Waterjetting 2d - Adding cracks to Nature

In the last few weeks I have focused on demonstrating, with examples, that water effectively removes material by penetrating into natural cracks in the material and causing them to grow. But what happens when there are not enough cracks to remove material at an economic rate? The modern approach has been to raise the pressure of the water so that smaller cracks grow faster, thus providing the production rates needed, but that option wasn’t available in the past.

I mentioned last time that miners in the Caucasus Mountains of what is now Georgia used the power of mountain streams to erode gold deposits over 3,000 years ago. Perhaps learning from that, when the Romans came to Las Médulas in Spain, some 2,000 years ago, they though of water again as a way of mining the gold-bearing sandstone of the local hills. And though they had to modify the initial idea, the result became the most important gold mine in the Roman Empire. It is now a World Heritage Site.

Figure 1. Location of Las Médulas in Spain. (Google Earth)

The sandstone was more resistant than soil, and so the Romans came up with two ideas to improve the rate at which the gold ore could be removed. The first idea was to run galleries into the sides of the hills, creating large chambers underground, with support for the roof from wooden supports that were left in place.

Figure 2. Tunnel driven into the bottom of the hill at Las Médulas.

Figure 3. Underground room at Las Médulas.

At the same time that the mining preparations were going on local streams were being diverted and dammed so that a large volume of water was held in reservoirs and then carried by manmade channels to a point over the mining chambers. With the water ready, the timbers were set on fire, which initially weakened the overlying rock so that it began to fail, falling into the opening, and as the support burned away more rock fell into the opening until the cavity worked its way up to the surface. At this point the reservoir gate was opened and water flooded down the channel to fall into the cavity. As the water fell it further broke the rock into grain-sized pieces, and carried these down and out through the original opening in the hillside.

Figure 4. A Collapsed cavity, not the two figures at the arrows to get a sense of scale.

The water and debris flow was directed into flumes, in much the same way as modern miners in Alaska practice today, except that where carpet is used to catch the gold particles in Alaska, in Spain the Romans used plant stems (silex) to catch the gold. After drying the plant could be burned, easing to recovery of the gold. (In more modern times Spanish miners have lined the flumes with oxen hides.)

Figure 5. Artist sketch of the troughs used to capture the gold particles at the Spanish mines.

The use of heat to weaken rock before using water pressure for cutting has been tried with a couple of interesting wrinkles both by researchers at Rolla, and at the then U.S. Bureau of Mines and in Colorado, among others. But those more modern trials will be described later in the series. Using water streams to erode surface outcrops of mineral survived as “hushing” in the North of England and elsewhere until fairly recently.

Move forward some 1800 years or so from Roman Spain, and at the turn of the 19th Century miners in both Russia and New Zealand had a problem in mining coal. In both countries there were good quality coal seams, but they sloped at a steep angle that made it difficult to move men around without their slipping and falling. It was also difficult to support the roof, which was achieved at the time by sawing wooden props to length and wedging them between the roof and floor. Both nations had the idea of modifying the Roman idea of using water to remove the mined coal, but coal was thought to be somewhat stronger and more resistant than the Spanish sandstone.

In the New Zealand case the mountainous countryside makes it expensive to drive roads and as early as 1891 wooden flumes were being used to carry coal to the consumer. However it was then realized that the water could be used to also remove the mined coal, particularly that which was left in regions of the mine where it was not safe for men to go. The coal was therefore initially blasted, and then the flow from the nearby streams was directed at the debris pile. The volume of water, and the slope of the mine combined to remove all the mined coal, often overnight, so that a new area could be worked the following day. It was not until 1947 that pumps began to be used to drive the water at greater pressures. At this point, with the higher pressures that pumping brought, it was no longer necessary to pre-crack and break the coal with explosives.

