Waterjetting 2c - using Nature's crack system

In this section (part 2) of the series on Waterjetting, the focus is on the way in which high-pressure waterjets grow cracks in their target. As John Field showed, even the presence of microscopic cracks on a glass surface are enough to initiate the larger cracks that lead to failure. In many cases, however, the most useful growth can be achieved if the cracks only extend to the point that they remove a desired amount of material. This becomes important where there are weaknesses and flaws in the material – such as the layers between plies of wood, or even Kevlar - which should not be grown as the jet cuts down through the material. And in a later article this topic will be a part of a discussion as exactly what happens as a jet drills a hole into a target. But, for today, I would like to talk about crack growths in rock and soil, both because it is one of the oldest ways in which water can penetrate into material, and also because it holds the potential to be one of the newest areas into which waterjetting is growing, and will likely further advance into a more significant business.

And to begin consider that, as water penetrates into the cracks in a rock, and grows those cracks slowly, under natural forces, rocks with minerals in them, will see those mineral particles separately broken out. The classic example of this is with gold. One of the ways in which the Forty-Niners found the gold in California was by panning for the gold particles in the rivers, and tracking the gold deposits back up-stream until they reached the original gold deposits of the Sierra Mountains. Not that this was the first time that water transport had helped in gold mining. One of my favorite stories to begin classes is to remind them of Jason and the Argonauts.

Figure 1. Movie poster for the 1963 film version of Jason and the Argonauts (iMDb )

It is a theme that has been made into a movie several times, (see, for example, here) and tells the story of how the Greek Prince Jason and a band of companions go in search of the Golden Fleece, and the adventures that he has along the way. Despite the mythical creatures the story is thought to be likely based on some measure of truth, with the voyage taking place some time before 1300 B.C. But our focus is on the fleece, rather than the voyagers.

Figure 2. Suggested path that Jason followed to get to the River Rhion in Georgia.(Google Earth)

Within the Caususus mountains of Georgia lies the modern town of Mestia, which was thought in Roman times, to be the site of Colchis, where Jason found the Golden Fleece. The reality is not quite as dramatic as the legend since, as the Roman historian Strabo noted

“It is said that in the country of Colchis, gold is carried down by mountain torrents, and that the barbarians obtain it by means of perforated troughs and fleecy skins, and that this is the origin of the myth of the Golden Fleece”

The torrents of water in the Svaneti valley outside Mestia, (Nika Shmeleva Google Earth at 43deg02’29.74”N, 42deg42’25.13E)

It is thought that the miners of the time directed the streams so that they flowed over the veins of gold and eroded out the particles so that the gold was carried down to the valley. Here it was fed through the troughs that Strabo described, and the heavy gold particles were captured as they tangled in the wool of the fleece. To recover the gold the miners would then hang the fleeces in trees, so that they would dry, and the gold could be shaken loose. Unfortunately as the fleeces hung in the trees they provided a tempting target for Greek thieves. (In a later version that I will write about in the next post the sheep fleece was replaced with brush that could be dried and burned to release the gold).

Water was thus, in one of the earliest “automated” mining processes, used to both dislodge and then carry the valuable mineral from the mining site The overall power of water to move soil has been used to wash away material for over a hundred years. In the 1973 War between Egypt and Israel the Egyptian Army gained a significant advantage in the early hours of the war by using waterjet monitors to wash away the defensive barrier along the edges of the Suez Canal, rather than using conventional mechanical excavators.

To deal with the massive earthen ramparts, the Egyptians used water cannons fashioned from hoses attached to dredging pumps in the canal. Other methods involving explosives, artillery, and bulldozers were too costly in time and required nearly ideal working conditions. For example, sixty men, 600 pounds of explosives, and one bulldozer required five to six hours, uninterrupted by Israeli fire, to clear 1,500 cubic meters of sand.

The quoted Sunday Times report of the time suggested that the Israeli Army had anticipated that it would take 24-hours to remove the barriers giving time for their Army to mobilize and arrive. However, using a set of five pumps per breech site the Egyptian Army was able to make an opening in as short as a 2-hour time, with the mobilized water cannon opening 81 breeches, and removing 106 million cubic feet of material in that first day of the war. They were thus able to initially advance into the Sinai with relatively little resistance.

The pressure of the water does not have to be high to disaggregate the soil, but large volumes were needed in that application both to break the soil loose and to move it out of the way. Moving the debris out of the way is an important part of the operation, and while, in the above case it could be just pushed to one side, in many more localized jobs, particularly in cities, that is not an answer. However if the soil can be collected with the water, then the fluid can help to move the soil down a pipe away from the working area. And, more importantly, if the soil can be captured as it is being broken loose, then both can be collected before the water has had a chance to penetrate into the soil around the hole, and so the walls of the hole will not get wet, and will remain stable and not fall in.

