SENTINEL Frequently Asked Questions

Acquisition & General Questions

What does it cost?

Rental prices begin at $675/month for a Model-C1 and range to $2,600/month for a Model A

Purchase prices begin at $8000 for a Model-C-1 and range to $31,000 for a Model A.

Should I rent or buy?

The availability of Sentinel was initially limited to direct rental only. This allowed Knew Value to monitor, make design adjustments and ensure success for each deployment. As our customer’s needs have evolved, we now proudly offer Sentinel skids for purchase. There are benefits to both leasing or purchasing. Our sales team is happy to help guide you based on your specific needs.

RENTAL • Very low initial cost. • Online Data Management included. • Full warranty on parts and equipment.

PURCHASE • Single, one-time capital expense. • Online data management optional. • Limited Warranty.

What is online data management?

Online Data Management includes capturing of pictures and exposure period data as well as transmission of both photos & data for reporting purposes. The transmission allows for experienced assistance in result interpretation. For leased units, this is included in the monthly cost.  It is available as an optional monthly contract for Sentinel units that are purchased.  An online customer dashboard will be coming in late 2018.

How does maintenance work?

Typically, following review of our operator’s manual and extensive video support page, your local site team (plant maintenance or I&E) can easily assist in the installation, initial startup, and periodic tube specimen changes in the Sentinel. In the event you would like us to assist directly, we are available, either for an in person site visit or via remote video link.

How is shipping handled?

All freight, licensing, customs fees, etc. are the responsibility of our customers.  Knew Value is not an equipment exporter due to the variable requirements from different locals.  We are happy to work directly with your logistics team to determine the best way to transport the equipment to you.

What are some evaluation options with the two exchangers?

The two exchanger design allows customers to set up a variety of evaluations.

• Two different metallurgies can be evaluated at identical skin temperatures and velocities.
• The same metallurgies can be evaluated at identical velocities and varying skin temperatures.
• The same metallurgies can be evaluated at identical skin temperatures and varying velocities.
• Two identical metallurgies at the same skin temperatures and velocities can be exposed for different periods (30 day and 90 day) similar to corrosion coupon exposure periods with the very significant difference of measuring the actual corrosion in the exchangers being modeled on the bulk water corrosion rate from a non-heated surface.

Technical & Operation Questions

Why is Sentinel better than a DATS unit?

The DATS technology is only monitoring scale and is not able to be visually inspected while online.  Likewise, there is also no measurement or real time monitoring of corrosion nor is there any ability to visually detect bacteria.

How does Sentinel measure corrosion?

The 0.5″ tube specimen inside the Sentinel is pre-weighed before use and then cleaned by the NACE standard method and re-weighed to determine metal loss over the exposure period.  Pit depths and other corrosion analysis is performed on the outside surface of the tube that has been exposed to the cooling water.

But what about my corrosion coupons?

A corrosion coupon is not a heated surface and does not have heat transferring through the metal.  This process, while having been used for decades, does not give realistic results and even possibly a false sense of security.  Sentinel not only takes the place of corrosion coupons but does triple duty by being a corrosion monitor, deposit monitor and a scale monitor.  The heart of Sentinel is a single tube annular exchanger which transfers heat into the cooling water just like a typical exchanger in the process.  It does this with a patented liquid-to-liquid design which insures uniform heat transfer and realistic results.

Will Sentinel corrosion rates match the coupon results in my system?

Not likely.  Coupons are not a heated surface and are not transferring heat through the metal like the plant exchangers or the Sentinel exchangers.  Corrosion mechanisms change significantly and exponentially when heat passes through the metal.

How does Sentinel measure scale or deposition?

There is no attempt to measure deposition online.  It is evaluated just like during a turnaround: by observation.  Samples are then taken and sent to the lab for analysis.  Because the tube specimen is pre-weighed before exposure to the cooling water, theoretically one could weigh the tube dirty and attempt to determine the accumulation of deposit.  This has proven difficult due to the deposit drying out rapidly and falling off the tube after it is removed.

Does Sentinel measure bacteria fouling?

