, must be able to
handle an additional 2,920 psi. Considering that the average depth of
the Atlantic Ocean is 3,926 meters and the Pacific Ocean 4,280 meters,
pressure becomes especially relevant. Of course, none of these
calculations address other issues that can affect pressure, such as
water temperature and salinity.
 To tackle the extreme pressure that these connectors must endure, rugged
connectors, such as Souriau’s 8810 series, have been developed.
Manufactured with shells of high-grade metal alloys, like nickel
aluminum bronze, these connectors are designed to be submerged to depths
of 3,000 meters. Rated at 500 mating/unmating cycles, these connectors
offer body shells with rugged, square-cut coupling threads to enhance
the suitability for repeated coupling and uncoupling in severe
environmental conditions, and make the connectors ergonomically easy to
mate.
 Another way to tackle
the extreme high pressures of underwater wet-mate applications is to use
glass-to-metal sealing, as seen in the Teledyne D.G. O’Brien 107 series.
These parts, manufactured using 316/316L stainless steel shells, are
available in three to 48 contacts, and provide a glass-to-metal seal
pressure barrier in the receptacles for maximum protection of equipment.
Designed to be molded to cables, the 14-pin and above layouts operate to
6,500 pounds per square inch gauge (psig) mated. Based on wire gauge and
contact size, these rugged metal shell connectors can handle both
instrumentation and power requirements.
Temperature
 Our oceans and seas are separated into three layers. Temperature ranges
within these three layers can fluctuate drastically. The surface layer,
which accounts for only about 10 percent of the total water, has an
average temperature of 17°C (62.6°F) and varies mainly with latitude.
Ocean water in high latitude areas, like polar seas, can be minus 2°C
(29.4°F) and in a low-latitude area, like the Persian Gulf, water
temperatures can be 36°C (96.8°F). The second layer, called the
thermocline, acts as a boundary between the surface water and the
sub-sea or deep ocean water. In the thermocline layer, water
temperatures drop drastically, as both depth and density increases.
Temperatures in sub-sea water range between zero and 3°C (32 to 32.5°F).
This wide change in temperature makes the selection of materials used in
connectors for sub-sea applications extremely critical.
At first glance, sub-sea temperature ratings do not appear to be
drastic, especially when realizing that the temperature rating of a
connector designed to be used in backplane applications is approximately
minus 55°C to 105°C. A connector in a backplane application, though,
does not have to accommodate for other environmental factors, such as
pressure- and corrosion-resistance, which a connector used in a sub-sea
environment does. It is these factors, along with the required
temperature ranges, that restrict or limit material selection.
To accommodate for these other factors, manufacturers of connectors used
in sub-sea applications provide both an ambient temperature rating and a
working temperature rating. Ambient temperature ratings will be
significantly different than working temperature ratings. An example of
this is seen in the previously mentioned Souriau 8810 series. Although
this connector possesses an ambient temperature rating of minus 30°C to
70°C, the working temperature is appreciably different at minus 3°C to
40°C.
Types of Wet-Mate Connectors
There are three types of wet-mate connectors used in deep sea
applications. The first type is designed to be mated using a remote
operated vehicle (ROV). The second is for manual diver mating, and the
third is intended for stab-plate mating.
  Connectors used with ROVs incorporate backshells with specially designed
handles to allow the arm of the ROV to grab the connector and cable
securely, and mate it to its fixed mount mate. The handle design is
determined by the manufacturer. As illustrated in the side photos, these
titanium CP Grade 2 metal shell connectors, part of Ocean Design Inc.’s
Nautilus series, are pressure-compensated for full ocean depth of 3,000
psi. Underwater mating is accomplished by using two redundant mechanical
barriers at all mechanical interfaces. During the mating action of the
two halves of the connector, the pin contact enters the socket chamber
by displacing the stopper. At the same time, its surface is wiped clean
of any seawater or contamination by a series of wiping seals at the
front of the chamber. The electrical connection is made up within the
benign fluid environment. During disconnection, the plug retracts from
the receptacle chamber and the insulating stopper fills the vacated
space and seals off the chamber to prevent any oil leakage or water
ingress.
