Vulcan the Offshore Experience: Installation of Conventional Platforms

Offshore oil was first explored and produced at Baku in the then Russian Empire at the beginning of the twentieth century. About the same time the discovery of onshore oil in Texas and Louisiana induced enormous changes in the economy of that region, making it not only a centre of oil production but also a centre for oil field services and equipment. The oilfield was and is a demanding environment for people and equipment, requiring extraordinary organisation of people and use of technology. We normally think of efforts such as the space programme spinning off technology, but the oilfield has done so as well, in ways that may not be as obvious to ordinary consumers but which are equally beneficial.

The move offshore in the Gulf of Mexico for the oil industry started after World War II. It started in the coastal areas of Louisiana, where land and sea tend to run together. The further out things went, the larger the platforms and the equipment needed to install them.

In this presentation we will concentrate on the Gulf of Mexico mainly because it is here where Vulcan’s foray into offshore oil construction first came, although both the industry and Vulcan were worldwide in scope.

Conventional Platforms

When we speak of “conventional platforms” we mean those which have a continuous rigid structure from the sea bed to the ocean surface. These were developed for water depths generally not exceeding 300 m, although a few exceed that in depth. These are generally tubular structures using large diameter pipe, much of which was rolled from plate at the yard and butt welded before being welded into the platform. The coping and sheer size of these structures–some of which were as tall as the original World Trade Centre in New York–required very specialised and competent fabrication capabilities.

Much of the construction portion of the offshore oil industry in the Gulf was centred in Morgan City, LA. The upper right inset above shows platforms being built in yards along the Bayou Boeuf south of Amelia, LA. Most conventional platforms were prefabricated onshore. They were then floated down the bayou and past Morgan City (shown in the lower middle inset above) into the Atchafalaya River and then into the Gulf.

Ready to be floated out, a conventional platform sits behind a yard crane in McDermott’s Batam, Indonesia yard in January 2000.

Once the jacket was finished, it was placed on a barge and floated out to the spot in the ocean where it was intended to be installed. Below is a view of the jacket and barge below it as they approach the derrick barge (the construction barge used to actually complete the construction of the platform.) The triangular plates on the bottom of the platform are mud mats; they prevent the platform sinking into the soft ocean floor after it is upright and resting on the bottom. Virtually all platforms are tapered to the top, as the moments from wind and wave action are the greatest at the ocean floor, the platform itself being a giant cantilever.

Most barges–and the derrick barges themselves before they became self-propelled–were towed by ocean going tugboats. These workhorses were an essential part of any offshore construction operation, operating in all seasons and in all types of weather, fair and foul. In the Gulf of Mexico, construction generally tapered off during the winter months due to the winter storms from onshore. The North Sea had an even more restrictive construction season, which led to a “quantum leap” of offshore technology of its own.

Once the jacket had arrived at the site, the legs were flooded and the jacket sank upright to the sea floor. Setting the jacket could be a trying task, as the photo below and the one to its right can attest. Sometimes it was necessary for the barge (or more than one) to pick up and move the jacket, as it would be “off station.”

A key element in platform installation: the derrick barge. The derrick barge shown below was a step forward from the construction barges used for bridges and the like, and certainly the spud-type barges such as is shown here. The flat-bottomed construction was very suitable for conventional platforms, both because of their size and the areas where they were the most suitable. The demanding conditions of the North Sea inspired the development of the semi-submersible self-propelled barges, which eventually became the state of the art in the field. Note that there is both the main installed crane on the barge and a smaller mobile deck crane. If carelessly handled, the latter could and did end up “in the drink.”

Once the jacket was set, pile driving could begin. The set platform became a template for the piles, which were driven through the legs. Below is a good view of a four-pile platform with two of its piles “stabbed” through the legs. Once driven, these would hold the platform to the sea bed.

Installation by Driving by T.J. Whipple and Wendell Vines, which is a summary of the operating environment of Vulcan hammers offshore–including procedures and derrick barges–when they were the busiest.

Crew and supply boats were the only method of transporting personnel and small supplies in the early years of offshore exploration. For platforms near the shore, they were practical and economical, but as the work went further and further offshore, crew boat rides became longer and longer, something Vulcan’s people found out the hard way.

Helicopters were indispensable in offshore exploration, drilling, construction and production, especially as platforms went further and further offshore. Like everyone else offshore, Vulcan personnel spent time in helicopters, enduring mechanical problems (which are potentially disastrous in a helicopter) and violent weather.

Offshore crews generally worked twelve hour on/twelve hour off for two weeks at a stretch. There was thus some idle time offshore; one favourite pastime was fishing. Derrick barge crews discovered what environmentalists hate to admit: offshore platforms are natural habitats for all kinds of fish and other marine life, which made for good fishing. Welding wire was a favourite type of fishing line, though other materials would get the job done too.

After the piling was complete and the piles grouted to the jacket, the actual superstructure of the platform was installed. With the long work season in the Gulf and other tropical and sub-tropical regions, the superstructure was brought out in modules and assembled as shown below. Again the North Sea’s hurried schedules forced the development of bringing out the entire superstructure in one piece and setting it on the jacket; this more than anything drove the construction of the very large derrick barges by McDermott and Heerema in the late 1970’s and early 1980’s. The superstructure had to be as light as possible, not only for lifting but for the structural economy of the platform. The question, “too much weight topsides?” was more than a personal one for designers of conventional platforms.

Stabbing the add-on. Virtually all offshore piles were driven on a batter. Since the weld integrity of the add-on had to be of good quality, a stable connection between the add-on and the pile segment already driven was a must. This common solution used a pipe inside of the pipe being driven with a tapered cut at the bottom for easy stabbing. This worked well for many years.

One important operation involving the piling separate from driving was the welding of add-ons. The literature tells us that adding on to steel piling is “easy” but with 1-2 metre diameter piles and up easy is a relative term. Even with a crew such an operation could take an entire shift, and the weld had to pass ultrasonic inspection or be done over. In cohesive soils, a big problem was that while the pile was being welded the soil would set up, making for harder driving for the next add on. Under pressure from the North Sea’s short construction season, the process was shortened by the use of “breech block” technology by which an add on was threaded onto another like the closing of an artillery piece.

When we think of a platform, we usually think of a single structure, but many platforms were in reality complexes of structures joined together into small offshore cities. The 1968 photo below shows the last module for such a structure about to be placed on the deck of the platform. Such complexes were not unique to the Gulf of Mexico; they also appeared in the North Sea and other places around the world.

Floating the topsides out: as the Vulcan hammers install the piles, the next step waits on the barge. Installation by Global Marine in September 1996.

Supply barges were an essential element in the marine construction process, bringing materials and equipment to keep the process going. Both hammers and pipe loaded up this barge. In the centre is a Menck hammer; Menck was Vulcan’s chief competitor for the offshore market. Since this was 1976, the Menck hammer was decorated in a patriotic way for the U.S. Bicentennial, but this could not change the fact that the Vulcan 3100 was the only American hammer on the barge.

A diagram illustrating the difference between the Vulcan (moving piston) and Menck (fixed piston) steam hammer construction. On the Vulcan (left) hammer, the “stroke control bar” is in reality the ram key, and the “exhaust port and valve” doesn’t exist on a Vulcan hammer, both handled through the “control valve.” This is a reminder that equipment details sometimes escape the civil engineers, even though their livlihood depends upon the equipment operating properly.

Conventional platforms are still an important constituent of offshore oil and gas production. Here’s one being fabricated in Ingleside, Texas, in March 2012.