On the basis that your 80mm hydraulic piston acts directly on the 7"piston, the maximum static pressure the pump can obtain is about 66 bar at 330 barg hydraulic pressure. The size of your pipe is not relevant.

However this is static pressure. Concrete pumping and piston pumps, often only two cylinders, can create large transient pressures which could be creating fatigue loads on your end coupling.

Shock loading might be an issue but not possible to tell from a distance.

66 bar end cap force on your hose is about 8 tonnes. What do you test the axial pull force on the end connections to?

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

Thank you for replying,
I have video of 10.2 ton on a dry end tensile, this was max length of stroke on the test rig 328mm.
I have also had a test piece under pressure of 100 bar for 7 days and nights, then increased to force the end off.
this a complicated test as the previous 7 days took all the 'stretch' out of the hose. this video is on Linkedin.

From your reply I take it you do not agree with my calcs that the blocked end on the 5" hose is 131 bar ?
The system becomes a totally hydraulic one when a blockage happens, Pascal says equal pressure in all parts of the system.
if you can reduce pressure going from 80mm to a bigger bore (177.8mm) you must increase it again if you reduce the bore to 5" is is on enclosed space.

330 bar at 80mm equates to 16.87 tons
330 bar at 7" equates to 66.8 bar (blank end area pressure)
330 bar at 5" equates to 131 bar

If as you say the size of my hose is not relevant, why do manufactures make hose that burst at over 200 bar (I have done this) when they could get away with making one to just 120 bar and make twice as much profit.
I have recorded video tests with data-log gauges to proof these figures, please can you ask me something that I can do to 'disprove' my findings.
thank you for quick reply.
peter

• https://files.engineering.com/getfile.aspx?folder=d0385c00-a2e1-48f4-a94b-6

I have done quite a bit of concrete pumping with 5 inch lines and have also experienced explosive failure at the hose ends on two occassions. I agree this is a fatality waiting to happen. My immediate comments are, the end user is making life difficult for himself by using all rubber hose , rather than maximising purpose built steel lines. Blockages are more frequent with hose than with steel pipe. Friction is way less than with steel pipe which implies pressure MIGHT be less but I cant comment on if this is valid. As I remember there are two separate hydraulic pressure gauges on the pump which give the operator a good understanding of how the system is operating but these values do not relate to the line pressures.

My experiences were 15 years ago and memory aint what it used to be but I do remember identifying a number of defective hose ends. These ends had clearly been crimped on to the hose , but there was a clear visual difference on the degree of deformation evident on the deformed end piece..... high deformation was good , low deformation was a dangerous situation.

I used a number of different pumps and altho I cant remember the details I would tend to agree with the pump suppliers, these units will not over pressurize properly fabricated hoses. I also used some 2 inch hoses and did not dramatically alter our operating pressures.

Are your hoses of foreign manufactuture??

Hello Mining man, Thanks for the input.
There are quite a few things going on here and your point about steel lines are correct, we have also done thousands of mtr of them.
I have been crimping hoses since 1993 and now can crimp up to 24" all my calc's are to same formula just the change of grip for different shore hardness of the rubber.
Most hose is made in Italy, but it is not the different manufacture. At the end of the day the material is 'elastic' that is why it is used on piling sites as the rig needs to move quite often to do a series of piles.
We can put screws through the crimp to the tail (which I am going to do) but this builds an even bigger danger to user's.
If you make users invulnerable they push the equipment farther to gain bonus.
The pump man was talking to the rig driver 30 yards from the pump when it blocked at the auger. He had to run to shut the pump down, all the while the relief valve coming on and off as the pistons tried to pump more into the line.
From my experience this then becomes a 'closed hydraulic system' the flex line being long makes it more explosive as more air is compressed. I have know some users to use extra long lines and keep the concrete moving back and forth while the rig re-positions.
We supplied two clients with the same batch of hose, same fittings, same fitting procedure, one user has had two failures the other none and over a longer time period.
I have a large jetting pump and burst short lengths at over 200 bar (equivelent to 30 ton tensile). The test piece we put on for 7 days at 100 bar slowly stretched so we kept topping up to 100 bar. after 7 days+nights we decided to see what it would take, it pushed off slowly at 104 bar (I expected this) as we had used up all the elasticity.

