Pressure and force in pumping concrete along a line to a piling rig. 2

[WEBALL]

HELLO, WE have supplied a large amount of 5" concrete pumping hose (MWP 100 bar - TBP 200 bar.
It has been fitted to a stationary concrete pump that pumps concrete over varying distances to a Piling rig up the mast and down a flight Auger (CFA Auger.
This is a VERY HIGH SAFETY issue.
Within 6 months they have had two ends disconnect from the hose. Be it called 'blown off' or 'forced off'.
I can post the user report, but names are mentioned and first I would like to confirm my suspicion.
I have already advised to withdraw all hoses and place them on a pressure test.

The hydraulic power cylinder is 80mm bore with relief valve pressure set at 330 bar. they are directly pushing a 7" diameter concrete piston (steel rod connection)stroke 55". there is a short steel reducing pipe to 5" bore, this is then the start of the flexible hose line can be 20-30 mtr to the rig then vertical up the mast 15 / 20 mtr.

The set up worked for 4 - 6 months (289 piles bored and filled) this is not a lot of work.

The first failure was directly at the pump (1st hose-1st end) this was replaced with a new hose. the 2nd hose failed the day after at the base of the mast directly in front of the driver. These failures are 'explosive' as air in the concrete is compressed.
They have contacted the pump supplier (brand new pump) large international supplier and they have stated it is impossible for the pump to exceed 65 bar concrete pumping pressure. So the failure is due to bad hose and or bad fittings.
These failures can KILL.
When a blockage happens (I am told there have been lots of blockages) from a independent site visitor. I believe the hydraulic pressure / force is delivered direct to the point of the blockage in the 5" line. I calculate this is 131 bar.
Prior to the relief valve being activated.
I am working on a 'frictionless' calculation as I do not wish to complicate the issue with 'slump' 'friction' 'temperature' calculations.
I have sent an email with my 'worries' to the pump manufacturer as I say they are misleading 'users' about safety and pressure. this is promoting an "invunrability" feeling to users. So far they have not replied to my email.
We have done thousands of these hoses and not had reports of failures. I am very confident our product is good and calculations correct, but we are up against a very large multinational company. I have stated this is not to apportion blame but to work together to gain safety.
I have done pressure and tensile tests to confirm calculations on video, but having a problem with getting my point across.
I am hoping for someone with greater knowledge on hydraulics (a third party) to confirm if I am correct or not.
thank you.

 

[WEBALL]

Hello all, Happy new year.
please see attachment, it is a little blurred as changed from a PDF, I will also try attach the pdf.
I know Littleinch you will shout me down, but I have drawn this up a different way as I am struggling with the amount of energy in the line.

I am going to build a rig to scale and do a test, but it will take a few weeks, please review attached and comment.

We know there is a lot going wrong with application - speed at start, bad practice, lack of information. But I want to get the basics in order.
best wishes to all for the new year.

 

[miningman]

WEBALL, I think Littleinch would be well justified to shout you down. He has clearly explaiined that it is likely shock loads around 300 -400% of normal running pressures that are causing these hose failures. He is probably correct . However I also believe that there are some fundamental misconceptions in the development of your analysis / thought processes. In no particular order, concrete is not incompressible. Concrete design specifically calls for the inclusion of air entrainment additives. You only have to observe the discharge of concrete at end of a line to see the amount of air contained within the concrete. Personally I believe this admixture contributes significantly to pumpability, others may disagree.

The specs for your Schwing pump shows this to be quite a large powerfull unit. The engine power is almost double that which I have previously used. If we accept that 65-67 bar is the maximum pressure that the pump can produce , then the next theoretical question becomes what volume of concrete are you trying to move thru the line ??? And this comes back to what speed does the absent operator start the pump at?? I have sucessfully pumped thru 2 inch rubber lines......what does that tell you about whether I was running at maximum theoretical volume or perhaps only 30% of that volume??? THE OPERATOR HAS TO CONTROL THE OPERATING SPEED!!

You have admitted to minimal experience with concrete mix design which is fair enough but if you intend continuing with your analyses, I suspect you are going to have to improve on this. Is it a harsh mix being pumped?? Would you recognise a harsh mix if you were at the pump?? Is segregation taking place??.

Sorry to seem blunt but I believe you need to change your focus.

 

[WEBALL]

Thank you Mining man, that is what I needed, to be told bluntly.
I am being told that this is a fault of the hose or fittings(both)yet not one other client has had a failure like these.
I was told the concrete was a HIGH SLUMP CFA mix.

