Plug Valve Inserts

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Cellular Manufacturing: result in short lead times, lower inventory, and better cash flow

In the oil and gas pressure pumping industry, where activities like hydraulic fracturing, acidizing, cementing, and other well interventions are performed, working fluids are nasty and pressures are dangerously high. Flow control of the highest-pressure fluids (15,000 psi) is achieved using plug valves. Due to this high-pressure environment these ductile iron plug valve inserts require frequent replacement. To function properly and safely, the inside diameter that mates with the plug must be manufactured with surface finish roughness < 2 rms and size tolerance less than 0.001 inches.

Challenge

Unpredictable Demand: Anyone familiar with the oil and gas industry knows how the volatility of demand can fluctuate, leaving various segments of the supply chain vulnerable to excess inventory.
O-ring Groove: These inserts have an O-ring groove in a 10° conical surface, a deceivingly complicated feature to machine accurately.
Expensive Raw Material: Plug valve inserts are traditionally made from trepanned continuous cast ductile iron round bar. While the iron itself is not relatively expensive, continuous casting and trepanning make the cost per pound on par with some super alloys.

Solution

“All solutions are simple” is a mantra and an ideal at LeanWerks. We start with a foundation of great people that includes journey level tradespeople and degreed engineers. Their expertise is strengthened by robust problem-solving processes to ensure successful results and manufacturing plans. In this case, the solution was a combination of our expertise in metallurgy and application of lean principles.

Metallurgy: Ductile iron gets its ductility from the addition of magnesium in the ladle called inoculation. Once magnesium is added, graphite inherent in the iron converts from flakes to spherical nodules imparting superior impact, fatigue, and ductility to the metal. However, this inoculation only lasts 14 minutes until the graphite converts back to flakes, so inoculated metal must be poured and frozen within that 14-minute window to maintain its superior properties. Understanding this, LeanWerks sought out a foundry with capabilities to create a near net casting with in-mold inoculation, which provides a much more uniform grain structure than that of continuous cast ductile iron. Each casting is consistent throughout the lot whereas a continuous cast bar has varying grain structure from the beginning of the bar to the end of the bar. A foundry was identified and a relationship forged that not only produced a near net casting with superior properties to bar stock, but also embraced small lots and frequent deliveries to combat the need to stockpile inventory. Raw material costs per part decreased by 66% (a huge impact since raw material accounted for nearly 50% of the finished part cost) and machining became more efficient as well due to reduced material removal and more consistent metal properties that allowed predictable cutting parameters and tool changes.

Lean: The traditional approach to this pressure pumping commodity was two lathe operations for the cylindrical features followed by two milling operations: one for the features normal to conical surface (O-ring groove and adjacent land) and one for the features normal to conical axis (side grooves). This approach was completed in large batches to optimize machine efficiency at each step. LeanWerks’ lean approach stared with a focus on the value-added operations and ensuring a smooth and continuous transition through the product realization cycle. Utilizing the latest in live tooled lathe and multi-tasking technology to facilitate the operation, LeanWerks eliminated huge amounts of work in process inventory, wasted movement, and scrap that dramatically reduced “dock to dock” time.

The next lean step was to equip the work area around the machining center with all the support equipment to finish the part while the next part was running on the machine. Those steps included: part marking, splitting, tumbling, oiling, bagging, and packaging. By mounting support equipment on wheels and having plentiful air and power drops around the machine, LeanWerks was able to achieve a “Single Minute Exchange of Cell” or SMEC so we could change from other parts to these valve inserts and back in a matter of minutes. The latest improvement implemented is standardizing pitch and predictive tool changes, both of which have netted additional reductions in scrap and increases in throughput.

Results

All of the improvements mentioned above, from higher quality raw material to lean value streams for production processes, significantly improved our customers’ experience through shorter lead times, lower cost per part, and lower inventory requirements ultimately improving customer cash flow and overall satisfaction. This was accomplished not by cutting corners to lower cost, but by using knowledge of the metallurgy combined with exceptional application of lean to increase value for all stakeholders.