One of a pump operator’s worst fears is a plugged pipeline. Some believe this to only be a concern when dealing with extremely heavy slurries but this is far from the truth. Today we will discuss several causes of plugged lines and how to avoid these highly expensive and time-consuming problems.

1. “Sanded in

Is the most common form of pipe plug. It stems from insufficient pipeline velocity (flow rate) to maintain solids in suspension. Generally it manifests slowly and can be avoided by monitoring flow instrumentation or energy consumption. Upon identification of a problem developing, the operator can correct the issue by flushing his line and increasing the flow rates. This will also help to avoid a reoccurrence. (see image below)

Fly Ash Slurry Pipeline

2. “Growth rings”

Are a gradual build-up of concentric deposits that, if viewed in section, resemble the growth rings of a tree. It is an insidious problem that quietly manifests itself over long periods of time. (see image below)

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Growth rings are most commonly associated with slurry systems that are transporting very fine particles.  Lime slurries would be a classic example of this. Every time a lime system is shut down, a thin coating of the lime is left deposited on the walls of the pipe. If the system remains shut down for long enough, the product will dry and a growth ring is formed. This will continue to happen each time until multiple growth rings are present.

System designers are generally aware that specific products/solids have a tendency to “plate out or build up” and form growth rings. They avoid the formation of growth rings by adding a flushing procedure as part of any shutdown operation.

In cases where preventative flushing has not been added to the shutdown operation, operators will observe a very slow increase in system back pressure. In most cases, chemicals can be added to reverse the growth and “pigs” can also be utilized to clean the line. However, sometimes line replacement is simply the best solution.

3. “Bottom Scale”

Is very similar to growth rings but does not necessitate a fine product that can coat the entire inside of the pipes surface. Instead, it is created when any product with a hardening factor is not flushed out over time, but is left to solidify in thin layers on the bottom of the pipe. (see image below)

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Detection, prevention and corrective action are the same as with growth rings for this issue.

4. “Zero Flush”

A pipe line which is not flushed relies on proper grading and very low solid settling velocities to stay “clean.” If either of these prerequisites are not met, problems can result.

If the grading is close and/or the product has a reasonably high settling velocity, partial blockage is highly likely. If the system is restarted before the product can harden, re-establishing the flow, the problem will normally be corrected. (see image below)

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If the grading is poor and the product has the ability to sluff, solids can move into low spots in the pipeline and completely block the pipe. In many cases, restarting the system will not reestablish flow and you will have a plugged pipeline.

5. “Corking the Line”

Continuity of flow in any system relies on a balance. At any given time the TDH (total dynamic head) output of the pumps must be able to match the resistance imposed by the flow through the piping system. In slurry systems, that balance must also be maintained with a flow that supports  velocities above the critical settling velocity.

When a pump suddenly ingests a very high level of solids, it is close to starved of liquid. As such the pump and the pipe immediately attached to the pump are saturated with solids. The impeller vanes, now plugged with solids, fail to provide liquid flow and pressure. At the same time the system head, due to the high concentration of solids within the pipeline, skyrockets and flow stops.  This sudden plugging of the line is referred to as corking the line (or pump) and is most commonly associated with a cave in on submersible dredge pumps. It can also be a result of over feeding solids or underfeeding liquids on process pumps.

6. “Bottom Ice”

A pipeline which is not perfectly graded (most pipelines are not) and completely drained can have “Bottom Ice” problems if restarted in cold weather.  This is an issue for both water and slurry systems. (see image below)

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Properly graded and drained pipelines still tend to have portions of the pipe where there is some residual liquid. This liquid pools in the bottom of the pipe and will freeze in extremely cold conditions. If the ice is gradually released into the liquid stream, there is little effect on the system.

I have however visited a site where this was not done. In an effort to make sure any potential frozen portions of the pipeline could be cleared; a hot liquid was rapidly diverted into the empty pipe.  The thermal shock immediately dislodged the half-moon chunks of ice that were attached to the bottom and instead of quickly melting, they formed a 100-meter-long ice jam. Unable to establish flow, the entire portion of the pipeline between there and the pump froze solid in the subzero weather. The pipeline was then abandoned until the spring thaw.

We have not covered all the potential ways in which pipelines can be plugged, but there is however a common thread within the ones we did discuss in this article. That being: “good systems planning can avoid almost every plugged pipeline”.

Plan out your system, have good operating procedures in place and, above all, don’t hesitate to ask for professional help.

Learn about the industrial pumps that Hevvy Pumps has to offer your project:

Read the Slurry pump maintenance guide to learn how to maintain your slurry pump for optimal performance. View slurry pumps USA options and distributor locations.

Talk to Hevvy Pumps for more information.

Bye for now!

RJ

In-depth Knowledge on Solving Seal Failure in Dewatering Applications

If you are an owner, operator or user of Electric Submersible pumps in Mine Dewatering and currently experience multiple seal failures within one year of start-up and installation… Please read on. Additionally, if you are a fellow professional in the field that wishes to share observations and constructive comments then please feel free to respond to this post.