I can understand the ends being 'knocked' off from sustained full pressure pumping.
This is why a did the 7 day test to take the hose far past any working conditions, this is the only way I managed to push ends off.
Yes I told them that the air in the concrete will compress this makes the 'explosive' danger, I agree air makes pumping easier. The client is adamant that they have done nothing wrong, this is mainly due to the pump manufacturer stating that the pump cannot pump more than 65 bar. They have not explained what Littleinch and yourself have worked out here that there could be 300-500% increase of static pressure by the pulse.

My drawing was to send to the client as an attempt to explain how the energy/pressure in the line can be increased more than what the manufacturer has NOT explained. The better quality the pump hose the more Natural rubber is used in the liner (the elasticity)it will last longer against abrasion if used within normal conditions.

Starting the pump slowly (as slow as possible) is natural to me, with over 100 mtr of 5" line this is approx 2.7 ton of concrete, plus friction. Getting this over to the client who is just answering back that the pump will cut-off at relief valve pressure is a challenge.

I know there is a lot of Kinetic energy but I have not wanted to put this to them as I have not the ability to calculate or articulate this to the client, (apart from saying you cannot run up to a 3 - 4 ton truck with the brakes off and expect it to move immediatley).

I will do some studying and try write a full explanation, I am surprised the pump manufacturer has not responded.

I do wish to thank you all, I apologise for my stubborn attitude, I have gained a lot from your answers.

 

[LittleInch]

WEBALL,

Happy New Year I hope...

I really hope you don't think I'm "shouting you down". I am only trying to explain to you the physical realities of your situation.

I understand where your thinking is going, however what you have drawn is simply incorrect. There is no easy way to say this but your suppositions are wrong.

The "Rod" that you have from the 7" piston simply doesn't exist. What you have is Pressure in a fluid, not a force in a solid. Now Fluids can be many things, liquid, gases and in this case slurries which is liquid with solid particles suspended in the liquid which acts like a dense liquid. The force from the original piston is not directly transferred, it is turned into pressure in the fluid. That pressure in a flat line in a static flow is the same at all points and all diameters. Basic laws of physics.

Now liquid concrete is relatively incompressible, but there is some air entrained in it so it has a bit of movement and some energy storage.

Now reading back through this saga I'm still not clear what the failure is? Did the hose actually part company with the coupling cleanly or did it tear off at the end of the coupling?

I'm not surprised the pump vendor isn't coming back to you as I don't really think the issue is anything to do with the pump. It is all about how the pump, hose and pumping operation works together and how it starts and stops. Transient pulse or shock loading can impart very high loads into the system and will find the weak point. Now it may take several shocks to deliver failure or could occur on the first occasion.

What you might need to explain to your client is that this length of concrete hose will act a little like a long set of railcars. When the pumping stops the cars move apart a little from each other. If when you re-start the train by pushing FROM THE BACK then the cars bump into each other as the gap and the buffers compress. Do that too quickly and the bump bump bump will result in a big force on the cars and they will de-rail. Same thing in your length of hose. You can only re-start this line slowly until flow is established at the far end and then slowly ramp up the speed.

SO its nothing to do with the pump which can only put out 66 bar (I really hope you can understand this now) and really little to do with your hose end coupling and 99.5% to do with how they are operating and starting / stopping this line.

Hope this helps.

LI

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[WEBALL]

Certainly happy new year, and I need shouting down by my betters at any time, if I stop listening I stop learning.
I also have to learn how to articulate better to explain what is happening.
I did think my drawing was wrong, but could not prove where the other energy was coming from.

You are more than welcome to visit and have a brew.

I have learned it is not just pressure going into the line, it is energy, and any way energy gets into the line is a potential danger. I could not find a way of explaining that there is only 'one' power source so the only way we managed to duplicate the energy to force an end off is by putting more than twice the pressure in the pump 135 bar with only a 'part crimped' end. ) 3.5" inside the crimp.
To force off a full crimp/swage it takes 200 bar + /// we can burst the hose at over 230 bar, but this done with a multi-piston-jetting pump (Harben).

We are increasing retention due to what we have learned, this is going to have a knock on effect of making the next 'weak-link' in the line. We are worried this may be the clamp they use to connect the hoses. An end being pushed off a hose is less explosive than a hose having a Mid-Burst OR a clamp coming apart, we have seen both.

This has however highlighted a good opportunity to design a gauge capable of fitting in the line that will show the amount of energy in the line compiled from any source.

We are also running the calcs on suction discharge hoses and will be increasing retention in these even though not required. We do crimp ends on hoses up to 24" bore, and not had a failure, so what you have taught us will increase our safety margin.

Can I ask what you think about the "Explosive or Catastrophic' failure as against a push off /force off in this particular application. Whip-checks should be fitted on all concrete and Grout lines. Sometimes now fitted with hose socks and 2ndry containment.

Thank you all again. and best wishes into the new year.