While the New Zealand coal seams outcropped at the surface in very hilly ground, the situation was somewhat different in the Donets coal seams in the Soviet Union, where the seams were thinner, and production was barely economic. The seams in these mines were much deeper than in New Zealand, and so jet pressure could be provided from the drop in height from the mine surface to the location of the large nozzle or monitor that was used to aim the water flow at the coal. As with the New Zealand experience the Soviet miners (at the Tyrganskie-Uklony mine) initially blasted the coal with explosives to weaken it with a high density of cracks, before applying the water. However the miners found that not only did the water double production (to 600 tons/shift) the streams were powerful enough that it wasn’t necessary to pre-blast the coal. The nozzle diameters of the time were up to 2-inches in diameter, and could throw a jet up to 60 ft.

Figure 6. Early Soviet underground coal miner

It was from these small beginnings that hydraulic mining began, it was, in its time the most productive method of mining gold in California, and was used for many years around the world for mining coal, and other minerals. But that again is a subject for more detailed discussion at a later time.

The combination of explosives and water power remains in use in harder rocks, particularly in South Africa in the gold mines. Here again the seams of gold are very narrow and can slope or dip at a steep grade, the working area is thus kept very cramped and difficult to work. By blasting the ore with explosive, it can again be moved with water pressure, although there is an additional advantage to water here that I will further explain when I write about cleaning rust from plates.

Gold, as is shown by the way it can be collected in flumes, is very heavy, and part of the problem in the South African mines is that small pieces can get trapped in small pockets on the floor of the seam. The higher pressure water flows can flush out these pockets driving the gold particles down to a common collection point. In that particular the practices haven’t changed that much in three thousand years.

OGPSS - Global crude oil and Iran

There has been a little stir in the news on Energy lately, as folks have begun to extrapolate the growth in American oil and gas production to the point that they predict that the United States may out-produce Saudi Arabia, in terms of the totality of hydrocarbon production. Of course, in some cases, it has been North American oil independence that is featured, rather then that of the USA. And the reason for the generalization is that by broadening the geography so that the region also includes Canadian and Mexican production then the US imports from those countries magically disappear (which does not mean that they don’t have to be paid for. The US imported around 2.5 mbd from Canada and 1 mbd from Mexico in July). The stories also don’t dwell on the comparison of apples and apples. Consider the following quote from NPR. It is that easily missed sentence at the end of the first paragraph that is critical.

In 2011 the U.S. produced 5.66 million barrels of crude oil a day, according to the Department of Energy's Energy Information Administration. By next year the agency projects that will increase 21 percent to 6.85 million barrels a day. Add in things like natural gas liquids, biofuels and processing gains at refineries and that number increases.

"By 2013, we'll probably be a little over 11 million barrels a day," says EIA administrator Adam Sieminski. "That puts you pretty close to Saudi Arabia's" production of more than 11 million barrels a day, he says.

In which regard it might be pertinent to note that some of the crude produced in the Kingdom of Saudi Arabia (KSA) will be refined in the US, providing refinery gains here, and further distorting the comparison. Ah, well!

The current production gain in the US has resumed, after a short plateau, although the gains following the shut-ins for Hurricane Isaac seem to be leveling off.

U.S. Crude Production through mid-October 2012 (EIA TWIP)

The information in the October Monthly Oil Market Report from OPEC, show that crude oil production from KSA is running at 9.85 mbd, as reported by other sources.

Figure 2. Reported production from the OPEC nations through September 2012, as reported by others (OPEC MOMR)

When one looks at the production that KSA itself is reporting the numbers are slightly reduced.

Figure 3. Reported production from the OPEC nations through September 2012, as they reported to OPEC (OPEC MOMR)

While the comparison of the two levels of crude suggest that the US has a long way to go in matching KSA crude production, the two sets of figures also point to the answer to another question.

