Square Kelly for Rotary Table Drilling Systems

Description

Goldenman Square Kelly is an API 7-1 rotary drill stem component designed to transmit torque from the rotary table and Kelly bushing to the drillstring while providing an internal passage for drilling-fluid circulation.

Available standard square drive-section sizes include 3-1/2, 4-1/4, 5-1/4, and 6 inches. The Kelly can be configured with different upper left-hand and lower right-hand rotary-shouldered connections to match the swivel, Kelly cock arrangement, and drillstring.

Manufactured from full-length heat-treated alloy steel, the Square Kelly is engineered for high torsional loading, axial load, repeated sliding through the Kelly bushing, and continuous drilling-fluid circulation.

Goldenman supplies Square Kelly bars with API certification, dimensional inspection, material traceability and project-specific quality documentation.

Product Highlights

• Manufactured according to API Spec 7-1
• Square drive-section sizes from 3-1/2 to 6 inches
• Standard 40 ft configurations available
• Full-length alloy steel construction
• 4145H-modified material option
• Full-length quenching and tempering
• Upper left-hand and lower right-hand connections
• API REG, NC, IF and FH connection options
• Precision-machined drive section
• Internal bore for drilling-fluid circulation
• Full-length straightness control
• Ultrasonic and surface inspection options
• Steel thread protectors supplied
• Custom length and connection configurations available

What Is a Square Kelly?

A Square Kelly is the upper rotary-driving member of a conventional rotary drillstring.

It passes through the square Kelly bushing in the rotary table. As the rotary table turns, torque is transferred through the Kelly bushing to the four flat drive surfaces of the Kelly and then through the lower connection into the drillstring.

The central bore allows drilling fluid to flow from the swivel through the Kelly and into the drill pipe.

The Square Kelly performs three key functions:

• Transfers rotary torque to the drillstring
• Provides a drilling-fluid circulation passage
• Allows controlled vertical movement through the Kelly bushing while drilling

A Kelly is not the same as conventional API 5DP drill pipe. It has a square or hexagonal drive section, different end-connection requirements and a different manufacturing and inspection standard.

Main Applications

Goldenman Square Kelly bars are suitable for:

• Conventional rotary drilling rigs
• Onshore oil and gas drilling
• Workover and well-servicing rigs
• Water-well drilling rigs
• Geothermal drilling
• Mineral and exploration drilling
• Replacement of worn or damaged Kelly bars
• Drilling-rig refurbishment projects
• New rotary-table drilling-rig packages

The Kelly must be matched to the rotary table, Kelly bushing, swivel, Kelly valves and drillstring connection.

General Technical Specifications

Parameter	Available Specification
Product name	Square Kelly
Product category	Rotary drill stem element
Applicable standard	API Spec 7-1
Drive-section type	Square
Standard nominal sizes	3-1/2, 4-1/4, 5-1/4 and 6 in
Standard length	40 ft
Material	AISI 4145H-modified alloy steel or approved equivalent
Heat treatment	Full-length quenching and tempering
Brinell hardness	285–341 HBW for the referenced 4145H configuration
Upper connection	Left-hand rotary-shouldered connection
Lower connection	Right-hand rotary-shouldered connection
Connection options	API REG, NC, IF, FH, or project-specific
Internal bore	According to the size and the approved drawing
Surface protection	Phosphating, corrosion protection, and thread protectors
Inspection	Dimensional, straightness, thread, and NDE inspection
Certification	API certificate
Customization	Size, length, bore, and connections

The final material, dimensions, hardness, impact properties, and connections must be confirmed through the approved product datasheet and manufacturing drawing.

Standard Square Kelly Size Configurations

The following table provides commonly supplied configurations. Final dimensions should be confirmed against the customer’s swivel, Kelly bushing and drillstring interfaces before production.

Square Size	Standard Length	Upper Connection, LH	Lower Connection, RH	Bore	Across Corners	Across Flats
3-1/2 in	40 ft	6-5/8 REG	NC38 / 3-1/2 IF	2-1/4 in	4.437 in	3-1/2 in
4-1/4 in	40 ft	6-5/8 REG	NC46 / 4 IF or NC50 / 4-1/2 IF	2-13/16 in	5.500 in	4-1/4 in
5-1/4 in	40 ft	6-5/8 REG	NC50 or 5-1/2 FH	3-1/4 in	6.750 in	5-1/4 in
6 in	40 ft	6-5/8 REG	NC50	3-1/2 in	7.625 in	6 in

Alternative upper and lower connections, bore dimensions, and overall lengths can be manufactured according to the approved purchase specification.

How to Select the Correct Square Kelly

Match the Kelly to the Kelly Bushing

The nominal square size and actual across-flats dimension must match the Kelly bushing.