 

[dhengr]

WEBALL:
Start by explaining that static friction is much higher than sliding or moving friction, and that it takes a lot of pressure to get things started and then immediately you have too much pressure and things take off like a bullet, until they impact a pipe or hose bend or obstruction or another mass of semi-solid conc. These movements and impacts cause high lateral loads and thrusts on various system components. If they have drawn a vacuum someplace, it will help pull the wet conc. behind it to get it started, at which location the moving conc. impacts the semi-solid conc. plug which caused the plug and vacuum, in the first place. Some of this is an energy, impulse, momentum problem, but not really a rigid body motion problem, rather a problem involving some fluid dynamics too. These are highly indeterminate problems, and maybe the best you can do is explaining the general thought process and concepts without expecting any exact calculated numbers as to forces, pressures, energies, etc. You could do some testing on some of these issues and get some average numbers for different conditions. You might want to enlist the help of a real fluid mechanics and dynamics expert to help you explain the problems in layman’s terms, for the field crew and contractor.

In your defense, I would want an anonymous observer on site, with video and sound. You need more proof and evidence like the e-mail you showed. I don’t think any of us are really blaming you or your couplings, but rather trying to help you explain why and how the failures could happen. List the things you know they are doing wrong and the potential consequences of each of those actions and operating methods, and present those at an educational meeting with them. That should be proof enough, since you are not having these same problems on systems which are being treated and operated properly.

 

[WEBALL]

Thank you, ... Happy new year.
I am keeping all these ways of explaining as it is great for any future problems, fortunately we do not get very many as we Hydro-test assemblies before they go out, with the data-log gauge and iphone photo that gives time date location that corresponds with the Gauge data-log.

Most things on safety are common sense, unfortunately the later is not the forma and we cannot know all aspects of all installations. This Forum is great to get much higher informed specifics thank you.

Going to take me a few days to write the report, even though we have not got numbers for Kinetic energy and Pulse - friction - vacuum and two more tests we wish to do first. All points taken on board.
Thank you.

 

[Compositepro]

It is amazing that concrete can be pumped at all. It is loaded with so much large aggregate with only "enough" cement paste to fill the space in between. Aggregate particles cannot slide past each other without moving apart first, which cannot happen under very high pressure. So I imagine that the flow regime is mainly plug flow, with the concrete moving as a plug sliding inside of the hose. The concrete mix needs to be appropriate. The size and shape distribution in the aggregate, and in comparison to the hose diameter, will play a major role in pumpability. I expect round aggregate will will flow better than crushed rock. Also important, is avoiding any steps on the inside of the hose that might catch on sliding aggregate and cause a "log-jam".

I think high-slump could mean more cement paste, which would be good for flowability. But it could also mean more water, which would cause easier segregation of the aggregate and therefore be bad for flowability.

 

[miningman]

WEBALL, in my opinion you are getting some very valuable advice here but I can see two areas where you might get yourself into trouble. By sending your pressure sketch to the client, which you now accept was erroneous, you will have lost a lot of credibility with the client. Any further communication with the client needs to be impeccably worded, because as you have alluded to , if the client continues with poor operating practices, you might find yourself as a reluctant witness at a fatality inquiry.

I might be wrong here (as a mining engineer, I'm much better with explosives than with hydraulics ) and I stand to be corrected here, but IMO Littleinche's statement that " pressure in a flat line in a static flow is the same at all points and all diameters. Basic laws of physics" is not 100% true. Regardless of pump pressure or line diameter, at the discharge point of any pump hose / line, the pressure, say 1 foot from the discharge end is almost zero. The difference in energy level along the line represents energy lost due to line friction,( but also as violent hose movements and noise). Probably mostly dissapated as heat.. Now I have no desire to get into a p*****g match with Littleinch over the pedantics of the english language, but you have had two hose failures at totally different locations and I will hazard a guess that the pressures associated with each failure were not identical.

Tied in with this, dhengr's last post seems to imply that in his opinion, there has been a blockage, or semi solidified mass of concrete in the line causing a rapid rise in local line pressure. He may well be correct but I can easily see circumstances where the "shock wave hydraulics " that have been previously suggested could arise without a blockage.

There is WAY too much relevant info, that your customer probably doesn't even recognise as being relevant. IMO,you should be taking legal advice as to how much more communication you might want to divulge to your client. You can easily generate a summary of some of what he is doing wrong. Litleinch again is probably correct that the pump manufacturer wants no part of this. He has supplied a unit which appears to be functioning as designed.... and I'm guessing you were not his customer. Having said that , if you managed to get a copy of his operating and maintenance manuals, I am sure that would provide both facts for you to put in front of your customer, and would also be exceedingly invaluable at a coroners inquest.