Looking at the figures for Iran, it is clear that the sanctions which have been imposed on that country by the West are having a serious impact. Not only is this seen in the fall in oil production, likely around 1 mbd, but in the more consequential cut to exports this fall is reflected in a $7 billion reduction in income. Iran has just started to admit that this bite in their export market is hurting production. And it is only now that they recognize that this will further fall, though they are now also threatening to carry this drop to its ultimate conclusion, and to stop exports entirely. An immediate impact to this would fall on Turkey, which has cut oil imports from Iran by about 20%, but which has a six month exemption from the full impact of the sanctions. It is currently importing around 200 kbd of crude. Some of the value of that oil is apparently returning to Iran as gold bullion, which can be easier to spend.

However the primary question might well be, if world oil markets are so tight, how come taking a million barrels out of production hasn’t had a more significant impact? And the answer to this comes in part because of the increase in production from KSA (Note that a year ago the country was producing around 500 kbd less than it currently is), and also from the gains in production from the United States. (As shown in Figure 1).

Further, given that the global economy, though regenerating from the depths of recession, is still not operating at levels sufficient to bring unemployment to more normal levels, overall demand also remains below what it might be.

Since we live in a global economy the problems of Europe and America are reflected in a reduced demand for goods from China and other Asian countries, which impacts the energy demand from factories. China has been taking some 40% of the Iranian export. OPEC has noted that Chinese demand has declined, and that part of this decline has been through an 18% reduction in imports from Iran. Interestingly this was partially made up through an increase in imports from Iraq.

Figure 4. Change in Chinese petroleum imports over the past year (OPEC MOMR )

One of the threats that Iran has made it that it will shut down its exports completely. The country was initially exporting some 2.3 mbd before sanctions occurred, and sanctions have dropped this already to around 860 kbd. Of this 200 kbd are going to Turkey, but this is a country with pipeline connections that give it options. There is a pipeline running from Iraq, the Kirkuk- Ceyhan connection which carries 300 kbd, and was briefly damaged by fire in August; and, more famously, there is the Baku-Tiblisi-Ceyhan pipeline from the Caspian. This can carry 1 mbd of crude, and having run 190 mb through September this year, it is running not quite full.

Figure 5. Oil and Natural gas pipelines through Turkey (Journal of Energy Security )

In short, as with the suggestions mentioned the other week, that Iran might seek to challenge Qatar in going into the natural gas LNG market, the threat this week that it might shut off exports of crude seems to be likely only geared for domestic consumption.

The global demand at present is not such that the Iranian supply is critical to ensuring a balance at an acceptable price between supply and demand. It would seem that the global economy would need to regenerate further, and for North American and KSA to reach some form of current peak in production against that potential of rising demand before this balance is threatened. But, in consolation to Iran, resting oilfields can sometimes help in terms of their longer-term production (as KSA have practiced for years).

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.

Waterjetting 2b - crack growth and granite sculpture

The last post in this series showed that the main way in which waterjets penetrate into materials is by growing cracks that already exist within the material, and I used glass as an example to show that this was true.

It is this process during which water penetrates into cracks, and then comes under pressure, either by the impact of more falling water (say under a waterfall in nature) or because the water freezes and then thaws, that causes the cracks in the rock to grow under natural attack, and the rock to slowly erode. As this happens the cracks slowly grow and extend to the point that they meet one another, separating small pieces of rock from the solid.

Within the body of a piece of rock the largest cracks that exist are normally at the boundaries of the grains of different minerals that make up the bulk of the rock. (Back in 1961 Bill Brace showed that the strength of a rock reduced as the square root of the increase in the grain size of that rock ).( Brace, W. F. (1961): Dependence of fracture strength of rocks on grain size. Bulletin of the Mineral Industries Experiment Station, Mining Engineering Series. Rock Mech. 76, 99± 103.) More recently, though still back in 1970, my second grad student, John Corwine, showed that it was possible to predict the strength of a block of granite, knowing the size of its crystals.

