Waterjetting 8d - Choosing angles

How times change! I was reading a column in the British Farmer’s Weekly, and came upon this, where the author is discussing the need for a generator.:

It will also be vital to keep the fuel flowing into the tractors, and power the pressure washer, and light the security lights, and all the other essentials of an average arable farm.

It is an indication of how far the use of pressurized water has come, that it is now seen, at the lower end of its application, as a vital farming tool. Which is a good introduction to talk a little further about the use of cleaning streams, and how to interact with differing target materials.

There was an initial first step, when someone would send the lab a mystery block of material and asked – how do I cut it? Generally the samples were small, but we would find a flat surface on the material, and carefully point a jet nozzle perpendicular to this surface. (In the early stages this was hand-held). When a jet strikes a surface, but can’t penetrate it, then it will flow out laterally around the impact point, under the driving force of the following water.

The test began with the jet at low pressure, and this was slowly raised, until the point was reached when the pressure was high enough to just start cutting into the material. At this point the jet had made a small hole in the target, and so the water flowing into that hole had to get out of the way of the water following. The sides of the hole stop it flowing laterally, and so it now shoots back along the original jet path. This spray can hit the lance operator if the nozzle is hand-held, but it is a fairly graphic way of determining the threshold pressure at which the material starts to cut. (and I’ll get into what happens as the pressure continues to go up in a future series of posts).

But for the purpose of cleaning, the jet has to move over the surface, once it has made that initial hole, at pressure. But, in many materials, if the jet comes vertically down onto the target, then only the material directly under the jet will be removed. And so the jet has to be played on every square inch of the surface in order to ensure that it is cleaned, or that the coating/layer is removed. In some sandstones, for example, two jet paths could be laid down, almost touching one another, and yet the rib of material between them would remain standing.


Figure 1. Adjacent jet passes in sandstone, the cuts are about an inch deep, but note that even though the narrowest rib is about 1/8th of an inch wide, it is only when the cuts touch that the intervening material is removed.

Yet that rib of material was, in that case, so weak that it was easy to break it off with a finger. (This turns out to be a weakness in making delicate sculptures out of rock). To use the full pressure of the water can be a waste of energy, if the material is very thick, since it all must be eroded with such a direct attack.

Yet the minimum amount of material that needs to be removed is that that attaches the layer to the underlying material (the substrate concrete, steel etc) and this can be quite thin. Thus, in attacking a softer material, particularly one that can be cut with a fan jet, a shallow angle directed at the edge of the substrate can be more effective.


Figure 2. Round v fan cleaning from Hughes (2nd US Waterjet Conference)

Because there is a balance between cutting down through the material to be removed, and cutting along the edge to grow the separation crack between the materials, some practice is needed to find, for a given condition, what that angle would be.


Figure 3. Choice of angle from Hughes (2nd Waterjet Conference)

The more brittle the material, then the greater the angle to the surface, since rather than just erode the material, the jet may also shatter the layer into fragments that extend beyond the cut path. But otherwise using an angled jet to the surface can be more effective. Hughes (from whose paper at the 2nd Waterjet Conference I took these illustrations) has a simple test for orifice choice.


Figure 4. How target response influences nozzle selection. (Hughes 2nd Waterjet Conference)

Some of the more advanced cutting heads use a series of nozzles that spin within an outer protective cover, as they remove anything from layers of damaged concrete to thin layers of paint from ship hulls. Increasingly these are connected to vacuum systems that will draw away the spent water and debris from within the contained space, without it entering the work space, and creating problems for the worker.

In order to reduce any collateral damage to the surroundings these jets are often made very small (thousandths of an inch in diameter) so that their range is short, and they are inclined outward to cut to the edges of the confining shield.

We have had some success in turning those angles the other way, so that they cut into the shield, rather than away from the center, and also so that each jet is directed towards the path of the next jet around the circumference. The intent in this case is to allow the use of a slightly larger jet, with a greater cutting range. In this case the individual cleaning/cutting path is a little larger, but because the jet at then end of the cut moves into the range of the adjacent jet, then any remaining energy that it and the dislodged debris still have, will not be enough to get through this second jet.


Figure 5. Inclined jet and shroud design.

The action of each jet then becomes not only to cut into and remove material, but also to contain the spent material from the other jets dispersed around the cutting arm, and to hold the debris in the center of the confinement for the very short time needed for it to be caught up in the vacuum line.

In all cases the choice of pressure, nozzle size, and operational factors such as angle of attack, come down to the target materials, those that have to be removed, and those that need to be left undamaged. And it is why it is useful, at the start of any new job, to take the time to do a little testing first, to make sure that the right choices of nozzle and angle have been made to get the job done quickly and efficiently.

Incidentally the idea behind the test of effective pressure, that the jet flows laterally when it hits something it can’t cut, can help, for example in easing the meat from the bone when a jet cuts a deer leg.


Figure 6. Cut across a deer leg, note how the jet has cleaned off the meat from the bone, undercutting the flesh.

Fixated on Katla

It has been more than a couple of years since I started to write on the potential for an eruption of the volcano at Katla in Iceland, following the eruption of its neighbor at Eyjafjallajokull, and the resulting disruption of air traffic.

One of the reasons that I continue to do so, apart from the historic pattern that Katla often erupts following Eyjafjallajokull, is the ongoing earthquake activity around the caldera. I noticed it clearly again today where with most of the zones of Iceland quiet, there is still that steady pattern. And this activity has persisted at a relatively low, but varying level, across this time. Doesn't say it will happen soon, but does continue to suggest that it is, nevertheless, going to happen. Patience is a good word.


Earthquakes in Iceland in the last 24 hours (Icelandic Met Office) Hopefully there won't be much more news for a while.