So when I am told the pump 'cannot' pump at more than 66 bar It makes me explore all possibilities. My findings are that at the time of the blockage the pump runs up to relief valve pressure "330 bar" at this point in time it is an 'Hydraulic' system as per Pascal's Principle. When a force is applied to a contained, in-compressible fluid, the pressure increases equally in all directions throughout the fluid. ... Since the pressure is transmitted equally throughout the fluid in all directions according to Pascal's Principle, P1 must equal P2 (psi calc's to the area of the blank) 5" = 131 bar ... 31 bar over max working pressure.

I have seen blockages cleared in hot climates where a 'slug' has formed at joints due to the concrete drying out. I have seen 'flash-overs' that have taken a full 100 mtrs in a matter of minutes. This one I think has 'frozen' in the line.

I am working on a gauge that will show both pressure and tonnage in a concrete line. In oil lines we set 'dry-breaks' this is not possible with concrete, but a 'wet-break' would be safer than a high pressure burst. Any one is welcome to visit to witness tests.
thank you.

Ok, Merry Christmas to you.

First off let's get the pressure thing sorted out.

You're halfway there already

"330 bar at 80mm equates to 16.87 tons
330 bar at 7" equates to 66.8 bar (blank end area pressure)"

The issue here is that pressure = Force/area.
For a piston, the only area that matters is the area of the face of the piston - in your case 7" diameter.
Once pressure is imparted to the fluid it can't magically increase.

If your PISTON AREA was a 5" piston then yes, you could get 131 bar, but it isn't, it's 7 inches. The force from the hydraulic piston is divided across those 38.5 square inches (7"), not 19.6 sq in (5").

Your hose though is more interesting and less straightforward. Hose and flexible design is much more art than science. Steel tube design has been studied for centuries, the material is ductile, has known properties and established limits and factors of safety.

Hoses and flexibles are much less studied, the materials are a mixture of types, sometimes they exhibit creep behaviour or non elastic behaviour and are a complex and everchanging design.

Hence establishing a reliable design limit is more difficult. Most hose and flexibles seem to work on a static burst pressure which is then divided by a factor of between 2.5 to 3.5 to establish a Max working pressure. Static testing cannot really simulate the actual conditions the hoses work under, with axial forces, bending moments, transient pressure pulses and other "shock" loading hence the large FoS used.

Your information to me says your 100 bar hose rating is actually set too high. With a factor of safety of only 2 plus the fact that at 100 bar the hose apparently yielded or has crept under sustained pressure - you describe this as having the "stretch" taken out of it, plus for the 100 bar test you had to keep putting more fluid in and then the burst pressure was only 104 bar after 7 days. I would term that excessive pressure myself and clearly shows the hose is yielding / failing over time at 100 bar.

SO are you the designer of the end connection? Can you post a sectional view?

Now why these hoses failed and other didn't seems to more about how they are operated and the forces being imposed on them. If there is more line and the pressure pulses from the piston are higher pressure than other locations then your end connection is simply easing off slowly over time. maybe. Either way from the data you've provided I really don't believe your 100 bar hose truly is a 100 bar hose. More like it has a Normal working pressure limit of 50-60 bar, with occasional transient pressure of 100 bar, but not a sustained pressure rating.

I realise this won't really help you, but that's how I see it from the data provided so far.

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

Hello LittleInch, happy Christmas.
Thank you, Yes I am a designer of hose ends, and a lot of years at it.
You are correct these hoses are NOT designed for 'sustained' pressure they are designed for pulse pressure (material handling)the tube (inside liner) is natural rubber, this is to resist the aggressive media.
Concrete pump hose is made by 'Spiral winding' of steel tyre cord on the mandrel at 55° 4 layers two each way. optimum bust angle is 45°.
The 10° is there to take the shock load/pulse. Spiral wound hose can stretch, A cross braided hose (hydraulic)is made more for sustained pressure. these are quite different constructions.