Which makes a good time to tell a little anecdote. Back when I was doing my own doctorate at the University of Leeds (UK) we were looking at how waterjets drilled through rock, and how that might be used to make a drill. We had already run some tests of different rocks that we placed under a nozzle, and gradually raised the pressure of the jet to see what pressure it took to make a hole in the rock. Tests on granite had shown that the jet (with a maximum pressure of just under 10,000 psi) would not drill a hole into those rock samples, and so the granite had been set aside. But, with the equipment just finished and yet having to go to lunch, I asked Dennis Flaxington, the lab technician helping me, to put a new sample into the rig so that we could run a test in the afternoon. When I came back I found that he had used a piece of granite. I made several disparaging remarks, at which point he noted that, having spent some significant time putting the rock in the apparatus, I should just go ahead and run the test (which normally took about 5 minutes) rather than being an unmentionable. And so we did, and as I posted earlier, this is the resulting hole in the rock, which we were now able to drill right through in a process that took about half-an-hour.

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

How could this now work, when a single jet clearly did not penetrate into the granite in the earlier tests? The answer is that as we moved the rock under the nozzle (we were slowly spinning the rock under the nozzle, and then raising the rock, since at the time there were no high-pressure swivels available for us to use) the jet passed successively over the edges of the different crystals in the granite. As it entered and pressurized these small fractures, the pressure in the crack was enough to grow the crack and remove individual crystals along the jet path. By starting at the center, and taking successive passes around the axis a large depression was cut into the surface, and the rock could then be raised, and a second smaller layer removed. Repeating this slowly removed the rock in front of the nozzle, and at the end of the test we had drilled through 9 inches of granite.

From this experience, over time we went on to cut, for a University, a lot of granite. Obviously, to cut at a competitive rate we had to cut at a higher pressure that just 10,000 psi. But, after showing that we could cut Georgia granite at a competitive rate in tests run at 15,000 psi down in Elberton, Georgia, Dr. Marian Mazurkiewicz and I led a group of our students in cutting 53 blacks of that granite to form the MS&T Stonehenge that now sits on the University campus.

Figure 2. View of the Stonehenge at Missouri University of Science and Technology, the vertical blocks are some 11 ft tall. The entire sculpture was cut by high pressure water jets operating at between 12,500 and 15,000 psi. (MS&T RMERC ).

Cutting commercially is not quite as simple as it might appear, since larger blocks such as those shown in Figure 2 will contain rock that varies quite significantly in properties as the cuts progress. In the Stonehenge case the rock came from close to the top of the quarry, and the cracks in the rock were quite well defined. Some fifteen years later we were fortunate enough to be asked to cut a second sculpture, but this time working with the internationally acclaimed artist, Edwina Sandys. Edwina had designed a sculpture for the campus, the Millennium Arch, which required that we cut two figures from blocks of Missouri granite, and polish them to create one group, while using the original pieces as part of an Arch that would stand some 50 ft away.

Figure 3. The Millennium Arch at Missouri University of Science and Technology. (Each vertical leg of the Arch is some 15 ft long, and the figures removed and in the background, are 11 ft tall). Better images can be found here.

The vertical legs were first cut to shape, and then the figures cut out from them. In order to contain the crack growth to limit the amount of material removed the cutting lance had two jets inclined outwards and the lance was rotated at around 90 rpm, as the lance made repeated passes over the surface, removing between a quarter and half-an-inch of rock on each pass, until it had penetrated through the rock. It took 22 hours of cutting to isolate the female figure from the host block. The slot width was around an inch, and there was some significant difficulty in cutting this slot as the quality of the rock changed within the blocks being cut. (The problem was solved by raising the cutting pressure).

Figure 4. Partial cut for one of the figures of the Millennium Arch, checking the depth.

This second sculpture illustrates both an advantage and a problem for the use of waterjets in cutting rock pieces. Use of the water gives a relatively natural look to the rock, although the vertical surfaces of the arch and the capstone were all actually “textured” to look natural using a hand-held lance at 15,000 psi. (The rock is a little harder than that from Georgia and most of the cutting took place at around 18,000 to 20,000 psi). But when the polished surfaces for the inside of the verticals and the isolated figures were prepared the rough initial surface required much more time to grind and polish flat, than a smoother initial cut would have needed.