OGPSS - OPEC and EIA short term projections

Just this month Saudi Aramco announced that production had begun at their Manifa oilfield, and by July would be supplying up to 500 kbd to the new refinery that is being built at Jamail with the collaboration of Total. The first oil from the refinery is expected to ship in August, and both projects are currently ahead of schedule. Manifa will further increase in production next year, to 900 kbd, with the additional flow going to the Yanbu refinery being built with the collaboration of Sinopec. Both these refineries are designed to take heavy crude, and can also accept oil from the ongoing projects to expand production at Safaniya. Collectively this is said to ensure that the company will be able to achieve a maximum sustainable production of 12 mbd.

The gains in available reserves are required as the current production from Ghawar and the other major fields in the Kingdom continue to decline in production, as was discussed last year. I remain relatively convinced that Saudi Aramco will not increase their crude oil production above 10 mbd, despite the wishes and projections of others that they will end up doing so. By the time that their domestic consumption reaches the point that it lowers exports to a level that would hurt the KSA economy at current prices, the shortages globally will have raised the price sufficiently that the available production at that time will continue to suffice to meet their needs. (This is, however, a projection only for this decade).

This month’s OPEC Monthly Oil Market Report continues to anticipate a significant increase in available crude over the next three years, although this is indirectly recognized through the growth in crude distillation unit (CDU) capacity around the globe in that interval.


Figure 1. Increase in crude distillation capacity by regions in the near term. (OPEC April MOMR.)

Given that the world must increasingly deal with a heavier crude supply, the need for new refineries, as exemplified by the new Saudi construction, is evident. Increased demand to absorb this supply will come, in part, by an increase in the growth rate of the GDP of the BRIC nations, although the poor growth in the developed nations continues to hamper their export markets.

Overall demand is still anticipated to increase by around 0.8 mbd, with half of that coming from China and the rest of the non-OECD nations contributing an additional 0.7 mbd, offset by a decline in demand from the OECD nations of around 0.3 mbd, taking global demand, by the end of the year to nearly 91 mbd. Internal demand in the Middle East will continue to sap a fraction of this relative to exports. Overall the Middle East demand is anticipated to increase by 280 kbd, though the impact of the turbulence in various nations is hard to estimate.


Figure 2. OPEC estimate of global demand for 2013. (OPEC April MOMR.)

Virtually all the growth in supply is anticipated to come from North America, with a slight increase in production from South America coming from Colombia and Brazil. There is some concern, however, over the impact of attacks on the energy structure in Colombia.


Figure 3. Anticipated regional change in supply in 2013. (OPEC April MOMR.)

For the US the OPEC report has the following projection:

The expected growth in 2013 is supported by the anticipated supply increase from shale oil plays in North Dakota and Texas, as well as by minor growth from other areas in Oklahoma, Kansas, Colorado and Wyoming. The infrastructure situation is improving in North Dakota, with reports suggesting that the railroad loading capacity will reach 1 mb/d. Eagle Ford oil production in January continued to increase from the same period a year earlier. On a quarterly basis, US supply is expected to average 10.57 mb/d, 10.62 mb/d, 10.56 mb/d and 10.55 mb/d respectively.

Canada is expected to reach a production total of 4 mbd by the end of the year, with the largest impact coming from the Kearl Oil Sands production anticipated to bring 110 kbd to market in the third quarter. (This is not dependent on the Keystone pipeline.) Mexico will see a slight decline in production though the Kambesah field (at 13.7 kbd) and increased production from Tsimin will offset most of that.

OPEC is anticipating that Norwegian production will fall 110 kbd this year, with a small decline of 40 kbd in UK production. OPEC expects that Russian production will increase to average 10.43 mbd in 2013, slightly down from first quarter numbers, while, in anticipation of Kashagan production, OPEC expects Kazakhstan to increase production to 1.67 mbd. The decline in production from the Azeri-Chirag-Guneshli field is expected to cause a slight ( 50 kbd) reduction in Azerbaijan production. There is, as previously, some difference between the production that the individual nations of OPEC report each month and that reported by secondary sources.


Figure 4. OPEC crude production from secondary sources.(OPEC April MOMR.)


Figure 5. OPEC crude production based on national direct reporting.(OPEC April MOMR.)

In short, over the course of this year OPEC remains relatively complacent that North American production gains will continue to meet the global demand, and that OPEC (i.e. largely the KSA) can back away from full production in order to balance supply and demand at a price level that keeps the OPEC bankers happy.

Back in March the EIA TWIP noted the change over the years, not only in amounts, but also in the sources of US imports, which remain significant. There has been quite a bit of change since 2005, when imports were at their highest level (10.1 mbd).


Figure 6. Change in the countries and volumes for the ten largest suppliers of crude to the USA. (EIA )

The EIA anticipates that US liquid fuels consumption will remain sensibly stable through the end of 2014, ending that year at 18.61 mbd. At this time production is expected to rise to 11.75 mbd.


Figure 7. EIA estimates of US liquid fuels production through 2014. ( EIA)

In that interval they anticipate that the price of gasoline in the United States will slowly decline. In contrast with the reports by the major oil companies that were discussed recently, these forecasts are short enough that it will be fairly quickly evident how accurate they are.

Waterjetting 8c - dealing with graffiti

When I began this series I mentioned that the target material plays an important part in deciding which pressure and flow rate is best for a particular task. Sometimes time also has a role, and not always in the way of "faster is better". I mention this because we made a mistake once. (Well we only made this mistake once, didn’t mean we haven’t made other mistakes). Almost thirty years ago we carved the granite blocks that make up the Missouri S&T Stonehenge, a half-scale Americanized version of the British megalith. The campus Americanized it when Dr. Joe Senne, the Civil Engineering professor who designed it, incorporated an analemma, based on the calendar developed by the Anesazi in New Mexico. This replaced the 19-stone inner bluestone ring of the original.