I think you have just highlighted the problem, Both our figures are correct, what is being lost is the 'way' the pressure leaves the pump and the way it is explained to the 'users'.
We both know the pressure cannot 'magically' increase..... BUT .... there is only 'one' power source.. -the pump-

These ends do not fall-off/drop-off and will not 'creep' with surge / pulse pressure to 100bar.
The 100 bar has only come in on the last several years, all concrete pump hoses used to be rated at 85 bar maximum working pulse pressure.
the hose we use used to be 2.5:1 (212.5 bar) under burst test condition would go between 220-240 bar.

One manufacturer (and there are many) decided to use a marketing ploy of saying 100 bar max working with a 2:1 safety. unfortunately this has been taken up now by most as some lost market share. Most now have two specs of hose ... 85 bar with 2:1 for 'land line' and 100 bar with 2:1 for mast hoses.

This has then dominoe'd to pump manufacturers and they lifted pump sizes / relief valve settings. This is a little of the history.
Back to the pressure problem. We do not have a 7" blank end (they can only call it that when they DO blank the end to test the pump.
What is being lost is that in 'operation' there is no 7" end there is a 1.5 mtr long tapered steel pipe down to 5"
direct from the concrete hopper/chamber.
So you have a 80mm hydraulic cylinder @ 330 bar then a 55mm steel rod pushing a 7" blind .... but ... this is a two piston pump, as one stroke pushes the other is pushing back on the annulus side to fill for the next stroke.
so this is increasing the hydraulic area by 4.11" giving 25.76 ton at 330 bar
In a 5" bore this is 200 bar.

66/67 bar is just not sufficient to push these ends off, it just does not happen.
there are 100's of crews working with the same hose / same ends and many with the same pump manufacturer.
I have duplicated as near as possible the failure 'figures' with no movement at all. I have had to exceed maximum safe usage by a huge factor before I have had a failure.
Yes, the hoses are 'elastic' they are meant to be, so if you do over capacitate them, they will fail.

I feel as you say, the operator is evading some answers to actions, or covering up on miss-use.

W.E. can send you a cross-section of the crimp, I need to do from work next week, but here is a picture of a failed end.
I can put screws through the crimp that will either pass the failure to the next weak point (burst the hose) this is more dangerous, or it will find the next weak point in the system.
I am not keen to do this, there are too many things I am not aware of.

• https://files.engineering.com/getfile.aspx?folder=760d6045-17f6-4dbb-8099-9

Ah ha, things are becoming clearer. I was reluctant to provide additional suggestions because all my previous experience was with pumps utlising 5 inch pistons. Posts suggesting that this problem originated with 7 inch pistons made me think this was a new generation of pump that I was unfamiliar with. It now seems wethat this is not the case. Since we are now looking at operator error / poor training . I offer the following.

Having an operator 30 metres away from the pump is extremely poor practice. A competent operator watching the gauges can get a warning as to impending problems, sufficient to institute corrective action. And the absolute worst thing to do when a blockage occurs is to hit the emergency stop. The correct course of action is to immediately hit the reversing switch which instantaneously
reverses the pump direction with a corresponding drop in line pressure.

As the supplier of the hoses , the OP might have a difficult time diplomatically telling the end user that his men need proper training, but thats what it looks like to me.

And if I am to offer additional comments , I would want to know what is the size of aggregate in the concrete, design compressive strength of the concrete, at what stage during the pumping cycle are these failures occuring , is the line being properly slicked prior to the introduction of concrete. slump value of the concrete and how much super P is being used.

Thank you Miningman, Happy Christmas.
I will blank out the names/ companies involved and download what I have been sent.
I also think it is operator error, but I still struggle to explain the ends failing with the tests I have done. There is only one source of power, and 65/68 bar is not a big pressure for these hoses or fittings.
When the fittings are crimped we take them to maximum displacement, we stop as the tail inside starts to reduce in size.
I do have vague details of the concrete, but this only given a week or so after the below statement.
May I do the same with you please. My experience of slump and mix is not great.
My main aim on this is to learn and make the equipment better/ safer. We fitted up a short piece of hose from the same batch and same fittings, but purposely crimped one end not fully in to create a crimp not as good as it could have been on test it took 135 bar to burst the hose at the weak crimp end.