Because water alone penetrates along crystal and grain boundaries in the rock the surface left is relatively rough. This gets to be even more of a problem if waterjets are used to cut wood. Here the “grain” boundaries are the fibers in the wood structure. Thus when a relatively low pressure jet (10,000 pai) cuts into the wood, it penetrates between the fibers and the cut quality is very poor. One of the first things I have asked students to do, when given the use of a high pressure lance for the first time, was to write their name on a piece of plywood. Here is an example:

Figure 5. Student name written with a high-pressure jet into plywood. Note that areas of the wood around the jet path are lifted by water getting into the ply beneath the surface layer, and that part of the top ply between cuts is removed in places.

I thought about having you guess the student name, Steve, but this is one of the more legible ones. (Female students generally cut the letters one at a time and were more legible, male students tried to write the whole name at once).

There are many similar examples that I could use to illustrate that, while there are tasks where waterjets alone work well, when it comes to precision cutting, then adding a form of sand to the jet stream to provide a much more limited range to the cutting zone can give a considerable advantage, and so the field of abrasive waterjet cutting was born, and discussion of that topic will lead, in time, to a whole series of posts.

OGPSS - Iran and the possibility of natural gas exports

There has been much talk in the current Presidential debates about possible changes in US Energy Policy, with Governor Romney suggesting that more Federal land be opened for prospecting for oil. Historically one of the regions included in such lists has been up in the National Petroleum Reserve in Alaska. And, perhaps anticipating the debate, the current Administration has already and recently moved toward opening those territories up for development.** However those fields have now been determined to be more natural gas than oil, and so hopes for finding more oil reserves has shifted into moves offshore, where Shell continues to be optimistic as it begins to sink new wells in the Chukchi sea – although well completions have now moved into next year. However it should be noted that there have been suggestions in the past that more of the hydrocarbons under the Arctic are gas deposits than oil, and this argument has been strengthened by the recent discovery in the Barents Sea of more gas, when oil had been anticipated.

The current large volumes of natural gas that are being developed and marketed, whether in the United States or from Turkmenistan, are making considerable changes in the economies of many countries. Russia, who lost the sales battle to supply natural gas to China now can no longer justify the expense of opening the Shtockman field, as alternate supplies are coming to the market at lower costs, and this will, in turn, cascade on to prices in Europe, where the advent of more gas in the UK is making it more difficult to justify a switch into a greater reliance on renewable sources such as wind and solar.

This entire scenario means that it is not necessarily a good time to have a huge reserve of natural gas, and to go to the market with this as a resource to generate income. This is particularly true, if the country in question is Iran.

Iranian Oil Minister Rostam Qasemi has announced that Iran’s exploitation of the South Pars gas field will equal Qatar’s exploitation of the gas field by the end of Iranian calendar year 1392 (ends March 20, 2014) if $54 billion is invested in gas projects.

Iran and Qatar share the largest natural gas field in the world, a reserve that is known as the North Field in Qatar, and as South Pars in Iran.

Figure 1, The South Pars field which lies between Qatar and Iran in the Persian Gulf (PetroPars Annual Report )

Qatar has been exporting Liquefied Natural Gas for a number of years, and has been well able to manage a steady growth in market penetration, as noted in a previous post, and this quote from two years ago:

Ras Laffan 3 Train 7 is the fourth 7.8 million tons per year LNG plant brought online by Qatar Petroleum and ExxonMobil joint ventures within the past 12 months. It matches the capacity of Ras Laffan 3 Train 6, one of the largest operating LNG production facilities in the world, inaugurated in October 2009. These mega facilities have sufficient scale to competitively reach markets around the globe. Qatar's giant North Field, which is estimated to contain in excess of 900 trillion cubic feet of natural gas, will supply both trains.

