Knife gate valve erosive wear from abrasive flow
Wear observed upon failure of the original valve, with leak path to atmosphere (site photo – standard knife gate valve – 2004).
The Beginning

In the early 2000’s, a Canadian Oil Sands facility was using knife gate valves to modulate slurry flow from their Primary Separation Cells. 

When throttling a knife gate valve, the highest flow velocities (and wear) will occur within the acute angles formed at gate to body interface. 

At that time, the service life of these heavy-duty valves was measured in days (typically 3 weeks). Upon failure, the system was shutdown, the knife gate valves were removed/discarded, and new units were installed.

These recurring expenditures in new valves and labor were significant; however they were minimal compared to the lost production revenue. The frequent shutdowns were costing the company millions annually. There had to be a better way…

Prototype 1.0

To improve valve performance, we initially manufactured a ‘metal seated’ valve with the gate and seat ring made of Hardox® wear plate (55 HRC). This harder material improved service life by 50%, to 4.5 weeks.

We noticed the same wear pattern was occurring between the gate edge and valve body.

Knife gate valve wear on Hardox gate and seat ring
Knife gate valve built with Hardox® 500 gate and seat ring.
Knife Gate Valve with smooth bore, flush with Pipe ID
Valve with smooth bore, flush with pipe ID.
Knife Gate Valve with Ni-Hard deflector ring
Ni-Hard deflector ring.
Prototype 2.0

To reduce turbulence, we manufactured a valve without the seat ring, providing a smooth bore that was flush with the pipe ID. The gate and bore were again made with Hardox®, and we included an additional Ni-Hard deflector ring.

Service life now tripled the original valve; pushing the benchmark to 9 weeks with this latest iteration.

Prototype 3.0

The third valve we worked on had the same basic design, but incorporated field replaceable gate and bore liners (again made with the Hardox® material). 

Service life remained at 9 weeks, however the client’s replacement expenditures were reduced, as the valve body could be re-used upon failure of the replaceable wear components.

Knife gate style valve with replaceable bore liners and gate.
Valve with replaceable Hardox® bore liners and gate.  
Valve with concave gate design
The bore liners and narrow gate (with convex tip) protect the valve body from erosive flow.
Acute angles between gate and bore liners valve
The acute angle formed at the gate to bore liner interface remained an area of high velocity flow.
Prototype 4.0

By narrowing the gate width, and modifying the tip from convex to concave, only the replaceable Hardox® gate and bore liners were exposed to abrasive flow. This was a design breakthrough for the team, and a feature we later Patented.

Although service life was bumped to 12 weeks, the acute angles between the gate and bore liners remained. These areas were ultimately the point of failure.  

Prototype 5.0

Upon failure of the latest Hardox® gate and seat plate, we manufactured the replacement components with stainless steel, which were hard coated with a Tungsten Carbide weld overlay (75 HRC).

The client inspected the valve upon 12 weeks in service, taking photos that clearly showed the excellent wear resistance of tungsten carbide. This latest material upgrade provided an impressive 26 weeks of service, with the mode of failure being high velocity flow within the acute angles.

Tungsten Carbide Overlay on valve replaceable wear components
Bore liner with Tungsten Carbide weld overlay, applied via PTAW process (75 HRC).
valve gate and bore liner showing no erosion wear
Concave gate tip and bore liner during a performance inspection (12 week milestone).
Control valve incorporating seat plate for centered orifice
New ‘seat plate’ design eliminates the acute angles.
No signs of wear to tungsten carbide overlay on valve gate or seat plate
Negligible wear to the tungsten carbide weld overlay. The six holes (intended to increase Cv) were removed on subsequent seat plate designs.
Prototype 6.0

To finally eliminate the acute angles, we modified the upstream bore liner to incorporate a seat plate. This trim geometry filled the gap on the sides of the gate, leaving a centered orifice with linear control. Again, these trim components were manufactured with stainless steel, and coated with our tungsten carbide overlay.

This latest prototype worked well, except for the wear experienced within the six holes (which could not be coated with tungsten carbide). A replacement seat plate without the holes was installed, and the service life of the valve increased to 54 weeks.

Production

SlurryFlo Valve Corp (now 'Special Alloy Fabricators') officially opened its doors in 2007, with a patented new linear control valve for abrasive mining applications. 

Our valve technology has been installed at every major oil sands facility in Alberta, and in hundreds of severe service applications throughout the world.

It is common for SlurryFlo control valves to remain in operation 10x longer than the heavy-duty control valves they replace.

SlurryFlo Control Valve
SlurryFlo control valve render showing centered orifice in modulating position

Patented Design

Our Patented technology centers flow like no other control valve. Our variable orifice technology will outlast anything you've ever used.

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