The Sparta Steel Mast
The story of how one small engineering firm set out to innovate the oilfield
SPARTA ENGINEERING got its start designing and building agricultural equipment with CBI Manufacturing out of Linden (Alberta) roughly 10 years ago.
“We didn’t start creating and producing oilfield equipment until an oil company driving through the area identified our ability. They told us if you can build a grainbox, you can build an equipment truck.”
And so…Sparta’s journey into oilfield products began.
Starting with basic 5-ton equipment trucks, Sparta now has a complete line of service rigs (workover rigs) and support equipment. Sparta’s flagship product is their service rig that was designed and engineered from the ground up. At the heart of the service rig is the unique plate steel mast – engineered using high tensile steel. When Sparta made the commitment to compete in the manufacturing of service rig equipment they set out to do things a little different. This is the design and development story of the Sparta Plate Steel Mast.
A Vision for a New Steel Mast
To gain a world class understanding of the engineering behind the entire service rig system, Sparta decided to start from the ground up. Rather than standing on the shoulders of what has been done in the past, Sparta set out to challenge the industry standard on material, weight, and manufacturing processes. Considering the mast or derrick design hasn’t changed in more than thirty years, their task was not an easy one. Their goals were simple:
- Utilize computer-based engineering software to take full advantage of modern manufacturing processes and modern materials
- Produce a mast that was at least 15% lighter (than standard) while maintaining a 200,000 lbs hook load
- Be period one legal with a fully dressed tand-tri axle configuration on the carrier
Conceptual Design of the New Steel Mast
At the beginning of the mast design phase, Sparta’s engineers concluded that by developing a rig mast out of QT 100 high tensile steel, there would be a substantial reduction in the weight of the mast. By using higher strength materials which are roughly twice the strength of normal mild steels, Sparta could reduce the amount of materials while maintaining an equivalent strength. These enhancements to the design of the service rig mast have revolutionized the industry.
The development phase of the period one double service rig took place in stages with the first stage seeing a redesign of the crown and upper mast. Once these components were developed to a point where they closely resembled the final design, work on the lower mast began. After the reactions from the base of the lower mast were calculated, the sub-frame (a-legs) was designed. A refining iteration was the next step, going from the crown through to the lower mast, making changes to some of the details of each major component.
The Development Phases of the Mast:
During the development phase, design details were refined and the analysis was completed. This included optimizing for manufacturing and weight. Here are a few snap shots of these iterations:
Each iteration (list to the left) was intertwined with a series of analyses proving the concept for each of the loading scenarios. This included a situational analysis specific to the mast.
Analysis was done using Finite Element Analysis (FEA) software (SolidWorks). Using computer software, engineers sectioned the entire geometry of mast into tiny triangles and associated a series of equations with each triangle.
After telling the computer what happens to the triangles at the boundaries of the geometry, one can apply a load to the geometry. The computer will calculate in a cascading effect how one triangle affects the triangle next to it and so on until deflection and stress is calculated for the whole body.
This proves to be very difficult on an object with geometry such as a mast. When analyzing an object 105’ long with members only 0.25” thick, the resolution required in order to get the 0.25” plate to behave properly results in an analysis that takes several hours if not days to run.
Step 1: Apply Loads
The first step is to define and apply the loads and restraints to the geometry. For example, adding in a hook load for lifting as well as a wind load as defined by API 4F.
Step 2: Mesh the Geometry
Next we tell the computer how to split the geometry up into individual triangles. There is a lot of finesse and refinement in order to get the right balance between resolution and analysis run time.
Step 3: Review the Results
As with any computer program, garbage input is equal to garbage output. Reviewing the results is an important stage to make sure the results being calculated are relevant and behaving the way they should.
Why Use This Style of Analysis:
There are approximately three different approaches to completing the engineering on a mast:
- Hand calculations using factored bending resistance of beams
- Beam analysis
- Solid geometry analysis
These are roughly in order of complexity and time from least to most. However, they are also ordered in the same way with respect to quality of answer. Each analysis class has a different set of assumptions and takes the analysis to a different level of detail.
The primary reason Sparta Engineering uses solid geometry analysis is that it doesn’t make any assumptions about the product being of uniformed geometry. Both hand calculations and beam analysis (to some degree) assume the cross-section of members is constant. With solid geometry analysis, one can get really fine results and implement stress coping strategies such as tapered gussets, repads and other complex geometry. This allows engineers to address localized stress with a localized solution rather than just increasing the thickness of the whole member. This strategy, when applied to an entire project, nets you a significantly lighter product.
- Sparta was able to meet their 15% weight saving goal through the use of high tensile steel for webbing and tubing. The higher strength material allowed for a reduction in steel thickness in areas of high stress while still maintaining equivalent strength.
- Through the use of quenched and tempered steel, Sparta was also able to improve the cold weather performance of the mast by reducing the risk to brittle failure caused by the ductile brittle transition point. This makes the product more versatile and adaptable for working in the cold Canadian winters (common in Alberta and Saskatchewan).
- A considerable amount of time was spent optimizing the weld pattern and cutting away steel that wasn’t needed. One of the concepts that arose from this process is the idea of cutting away material where welds were unnecessary. Where intermittent stich welding is sufficiently strong, holes were cut in the plate so it is impossible for the welder to add more welds than engineering intended. It also made it obvious if the welder missed a weld that was required. Anywhere two pieces of steel meet – a weld was required. This ensured a consistent product and kept welding related decisions in engineering rather than relying on the welders themselves.
All the components are designed around 20’-24’ sheets of plate steel and parts were optimized for minimal waste and efficient handling time. These parts can be on a plasma table which has high linear inches per minute cut on the waterjet (where parts can be stacked to cut multiple units at once).
The plate steel mast project was a huge success for Sparta Engineering and Sparta has continued to develop the product to this date. Recent innovations include:
- a laser guided jig used to weld the main hinges without having to test-fit the mast
- a bolt together crown section to improve material handling and make the mast size adjustable
- a three-sided version for use on smaller flush by rigs and rod rigs