Running casing is one of the most critical stages of drilling a well. Whether drilling for oil and gas, geothermal energy, mining or water wells, the entire weight of the casing string must be safely supported while connections are made. That responsibility falls on one essential tool—the API 7K Casing Slip.
Designed to grip large-diameter casing securely without damaging the pipe, casing slips are used on virtually every drilling rig worldwide. In this guide, we'll explain how casing slips work, the different CMS models available, how to choose the correct size, and what to look for when purchasing replacement inserts and spare parts.
What Are Casing Slips?
Casing slips are heavy-duty manual gripping devices that suspend casing inside the rotary table during casing running operations.
Unlike drill pipe slips, which grip smaller drill pipe and are available in Short, Medium and Extra Long versions, casing slips are designed specifically for larger, heavier casing strings. Most modern casing slips use circular button inserts that provide excellent grip while minimising damage to the casing body.
Typical applications include:
- Oil & Gas drilling
- Geothermal drilling
- Water well drilling
- Mining exploration
- Foundation drilling
- Workover operations
How Do Casing Slips Work?
When the casing string is lowered into the well, the slips are placed around the outside of the casing and lowered into the rotary table bowl.
As the weight of the casing is transferred onto the slips:
- The tapered body slides into the insert bowl.
- The weight forces the slips inward.
- Circular button inserts grip the casing uniformly around its circumference.
- The entire casing string is securely suspended while the next joint is made up.
The heavier the load, the tighter the grip becomes.
Why Are Casing Slips Important?
Modern casing strings can weigh hundreds of tonnes.
Proper casing slips provide:
- Safe support of the casing string
- Even load distribution
- Reduced casing damage
- Faster casing running
- Improved rig floor safety
- Reliable operation in harsh drilling environments
CMS Casing Slips
The most common style used worldwide is the CMS (Casing Manual Slip).
CMS slips are manufactured in accordance with API Specification 7K and are compatible with standard API insert bowls featuring a 4 in/ft taper. They are available for casing sizes from approximately 4 1/2" to 30" OD, with different segment configurations used to suit the pipe size.
| Specification | 3" – 4" | 4" – 4 7/8" | 4 1/2" – 6" | 5 1/2" – 7" | 6 3/4" – 8 1/4" |
| Model | DCS-S | DCS-S | DCS-R | DCS-R | DCS-L |
| PN: Complete | 20201 | 20202 | 20203 | 20204 | 20205 |
| Grip Length | Short | Short | Regular | Regular | Long |
| Weight (kg) | 51 | 47 | 54 | 51 | 70 |
| Total Segments | 7 | 7 | 9 | 9 | 11 |
| Intermediate Segments | 5 | 5 | 7 | 7 | 9 |
| Hinge Pins | 6 | 6 | 8 | 8 | 10 |
| Insert Bowl | No.3 | No.3 | No.3 | No.3 | No.3 |
| Die | 20228-49 | 20220-49 | 20228-63 | 20220-63 | 20230-88 |
| Specification | 8" – 9 1/2" | 8 1/2" – 10" | 9 1/4" – 11 1/4" | 11" – 12 3/4" | 12" – 14" |
| Model | DCS-L | DCS-L | DCS-L | DCS-L | DCS-L |
| PN: Complete | 20206 | 20207 | 20208 | 20209 | 20210 |
| Grip Length | Long | Long | Long | Long | Long |
| Weight (kg) | 78 | 84 | 90 | 96 | 94 |
| Total Segments | 12 | 13 | 14 | 17 | 17 |
| Intermediate Segments | 10 | 11 | 12 | 15 | 15 |
| Hinge Pins | 11 | 12 | 13 | 16 | 16 |
| Insert Bowl | No.3 | No.2 | No.1 | No.1 | No.1 |
| Die | 20230-96 | 20227-104 | 20230-112 | 20225-136 | 20230-136 |
Circular Button Inserts
Unlike drill pipe slips that use long die inserts, casing slips generally use hardened circular buttons.
Benefits include:
- Larger contact area
- Reduced marking of casing
- Better grip under heavy loads
- Longer service life
- Easy replacement during maintenance
Replacing worn inserts before they become damaged helps maintain gripping performance and protects expensive casing strings.
Choosing the Correct Casing Slip
Selecting the correct casing slip depends on several factors:
Casing Outside Diameter
Each slip is designed for a specific casing OD.
Load Capacity
Always ensure the slip's rated capacity exceeds the maximum suspended casing weight.