Ground Hose – November 13, 2018
• On Nov 13th one of the ground hose ends blew off. The end that failed was attached to the pump.
• Rig and pump set up on the day (starting at the pump) - ******** concrete pump - 40m long ground hose – 6.6m long steel catwalk piping - 4.6m long cab hose - 7m long steel mast pipe - 20m long hanging hose between the mast piping and swan neck. The drill rig was a SR65 with 19.5m of auger and a 6m extension.
• The outside temperature was ~ +6°C at the time of incident.
• This ground hose has been with this rig since it was purchased. So it would have been used to install 289 piles.
• We were just starting to concrete the second pile of the day. We were not aware of any blockages as the first pile poured fine, the move between the first and second pile was timely and there was no delay waiting for concrete. The crew said the hose blew immediately after kicking the pump on (2 pump stokes).
• The pump operator indicated the pump was reading a hydraulic pressure of 3,200 psi when the line failed, this would correspond with an approximate concrete pressure of 50 bar (725psi) based on the manufacturers documentation. The maximum concrete pressure is listed as 65 bar (942psi) for this pump.

Cab Hose – November 14, 2018
• On Nov 14th one of the cab hose ends blew off while starting the concreting phase of the pile installation. The end that failed was attached to the catwalk piping.
• Rig and pump set up on the day (starting at the pump) - ******** concrete pump - 20m long ground hose – 6.6m long steel catwalk piping - 4.6m long cab hose - 7m long steel mast pipe - 20m long hanging hose between the mast piping and swan neck. The drill rig was a SR65 with 19.5m of auger and a 6m extension.
• The outside temperature was ~ +8°C at the time of incident.
• This cab hose has been on this rig since it was commissioned this summer. This rig has only installed 289 piles.
• We were just starting to concrete the second pile of the day. We were not aware of any blockages as the first pile poured fine, the move between the first and second pile was timely and there was no delay waiting for concrete. The crew said the hose blew immediately after kicking the pump on (2 pump strokes).
• The pump operator indicated the pump was reading a hydraulic pressure of 3,200 psi when the line failed, this would correspond with an approximate concrete pressure of 44 bar (640psi) based on the manufacturers documentation. The maximum concrete pressure for this pump is listed as 65 bar (942psi).


Thank you for your time on this, your comments are highly valued, Both Miningman and Littleinch.

Well I suppose there are two totally different possible lines of investigation here. One would relate to theoretical hydraulics and results of lab tests etc, the other would relate to field practices etc. One of the problems with the former is that it essentially assumes a system in equilibrium , at least to the point of incipient failure.

I quote "• We were just starting to concrete the second pile of the day. We were not aware of any blockages as the first pile poured fine, the move between the first and second pile was timely and there was no delay waiting for concrete. The crew said the hose blew immediately after kicking the pump on (2 pump stokes)

To have this sentence on both failure reports , IMO, is a major hint. Something is changing between the completion of one pile and starting the second. What time frame are we talking here??? What steps are being taken to prevent the rheology of the concrete in the line changing, or is the line being flushed between piles?? Is the start up , slow and steady at reduced pressure untill flow is established or is it " full hydraulic pressure immediately upon call for concrete???

Who is converting 3200psi hydraulic pressure to 650-725 psi line pressure and how confident are we in these values.?? I dont know how to make those conversions , but I do know the pumps I used maxed out at around 2400 psi hydraulic. Normal running was 1600- 1800 psi and as soon as 2100 showed on the gauge it was sign of an imminent blockage and time to reverse the pump rfn.

On one job I was pumpimg thru 800 feet of steel line. Some initial difficuties getting flow established but after that no major problemo.