Figure 1. The MS&T Stonehenge

The MS&T Stonehenge was chosen as one of the ten Outstanding Engineering Achievements of 1984, by the National Society of Professional Engineers, in part because the 160-ton 53-stone structure was carved from Georgia granite by high-pressure waterjets, without the use of abrasive. It has, over the years, generated a lot of interest (even getting me onto the Tonight Show with Jay Leno) but that has also included the odd local “artist” who has adorned it with graffiti.

My initial response, when this first happened, was to go over to the monument immediately with a high-pressure pump and start to wash the paint off. And that was the mistake, for two reasons. Firstly the paint was not totally dry, and secondly we had not protected the stone with an invisible protective coating to seal it. Thus when we tried to wash the paint away, while we removed all the surface paint, and to a casual observer it remains clean, we had driven a small fraction of the still liquid part of the paint into the pores and grain boundaries of the granite. Thus, if you know where to look, there is still a slight discoloration where that first writing was removed.

Shortly after that, on the advice of the Georgia Granite Association, the campus found a coating that was applied to the rock, sealing the pores and grain boundaries, and future cleaning was made a lot easier and more effective. However it did not completely solve the problem, since future cleaning had to be done in such a way as to remove the spray paint, while leaving the protective coating.

And that reminds me of a funny story. Graffiti is a significant urban problem, and it costs cities like Albuquerque in New Mexico about $1.3 million a year in clean-up costs. Much of incentive for almost immediate removal is because it is a way for street gangs to mark their territory, and this motivates police to urge an aggressive treatment policy.

But what happens if it is art? There are street artists who, in various ways, not related to gang activity, have chosen to decorate, for free, generally abandoned buildings. Perhaps the most famous of these is Banksy, recently making the news when a piece he painted on a London wall appeared in a Miami auction house, where it was anticipated to be worth around $600,000 before being withdrawn from the auction.


Figure 2. Bansky "wall art" estimated to be worth up to $600,000. (Banksy)

At one time Albuquerque had a similar idea, of hiring those who were spraying the town walls to instead create works of art on some of the otherwise blank concrete surfaces such as bridge abutments around town.

Unfortunately this led to an awkward situation. One of the local artists had painted some of his art on a fly-over. Shortly thereafter the city sent a crew out to cover up the remaining graffiti with a coat of whitewash. Unfortunately the crew were not artistically trained, and so covered up the new work of art.

For some years I had a photograph of a waterjetting crew working on that site. At first glance they were removing graffiti, but in reality they were taking the white coating from the painting to re-expose it to public view.

And this is one of the advantages that waterjets possess in that they can, with care and training of the personnel, be used to preferentially remove individual layers of material, whether of dirt or paint, without doing any damage to the material underneath, the substrate of the surface.

This is important, for example, in removing paint from buildings where the underlying substrate may be a relatively weak wood surface, where any high jet pressure would be enough to eat away the softer parts of the wood turning a smooth wooden sill into an etched and rough surface far from the desired result. Thus, in these circumstances, there is a need for very fine pressure control if the desired result is to be obtained.

And sometimes the material that is to be removed is not that easy to remove with water power alone, at an acceptable rate, because the pressure has to be lowered to the point that it only removes the paint at a slow, and uneconomic rate. At that point it is possible to add a relatively soft abrasive, something like a baking soda, that will not only be effective in removing the material, but is soft enough that it will do relatively little damage to the surface. At the same time many of these softer abrasives are also soluble, which means that the costs of clean-up can also be reduced.

In some cases the water pressure need be little more than tap pressure.


Figure 3. Figure 3. low pressure waterjet graffiti removal using soluble abrasive.

OGPSS - The BP look into the future

So I suspect I should apologize. Here I am talking about the future projections for energy production that have been made by companies such as ExxonMobil and Shell, as though they were still the key and only players in the world. Yet, in reality, Saudi Aramco (12.5 mbdoe); Gazprom (9.7 mbdoe) and National Iranian Oil (6.4 mbdoe); appear in the list before ExxonMobil arrives (at 5.3 mbdoe), and then there is PetroChina (at 4.4 mbdoe) before BP arrives (at 4.1 mbdoe) and it is only then that we find Shell, which lies 7th at 3.9 mbdoe.

So the projections of the ExxonMobil’s of the world are of somewhat lesser value than they might, at one time, have been. (For those curious the list continues with Pemex (at 3.6 mbdoe); Chevron (at 3.5 mbdoe) and Kuwait Petroleum Co (3.2 mbdoe). This not only rounds out the top ten, it also closes out the list of those producing more than 3 mbdoe. (Abu Dhabi comes next at 2.9 mbdoe).

Yet, with those caveats, and recognizing that Saudi Arabia now produces only slightly less than ExxonMobil, Shell and BP combined, let me review the BP forecast, having already completed that for ExxonMobil and Shell. And while the latter two looked sufficiently far into the future as to obfuscate a little their shorter-term projections, BP is still focusing on the relatively short-term that runs to 2030.

Within that time frame BP expects overall energy demand to grow by 36%, though, as with the ExxonMobil projection, BP expects that a “tremendous increase” in energy efficiency will continue to develop, thereby slowing the need for future resources. They point out that, without this improvement in efficiency, global energy supply will need to double by 2030 in order to sustain economic growth.

This is particularly true for the United States, which BP sees approaching self-sufficiency in Energy, while it is the continued growth in demand from countries such as China and India and the Asian Pacific countries that provide most of additional need. Comparing their view from 2 years ago with the present there does not appear to be much change in the overall forecast. (Note that after the first two figures all the remainder come from the 2030 BP Energy Outlook).


Figure 1. Comparison of BP data and projections for population growth between their 2011 report (left) and that for 2013 (right)


Figure 2. Comparison of current and anticipated energy demand through 2030, from 2011 (left) and 2013 (right) BP reports.

