Laqnican Joint
Mechanical Joints for Steel Pipe Piles and Steel Pipe Sheet Piles

The Concept of Laqnican Joint
In the construction of steel pipe piles and steel
pipe sheet piles, the common practice for joining these piles has been the on-site weld-joining of the piles carried onto the construction
site.
In weld-joining operations, however, carefulconstruction managements are required suchas the confirmation of the skill of welding operators, securement of appropriate operating
conditions and weld quality confirmation
inspections by means of Radiographic Test (RT)and Ultrasonic Test (UT).
Further, because the application of steel pipe
piles with larger outside dimeters and heavier
wall thickness tends to increase, and as a result
the ratio of welding operations to total pile construction time also tends to increase, there has
been a need for the development of a highly
reliable, simple, low-cost pile joining systemthat replaces conventional weld-joining.
Laqnican joint are mechanical joints developed as a pile joining system that replaces theon-site weld-joining of steel pipe piles and steel
pipe sheet piles. The trade name Laqnicancomes from the Japanese word “laqni” (easily)and “can” (fitting together). The application of
Laqnican joint in the on-site joining of piles
offers many advantages such as securing
stable quality, reducing pile construction times
and mitigating joining load, which will contribute to cutting down construction costs.
Laqnican joint demonstrate a rich record of
applications in the field of highways, railways,
ports and harbors, rivers and electric utilities.

Achievement ofeasy pile construction managementwith stable quality and without worries
about weather conditions
Possible to easily confirm
the joining quality of every pileand junction

On-site joining time: About 5 minutes
Quality control time: About 3 minutes
Completion of joining

Steel pipe pile

■ CONTENTS ■Features ………………………………………………… 1
Load-transfer Mechanism …………………………… 1
Structure and Conceptual Drawing ………………… 2
Product Specifications ………………………………… 3
Available Sizes ………………………………………… 3

Bolt forpushing andfixing key

Box joint

Load-transfer
key

Pin joint

Joining Procedures …………………………………… 4
Effect on Joining Time Reduction …………………… 5
Load-carrying Capacity and Corrosion Resistance … 5
Examples of Piling Methods ………………………… 6
Application Examples ………………………………… 7
Various Optional Functions …………………………… 8
Removal Procedures

Rotationsuppression key
Steel pipe pile………………………………… 8

Various Certificates …………………………………… 9Name of Respective Parts

Features of Laqnican Joint
Higher strength than steel pipes
Joining with higher strength is available regardless of weather conditions andoperator skills.
(Steel pipes with Laqnican joint possess strength and deformation capacity equal
or superior to those of steel pipes with no joints.)

Faster Joining of Steel Pipes even with
Larger Outside Diameters and Heavy Wall Thickness
Faster joining is achieved regardless of steel pipe sizes.
Steel pipes with different wall thicknesses can be joined at the construction site.

Simple Joining Procedures
Joining is achieved by just inserting joints and fastening bolt for pushing andfixing key.
No special skills or qualifications are required.

Contribution toward…… higher quality of
on-site joints
Contribution toward…… the reduction of
construction term
Anyone can…… easily join pipes

Simple Pile construction management
Construction management is achieved by only confirming fastening depth of bolt
for pushing and fixing key using a depth gauge.
No particular inspection devices are required for joining confirmation andconstruction management.

Inspection of…… every joint section

Load-transfer Mechanism of Laqnican Joint
During working of compression force

During working of tension force

Compression force is transferred by the useof contact surface (metal touch section)
perpendicular to the axial direction of box
joint and pin joint.
Tension force is transferred from the joint
key channel to the other joint via theload-transfer key.

(Reference) A List of Steel Pipe Sizes Employing Laqnican Joint in Past Construction Projects

mm(inch)

Wall thickness of steel pipe

23〜30

（Around 1 ）Symbol20〜22

Application field: Highway: Railway

17〜19: Port and harbor

12〜16: River（Around 1/2 ）: Energy

9〜11: Others

400
500
600
700
800
900 1000 1100 1200 1300 1400 1500（16”）（20”）（24”）（28”） （32”）（36”）（40”）（44”）（48”）（52”）（56”）（60”）
Outside diameter of steel pipe

1Structure of Laqnican Joint
Laqnican Joint are composed of a box joint, pin joint, load-transfer key, bolt for pushing and fixing key and rotation-suppression key.
The box joint has a structure in which multiple arc-shaped plates (divided in the circumferential direction) called theload-transfer key are housed in circumferential channels inside the joint, and the load-transfer key can be pushed out to thepipe center direction by rotating the bolt for pushing and fixing keys. The pin joint has a structure in which peripheral circumferential channels are cut in a position relative to the box joint channel.
Joining steel pipes with Laqnican joint is completed in the following sequence: Insert a box joint which is shop-welded withthe upper steel pipe pile is inserted into a pin joint which is shop-welded with the lower steel pipe pile; Then rotate the bolt for
pushing and fixing key to push out the load-transfer key housed in the box joint in order to make the load-transfer key enter
into the channel of the pin joint; Finally integrate the joining members to join the pipes. Every piece of completed junctions
employing Laqnican joint can easily be inspected by confirming the fastening depth of bolt for pushing and fixing key.
Further, rotation torque occurring during the pile construction can be transferred by arranging the rotation-suppression key
outside the surface of the Laqnican joining members. Meanwhile, in the case of adopting Laqnican joint in Pile driving Method
and Vibro-hammer Method, measures (stop ring, etc.) are provided that prevent from loosening of bolt for pushing and fixing key.

