CASE STUDY | Tailings Knife Gate Valve

The following case study documents the results of a trial installation of a Delta Industrial knife gate valve. The valve was installed in a slurry and tailings system for a major copper, uranium and gold producer.

The client for this case study is a major copper, uranium and gold producer. The mine has a unique slurry and tailings system which operates at a pH of 0.9 to 1.2. The slurry is abrasive, corrosive, scale forming and slightly radioactive. Valve failures reduce the plant’s mechanical reliability and also contribute to safety and environmental challenges. These failures result in additional costs for maintenance and repairs and negatively impact the total cost of ownership of the valving assets.

pushthroughstyleknifegate[1]

The Problem

Push-through style knife gates were used to isolate the mine’s 400mm class 300 tailings system. The previous knife gate valves used a SAF2507 body and gate with an EPDM sleeve. The valve had to be “wide-bodied” to sustain class 300 operating pressure. However, it had recurring issues including:

  • Frequent seat failures as often as every 2 months or around 140-160 cycles
  • Valve body blow outs
  • Slurry leaking from the top of the sleeve
  • Recurring blockage of the bottom drain port and subsequent drain pipe work

These valves were maintained on a weekly basis by a designated maintenance team.

In order to prevent seat failure, the OEM recommended a lubrication system placed directly on the valves. This then lead to yet another system to maintain, another potential failure mode, another potential environmental issue, more products inventory and a significant increase to the total valve asset cost.

The cost of a new sleeve was $13,000. Additional associated costs include a crane rental, labour to replace the sleeve and higher weekly maintenance. Added together, each valve asset would cost approximately $20,000 to $30,000 ever 2-3 months. This valuation does not include the price to repair a valve from a body blowout or the addition of the proposed lubrication system.

CGIS was retained to find a valve that would last longer and required little to no maintenance. With reduced time spent on maintaining valves, CGIS consultants believe the maintenance team could concentrate its efforts on more critical equipment and at the same time reduce risk of catastrophic failure and the need to stop production.

CGIS Solution

CGIS visited the site in 2012 and after reviewing the application, recommended the following specification:

  • SAF2507 body and gate, Xylan coated
  • Chrome carbide overlay on the gate tip and bore of the valve
  • Valve bore matched to the pipeline.
  • SAF2507 upstream wear ring with tungsten carbide overlay.
  • Aflas primary seal, metal to metal secondary seal

A trial valve was installed in May 2013. The Delta Knife Gate was lighter and quicker to install than other valves. Bi-monthly inspections were completed with the final inspection in December 2013, after 6.5 months of operation and 303 cycles.

CGIS observed that there was zero maintenance and zero failures during the trial period and the valve proved a reliable bi-directional seal when required. The final inspection showed no visible wear on the gate tip, seat or wear ring. It was recommended that the valve be put back into service.

deltaknifegate

Conclusion

As of January 2015, the same trial valve has been in service for nearly 20 months with zero maintenance and zero failures. Upon further inspection, the upstream wear ring was deemed to have worn from the 4 o’clock position to the 7 o’clock position. During the installation of the new wear ring it was noted that the original wear ring could have been rotated 180° to extend its life. Delta Industrial’s ability to achieve the full class 300 pressure rating with thinner face to face dimensions was impressive. These dimensions made removal and inspections easier, quicker and more cost effective.

For 20 months of continuous service, the cost to maintain the trail valve was $10,000 – including the cost and installation of the new wear ring. Taking into account the best case scenario, the original push-through valve would have cost a staggering $140,000 for the same time period. This estimated cost does not include loss of production, especially if a catastrophic failure occurred, and valve body repairs. It is also important to highlight that the initial purchase cost of both the push-through valve and Delta Industrial knife gate valve were comparable.

CGIS observed that the Delta Industrial knife gate valve has given the site much more reliable tailings disposal isolation. The Delta Industrial knife gate is a more predictable valve that has significantly extended the life of their valving assets, allowing seamless preventative maintenance and dramatically reducing maintenance costs.

Because the Delta Industrial valve is not a push-through style knife gate valve, it eliminates all of the typical knife gate failure modes seen on mine sites around the world.

Delta Industrial’s ability to provide repeatable zero leakage isolation is proven through the flexibility in its design. It has the ability to withstand high solids, abrasive, corrosive, and scale forming media in low or high cycle applications.

It has proven to be a truly low cost valve solution.

Written by Pascal Hatzipalousis

Business Development Leader, CGIS

As published in the IPP&T September 2015 issue.

Contact Us

Please complete the form below

558 East Kent Avenue South
Vancouver, British Columbia
Canada V5X4V6
Phone: 604.263.1671
Fax: 604.263.0947