Rotary Table Compatibility
Most API 7K casing slips fit standard API insert bowls, but bowl size and taper should always be confirmed before use.
Insert Type
Use the correct button inserts recommended for your casing size and application.
API 7K Compliance
API Specification 7K establishes requirements for the design, manufacture and testing of drilling and well-servicing equipment, including rotary slips, slip bowls and spiders. API 7K casing slips are manufactured to meet these requirements, providing consistent performance and compatibility with standard drilling equipment.
Inspection and Maintenance
Regular inspection helps maximise safety and service life.
Inspect for:
- Worn or broken inserts
- Cracked slip bodies
- Damaged hinge pins
- Bent handles
- Excessive corrosion
- Uneven wear
- Proper seating in the bowl
Replace worn components immediately. Never weld or repair cracked load-bearing components.
Common Applications
API 7K casing slips are commonly used during:
- Surface casing installation
- Intermediate casing running
- Production casing running
- Geothermal wells
- Mining exploration
- Water well drilling
- Well servicing
- Workover operations
Why Choose Safety Shark Casing Slips?
Safety Shark supplies high-quality API-style casing slips designed for demanding drilling environments.
Our range offers:
- Heavy-duty forged alloy steel construction
- API 7K compatible design
- Standard API insert bowl compatibility
- Replaceable circular button inserts
- Large casing size range
- Spare parts available
- OEM-compatible replacement components
- Suitable for oil & gas, geothermal, mining and water well drilling
Whether you're running 5" casing or 30" conductor pipe, Safety Shark can supply dependable casing slips to help keep your operation safe and efficient.
Inspection & Preventive Maintenance Best Practices
Handling equipment is subjected to high loads, impact, abrasion and harsh drilling environments. Regular inspection and maintenance are essential to maximise equipment life, reduce downtime and maintain a safe working environment.
Daily Pre-Use Inspection
Before each use, operators should:
- Remove mud, drilling fluids and debris from all components.
- Check for cracks, distortion or signs of impact damage.
- Inspect all load-bearing surfaces for excessive wear.
- Ensure moving parts operate freely.
- Verify retaining pins, springs and locking mechanisms are secure.
- Check that replaceable inserts or dies are properly fitted and show no signs of excessive wear.
- Confirm all identification markings and load ratings remain legible.
Any equipment showing signs of structural damage should be removed from service immediately.
Routine Preventive Maintenance
Establish a planned maintenance schedule based on operating hours and drilling conditions.
Maintenance should include:
- Thorough cleaning after each job.
- Lubrication of hinges, pins and moving components.
- Replacement of worn inserts before they begin damaging tubulars.
- Inspection of tapered seating surfaces for uneven wear.
- Verification that bolts, retaining pins and fasteners remain tight.
- Touch-up coating or corrosion protection where required.
- Proper storage in a dry location to minimise corrosion.
Periodic Detailed Inspection
At scheduled maintenance intervals, equipment should undergo a more comprehensive inspection by qualified personnel.
Best practice includes:
- Complete disassembly where applicable.
- Dimensional inspection of critical components.
- Non-destructive testing (NDT) of load-bearing parts.
- Inspection for fatigue cracking around high-stress areas.
- Measurement of wear against manufacturer tolerances.
- Replacement of worn pins, bushes, springs and inserts.
- Functional testing after reassembly.
Non-Destructive Testing (NDT)
Many drilling contractors incorporate periodic NDT into their maintenance programs for critical handling equipment.
Depending on the equipment and service conditions, inspection methods may include:
- Magnetic Particle Inspection (MPI)
- Dye Penetrant Inspection (PT)
- Ultrasonic Testing (UT)
- Visual inspection under adequate lighting
NDT is particularly valuable for detecting fatigue cracks before they become visible during routine inspections.
Frequently Asked Questions
What is the difference between drill pipe slips and casing slips?
Drill pipe slips grip drill pipe during drilling operations, while casing slips are designed specifically to support larger and heavier casing strings.
What does CMS stand for?
CMS generally refers to Casing Manual Slip, the most common style of manual casing slip used on drilling rigs.
Are casing slips interchangeable?
Most API-style casing slips are designed to fit standard API insert bowls with a 4 in/ft taper, but compatibility should always be confirmed with the manufacturer.
Can inserts be replaced?
Yes. Circular button inserts are designed as replaceable wear components and should be changed when worn or damaged.
What casing sizes are available?
CMS casing slips are commonly available for casing sizes ranging from 4 1/2" to 30" OD, depending on the model and segment configuration.