"So you have a 80mm hydraulic cylinder @ 330 bar then a 55mm steel rod pushing a 7" blind .... but ... this is a two piston pump, as one stroke pushes the other is pushing back on the annulus side to fill for the next stroke.
so this is increasing the hydraulic area by 4.11" giving 25.76 ton at 330 bar
In a 5" bore this is 200 bar"

In concrete pumps the action of one cylinder filling whilst the other empties is separate. There is no increase in hydraulic area and NO increase in static pressure above 66 bar for a 7" piston. I repeat, the size of the hose has no impact on pressure. Please accept this as elementary physics and start looking for other reasons your hoses have failed.

Miningman - the "conversion" of hydraulic pressure to concrete pressure takes place as the diameter of the connected pistons between hydraulic end and concrete end increases (80mm / 3.1" to 7 "). The force from the hydraulic end is essentially spread about a larger area resulting in lower pressure.

Now I say static pressure for a reason. I think that your system is suffering from high impulse loads caused by a vacuum developing in the high vertical leg. When you reapply flow the concrete is closing this vacuum up very quickly and hence you have two high density fluid elements hitting each other at some velocity. This can give you peak pressure pulses of easily 4-5 times the static pressure.

Also when by the look of it when you say the hose end fell off, it doesn't look to me like the hose and the coupling came apart, but that it failed at the point where the hard fixed coupling suddenly changes to the hose. This is peak stress concentration territory and especially if there are no bend restrictors then it is not surprising this is the point of failure. I would recommend that the first 1m of hose is kept absolutely dead straight before any bending.

My suggestion for operating procedures is that on re-start with a full pipe of concrete, the pump is started as slowly as possible for ~ 30 seconds to close up any vacuum gaps and then slowly increased in pumping speed, if this is possible for the pump. If you ask about how they re-start might get you some interesting answers. I think miningman is having similar thoughts on the speed of start up.

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

WEBALL, I concur with Littleinch's comments regarding hose geometry at the base of the tower. I couldn't articulate why I don't like it, but Littleinch's suggestion, or at least a long sweep 90 degree elbow would eliminate my concerns. I have to admit that I have zero experience with piling but I do know that pumping downhill is a lot more problematic than pumping against gravity. And there was something about having a long vertical hose on the hose discharge that concerned me , but again I couldn't articulate why. So yeah , Littleinch's suggestion regarding vacuum makes sense, and yes, slow, low pressure at restart up is just good practice at all times. Of course all of this is leading towards poor operating practice as the root cause. As a lowly equipment supplier, trying to defend the integrity of your product, you and the end user may want to engage the services of an experienced independent pumping specialist to provide review and recommendations on the existing operating techniques.

Having said that , perhaps it would make sense to inquire as to any possible changes in the chain, since almost 300 piles appear to have been sucessfully completed. Any personnel changes at the batch plant or pump?? Any reason to think the mix design has changed, either deliberately or inadvertently?? Is air entrainment or Super P being used in ideal quantities. Has the overall length of pump hose increased??

PLEASE STOP THIS POST ... There is a reply missing I made to Miningman with details of the pump and a proposed question to Little inch.
This is a large amount of missing information.
I will try go back to my post to Miningman as it was extensive. thank you

There is something wrong with this thread, I made a big reply to Miningman with attachments.
the attachments where the details company specs of the concrete pump. and pictures.
I can remember most but I will need to post again.
Can I ask please did either of you receive a post that had "Occam's Razor" in the last few lines ?

nope, nothing at this end. There is probably a limit as to size of attahments

Never saw it either. Maybe the site was doing some maintenence during the quiet period?

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

Hello Littleinch - Miningman,
My reply to Miningman was approx 8:00 and 9:00 am on the 28th with the full spec of the pump and a reply from a third party that visited the site and witnessed a lot of blockages.

Littleinch you must have seen part of the reply as you have made comment on the two cylinder rod adding annulus side to piston size yet it does not show my post above proposing this.

** it mixes things up a little and will mean me going over - re sending details. But I will reduce size of files.
(not sure if there is a way of asking the administrator for lost sections of threads).

My reply to Mining man was a copy of an email from site visitor, this is it :- below
""I agree, as I have said previously, I don’t think we have got the full story of exactly what happened in both these failures, nor do I think we ever will.