There is a small increase in the overall demand from non-OECD countries in the more recent projection, but not a great difference. But this increase in demand reduces from a growth averaging 2.1% in the 2010-2020 time frame, to a growth of 1.3% in the following decade.

Within the period to 2030 BP anticipates that all major energy sources will continue to see an increase in overall energy production.

The fastest growing fuels are renewables (including biofuels) with growth averaging 7.6% p.a. 2011-30. Nuclear (2.6% p.a.) and hydro (2.0% p.a.) both grow faster than total energy. Among fossil fuels, gas grows the fastest (2.0% p.a.), followed by coal (1.2% p.a.), and oil (0.8% p.a.).

Figure 3. Growth in different energy sources through 2030

However, there is a change in the ranking of the different fossil fuels from the earlier projection. For while, two years ago, BP were projecting that coal, oil and natural gas would virtually tie in terms of market share by 2030, coal is now given a more dominant role, with natural gas falling below oil.


Figure 4. Change in market share for the different energy sources.

Coal is, within this time frame, not really bounded by available supply, though BP anticipate that more will be produced indigenously in the Asian Pacific than at present. Partly one assumes that this is necessary for financial reasons, although it will also be a need-based growth as the countries increasingly need electric power.

In terms of natural gas and oil supply questions are more urgent, and BP provide the following answer.


Figure 5. BP anticipated sources for the anticipated growth in demand for energy.

By far the largest production from the tight oil and gas shales will come from North America, where the current growth in production is anticipated to continue.


Figure 6. Anticipated production of tight oil and shale gas by region in 2030

One of the drivers that BP see, in the fall in oil demand, comes from its continued high price. This has already significantly lowered the use of oil as a power generating fuel, and the continued high price will drive the move to vehicles of increasingly greater efficiency. Thus, although global liquid fuel demand will continue to grow, it will only be at the rate of 0.8% pa, reaching 104 mbd by 2030. The sources to meet this are various:


Figure 7. Liquid fuel supplies through 2030

With the conventional supply of crude from non-OPEC countries diminishing, OPEC crude levels can be seen to increase over the next seventeen years, while the major increase in production from tight oils is anticipated to come from North America. In 2030 it will provide 9% of overall demand, providing almost half of the 16.1 mbd of overall increase in production. The increase will, however, slow post 2020, as the costs of production and the limits of the resource base. BP make the following prediction:

The US will likely surpass Russia and Saudi Arabia in 2013 as the largest liquids producer in the world (crude and biofuels) due to tight oil and biofuels growth, but also due to expected OPEC production cuts. Russia will likely pass Saudi Arabia for the second slot in 2013 and hold that until 2023. Saudi Arabia regains the top oil producer slot by 2027.

Other than tight oil, BP anticipates some increase in biofuel production, and from the oil sands, with significant increase in Iraqi production, and some gain from the remaining OPEC countries (one suspects Venezuela is included here) and from NGL production.

The largest increments of non-OPEC supply will come from the US (4.5 Mb/d), Canada (2.9 Mb/d), and Brazil (2.7 Mb/d), which offset declines in mature provinces such as Mexico and the North Sea. The largest increments of new OPEC supply will come from NGLs (2.5 Mb/d) and crude oil in Iraq (2.8 Mb/d).

In this regard BP believes that currently OPEC has a spare capacity of around 6 mbd, but will continue to cut production to sustain prices over the decade.

BP see roughly a 7% p.a. increase in shale gas production with most coming from the United States, Mexico and Canada. This will bring total natural gas production to 459 bcf/day by 2030. Of this North America will see a growth in production of 5.3% pa and by 2030 will be exporting roughly 8 bcf/d. In other countries the biggest growth will be in more conventional natural gas production, coming from the Middle East (31 bcf/d), Africa (15 bcf/d) and Russia (11 bcf/d).

This increase in supply, and the greater use of LNG tankers is likely to keep natural gas prices relatively stable.

Waterjetting 8b - Repairing concrete

Some years ago we were on a bridge in Michigan, working on a demonstration of the ability of high-pressure jets to remove damaged concrete from the surface of the bridge. Before the demonstration began the state bridge inspector walked over the bridge armed with a length of chain. He would drop the lower links of the chain against the concrete at regular intervals, and depending on the sound made by the contact, would decide if the concrete was good, or not. He then marked out the damaged zones on the concrete, and suggested that we get to work and remove those patches.


Figure 1. Automated removal of damaged concrete from a bridge in Michigan

The change in the sound that he heard, and used to find the bad patches in the 1concrete, was caused by the growth of cracks in that concrete. It was these longer cracks, and delaminations in the concrete that made it sound “drummy” and which identified it as bad concrete.

Now here is the initial advantage that a high-pressure waterjet has in such a case. The water will penetrate into these cracks. As I mentioned in an earlier post, water removes material by growing existing cracks until they intersect, and pieces of the surface are removed. The bigger the cracks in the surface, the lower the pressure that is needed to cause them to grow. This is because the water fills the crack, and pressurizes the water, the longer the crack, the greater the resulting force, and thus the greater the ease in removing material.

At an operating waterjet pressure of between 11,000 and 12,500 psi, for a normal bridge-deck concrete, the cracks that are long enough for an inspector to call the bridge “damaged” will grow and cause the damaged material to break off. The pressure is low enough, however, that it will not grow the smaller cracks in “good” concrete, which is therefore left in place.


Figure 2. Damaged area of bridge after jet passes.

In order to cover the bridge effectively and at a reasonable speed, six jets were directed down from the ends of a set of rotating crossheads, within a protective cover. The diameter of the path was around 2 feet, and the head was traversed over the bridge so that it took about a minute for the head to sweep the width of a traffic lane.


Figure 3. Scarifying jets, with the head raised above the deck so that their location can be seen. Normally the nozzles are positioned just above the deck, so that the rebounding material is caught in the shroud.