For Iran to anticipate that they can generate the infrastructure to compete with Qatar in the short term, given the time taken to invest, not only in the surface plant, but also in the tankers that become dedicated to the customers and the routes that must be followed, is more than naïve. That they can expect to do this at a time when, more than in any time in the recent past, there is an adequacy of supply unseen in a generation, suggests a message that can be meant for local consumption only.

But Iran has other problems. At present, as noted last time, natural gas supplies are barely keeping pace with an acceleration in the volumes required to meet internal demand. Any move to increase production will face competition not only from Russia (with available natural gas supplies once anticipated to be sold to the USA, and, when that fell through, then to China) and Qatar but also potentially from the United States itself, since as The OGJ recently noted

“U.S. LNG export potential is a major issue in Asia, particularly in Seoul and Tokyo,” said Mikkal E. Herberg, research director at the National Bureau of Asian Research (NBR)’s Energy Security Program and the report’s editor, “That’s especially true for the next 5 years until major Australian and other export projects come on line.”

With China getting more of its supply through pipelines this may also weaken the LNG market, even as Iran moves to step into these waters.

So can Iran also move its natural gas by pipeline, it is, after all connected by land to potential customers. Well, apart from the relatively obvious problems of trying to do this at a time when the nations concerned with Iranian nuclear policy are tightening their sanctions on Iran, as they are being seen to have more effect, the question comes back to who might be a potential customer. At present Turkey buys the bulk of Iranian natural gas exports but the European Union is expected to include natural gas in the list of banned exports at the meeting on October 15th. (Armenia and Azerbaijan buy the remainder of the current export volumes). There was a recent explosion in a gas pipeline carrying natural gas from Iran into Turkey, stopping the flow. But while that initially imposed a supply problem for Turkey, this has been met through increased purchases from Russia which currently has plenty. Thus it would appear that while Iran has more than sufficient supplies to move into an increased export position, the current political situation will likely preclude this happening in the short term, and the global over supply may well restrict Iranian penetration into that market in the longer term.

** September Alaskan pipeline flows were at 517 kbdm against the average for this year of 537 kbd, however as winter gets established the latest volume reported for 10/09/12 was 580 kbd, moving the pipeline away for the critical numbers.

Waterjetting 2a - growing cracks and glass cutting

High pressure abrasive waterjets (AWJ) are able to cut glass with considerable precision, and maintain the accuracy of cut through thick material.

Figure 1. Cutting an Eagle from glass using AWJ (courtesy of KMT)

Because of this precision, and because the glass can be cut to leave very delicate webs between adjacent cuts, AWJ glass-cutting has been used to create art objects for a number of years. It is not as easy as it might at first seem, and Dr. Vanessa Cutler an international leader in advanced cutting, has used the tool to create significant works of art, She has also written on the problems that can arise in cutting what often seems to be a simple, consistent material. (Noting, in passing that through the combination of computer control and memory it is easier at times to re-create works that break than would be the case with other tools for artistic creation). For the more mundane cutting world that comprises the rest of us, cutting glass is more likely restricted to simple activities such as cutting the parts for the windows of wood furnaces.

When the cuts are this simple, time can be saved by stacking two or more sheets of glass, one on top of the other, and cutting all of them at the same time. As one learns the parameters, thicker and greater numbers of plates can be stacked, and still successfully cut.

Figure 2. Cutting through four sheets of glass simultaneously (courtesy of KMT)

However, if one gets too ambitious, and stacks too many plates then the lower plates may start to crack, often after the cut has started into the plate. As Dr. Cutler has noted in her new book “New Technologies in Glass”, cracks can also create problems for the unwary in dealing with internal stresses in the structure of the glass.

There can be several reasons for this, but it primarily goes back to the point I made in the introduction, about water pressure causing existing cracks and weakness planes to grow, as a way of removing material. There are two sorts of cracks that exist in glass, those created by the impact of the abrasive particles themselves, and those that were already present in the glass.

Figure 3. Micro-photograph showing cracks growing out from the point where two abrasive particles struck a piece of glass. (This was adjacent to the main cutting path).