An incorrect combination can result in:

• Excessive clearance
• Impact loading between the Kelly and bushing
• Uneven contact on the drive surfaces
• Accelerated corner wear
• Vibration
• Poor torque transfer
• Localized twisting or deformation

The purchaser should provide the Kelly bushing manufacturer, model, nominal size, and internal drive dimensions.

Confirm the Upper Left-Hand Connection

The upper connection normally interfaces with the swivel or upper Kelly valve and is typically a left-hand rotary-shouldered connection.

The required information includes:

• Connection type
• Connection size
• Left-hand designation
• Swivel connection
• Upper Kelly valve arrangement
• Required upset dimensions

The expression “6-5/8 REG” alone is not sufficient unless the connecting hand and mating component are also confirmed.

Confirm the Lower Right-Hand Connection

The lower connection interfaces with the lower Kelly valve, saver sub or drillstring.

Depending on the Kelly size, common configurations may include:

• NC38
• NC46
• NC50
• 3-1/2 IF
• 4 IF
• 4-1/2 IF
• 5-1/2 FH

The purchaser should confirm whether the Kelly will connect directly to the drill pipe, a Kelly saver sub or a lower Kelly valve.

Check the Internal Bore

The internal bore affects drilling-fluid flow and pressure loss.

The bore should be reviewed against:

• Required pump flow rate
• Drilling-fluid properties
• Standpipe pressure
• Bit hydraulic requirements
• Swivel bore
• Kelly valve bore
• Drillstring internal diameter

The selected Kelly should not create an unnecessary restriction in the circulating system.

Confirm the Required Length

A standard configuration may use a 40 ft overall length, but the required Kelly length depends on:

• Rig design
• Mast height
• Rotary table position
• Swivel travel
• Kelly bushing arrangement
• Available drilling stroke
• Existing replacement dimensions

For replacement orders, measure the existing Kelly rather than relying only on the nominal rig model.

Material and Heat Treatment

The Square Kelly may be manufactured from AISI 4145H-modified alloy steel or an approved equivalent suitable for high torque, axial load and repeated rig-floor operation.

Full-length quenching and tempering help achieve controlled mechanical properties through the drive section, upset areas and end connections.

The material and heat-treatment process should provide:

• High torsional strength
• Adequate tensile capacity
• Resistance to impact loading
• Controlled hardness
• Uniform mechanical properties
• Resistance to drive-section deformation
• Reliable thread and shoulder performance

Material substitution should not be accepted without reviewing the mechanical property requirements and the approved manufacturing specification.

Why Straightness Is Critical

Kelly straightness directly affects its movement through the Kelly bushing and the stability of the rotary drilling system.

Poor straightness can cause:

• Uneven contact with the Kelly bushing
• Excessive vibration
• Irregular drive-section wear
• Additional side loading on the swivel
• Difficult movement through the rotary table
• Increased stress at the connections
• Premature fatigue or twisting failure

Straightness should be monitored before machining, during drive-section machining and during final inspection.

Drive-Section Machining and Wear Control

The four drive surfaces must be machined to controlled across-flats and across-corners dimensions.

Critical drive-section characteristics include:

• Flatness of the four drive surfaces
• Parallelism of opposite flats
• Corner geometry
• Surface finish
• Straightness
• Dimensional consistency along the working length
• Transition geometry between the drive section and upset areas

Excessive clearance between the Kelly and Kelly bushing can increase impact loading. Insufficient clearance can restrict movement and cause binding.

Kelly-bushing condition should therefore be inspected whenever a replacement Kelly is installed.

API Certification and Quality Control

Goldenman supplies Square Kelly bars with API certification under the applicable API Spec 7-1 product scope.

Quality-control activities may include:

• Raw-material verification
• Heat-number traceability
• Chemical-composition review
• Mechanical-property testing
• Heat-treatment record review
• Full-length ultrasonic testing
• Magnetic-particle inspection of critical areas
• Hardness inspection
• Impact-property verification
• Overall straightness inspection
• Across-flats and across-corners measurement
• Internal-bore inspection
• Upper and lower connection inspection
• Thread-gauge inspection
• Shoulder and seal-face inspection
• Final visual inspection
• Product marking verification
• Coating and thread-protector inspection

The exact testing and documentation scope should be defined in the purchase order or the approved inspection and test plan.

Replacement and Compatibility Requirements

A replacement Square Kelly should not be ordered using only the rig model or nominal square size.

For reliable interchangeability, confirm:

• Existing Kelly nominal size
• Across-flats dimension
• Across-corners dimension
• Overall length
• Effective drive-section length
• Upper connection and thread hand
• Lower connection and thread hand
• Internal bore
• Upper and lower upset dimensions
• Swivel connection
• Kelly valve connections
• Kelly bushing dimensions
• Mating drillstring connection

A general arrangement drawing or dimensional sketch of the existing Kelly is strongly recommended.