Yes.  Bacteria can be observed online following an excursion or whether treatment is insufficient for control.  When the tube specimen is removed the tube can be swabbed and analyzed.

How quickly will Sentinel tubes reflect the cooling water performance?

This all depends on the quality of your cooling water treatment program.  In systems where severe corrosion is being experienced, we have seen carbon steel tube specimen visually exhibit pitting corrosion within just seven days.  In systems where the value of Sentinel is for ongoing visual results, we have seen plants leave tubes in for up to 180 days.

What are the power requirements for installation of the Sentinel?

For all models, there is a specific terminal block to land power directly to into the unit, typically directly from a dedicated breaker.  For standard 120v configuration the requirements are as follows:

Model A: 120vac – 30amps

Model B-2: 120vac – 20amps

Model B-3: 120vac – 30amps

Model C-1: 120vac – 15amps

Model C-2: 120vac – 20amps

Please contact us if you have questions about configurations and power requirements where 240vac is standard.

How often should we pull the tubes to measure corrosion and fouling?

There is no set exposure time for Sentinel exchanger tubes.  As referenced in the question about the speed of visual results, this might be as soon as a few days or as long as multiple months.  This is up to whoever is operating the deployed Sentinel.  Generally, it is based on seeing significant results that may need further analysis by removing the tube specimen.

Why do I need Sentinel if we are monitoring performance via sensors or periodic exchanger monitoring?

Sensors and exchanger monitoring do not measure corrosion.  Results cannot be visually observed online during the exposure period. The clear shell of the Sentinel exchangers allow for ongoing observation and photographs while in service.  The camera installed in the Model A & B units transmit pictures to our server for ongoing hands-off reporting.

How is Sentinel monitored to insure the plant exchanger conditions are accurately modeled?

Knew Value data logs the flows and temperatures of the exchangers and records the information locally on an SD card as well as transmitting it to our server where is can be reviewed by Knew Value or customer personnel.

Is Sentinel certified for Class I Div II locations?

The primary design of the skid is non-classified, however we can equip it with an optional air purge which typically satisfies requirements for classified areas.  For more stringent classified areas, independent lab certification is also available at cost.

History of Sentinel

Why was Sentinel developed?

Sentinel was designed and built to fit a need in the monitoring of industrial and HVAC cooling water performance that has existed for many years.  Previous methods of simulating a heat transfer surface resulted in poor, unrealistic results due to non-uniform contact between the electric heating elements being used and the inside of the tubes.  This was overcome in Sentinel by using a liquid simulated process that provides uniform contact and heat transfer to the tubes.  Therefore it provided much more realistic results.

Knew Value has an extensive database of cooling water exchanger design and actual performance conditions as a result of being in the cooling water exchanger monitoring business for a number of years.  This database was used to create the design parameters we had to meet to create a tool that would realistically meet industry’s needs.  We sampled over 1,000 exchangers in refineries and chemical plants in North America to determine the following conditions:

Design versus Actual conditions for

• Skin Temperature
• Velocity
• Heat Flux

We then compared average, minimum and maximum values for each criteria.

From this analysis we determined the design criteria for the skid and set out to achieve our objective.

Has Sentinel changed over the years?

The first design was a multiple tube, removable bundle exchanger approximately 3 inches in diameter containing from 10 to 20 tubes which were 18 to 20 inches long.  This very large surface area presented some unique challenges in heating the simulated process stream sufficiently to achieve the desired cooling water skin temperature.  In order to accomplish this a 480 Volt, 3 Phase heater was required.  While this model achieved all of our design criteria the resulting tool was very expensive and a challenge to get plant acceptance for its use.

What does the design look like now?

In an attempt to make the skid more user friendly and cost effective we modified our exchanger design from a multiple tube, removable bundle to an annular exchanger.  This is a 0.5 inch tube inside a 1.0 inch outer tube which is a clear polycarbonate material which allows users to observe the cooling water results during the exposure period.  This significantly reduced the surface area of the exchanger and allowed us to mount two exchangers in the skid which are piped in parallel.  This affords the opportunity to run simultaneous tests during the exposure period.  The much smaller surface area also resulted in a heater design which lowered the power requirement to a max 120vac, 30 amps.