Waterjetting 29e - Back and Forth again

When the International Symposia on Waterjet Cutting (ISJCT) began (back in 1972) the uses of the tool were severely limited, both by the pressures available to customers, and by the limited knowledge of the capabilities of the system. Skip forward four decades and while the various tools available have widely broadened (the maximum pressure we have operated at runs well over a million psi) with cavitation, abrasive and polymer injection being just some of the more productive additions to the tool box, knowledge of system capabilities still lags in the general public.

The public wandering past a hydro-demolition site, where jets may be operating at 50,000 psi to remove damaged concrete – or by a civil construction site where hydro-excavation is digging a dry trench faster and safer than before, and the observer will likely have little clue as to the changes in technology that have taken place and the tool being used, since the jets are usually hidden by their surrounding shrouds.

Yet even in the industry that uses the tools – either for cutting aircraft parts, art pieces or for more mundane cleaning, the advanced technical capabilities of the tools they use are often a mystery to them.

Part of the reason for this, I suspect, is that the generation of scientists and engineers who pioneered the research that developed the industry have now, in most countries, retired. There has been a change in emphasis also for the research effort. There are many fewer opportunities for university teams to go out and demonstrate (as we did) that an abrasive waterjet system could be used to effectively cut a rock wall 20 feet deep within 50 ft of the Gateway Arch in St Louis, without any risk of the Arch crossing its legs. (Which was a major concern that the Park Service had when we did the work). In that project we also had to develop a 5,000 psi DIAjet drill to install rock bolts through 15 ft of dolomite, clay and chert to ensure that the walls remained stable (something not used much thereafter).

More of the research now (at a much smaller cadre of universities) is focused on enhancing the performance of jets in a much smaller range of applications, rather than finding and developing new markets in places where waterjets have not been used before. I will exclude the medical field from this restriction, since, particularly in Germany, new applications continue to appear.

What is also unfortunate is that the advent of the internet means that many of the earlier papers where, as with the case of hydro-demolition, the exploratory work was undertaken, are not easily accessible. And (writing as an academic who reviewed many theses and dissertations) few students go back much more than five years in assessing the previous state of the art.

As a result of this there is almost no effort to exploit some of the ideas that were developed over the early decades, where potential new applications were found, but which could not, at the time, be developed because of either technical constraints, or because (in our case) there were other more immediately rewarding paths to follow.

The movement at universities has seen high pressure waterjet systems move from the research laboratories into the machine shops of the support complex. As they thus become classified as “conventional systems” so there is less incentive to see them as places where innovation can bring the sort of rewards that can be found in developing other avenues of research.

This is a great pity since, although the industry has grown from being just a lab curiosity to an integral part of a number of industries (collectively doing billions of dollars of work a year), the range of applications for which it is uniquely suited have, as yet, only been tapped to a limited extent. As an example, the ability of waterjets to work in explosive environments to cut through different materials has yet to be fully recognized. Yes abrasive waterjets are used to cut the tops from oil and gas tanks, where remedial hydrocarbons pose a threat, but there are many other situations where – on a smaller scale – this ability could provide a number of benefits. (The coal mining industry comes to mind).

I remember watching an early demonstration of the use of a hand-held waterjet by a diver, as a way of cleaning barnacles and growths from an undersea platform. Previously the divers had to cling to the structure with their legs to give them support as they chiseled away at the growths with jackhammers. By putting a reverse jet on the lance, the diver could now float around the rig, removing growths without that sharp intrusion into his comfort zone. As I recall it took less than two years for the concept to sweep the industry, around the world, and I have mentioned before the reaction of one diver, who threw the jackhammer over the side of the rig with a profanity, after using a waterjet cleaning lance for the first time.

The above is another explanation for the focus that this site is going to have on some of the earlier papers in the technology over the next few months. It will try and provide a deeper explanation as to why certain things are done, based on the research of those earlier investigations, and also some pointers as to where we can expect the industry to move in the future. It should be fun!

Waterjetting 29d - Fixing an Oops.

There was a story that is told in Mining Engineering classes about a tunnel that collapsed, even after there had been a whole series of tests carried out to make sure that the rock was strong enough before the tunnel excavation was started. In working out why the tunnel had collapsed some questions were raised about the tests made on the rock samples. It turned out that the testing technicians had received the samples and struggled to find good enough quality pieces of rock in the sample from which they could extract the required sample sizes to run the standard strength tests.