Anything else you chose to provide needs to be completely umamibigous and factual. Again way too many imponderables to cover all the possible scenarios that might be taking place.

 

[LittleInch]

By "static flow" I meant no flow.

In a flowing condition the will be a change along the pipe.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[WEBALL]

Hi Miningman - Littleinch,
My third party that visited the site is very experienced and worked on three continents that covers every aspect of this type of concreting. He said lots of blockages were accruing (5 out of 6 attempts).
At the bottom of the CFA (Drill-bit) there is an egress hole for the concrete to be pumped out of, sometimes they have a 'flap valve' that is shut while the drill drills, the spoil rises up the flights and cleared at the top by an excavator, once required depth is achieved the auger is lifted slightly, allowing the flap plate to open and the concrete to be pumped out. Another way is the egress hole to be 'bunged' by a CFA disposable cap that is pushed out with concrete once the auger is lifted a little.
I know there is a lot of high skill required by the rig driver, to much lift allows the hole to collapse before the concrete fills the void to little and the concrete being pumped can be restricted/blocked as it cannot lift the weight of the auger as these can be several tons (depending on diameter and depth.
As the auger is lifted the void filled, as it gets closer to the surface the weight is less so sometimes if the pump pressure is to great it can lift the auger with possibility of de-roping the lift wire off the top sheave. So a high level of skill and communication is required of the crew, especially as miningman says the pump man must control the flow but in close communication with the rig driver.
An open ended line and auger only has the friction + weight + line length and mix to impede the flow, if primed properly and the period between pumping (re-position and drilling) is not long for the mix to start to set.
In hotter countries in summer this is very important as every joint the steel coupling gets warm and dries a 'slug' in the line, I am told another skill is the pump man keeping the concrete going backwards - suction - and forward to help stop this, if a slug gets to dry, once it hits a tight bend it can cause a block.
In colder climates the concrete can freeze.
So skill in priming - slicking the first line and starting subsequent piles needs great care.
I think Littleinch meaning 'Static flow' is a 'full line with air compressed and to start this moving takes greater care and is more difficult than the first pile. pushing upwards of 3.0 ton and any blockage will take the pump to max, but a long line, the concrete will act like a sponge as the air compresses along the line so it does not activate the relief valve straight away and if started to fast would give a few beats (or several) of near max kinetic energy (pulse). This not being sufficient energy to burst the hose, but will initiate 'creep' with a new low shore hardness elastic liner rubber, the accumulated compression of air will accentuate this as littleinch said leads to 'Peak Pressure pulses' hitting each other at pertinent points.

There have been several teams/crews working in this area for 4 years with same hose same couplings, no reported failures as these, but knowing this now, in one way an end failure could be the lesser danger than a explosive or catastrophic fail. There are hundreds of crews in Europe.
I am happy with the views I can not put to the client after it being checked by the third party.
I would like to know how much pulse energy a 7" piston can put out with a big cat engine to power it, without triggering the relief valve. There are a LOT of unknown points in this thread, but I think all agree that there is just one source of power and a large degree of naivety / bad practice / lack of knowledge has accumulated to the failure, or could you call it a safety break failure as if these did not push the ends off a burst pressure would be 220 bar (or equivalent energy there of).
I think a large view-able energy gauge would be a huge added safety aspect. I have one drawn up to make a prototype.
thanks all, please do not argue it is the new year and no-one has been hurt, and we have found out a lot.
best regards to all.

 

[LittleInch]

WEBALL,

Sadly I'm not up in sunny Lancashire too often to pop in for a cuppa, but thanks for the offer.

The thing here is I think mainly with how the "concrete" acts when it is not being pumped and how violent these to and fro actions are that are used in practice to maintain the concrete in a pumpable condition. The peak transients of those sorts of repeated actions can be very high. Slurries are not easy to work out when flow is steady, but when it starts and stops / starts curing then it is anyone's guess as to what is actually happening inside the hose.

In any investigation like this where something works well in other locations and for previous operations, it is finding the sometimes small difference between those operations and these ones causing failure which is the key to understanding the issue. Not being there makes it so much more difficult for a supplier like yourself, but keep digging and I'm sure you'll find it.

LI

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[WEBALL]

Thank you, ... ha ha Sunny Lancashire is a contradiction in terms.
I have learned a lot, I have now had two other clients come back and never had ends off, but they are very interested in a 'breakaway' type fitting, just for safety.
They also said the best place would be just before the vertical so the line could be self-cleared and would prefer this to an actual 'Hose Burst' or high pressure clamp fail.
Pushing an end off is safer than a burst. We have never done this as a 'planned action' but I can understand them saying this as having seen a few pressure burst with concrete in is scary.
I was sent a picture from another client who uses a cheaper hose as a safety fail
I will get you a picture.
thanks
Peter