Figure 4. Micro-photograph of the edge of the main cut by an AWJ on glass, showing that it is made up of the intersection of adjacent cracks created by the abrasive impact.

I’ll write about the mechanics of cutting glass in a later post or two, but for the moment I would like to write about the basics of crack growth from the point of view of cracks that already exist in the material. In large part this won’t be using waterjets alone to cut glass. Rather there are lots of other materials, particularly soil and rock, which have much higher crack densities, and longer cracks which make it easier to cut and remove material.

But first a little demonstration you can carry out. Take a strip of paper, and cut a slit in it half way along the strip and half way through the paper. Now take both ends of the paper in your hands and pull them apart. This causes the cut (the crack) to grow through the paper and gives you two halves. If you do this a second time you should find that by stopping moving your hands you can stop the cut from growing all the way through the paper. Now repeat the process, but use a piece of paper that you have not cut a slot in. The amount of force you need to pull the paper apart is much higher, and I seriously doubt that one you get the tear (crack) to start that you can stop it before it goes all the way through the paper. (Remember this, and I'll come back to it a bit later in time).

The idea of putting cracks on the edge of packages to lower the force you need to tear them open can be found on the edge of lots of candy bars, packs of peanuts and other goodies in stores. The serrated edge acts as a series of cuts or cracks, that concentrate the force applied when you pull on the edges of the packet so that the package tears at a much lower force, and you can control the tear so that you don’t end up throwing all the contents around the room.

Figure 5. Serrations and tear at the top of a packet of honey

Now at this point you might say that there aren’t any cracks in glass, when we start to cut it. If the glass is very new this is true, but with all the chemicals in the air, and the dust that is carried in the wind, although glass can look clear, the surface actually contains a lot of very fine cracks.

John Field, one of the earlier investigators of high-pressure waterjet impact, showed this in one of those brilliant, yet simple demonstrations that, in this case, he carried out some forty-five-odd years ago. If waterjet impact grows surface cracks, and glass acquires surface cracks from damage through being out in the air, then if that surface layer is removed, then the underlying glass will have no cracks. So John took a glass slide, and etched off the surface of the lower half of the slide, by immersing it in acid. Then he fired a very high-speed droplet of water at the point on the slide where the acid etch stopped.

Figure 6. Impact of a high-speed droplet of water on glass. Above the dividing line the glass surface contains the micro-cracks and flaws that come with being exposed to the air over time. The lower section below the line has had these flaws removed. As can be seen the cracks only develop in the unetched part of the glass, where they grow pre-existing cracks, even into the side of the glass that was etched. (Field J.E. “Stress Waves, Deformation and Fracture Caused by Liquid Impact,” Phil. Trans. Royal Society, 260A, July 1966, pp. 86 – 93.)

In a single picture he captured the evidence that waterjets work by growing cracks (top half), and that without cracks there is no damage (bottom half). Understanding this opens up a whole vista of different applications, from the removal of soil from around pipelines underground (the new technology of hydro-excavation) to the removal of damaged concrete, while leaving healthy concrete in place (the developed field of hydro-demolition). And these, and other topics will be part of this series, as it moves forward.

But as John showed, not all the cracks a jet will grow can be seen, and as Vanessa found, they don’t have to be at the surface to create problems. One of her early pieces was entitled “p1.” Within it are an uncountable series of holes, drilled deep into the glass.

Figure 7. Detail of the glass sculpture "p1", by Vanessa Cutler.

One of the skills Vanessa has learned is in controlling the quality of the pierce, and its dimension, but initially there had to be a period of learning.

Figure 8. Single cracks growing out from partial piercings in a test piece during development (Vanessa Cutler).

And so, in the next sequence of posts the simple idea of growing existing cracks will be explored. Mainly, in the beginning, this will focus on cracks that are already there, and how to usefully make them grow. But in some cases we don’t want all those cracks to grow, and that will also come up, as this series continues.