When they reported the results of their tests these predicted that the rock would be strong enough to stand, without collapse, for a long enough time for artificial supports to be placed under the rock and to hold it in place. But it was not that strong segment of the rock that failed, rather it was the rather more rotten rock that surrounded it which provided the weakest link in the tunnel wall. That material had been too weak to make into a sample, and the technician had therefore not reported the lack of strength.

Knowing the properties of a target material before starting a job is an important part of correctly forecasting how how long it will take to perform the cutting tasks required and, as a result, how much to charge for the work. And further to ensure that there is no unanticipated cost that will come from the use of the waterjet tool at the parameters planned.

These unintended consequences have, for example arisen in the past when a high-pressure waterjet system was being used to remove damaged concrete from the surface of a bridge. (As with the tunnel we’ll keep the bridge as an unidentified example).

In repairing a bridge deck it is usually required that the top layer of concrete be removed just past the top layer of reinforcing steel (rebar). This allows a good bond between the previous concrete and the repair pour, which also bonds to the rebar giving a repair that will last for some time. (More conventional repairs leave a weakened joint between the repair and the old concrete which fails more rapidly in many cases).

However the waterjet system is only discriminatory to some extent. The jet pressure can be set so that it will only remove damaged concrete, for example, but does not have sufficient pressure to remove healthy (and less cracked) material. But if the material is weaker than expected, or the damage extends further into the deck than was expected, then the waterjet system will continue to remove damaged concrete, even if this means it ends up removing material all the way through the deck. This can be a real problem, given the extra money and time that must now be spent in replacing that additional concrete, and ensuring that full integrity is restored to the deck. This additional cost can be more than the price of the original repair work, and do serious damage to the economic health of the waterjet company. Unfortunately with many of the systems today becoming more and more automated, it requires close attention the machine at all times to ensure that only the required amount of material is removed and no more.

One solution to the problem is, at least initially, the very opposite of what you might think would be the best answer. It is to increase the pressure of the jets removing the material. For a system with the same horsepower as the machine that was being used first, this means that the amount of water used will be less, and the nozzle diameters will, as a result, also shrink in size.

The smaller jet diameters and higher pressures mean that the cutting distance of the jets themselves will become shorter, as the jet decays more rapidly with distance. (To give an extreme example a 1200 psi jet at a diameter of about an inch-and-a-half can throw a jet about 125 ft. At 50,000 psi and at a diameter of about 0.005 inches the range of the jet is usually less than 2 inches*.) Within their effective range, the higher pressure jets will cut much faster, and so it is possible, by mounting the cutting nozzles in an array that spins around a common axis, to rapidly clean a swath of material (say up to 2 ft in width) as the head moves across a traffic lane at an advance rate of roughly 1 pass a minute as it moves up over the bridge. The higher rotational speeds will also restrict the depth to which the jets can cut on a single pass, so that the depth of material removed can be relatively accurately programmed into the machine by adjusting some of the operating controls. (After first finding out what the best parameters will be for THAT bridge concrete in a small test area off the main work site).

There is an additional advantage to using the higher pressures, and that comes with the smaller volumes of water that will be required to take the damaged layer of concrete from the surface. This water will be contaminated by the different fluids that may have soaked into the bridge over time, and by the corrosion products of the deterioration. For these reasons all the debris and water from the demolition operation will have to be collected, removed and properly (and expensively) disposed of. The higher the volume of water then the greater the collection and disposal cost, and the lower water volumes needed with higher pressures will thus carry a lower disposal price.

The example given here is for the removal of damaged concrete from bridge decks and garage floors, but the underlying principle also applies in the milling of pockets into materials of differing composition, where a controlled depth of cut needs to be held, even if the material strength changes.

*The word “usually” is used since there are ways of increasing the jet throw to several thousand orifice diameters.

Waterjetting 29c - If at first you don't succeed

In my last post on this topic I wrote about two of the most influential papers that were published in the Proceedings of the First International Symposium on Jet Cutting Technology (hereafter ISJCT) back in 1972. Yet there was one more paper that I remembered over the years. And it has been for an entirely different reason.