Unfortunately, while this means that the rotating waterjet head could distinguish between good and bad, and remove the latter while leaving the former, it could not read marks on concrete. So where the bridge inspector was not totally accurate, the jet removal did not follow his recommendations. It was, however, quite good at removing damaged concrete from reinforcing bar in the concrete, where the water migration along the rebar had also caused the metal to rust. And, since the pressure was low enough to remove the cement bonding, without digging out or breaking the small pebbles in the concrete, they remained partially anchored in the residual concrete. As a result when the new pour was made over the cleaned surface, the new cement could bond to the original pebbles, and this gave a rough non-laminar surface, which provided a much better bond than that left had the damaged material been removed mechanically with a grinding tool.


Figure 4. Rebar cleaned by the action of the jet as it removes the surrounding damaged concrete.

Waterjets had an additional advantage at this point in that, in contrast with the jackhammer that had previously been used to dig out the damaged region, but which vibrated the rebar when it was hit, so that damage spread along the bar outside the zone being repaired, with the jet action there was no similar force, so that the delamination was largely eliminated.

Now this ability to sense and remove all the damaged concrete is not an unmixed blessing. Consider that a bridge deck is typically several inches thick, and it is usually sufficient to remove damaged concrete to a point just below the top layer of the reinforcing rods. Once the damaged material is removed, then the new pour bonds to the underlying cement and the cleaned rebar. But the waterjets cannot read rulers either. So in early cases where the deck was more thoroughly damaged than the contractor knew at the time that the job began, the jet might remove all the damaged concrete, and this might mean the entire thickness of the bridge deck. And OOPS this could be very expensive in time and material to replace.

What was therefore needed was a tool that still retained some of the advantages of the existing waterjet system, that it cut through weakened concrete, and cleaned the rebar without vibration, but that it did so with a more limited range, so that the depth of material removal could be controlled.

There was an additional problem that also developed with the original concept. For though the jets removed damaged concrete well in this pressure range, the jets were characteristically quite large (about 0.04 inches or so). The damaged concrete is contaminated with grease and other deposits from the vehicles that passed over it. Thus any large volumes of cleaning water would also become contaminated, and, as a result will have to be collected and treated. That can be expensive, and so any way of reducing the water volume would be helpful.

The answer to both problems was to use smaller jets at higher pressures. Because of the smaller size, their range is limited, and at the same time the amount of water involved can be dramatically reduced. It does mean that the jet is no longer as discriminatory between “good” concrete and “bad.” This is not, however, a totally bad thing, since when working to clean around the reinforcing rods, there has to be a large enough passage for the new fill to be able to easily spread into all the gaps and establish a good bond.

Thus the vast majority of concrete removal tools that are currently in use are operated at higher pressures, and lower flow rates. This allows the floor to be relatively evenly removed down to a designated depth, and this makes the quantification of the amount of material to be used in repair to be better estimated, and the costs of disposal of the spent fluid and material to be minimized.


Figure 5. Scarified garage floor showing the rough underlying surface. This will give a good bond to the repair material, as will the cleaned rebar.

The higher pressure system has the incidental advantage of reducing the back thrust on the cutting heads, so that the overall size of the equipment can be reduced, allowing repair in more confined conditions.

Waterjetting 8a - cleaning with heat

Water is used almost everywhere as a way of cleaning surfaces. Several times a day we typically rub our hands together with water, and usually with some soap, to clean them. Pediatricians and others suggest that children recite a short rhythm, such as a chorus of “Happy Birthday” while doing so to allow the water, soap and mechanical actions to combine and effectively remove dirt. That teaches the child that it takes some 20 seconds for the cleaning action to be effective. The cleaning action is not to sterilize germs, viruses and other obnoxious things on the hands. Rather it is to ensure that they and other dirt particles are physically removed, leaving the hands clean. (This is a different action to the chemical washes that are becoming popular.)

This is not an instantaneous process since the soap and water must reach into all the dirt-collecting parts of the hand, hence the need for the nursery rhythm. The same basic sequence occurs in the cleaning action of a high-pressure waterjet on a surface, although the pressure of the spray means that the water can penetrate faster. But it is why, in using a car wash lance in cleaning a car, it is smart to spray the body of the car with a detergent first, then allow this to work in creating micelle clusters around the dirt particles, so that the mechanical action of the subsequent jet spray will dislodge and remove them. Merely adding detergent to the cleaning water as it goes through the cleaning lance, and strikes the car surface does not give the chemicals in the water time to act before they are gone. Bear in mind that the jet is moving at several hundred feet per second, and that it hits and rebounds from the surface over a path length of perhaps an inch or two. As a result the residence time of the jet on the surface is measured in fractions of a millisecond. This is not enough time for the chemicals to work. (On the other hand it does help keep the sewers under the car wash cleaner than might be otherwise expected.)

With an increase in jet pressure, the speed of the mechanical removal of dirt and other particles from a surface can be fast and effective. The ability of the jet to penetrate into and flush out surface cracks, and joints, means that it becomes a good tool for removing debris from the joints in concrete decks, and, at a little higher pressure, it can also be used to remove deteriorated concrete from surfaces. But I am going to leave that topic until next week.

The other “treatment” that we use when we wash our hands is to heat the water. When used with soap it helps to remove the surface oils on the skin that act as a host to bacteria. Heat is becoming a less common tool than it used to be in high-pressure jet cleaning. At one time steam cleaning, which was followed by hot pressure-washing, had a larger sector of the market. It is a bit more difficult to work with (the handles of the gun get hot, and the operator needs more protection) but for some work it is still the more effective way to go.

Steam, however, loses both heat and mechanical energy very quickly after it leaves the nozzle. It will, for example, lose some 30% of its temperature within a foot of the nozzle. Hot sprays of water can thus be more effective, but when cleaning grease and oils a lower temperature spray will merely move the globs of grease around the surface. Heating the water to around 185 degrees Fahrenheit, or 85 degrees C, will stop that happening and works much more effectively in getting the surface clean.