During my time on the project they did not have a dedicated pump operator stationed at the controls of the pump, one of the crew would start pumping and walk away to the rig, when there was a blockage (which was often, as I recall 5 out of 6 attempts) he would run back over to the pump and stop the pump. Bad practice was most certainly occurring during my visit.

This type of pump can be set up rod or piston side, one higher pressures than the other, one for vertical distance the other for horizontal distance.not sure how Roterra pump was set up, no one ever checks this.

As I have said before, I do know they have had a lot of blockages due to their inexperience""

The pump manufacturer has not relied to my email and it has been a month, I do not have first hand experience with pumps, this one I am told was brand new. I do not think there is anything wrong with the pump, but I wanted their feedback in the interest of safety and correct operating procedures.
The pump is a Schwing SP 1250
I have attached a single sheet of the pump specs it is a PDF file.
I have had to put more than twice the 'energy' into the 5" line to get the hose to fail, even on a part crimped end. there is something happening that I am not aware of.
I will post more later.

• https://files.engineering.com/getfile.aspx?folder=e4458e24-d634-478a-8f44-7

WEBALL:
To add to LittleInch’s and Miningman’s posts, there will also be some funny and indeterminate pressure pulses, thrusts, forces/stresses and hose movements around and either side of any direction changes, elbows and the like. I would make some length of straight solid pipe at these locations and then the coupling to hose, on the straight. I would be inclined to make as much of the total run solid pipe (not flexible hose) as I could, and carry the solid pipe a length or two away from any size or direction changes. Certainly, going up and half way down the pilling leads could be semi-permanently fixed to the leads, with the last 30-40’ being hose for the flexibility needed at the end. Then, at the foot of the leads you would have an elbow and several sections of solid pipe to some hose which allowed some flexibility and rigging movement. then you could have solid piping to the pump.

You (we) have a better handle on what’s going on with real straight/linear conc. flow and a much more uniform and constant pressure and stress, while you could have some nasty pulsating, lateral forces/trusts and thus stresses and hose movements in the immediate area of any change in pumping line direction. Maybe, as part of your hose package, you should offer (insist on) various solid pipe elbows and bends with 5-10’ of straight pipe on each side of the bend, along with the appropriate hardware for a hose coupling connection.

Finally, you are building a good record (file, defense?) for your case, that your hose and connections are generally good when not abused, and not used forever. Your testing, things like the e-mail from the site observer and discussion here, should be giving you some good ammo to go to the contractor with, to try to resolve this matter. While we all strive to please our customers or clients, honesty should flow both ways (without a conc. pump) when a project runs into problems like this. Don’t let them blow smoke up your leg.

Thank you dhengr, Merry xmas.
These jobs have been done with this type of equipment for over 25 years, I have been making them since 1994 ish and the 10ft/3mtr steel pipes. They do not use the steel pipes much on piling rig sites as they cannot flush/clean the line every time they reposition.
we know it was very bad practice and inexperience with a good amount of naivety that caused these failures.

I have been on sites and seen the rig track over pipes to break a 'slug' in hot sunny weather and many other bad things. But this investigation is more to get safety to the top. In Oil hoses you can fit Dry-breaks and put gauges direct in the line, but not possible with concrete.

The pump companies are not trying to create pressure, that is just the bad side of creating force to push wet concrete along a line.
I can keep fitting hoses and testing all day, but my results are similar each time. We have supplied thousands of hoses and pipes, normally they get changed when they show external wires from pulsating along the floor or burst from external damage, sharp edges, around corners, it is about the most aggressive use a hose can get on rough stone sites.

What I am striving to find is how this much energy is getting in the line. The man I had visit the site has 30 years experience and was a Rig driver. They have now started a new rule in the UK where there has to be 2ndary containment, but this is last resort, and still dangerous. putting lower pressure flex's for land lines is a good thing as these go first, but if you have a well trained crew they can get a set of 100 mtr hoses lasting over a year. There is a good amount of skill in a good team.
i am doing a set of drawings to post as I think something is happening that we are not aware of. Occam's Razor is a good place to start.
thank you, have a good new year.

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.

• https://files.engineering.com/getfile.aspx?folder=41deab46-b2a6-4371-ba52-5

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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