The paper was “Application of Water Jet Cutting Technology to Cement Grouts and Concrete,” by L. McCurrich and B. Browne of Taylor Woodrow in the UK. The company had looked at the use of waterjets as a means for cutting concrete, either for demolition or inserting the grooves used, for example on highways for “rumble” strips. They concluded that such a tool would have to operate at a pressure of 54,000 psi, and using 3 jets in a cutting head, would require a power demand of around 550 hp. To quote from the paper:

This scale of research to develop a practicable cutting tool would be at least one hundred thousand English pounds. (Then around $250,000). No single firm involved in demolition is likely to be able to afford this sum on a speculative development of this nature, and if a commercially viable proposition can be shown to be likely, funds will have to come from a central Government or Trade Association body.

Jake Frank and I visited the company in London after the conference was over, and the authors were explicit in their views that a waterjet tool would be too expensive for any individual company to purchase for use in concrete work. Skip forward a few years and I was at the Liquid Waste Haulers Show in Nashville TN. (This became the Pumper & Cleaner Environmental Expo International and this year is, I gather, the Water & Wastewater Equipment, Treatment & Transport Show and will be in Indianapolis next month). A friend of mine was chatting with me on his booth, when a salesman come over. He suggested I join him while we wandered over to the sales table where the customer happily signed an order for a $250,000 unit that would leave the show and be used for the hydro-demolition of concrete.

Times had certainly changed in the intervening years, and I rather suspect that the estimate that the two authors had given for the project development costs were exceeded as both the Gas Research Institute (now the Gas Technology Institute) and the Electric Power Research Institute, as well as the National Science Foundation, helped to develop technologies, both through funding research and in encouraging companies to develop the needed tools for the industry that has since grown to use it. Not that the research effort was limited to the United States.

By the time of the 2nd ISJCT in Cambridge, two years after that first paper, there were three papers dealing with studies on concrete cutting. These included studies carried out in the United States, Japan, and Canada. There were two drivers to this growth in effort, despite the pessimism of the original paper, the first being the size of the market. McCurrich and Browne had pointed out that back in 1970 the UK was emplacing about 1 ton of cement for each inhabitant of the nation, much of which would later have to be demolished or repaired. One of the other drivers was that, in contrast to rock and other materials that were being used as targets, cement properties can, to a degree, be controlled by the manufacturer so that the effect of changing concrete properties on the cutting performance could also be established.

The work was, however, constrained to the laboratory for these studies at that time and focused on jet slotting of the concrete at pressures ranging up to 60,000 psi.

There was only one paper on concrete cutting at the Third ISJCT, and that dealt with cutting underwater, which at pressures of 60,000 psi jet pressure and shallow depth appeared to be little different to cutting in air, where the nozzle was held close to the target surface.

The fourth ISJCT was held in Canterbury, UK and marked a change in emphasis for the research on concrete removal. The teams reporting differed from those of the earlier papers, and now included funding from NSF. The emphasis for the three papers was also more focused on concrete demolition, using pulsed waterjet systems in two cases and on a portable system for removing concrete and asphalt for utility repair in the third.

The idea of using a pulsed jet to shatter concrete due to the impact of the jet on the surface, the rapid generation and penetration of cracks from that impact, and the consequent rupture of a block into pieces had a number of advantages. Tools could be built with relatively simple charging mechanisms (the simplest of which – that came later from Germany – used a small cartridge similar to a shotgun shell to generate the pressure) and without the noise and dust generation of impact breakers. Unfortunately, as these tools were developed over the subsequent years, a consistent problem arose for the devices being developed. This was that the pulse that generated the damage had to be repeated relatively rapidly if it were to be able to match the performance of the impact breaker. This required that the pressure chamber holding the water had to be rapidly refilled, and this in turn required a valve between the water supply and that chamber. The valve then had to withstand the repeated high-pressure cycles each time that the device fired. This turned out to be a bigger problem than had been anticipated, and there were several efforts to develop the pulsed waterjet concrete breaker that foundered because of the complexity of the problem.

It was only at the 5th Conference, held in Hanover in Germany, that the first paper appeared noting the benefits of removing damaged concrete. Concurrently the paper that discussed this also described field trials carried out in Chicago, demonstrating that the waterjetting method was able to remove damaged surface concrete preferentially, and to a controlled depth at a rate more than twice that of existing jack hammers, while using roughly the same amount of power. It had taken ten years to reach this point, which presaged the development of the hydro-demolition industry, although it took several more years and the interest of larger companies before the technology finally took off.