Figure 1. The effect of water temperature on cleaning different surfaces (A, B and C) of different types of dirt.

But, as with many tools, heated water needs to be applied with a little bit of background knowledge. I mentioned that just pointing a large jet of water at, for the sake of discussion, a boulder covered with an oil spill would, at lower water temperatures, just move the oil around the surface. At higher temperatures the oil would break into smaller fragments that are removed from the surface, but they need to be captured, otherwise the treatment is just spreading the problem over a larger area. This is why it becomes more effective to use smaller, higher pressure systems that have lower contained jet energy, and which can be used with a vacuum collection system to pick up the displaced water, oil and debris.


Figure 2. Using hot, pressurized water streams in cleaning up after the Exxon Valdez oil spill (NOAA )

With the streams used in the picture shown in Figure 2, the energy in the jet will move the oil, but without containment it was being washed down to the water, where it was collected using booms. This is not particularly effective, since in the process the jets also washed the silt out of the beach, and drove some of the oil down into the underling beach structure, so that it continued to emerge in later years contributing to an ongoing problem.

What is needed is to provide enough energy to drive the oil away from the surface, and yet not enough to move it great distances or to disrupt the surrounding material. This can be achieved by using a higher-pressure, but lower flow rate jet. Because some of the water will turn to steam as it leaves the nozzle, Short (PhD U Michigan, 1963) showed that the droplet size will fall from 250 microns to 50 microns when the water is heated above 100 degC.

Obviously that also will reduce the distance that the jet is effective, and so a balance needs to be achieved between the heat put into the water, and the size of the orifice(s) if the jets are to remove the contamination, but in such a way that it can be captured. And here again there is a benefit from having a suction tool associated with the cleaning spray. Because of the problems that oil and grease can cause, it will require special care in designing the capture systems downstream. Incidentally it is generally better if the water is heated downstream of the pump, since there are higher risks of cavitation in the inlet ports if the water is too hot.

And sometimes the two can be combined in ingenious ways. For example Bury (2nd BHRA ISJCT, Cambridge, 1974) added a steam shroud around a conventional waterjet at 5,000 psi as a way of cleaning hardened plastic from the insides of a chemical plant pipe.


Figure 3. Wrapping a conventional waterjet in a steam shroud (Bury et al 2nd BHRA ISJCT, Cambridge, 1974)

Without the steam assist the plastic was not removable, even at higher jet pressures, but with the steam to soften the plastic the pipe was successfully cleaned.


Figure 4. High-pressure water fails to remove hardened plastic, (lhs) but with a steam shroud a lower-pressure jet effectively cleans the pipe (rhs). (Bury et al 2nd BHRA ISJCT, Cambridge, 1974).

OGPSS - Shell looks to the future

Each year the larger oil production companies provide their views of the future, and I recently reviewed that for ExxonMobil. Shell has now produced their projections, though in a somewhat different format as the document “New Lens Scenarios” which deals with future projections as a set of differing options. That does not make these views less informative.

In reviewing where the world will go, Shell looks more to political impact as the future unrolls. They see the European Union stuck in a Trapped Transition” where:

the ‘can’ keeps being ‘kicked down the road’ while leaders struggle to create some political and social breathing space.
so there is continuing drift, punctuated by a series
of mini-crises, which will eventually culminate in either a reset involving the writing off of sign and political capital (through pooling for example) or the euro unravelling.

On the other hand countries such as China and Brazil are resilient:

in their different ways, they had the financial, social, political, or resource ‘capital’ to respond and reform, following a room to Manoeuvre pathway.

Within the next thirty years, as the population grows, so a greater percentage, up to 75%, will live in cities. And these will consume a greater fraction of the global energy supply, perhaps as high as 80%, up from the current 66%.

The document is very much slanted as a Socio-political forecast, with considerable polemic in regard to the weaknesses that the company perceives to exist in the West.

Shell postulate two different scenarios for the future. There is the Mountain scenario, where business continues very much as usual, and then there is an Oceans scenario where the” powers that are” work toward a more accommodative approach to those in the developing world, and the less fortunate layers of society.

The document begins with the impact if the Mountain scenario is to prevail, driven through a top down control, largely through existing institutions. Shell is not enamoured of this:

In the US, for example, income and wealth inequality continue to increase, with stagnating middle-class earnings, reduced social mobility, and an allegedly meritocratic higher education system, generously supported by tax exemptions, whose main beneficiaries are the children of the successful. superimposed on this class divide is an increasingly serious intergenerational divide, as commitments to the elderly via entitlement programmes crowd out discretionary expenditures that could rebuild economic and social infrastructure. Similarly, in Europe an ageing population and commitments to high levels of entitlement, which are frequently underfunded, create a mixture of social and political strains that deflect attention from the core structural economic issues facing the region.

Driven by this gloomy picture of the future Shell anticipate that global GDP growth through the 2030’s will average under 2%. This will, in turn, moderate the growth in energy demand. Increasing urbanization, the growth of the service sector and the greater use of electricity in developing countries, Shell anticipate that the strong correlation between economic and energy demand growth will be broken.


Figure 1. Shell projection of future energy supply, through 2060 under the Mountain scenario. (Shell)

N.B. All the illustrations come from the Shell New Lens Scenarios document.
Shell anticipates that hydrogen, an up and comer just a few years ago, and now largely neglected, will undergo a “phoenix-like” resurrection and find a market both in industrial and transportation as an alliance of government and private industry push a hydrogen infrastructure post-2020. They anticipate that the use of liquid fuels for passenger road transport will peak in 2035, and that by 2070 the global passenger transportation network, using roads, could be nearly oil-free, as hydrogen and electric powered vehicles take over.