To accommodate the loss of dexterity created by the use of diver’s
gloves, wet-mate connectors designed for manual diver mating incorporate
longer backshells with easy-to-grip-and-turn coupling mechanisms. Stab
plates, which allow multiple connectors to be mated at one time, are
commonly used in underwater junction and control boxes. Wet-mate
connectors designed for stab plates incorporate retaining rings to hold
connectors securely in place once mounted and to assist in mating.
Generally, along with the electrical or electronic connections, are also
hydraulic couplers that are connected to a variety of valves. Connectors
and hydraulic connectors on a stab plate are generally mated using an
ROV.
Additional Requirements
In addition to the many connector attributes discussed above, many
sub-sea connectors must also be certified to specific navy or industry
specifications. These specifications include connectors built to
military specifications Mil-C-24217, Mil-C-24231, Mil-S-901C (navy), HI,
Det Norske Veritas specifications (DNV), and connectors built to the
American Petroleum Institute Standards (API-16D).
 Mil-C-24217 covers deep submergence electrical connectors for submarine
applications. Connectors built to this specification must be capable of
handling a hydrostatic pressure range from zero psi to 10,000 psi, with
a maximum recommended operating pressure of 6,500 psi. Mil-C-24231
includes pressure-proof single and multiple cable connectors, plugs,
receptacles, adapters, hull inserts, and hull insert plugs. Connectors
designed to comply with Mil-S-901D must have the ability to withstand
shock loading, which incur during wartime service due to the effects of
nuclear or conventional weapons. Connectors, like Souriau’s 8810 series,
carry an “A” grade and “I” classification, indicating they are essential
to the safety and continued combat capability of the ship and must meet
these shock requirements without the use of resilient mounting installed
between the equipment and the ship structure or foundation.
 Connectors, like Teledyne D.G. O’Brien’s API-16D, have pressure test
ports to verify the seal integrity prior to deployment of sub-sea
drilling or production equipment as required by API-16D. These robust
underwater connectors are pressure-rated to 10,000 psi, have redundant
seals in all interfaces, and have an operating temperature of minus 40
to 75°C.
Taking the Plunge
When selecting a connector to be used in a wet or submerged environment,
the answer to obtaining long life, highly reliable underwater electrical
or electronic connections is to look beyond standard price and delivery.
This is particularly true in underwater applications, where failure is
most often associated with the inability of the connector to withstand
the extreme operating and handling conditions associated with sub-sea
installations. Unlike more traditional interconnects found in computer
peripheral equipment or consumer goods, connector failure in an
underwater application not only creates a major inconvenience, product
downtime, repair charges, and the cost of a replacement connector, but
it can also include total system downtime as well as replacement and
repair charges. These charges can run into the thousands of dollars,
when the cost of bringing up the cable and repositioning it is included.
Summary
There is nothing new about using connectors in underwater or surface
water applications; in fact, underwater mateable or wet-mate connectors
have been around for almost 45 years. What is new is the variety of
available to connectors and the depths and environmental obstacles these
connectors can now accommodate. This is especially evident when one
realizes the impact in production and production costs sub-sea control
systems, incorporating wet-mate connectors, have had on the offshore oil
industry. What is also new is the extent to which fiber optics is being
used and the advantages fiber optic underwater wet-mateable connectors
can offer, including weight and size reduction. In fact, sub-sea
telecommunications networks have already been deployed in a number of
areas. With more than 90 percent of the earth’s surface covered in
water, the applications for reliable, long-life and cost-effective
dry-mate or wet-mate connections are only limited by where humans or
machines can go.
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Lynda Nolen
Product Specialist, Bishop & Associates Inc.
Lynda
Nolen has been in the interconnect industry for over 28
years. She has worked in sales, sales management, marketing,
and product management for such companies as TRW Electronics
Components Group, Sunbelt Components, Cinch Connectors,
Arrow Electronics, PEI Genesis, and Delphi Interconnect.
Nolen has extensive experience in competitive
cross-referencing, drawing, web and catalog review, new
product introduction programs, harness and connector
assembly programs, account management, and customer service
programs. Lynda received her Bachelor of Arts degree from
Roger Williams University in Rhode Island in 1979, and has
completed various electrical engineering courses.
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