One way that we have achieved this is to rotate a pair of waterjets relatively rapidly (depending on the material the jet pressure can range from 2,000 psi to 10,000 psi) so that the surface layer is removed, and to immediately take this away by combining the jet action with a vacuum for removal. (In the initial trials we used a Shop Vac to remove both water and debris). This combination has become known as hydro-excavation, and will be the topic of a couple of posts in the future.

Similarly the use of high pressure to break an ore down into its different parts, so that the valuable mineral can be separated from the host rock at the mining machine, is become a new way to reduce the costs of transporting and processing the ore, and make mining more efficient. As yet this latter is still more of a laboratory development, though it will develop for greater use in the future, and there will be additional posts on this too in the future. But, in both cases, the use of waterjets to effectively rely on extending pre-existing cracks makes the systems work. In the next post I’ll write about a couple of other ways of getting enough cracks into the rock as ways of making it easier to separate and remove valuable materials from underground.

OGPSS - Oil tankers in the wake of the Egyptian crisis

Gail Tverberg’s analysis of some of the underlying causes of the current Egyptian crisis is cogent, but it one of the other consequences that caught my attention today. For, as was noted in Forbes

While most equity-related assets got battered, a select group of stocks, oil shippers, were corking champagne bottles. Apart from Overseas Shipholding, Frontline Ltd. had a killer day, gaining 7.8% or $1.96 to $27.10.

An analyst for a shipping hedge fund explained that the spike is connected to fears surrounding the continued operations of the Suez Canal, amidst social unrest caused by massive riots against President Hosni Mubarak’s 30 year rule. “While Suez closure is not much of a threat, shippers are refusing to load in the Red Sea and transit the Canal,” explained the trader. “What’s probably going to happen is that they re-rout ships to the Cape [of Good Hope],” he noted.

“[Re-routing] makes voyages longer, which ties up ships and in turn diminishes supply,” said the analyst, “[this] is positive for the tanker market.”

The change involved is not just giving a tanker captain a different map and saying “get on with it.” Because of the relative size of the Suez Canal, there are different sizes of tankers involved, and so I thought it useful to talk about the different sizes of tankers, how fast and where they go, (and what the cost of that re-routing might be) in the post today.

To begin with let’s look at the traffic along the Suez Canal itself. Note that there is no immediate port of access into the Mediterranean, and thus to Europe, from Saudi Arabia or the nations of the Gulf.

Overview of the Suez Region (EIA)

The EIA, in writing about the Canal noted that

Almost 35,000 ships transited the Suez Canal in 2009, of which about 10 percent were petroleum tankers. With only 1,000 feet at its narrowest point, the Canal is unable to handle the VLCC (Very Large Crude Carriers) and ULCC (Ultra Large Crude Carriers) class crude oil tankers. The Suez Canal Authority is continuing enhancement and enlargement projects on the canal, and extended the depth to 66 ft in 2010 to allow over 60 percent of all tankers to use the Canal.

There are restrictions on the tanker size that can fit through the canal. This is mainly based on draft, or the depth of the tanker underwater, which has to be less than the 66 ft depth of the Canal, but there is also a bridge over the canal that the tankers must pass under. Those that fit into this range are designated as Suezmax tankers. In terms of the classification of tanker sizes they lie in the mid-range of those available. In a typical day about 1.8 mbd of oil passes through the Canal, which is about 5% of the global oil tanker trade.

The smallest of the tankers are those that act as coastal tankers. Typically from 300 to 670 ft long, with a draft that can go from 20 to 52.5 ft, they are used locally for the trans-shipment of refined fuel products. Ranging from 1,000 to 50,000 tons deadweight they are, most typically, the small local vessels that are often the only tankers that folk will see coming into harbor.

The design objectives for coastal tankers are demanding and sometimes contradictory, maximum volume in minimum dimensions. Operation in coastal service means frequent harbor calls, often through very restricted waterways having high currents and winds. Good manoeuvring capabilities are thus also required and, of course, high system availability to avoid incidents and accidents in case of system malfunction.

One of the more modern ones is fitted to carry either oil or liquefied gas.

The coastal tanker Seychelles Paradise.

But before I go on, I now need to define deadweight (DWT). It is not the weight of the empty tanker, but rather the weight of the cargo and fuel that the ship carries. In other words almost everything but the weight of the ship (which, just to be confusing, is known as the lightweight). Put them both together and you get the displacement of the vessel. So, that a tanker with a 50,000 ton DWT, with 6.3 barrels to the ton, would carry 315,000 barrels of oil. Now this is not all cargo since perhaps 5% of that total would be the fuel oil to drive the ship, which in this case would be around 15,000 bbl, giving a capacity of around 300,000 bbl. The density of the oil varies, and I used a value from one of the shipping companies, rather than the 7.3 value I have used in the past when converting shipped product.

And remember that bridge over the Canal that I mentioned? Well that brings in the other measure, known as “air draft.” This is the head room that the tanker needs, and for Suezmax this is 223 ft.