Figure 2. Shell future projection of vehicular fuel sources.

The energy burden will transfer from crude oil to natural gas, which will increasingly underpin the global economies, as China joins the top tier of natural gas producers.


Figure 3. Sources of liquid fuels through 2060 (Shell)

The increase in the volumes of natural gas that become available from tight shales and coalbed sources are sufficient that, by 2035 Shell anticipates that natural gas will not only displace crude oil as the primary transportation fuel, but that it will also encourage a robust pretrochemical industry based on methane. Shell sees the possibility of US energy self-sufficiency in the 2030’s as peak oil theories are abandoned.

The availability and broad use of natural gas will also allow time for credible carbon capture and sequestration technology to be developed and demonstrated, so that by the time that coal is needed as a fuel (around 2075) it will be usable while sustaining the zero-carbon dioxide levels for electricity generation that become widespread by 2060.

In the alternative Oceans scenario, the more accommodative approach, Shell looks to a willingness to share technology and compromise on issues of ownership and profit as a way of encouraging globalization and developing productivity. Societal interconnectivity is encouraged by greater use of the Web, and this leads to significant changes, with existing leaderships yielding to allow a broadening of governance and significant reform. The greater spread of information and connectivity makes for the more fluid nature of geopolitics that names the scenario, as increasing populism is both a source of innovation and a challenge to stability. Populism is seen as a challenge to US dominance, and is considered likely to cause “destructive and violent reactions” as globalization progresses.

This progress is seen as most likely to through technological interconnection between entities that creates a new class of Mandarin who is less accountable to traditional masters. In this scenario Shell see the world increasingly run by more flexible, and decentralized governments “that have embraced radical pathways 
to economic sustainability”. And this includes both the United States and China. In this regard they quote the work of Anne-Marie Slaughter of Princeton on a New World Order.

This change from the current business-as-usual (BAU) model has an impact on fuel availability and use. The encouragement of entrepreneurship is seen to significantly increase the penetration of solar power into the energy mix, while sustaining the era in which crude oil contributes beyond that of the Mountains scenario.


Figure 4. Energy Sources under the Oceans scenario projected by Shell.

In comparison with the projections under the BAU natural gas is less of a player, though Shell don’t explain either where the additional oil will come from, or why the rush to invest in natural gas is turned off. They anticipate that the reliance on hydrocarbons will cause a rise in price that will open the door to new resources and technologies, particularly with solar power.

In this future Shell sees the developing world taking more of the energy pie, yet transitioning rapidly into a lighter industrial society, with a large service component. (One wonders where the necessary heavy industry goes, as it also transitions to become 80% more efficient?) Heat pumps become a widespread domestic unit, with their benefits in energy efficiency. And, in order to sustain their market share, internal combustion engines become increasingly efficient and technically advanced. While crude oil use will increase until the 2040’s, beyond that time the increased use of biofuels will allow liquid fuel dominance to continue in vehicular use. There are two main sources for these biofuels, first generation fuels, mainly sugar based ethanol, which will contribute some 4 mbd by 2050, and second generation biofuels from non-food crops which come to dominate beyond that time. As this transition occurs so traditional biomass use will disappear by the end of the century.

The different consequences of the two scenarios, as they impact fuel sources, and the unconventional nature of the Shell answers to “where will the resource come from” is shown in two plots that summarize the two energy futures.


Figure 5. Energy sources of the future, as seen by Shell under two different scenarios – Mountains and Oceans.

Under the BAU Mountain view the additional required energy will come in the natural gas side of the house, with Methane Hydrates being the major new source of fuel. With the competing Oceans scenario the energy comes from the development of kerogen from the oil shales of Colorado, Wyoming and Utah. By the end of the century renewable energy will supply more than half the electricity demand around the world, with solar carrying the greatest share of this. However they do not see the electricity generating industry becoming carbon neutral until the 2090’s, as CCS penetrates the industry.


Figure 6. Shell’s view of electricity power sources by 2100.

Shell foresee that the problems of energy storage (80% of the solar power in many OECD countries is generated in the summer) will be overcome through the use of electrolysis and the storage of the resulting hydrogen.

There is much to debate over the basis on which Shell have derived the scenarios that form this report. It remains more optimistic about the oil and gas futures that I can find a basis for accepting, but nevertheless it is well worth reading as it provides two views of what might come about. The impact of societal pressures and drivers produce two different energy futures, and while I suspect that reality will be quite different, with “unknown unknowns” having great influence, the effort is worthwhile.

OGPSS - update

For a couple of reasons I will not be putting up a post on energy this week, but hope to bring it back next week. And here is the rest of it.

Waterjetting 7d - High-pressure Waterjet cleaning over sandblasting paint

Over the years I have been caught up in “discussions” with several folk about how good high-pressure and ultra-high pressure waterjet streams were as a surface cleaning tool, in contrast with chemical and abrasive use in removing paint and other surface layers. One debate was about cleaning some particularly toxic chemicals from various surfaces. The point that often comes up in these discussions is that of “how clean is clean?” And in this particular case it was stated that the surface could never be completely cleaned. The rationale for that position was because the chemicals would enter into any cracks and flaws in the paint, and could therefore be retained either in the top coat, or the underlying primer. My answer to that was to take a small sample and clean the surface over the first quarter, raise the pressure and remove the top coat on the second quarter, raise the pressure further and remove the primer down to bare metal on the third quarter, and then, after adding a small amount of abrasive to the water, remove a thin surface coat of metal from the sample. It seemed to be a convincing demonstration, though I will come back to one problem in a later post, and for this post I will discuss taking the paint off.

It is now reasonably well known that high-pressure water can be cost effective as a way of removing paint, particularly from large structures such as bridges, and ship hulls, but it took a while for some of the benefits to become evident.