Most customers who I meet spend large amounts of time constantly changing seals and/or repairing and rewinding motors as a knock on result of an initial seal failure. The fact is that a majority of the failures that occur in electric submersibles are attributable primarily to seal failures.

Ask your maintenance team this one questions:

How many submersible pumps have we repaired in the past 2 years?

I would make a sportsman’s bet with you that nearly all of those pumps have been pulled from their installation because of performance concerns related to the seals.  If that was your new vehicle, would you accept having to hand it back to the dealer once, twice or three times a year for a full strip down of the engine, transmission and chassis? Some of these pumps cost more than your average family car, so why do we accept failure on this scale?

Is it the fault of the seal? In most cases the answer is no. It is simply the wrong seal for the application.

After traveling to various sites I’ve noticed that most owners are more focused on keeping the process running while the multi-tasked maintenance foreman does his best to keep up with never ending pump failures. Here is prime example:

I recently visited an underground mine where the population of electric submersible “Dewatering” pumps numbered close to 80 pumps. Up to the first 6 months of this year (2017) the mine had spent close to $600k on pump repairs and replacements. This was a pretty typical application pumping runoff sump water and slimes from level to level via 4” piping laid overhead along the ramps.  The mine superintendent advised me that he received great service from his local pump supplier and qualified that by adding that: “Everytime a pump breaks down they bring us a new or refurbished pump.”    Pardon me for asking but isn’t that just buying into a model that rewards failure?  Much of this culture is driven by the desire to keep the mines dewatered and de-slimed at almost any cost and I totally get that. However the deeper question is: Why do these pumps keep failing and is there a more reliable pump solution that will allow me to spend $600k where it is really adding value to my company?

Does this look familiar?  This is a typical submersible dewatering pump return blocked up with dry slimes.

The video link below will partially explain why most dewatering pumps fail in de-sliming services.

Quite simply put you are asking an unmonitored and unattended pump, designed to pump water with no more than 1 to 2% solids, to pump a 30% cw (Concentration by Weight) slurry that consists of highly abrasive media suspended in clay and other abrasive substrates. The Hydraulic Institute would categorize this as Class 2 or Class 3 slurry. The majority of pumps in service underground are light to medium duty dewatering pumps and not slurry pumps and once the water level is drawn down they find themselves immersed in the settled solids. These clog the basket strainers resulting in dry running and overheating of the motors. The dry running will certainly kill the mechanical seal and the subsequent overheating will kill the motor if not fitted with thermal protection.

So what is the solution?  It is here that I should offer you a Hevvy/Toyo Pump solution but unfortunately it is not that straightforward. Providing a high head, dry running slurry pump that can handle the solids up to 75% cw is the easy part; we face and meet that challenge on a daily basis. 

The challenge is to pump the much heavier solids through existing piping infrastructure that was originally designed to carry water and light slurries.  Friction losses increase, pumping pressure increases, wear increases, power increases; all of which the pump can be designed to overcome.

A balance has to be struck whereby the consistency and SG is altered by producing a more homogenized and lighter mix of water with solids.  By utilizing the correct design of agitated submersible slurry pumps it is possible to create a mix that can be readily pumped through the existing pipeline without the need to upgrade the line. If done properly, this can totally eradicate the need for “mucking out” with the UG mine front end loaders thus realizing another saving. The longer term trade-off is replacement of piping periodically. This all sounds simple, and it is, but a commercially viable compromise has to be made whereby the cost of installing a submersible slurry pump provides maintenance and process benefits as well as lower operational costs…..BUT ABOVE ALL a reduction in the amount of unnecessary time entering the sump areas which present  many safety hazards.

So back to the the constant failure of seals. If the pumps are not fitted with a suitable slurry seal then you cannot reasonably expect them to last a long period of time in a slurry application. You need to assume that if it’s going into an underground or any open pit sump that it will see abrasive particles and slurries at some time during its life and that is where you ask if the seal is capable of handling slurry.

I would invite you to contact our experts at Hevvy/Toyo Pumps. We will conduct a complete audit of your pumps and demonstrate where it makes sense to utilize slurry submersibles. We offer comprehensive no hassle Try and Buy programs to prove the integrity of our pumps in your system. We will perform hydraulic design calculations for your existing pipework to ensure that your performance and system curves intersect at or as close to best efficiency point (BEP).  Our network of regional sales and service managers as well as extensive distribution coverage ensures that you will always receive prompt, professional and courteous advice.

Learn about the industrial pumps that Hevvy Pumps has to offer your project:

Read the Slurry pump maintenance guide to learn how to maintain your slurry pump for optimal performance. View slurry pumps in USA options.

Talk to Hevvy Pumps for more information.

To discuss the right Hevvy Pump Solution for your sumps please contact us at: mining@hevvypumps.com