Unfortunately the work on pulsed-jet concrete demolition which was still ongoing at the 5th ISJCT did not lead to a commercial product, for the reasons cited above, while concrete trenching and more detailed contour cutting, although developed by the this conference into a field portable device, also was later subsumed into the overall development of hydro-demolition.

These developments took much more money that the original authors had foreseen, but the final devices put into the field ran at lower pressures and required less power than those original experiments had anticipated. It also took a number of years for the capabilities of the technical equipment to reach to capabilities needed to field the tools that are now ubiquitous.

Waterjetting Technology - Dr. Andrej Lichtarowicz

I was saddened, this week, to hear of the passing of Dr. Andrej Lichtarowicz, who died on the the 6th of this month. As Mark Fairhurst noted, Dr. Lichtarowicz, on the faculty at Nottingham University, was a sterling early contributor to the waterjetting community, from its birth back in the early 1970’s. He gave a paper at the first BHRA conference in 1972, and serving as the editor of the 11th Proceedings in 1992.

There were 201 delegates to that first meeting, which was held at the University of Warwick, in Coventry, UK. with 37 papers being given over the course of two and a half days. The use of high pressure waterjet technology was very new at the time, and this was the first time I was able to get together with peer scientists from around the world to discuss what they were doing as well as make a small contribution of our own. But the papers that influenced our lab the most were the two given on cavitation. (One was given by Dr. Andrew Conn and the other by Dr. Lichtarowicz). The reason for this interest was that back in those days the pressures available from high-pressure pumps were restricted to about 30,000 psi, and (without abrasives which only showed up about eight years later) this significantly limited what materials could be cut.

Dr. Conn’s paper related to cavitation at lower pressures and higher volume flow rates, while Dr. Lichtarowicz’ paper covered smaller jet testing at pressures of up to 10,000 psi. Using such a jet he had been able to drill holes in aluminum, which he could not do when the jet was not cavitating. The results were sufficient that we shortly thereafter tried to repeat , and were able to exceed, these results, drilling a hole in a small piece of alumina in less that a minute, although at a pressure of around 18,000 psi.

This led to considerable discussion at the 2nd conference, which was held in Cambridge in 1974, as to whether the results that were being reported were because the jet was breaking up into droplets, or if the result was true cavitation. It was a discussion that Dr. Lichtarowicz, as always, took a significant part in, and although he could not make the third conference (which was in Chicago) by the time of the fourth, in Canterbury in 1978, he was carrying out his research with the nozzle and target submerged with enhanced results from the earlier work.

Over time he developed a small cell, with windows so that the action of the jet could be seen.

Figure 1. Initial design of the Lichtarowicz Cell

The small size of the unit, and the relative simplicity of construction, meant that a number of us, around the world, built such units and used them to help develop a better understanding of what was happening, and how damage could be increased.

One of the early discoveries he made was that, by adjusting the pressure in the chamber, the amount of overall damage (measured by mass loss) could be significantly intensified, and the rate of erosion increased. It was on that basis that we, among others, were able to use cavitating jets to disaggregate rock and coal into fine particles.

Figure 2. View through the port of a Lichtarowicz cell, showing the cavitating jet impacting a metal target.

One of the major uses of the cell was, however, not as a tool to develop faster ways of drilling rock (though it did) but instead to accelerate the rate at which the cavitation resistance of different materials could be determined. Until that time the standard tool for determining cavitation resistance had been the vibrating horn device recommended by ASTM. The problem with this was that it took hours (typically about 24) to generate the data and plot the rate of material removal, because it was so slow. With the cell a similar result could be obtained in minutes. His work led to the development of an ASTM standard first adopted in 1995, and reapproved in 2001 and 2006, with current interest in revision. It went on to be incorporated as part of the International Cavitation Erosion Test.

And so the technology moved forward, Dr. Lichtarowicz gave his last BHR paper at the 12th Conference in Rouen in 1994, and this was a review of some of his earlier work, showing its relevance as industry sought to find cleaner, greener methods for cleaning and material removal. His fundamental work, however, fostered studies that continue to live on, particularly in Japan, where laboratories continue to develop the techniques and ideas that he pioneered over the years. Certainly our own work would not have progressed as far, or in as many directions, without the inspiration of his work, and the many discussions on the technology we held over the years.