The next significant size category up are known as Aframax, and for a long while I thought that this related to some African capability. However it actually refers to the Average Freight Rate Assessment (AFRA) for the classification. A typical tanker will have DWT range from 80,000 to 120,000 tons (i.e. typically a useful cargo of around 690,000 bbl), a draft of 49 ft and a length of 820 ft. It has a typical speed of 14.7 knots. For those interested, Venezuela just bought 10 of these for $70 million each from Russia. Lloyds see a continuing oversupply of this category, to the point that (until this weekend) they projected rental costs of $10,000 a day or less, below operating costs. However there is a current hope in the industry that the rates may now rise (hence the champagne).

The Aframax tanker Tamara (currently for sale )

The next category will be the Suezmax category which has the restrictions that I mentioned above. They range up to 160,000 tons DWT.

Tanker in the Suez Canal (photo by Bob Wallace )

In addition to the air draft, the vessels are limited to a maximum width of 230 ft. Such a tanker might consume 410 barrels of oil a day, and travel at about 15 knots.

Those vessels that are too large for the Suez Canal, (and for that matter many ports) divide into two categories. The smaller is the VLCC (very large crude carrier) which are those carriers above 200,000 tons DWT, and then there are the ULCC (Ultra Large Crude Carriers) carriers, which are those above 320,000 tons DWT. These are large enough that they have been used for oil storage, as well as for transport. Just over a year ago there were more than 30 such supertankers parked around the globe. At that time rates of up to $75,000/day were being charged for the use of those tankers. In September 2010 Lloyds reported that the number was around 57, holding around 70 million bbl. These are the vessels that are very hard to turn, and take a long time and distance to stop. (Don't for example try throwing out an anchor.)

VLCC at sea

Once one gets to this size of vessel, the amount of fuel that is used in making a voyage becomes a significant factor in deciding how fast the ship will steam. Though that, in turn, is controlled by how valuable and necessary the cargo is at the time. For example in 2007 spot rates went from $30,000 a day to $300,000, but more recently have fallen steadily.

Recent VLCC market (after Devanney )

According to Devanney VLCC move at between12.5 knots, (50% power) and 18 knots, though at increasing fuel demand (which at top speed and loaded may reach up to 800 barrels of fuel oil a day.) As he notes in one example:

Once we get to 12.5/14 kts, we note that by speeding up another half knot, we can save 1.53 days at a cost of $63,000. This is a good idea if and only if we can earn $44,000 per day (about WS53)) or better with the days saved.

The 12.5/14 knot selection refers to the difference in speeds between when running loaded, and when in ballast (i.e. empty).

If one knows the intended travel speed, then one can look up the relative distances to be travelled (remembering that the vessel has to go both ways to complete one trip). The distance from Ras Tanura in Saudi Arabia to Port Sucre in Venezuela, for example, is 10,245 nautical miles. At 12.5 knots this would take 35.6 days at sea, each way (providing that the tanker was small enough to fit through the Suez Canal).

Going from Ras Tanura to Rotterdam via the Cape of Good Hope adds an additional 74% of the miles traveled going through the Suez Canal (from 6,399 to 11,109) while adding 20 days (from 41 to 61) to the round trip .

The costs incurred from going round the Cape is related to the extra fuel consumption but also to the extra capacity required and related insurance premium increase in order to lift the same quantum of cargo in the same amount of time. Conversely, the costs incurred in going through the Suez Canal consist of canal tolls, extra insurance risk premium and the use of services such as tugs, pilotage and mooring. Canal costs have decreased by 5% over the last five months.

The break-even point at the moment is related to the cost of bunker fuel. Should this be below $370 a tonne, then it is cheaper to go around the Cape, should it be over $370 a tonne then it is cheaper to go through the Canal. (It is currently well above that price). However the break-even is a function of charter rates and other values, and so varies with time.

There is one other way of shipping oil through Egypt and that is to put some of the liquid in a Suezmax vessel to transship the canal, and send the surplus up through the Suez-Mediterranean pipeline. With the enlargement of the canal this option is less favored, and the EIA note that volume in the pipeline dropped from 2.3 mbd in 2007 to 1.1 mbd in 2009.

I have not written much on ULCC since they have proved unpopular.

As of 2010, only 12 tankers above 320,000 dwt remain. Of this, only two "true" ULCC of around 430,000 dwt are left in operation, the TI Europe and the TI Oceana, which were part of a group of four ships constructed between 2002 and 2003. The other two ships, TI Africa and TI Asia were converted into floating storage and mooring units in 2010.

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The TI Europe

The vessel TI Europe was built in 2002. It is 1,246 ft long, it is 223 ft wide and has a draught of 80 ft. It can carry 3.2 mb of oil. (DWT 441,893 tons.) The optimal speed of TI Europe is 16.5 knots laden and 17.5 knots in ballast.