Common Square Kelly Procurement Mistakes

Using API 5DP Drill Pipe Parameters

Ordinary drill pipe grades, upset forms and tool-joint tables cannot be used as a Square Kelly purchase specification. A Kelly should be ordered according to API 7-1 dimensions, connections and manufacturing requirements.

Selecting Only by Nominal Square Size

The Kelly must also match the actual across-flats dimension, Kelly bushing, connections, bore and length.

Ignoring Connection Hand

The upper connection is typically left-hand, while the lower connection is typically right-hand. Incorrect thread-hand selection prevents installation.

Reusing a Worn Kelly Bushing

A new Kelly operating in an excessively worn bushing can develop rapid corner and drive-surface wear.

Failing to Confirm Straightness and NDE

Material grade alone does not demonstrate Kelly quality. Straightness, heat treatment, ultrasonic inspection and connection inspection are also critical.

Frequently Asked Questions

Can the API 5DP drill pipe specification table be used to order a Square Kelly?

No. API 5DP covers conventional drill pipe body and welded tool-joint requirements. A Square Kelly is a rotary drill stem element with a square drive section and is specified under API Spec 7-1.

The Kelly purchase specification must define its drive-section size, length, bore, upper left-hand connection, lower right-hand connection and inspection requirements.

How is the correct Square Kelly size matched to the Kelly bushing?

The nominal square size and actual across-flats dimension must correspond to the Kelly bushing’s internal drive profile.

Buyers should provide the bushing model, internal dimensions and allowable clearance. Excessive clearance can cause impact loading and accelerated wear, while insufficient clearance can cause binding.

Why does a Square Kelly normally use a left-hand upper connection?

The upper connection interfaces with the swivel or upper Kelly-valve assembly. A left-hand thread helps prevent the upper connection from loosening under the normal rotary direction used in drilling.

The connection hand must still be explicitly stated in the purchase order.

What information is required to replace an existing Square Kelly?

Provide the overall length, effective drive-section length, square size, across-flats dimension, bore, upper connection, lower connection, thread hands, upset dimensions and photographs of both ends.

The existing nameplate and dimensional drawing should also be supplied when available.

What causes premature wear on the Kelly drive surfaces?

Common causes include an oversized or worn Kelly bushing, poor alignment, insufficient lubrication, excessive clearance, contaminated contact surfaces and operation with damaged drive corners.

Wear should be evaluated on both the Kelly and the bushing rather than replacing only one component.

Why is full-length ultrasonic testing important for a Kelly?

The Kelly is subjected to combined torque, tension, impact and repeated sliding loads. Full-length ultrasonic testing helps detect internal discontinuities that may not be visible from the surface.

Surface NDE should also be considered for the drive section, upset transitions and threaded ends.

How should the upper and lower connections be selected?

The upper connection must match the swivel or upper Kelly valve, while the lower connection must match the lower Kelly valve, saver sub or drillstring.

Connection type, size, thread hand, bore and shoulder dimensions must all be confirmed.

Can a Square Kelly be manufactured with custom length and connections?

Yes. Length, drive-section size, bore and end connections can be configured according to the rig and drillstring interface.

Custom configurations should be produced only after approval of the final drawing and technical datasheet.

What inspection documents should be supplied with an API Square Kelly?

The agreed documentation package may include the API certificate, material certificate, heat-treatment record, mechanical-property report, UT report, MPI report, hardness report, dimensional inspection report, thread inspection report and Certificate of Conformity.

Information Required for Quotation

For an accurate technical quotation, please provide:

• Square Kelly nominal size
• Overall length
• Effective drive-section length
• Across-flats dimension
• Across-corners dimension
• Upper connection
• Upper thread hand
• Lower connection
• Lower thread hand
• Internal bore
• Upper upset dimensions
• Lower upset dimensions
• Kelly bushing manufacturer and model
• Swivel connection
• Upper and lower Kelly valve arrangement
• Drillstring connection
• Material requirement
• Required mechanical properties
• API certificate requirement
• NDE and inspection requirements
• Third-party inspection requirement
• Quantity
• Destination country
• Required delivery schedule

For replacement orders, please also provide photographs and the existing Kelly drawing or dimensional sketch.

Request a Technical Quotation

Goldenman supplies API 7-1 Square Kelly bars for conventional rotary drilling rigs, replacement projects and complete rig packages.

Send your Kelly size, length, bore, upper and lower connections, Kelly bushing details and inspection requirements to:

Email: info@goldenman.com

Goldenman will review the drilling-rig interfaces and prepare the appropriate Square Kelly drawing, technical datasheet and commercial quotation.