Figure 1. It was originally estimated that it would save some $1.75 Canadian per square foot to clean the Quebec Bridge with ultra-high pressure waterjets, rather than sandblasting. That increases to $4.50 per sq. ft. were hand tools the alternative (WJTA Jet News, March 2000)

There are 8-million square feet of surface in the bridge. As I noted at the end of the last post, the historic method for cleaning surfaces, and removing deteriorated paint has been to suspend abrasive particles in an air stream, and to use those particles to abrade and erode the paint from the surface. When the paint, rust and other coatings have been removed the job is often considered finished when the surface is restored to a nice shiny surface finish. There is, however, a snag, when one does this. The numbers that I was once given were on the order of: from the time that a railroad wagon was put into service, it would take 5 years before it would require stripping and repainting. After that first treatment, however, the paint would deteriorate more quickly and often within another 18-months the wagon would have to be taken back for repainting.

So why is this, and why does high/ultra-high pressure paint removal help extend the life of that second paint coating? I, and the industry, are deeply indebted to Dr. Lydia Frenzel who did a lot of the pioneering work in helping to define the benefits of the technology, and then spread the word about them. The problem begins as the surface begins to corrode, and I will continue to use the wagon as the example, though the result holds true for many surfaces. As the rust and damage continues to eat through the paint and into the underlying metal, that surface is not attacked evenly, but, instead small pockets of corrosion develop, where the metal is eaten away more in the middle or along the sides of the pocket.

By the time that the surface is ready to be painted it is no longer, therefore, smooth, but rather is pitted and covered in corrosion.


Figure 2. Exaggerated illustration of the condition of the surface, with the overlying corrosion shown in green.

When the surface is cleaned with an abrasive, typically driven using an air stream to sandblast the surface, the particles will impact and distort the surface. Thus while the majority of the corrosion will be removed by the impact and scouring action of the abrasive, some will not. Further the impact of the abrasive particles will bend over the weaker structures on the surface as well as peeling over some of the metal on the surface.


Figure 3. Electron microscope picture of a piece of metal on the edge of a pass by an abrasive laden stream, so that the action of the individual particles in cutting into and plowing the surface can be seen. Note that this peels over metal edges, for example at the arrows.

The peeling over of the surface, and the flattening of it give the shine that used to be the sign that the job had been effectively done. There are, however, two disadvantages to this. The first is that by distorting the surface, the bending over of the metal traps small pockets of corrosion within the surface layer of the metal.


Figure 4. Representation of the metal surface after it has been cleaned with abrasive. Note the folding over of metal to trap corrosion products. The abrasive particles are also not small enough to penetrate into the smallest tendrils of corrosion migrating into the metal, and these pockets (green) also are trapped.

With corrosion already embedded in the surface, before it is painted, that will develop immediately and thus the relatively short time before it undercuts the paint and causes it to fall off. There is also another reason for this. As air pressure is increased to speed up the cleaning, and give that “shinier” surface it smooths the surface and makes it more difficult to anchor the paint on the metal. This was shown by F.W. Neville (and is quoted in the book “Blast Cleaning and Allied Processes, by H.J. Plaster) with this table:


Figure 5. Relative paint pull strength as a function of the pressure of the air driving the sandblasting stream in pre-cleaning the surface of the old paint, prior to repainting.

As the table shows, the higher the air pressure then the smoother the surface, and the poorer the bond made with the paint.

Now consider what happens when a high-pressure jet cleans the surface. The water does not have the power to distort the metal, but rather does have the ability to penetrate all the cracks and pits on the surface, and flush them clean. As a result the surface is left rough (to give a good paint bond) and corrosion free.


Figure 6. Illustration of the relative condition in which a high-pressure waterjet will leave the surface.

One of the difficulties that early proponents such as Lydia had in getting the technique accepted, however, lay in the cleanliness of the surface. Because the metal had not been distorted back into a smooth upper surface, it does not reflect light in the “shiny” manner that an abrasive cleaned surface does. Thus to those trained to the latter, it did not appear clean. There had to be a considerable amount of demonstration, explanation and training before it was accepted that this “grey” surface was actually cleaner. And there are now standards, issued by the Steel Structure Painting Council, that recognize this.


Figure 7. A primer coated plate (left) that has been cleaned to white metal (right) using a high pressure waterjet.

Note that actual microphotos of abrasive and waterjet cleaned metal surfaces can be found in the paper by Howlett and Dupuy (Howlett & Dupuy, NACE Corrosion/92, paper No. 253; Mat. Perf, Jan. 1993, p. 38, the waterjet pressure was 30,000 psi).

Iceland's quake activity

After a quiet few months, I see that Iceland is seeing a fair number of earthquakes above 3 in a confined region at the North end of the island. (Those are the events marked with green stars).


Figure 1. Earthquakes in Iceland in the last 24 hours (Iceland Met Office)

A closer look shows how linear the different events have been.


Figure 2. More detailed view of the events shown in Figure 1. (Iceland Met Office).
This post was updated late in the day. (see below the fold).

UPDATE 3. By late evening Wednesday the activity was still strong, though perhaps a few less 4's. (map appended).

UPDATE 4. Friday afternoon and the activity seems to be tapering off a little - and as The Earthquake Report notes quake swarms of this type are quite frequent in the region, and usually peter out after a few days or weeks.

UPDATE 1 Well the situation has not yet stabilized, and as I go to bed, some 12 hours later, the quakes are spreading along the fault line to the mainland.

UPDATE 2. The activity is occurring along the Tjörnes Fraction Zone,, and is being followed and described by Jón Frímann over at the Iceland Geology blog.


Figure 3. The situation at 11 pm Tuesday evening (Missouri time)(Iceland Met Office)

And this is the situation at around the same time on Wednesday evening.


Figure 4. Change in the pattern late Wednesday evening (Iceland Met Office)