He was a good friend, not only to young faculty – as I was when we first met – but to the industry as a whole, and the students that he taught over the years. He was a much respected scientist and colleague and the tools that he developed and helped us learn to use will continue.

Waterjetting 29a - Looking Backward and Forward

The great advantage in teaching the same academic course each year for a relatively long period of time was that, after a while, it became easier to look at the contents of each individual lecture, and then adjust the material to fit the changes in what we knew since the lecture had last been given. In many fields of study the basic knowledge has been around for many years, and so there is not that much change in the content each year, rather one tries to find better ways of getting the information from one side of the lectern to the other.

Over the period that I was an active academic this latter case was never really true for the class I taught in Waterjet Technology and Use. Each year, as I prepared the material some of the information in almost every lecture had changed or been added to, and so the material was largely redone. This was particularly true when students wanted to take the course through distance learning – where the lectures were pre-taped ahead of time, and then sent out on disc, or downloaded from the campus servers.

The changed information came from a number of places, some came from research that was being carried out in our laboratories, or from colleagues we were working with. But the majority of the new material came from conferences that were run every year, the papers given there and also those articles and papers that appeared in the technical journals and magazines. And, not to be completely neglected, it was often possible to get quite a bit of new information from just wandering around the trade shows and chatting to those in the booths and their visitors. Technical papers themselves only tell part of the story. The information has typically to be compressed into a paper that has to be presented in about 20 minutes, and must fit within a very restricted page limit (typically 10) in the conference proceedings. Getting to ask questions in the presentation, and then chatting with the folks that did the work afterwards (particularly in a more convivial place) meant that a much better idea could be grasped as to the real meaning and usefulness of the work.

The results of those meetings would often only change one or two slides in a class presentation that typically contained about 40, but the class itself could, as with this site, only cover topics with relatively broad brush strokes, because only one or two of those in the class (or current readers) might, for example, be interested in the use of waterjets in spinal surgery. Time for greater discussion was/is therefore limited. Further the information in the papers was of only limited availability to students since in many cases my library held the only copy of the information within a couple of hundred miles or more.

However the great advantage that is increasingly here today is that different organizations are not only putting their current conference proceedings on the Internet, but are also going back and publishing the earlier conference proceedings through the same channels. For example the entire set of proceedings of the biennial U.S. Waterjet Conferences are available for download. The older ones can be found on the WJTA site while the last three (since this year’s conference is not until November) can be found at the WJTA-IMCA site.

This means that, for example, those of us who may, back in 2007, not been that interested in the removal of rust and the use of high-pressure waterjets to clean surfaces for recoating, can now go back and read the excellent review and discussion paper that Dr. Lydia Frenzel gave back then. This then provides a background for the paper that she gave on "How to Inspect for Flash Rust" in 2009, as well as the description of a Chinese technique for rust removal given in the same venue. This was followed by an update in 2011 and then an explanation in 2013 as to why it has been so difficult to write standards for the use of waterjetting in the coatings removal and surface preparation industry.

This relatively simple illustration tries to show how, with access through the web, it is now easier to track developments of technology, and through the insights provided in those papers, to understand some of the underlying reasons why technology has evolved the way that it has.

The older conferences on the technology are those run, also on a two-year schedule, by the BHR Group with meetings being held mainly, although not exclusively, in Europe. These alternate with the American Meetings, so that the last BHR Conference was held in September 2014 in Haarlem in the Netherlands. These proceedings, although available on CD for over a decade, are not available on the web, and some of the earlier proceedings have gone out of print. Papers are thus somewhat more difficult to find, although I do retain copies of all of these up to 2010.

It is possible, in some cases, to find those earlier papers, where the authors are known. Unfortunately many of the earlier papers, which provided more of the basic reasons why certain steps were taken (and some approaches that did not work) are not that simple to find where the authors (who often worked on this as part of a program of graduate study) moved on into other fields.

I make mention of this in part to encourage folk to attend these professional technical meetings, since it provides one of the few places where one can meet other folk working in the field, and share experiences and knowledge. But also to indicate that there will be a slight change in emphasis in some of the posts from now on, to recognize that there is now a way that one can trace (as I tried to show with the very short example of Dr. Franzel’s work) how some aspects of the technology evolved and why. Thus some of the posts that will follow, over the course of this year, will try and link sequential papers showing how some of the ideas in the technology have evolved over the years.

And may I wish everyone a Happy, Prosperous and Successful Year!