■ Conceptual Drawing of Laqnican Joint Structure

Bolt forpushing andfixing key

Steel
pipe

Bolt forpushing andfixing key
Loadtransfer
key

Load-transfer
key

Steel
pipe
Shop-welded
sectionBox joint

Rotationsuppression key
Pin joint

Steel
pipe

Steel
pipe

Shop-welded
section■ Step type■ Flat type■ Basic Flow of Joining Processes Employing Laqnican JointBox joint
Load-transfer key
Bolt fortemporaryfixing key

Rotation

Bolt forpushing andfixing key

Rotation

Depth gauge

Pin joint
Positioning

2

Insertion of
Laqnican Joint

Removal ofbolt for temporary
fixing key

Attachment ofbolt for pushingand fixing key

Fastening ofbolt for pushingand fixing key

6 Confirmation of joining(completion of inspection)

Product Specifications of Laqnican Joint
1. Material Quality of Base Steel Pipe
The material quality of base steel pipe shall apply or conform to JIS A 5525 (steel
pipe pile) and JIS A 5530 (steel pipe sheet pile).

Production Process

2. Material Quality of Laqnican Joint
The material quality of box joint and pin joint conforms to SFCM880R (chromium-molybdenum steel forged product) or POSTEN780 (high-strength steel plate).
The material quality of load-transfer key conforms to SFCM980S (chromium-molybdenum steel forged product).

Manufacture andinspection of steel pipes

Manufacture andinspection of
Laqnican Joint■ Chemical Composition(%) SFCM880R, SFCM980S
≦0.48

0.15

〜0.35

0.30

〜0.85

≦0.030≦0.030

0.90

〜1.50

0.15

〜0.30
Shop circumferential
weld-joining of
Laqnican Joint and steel pipes■ Chemical Composition(%) POSTEN780
≦0.16

0.10

〜0.40

≦1.50

≦0.030≦0.030

0.40

〜0.80

ー

■ Mechanical Properties
Ex.

Final Product inspection

MemberYield point

Tensile strength

Elongation

Pin joint
Box joint≧705MPa（≒102 ksi）

880〜1030MPa（≒128〜149 ksi）

≧13%

Load-transfer key≧755MPa（≒109 ksi）

980〜1130MPa（≒142〜164 ksi）

≧11%

Shipment

Available Size of Laqnican Joint
Laqnican Joint can be applied as the joints for steel pipes with sizes shown in the table below.

■ Step TypeEx.
Material quality applied

EN10025

OD 400〜600 mm

OD 700〜1500 mm

S235 JR〜 t25 mm

〜 t33 mm

S275 JR〜 t19 mm

〜 t25 mm

S355 JR〜 t16 mm ※〜 t19 mm ※OD 16 〜24

OD 25 〜60

Grade 1

〜 t0.98〜 t1.29

Grade 2

〜 t0.74〜 t0.98

Grade 3

〜 t0.74〜 t0.98

Material quality applied

ASTM A252■ Flat Type※ Please inquire

OD : φ400mm 〜 1500mm / around 16 〜 60
Wall Thickness : t9mm 〜 t30mm / t0.35 〜 t1.18
For pipe diameters, pipe thicknesses, and other specifications not listed above, please contact us.

3

Joining Procedures for Laqnican Joint

1 Suspending upper pile
Attachment and fastening of

Attachment and fastening of
5 boltfor pushing and fixing key

2 Positioning
6 Completion of attachment of all joining members

3 Joining of Laqnican Joint
7 Inspection employing depth gauge

4 Removal of Bolt for temporary fixing key
Completion of inspection of

8 joining employing Laqnican Joint
4

Effects of Laqnican Joint on Joining Time Reduction
In the recent design of foundation pile structures, the application of steel pipe piles with large outside diameters and heavy
wall thicknesses tends to increase. Due to the application of these piles, the ratio of welding time to total pile consturction timeis increasing. Because the time required for the on-site joining of steel pipe piles with Laqnican Joint is about 5 minutes perjunction regardless of the outside diameter and wall thickness of the steel pipe, steel pile joining times can be reduced using
Laqnican Joint, and as a result Laqnican Joint can contribute to construction cost reduction due to reduced constructionterm.
The table below shows examples of comparison between the Laqnican Joint method and the weld-joining method
conventionally applied. In the table, the joining time using Laqnican Joint is set as the time required from attaching bolt for
pushing and fixing keys to their fastening. The joining time using weld joining is as shown in the Estimation Standard forConstruction Contracts of Port/Harbor Civil Works (2015).

■ Comparison between Laqnican Joint and Weld Joint
Item

Laqnican Joint

Weld joint

Influence of weather condition

Joining can be undertaken regardless of
weather conditions.

Impossible to conduct welding during rainfall and snowfall
Shutting-out device required in the case of wind velocity of
10 m/s or higher

Main tools applied

Hexagonal wrench

Welding machine, generator

Joining time

Pile diameter ×
Wall thickness

Joining time

Joining time

Site A

φ1000×t22

5 minutes

105 minutes

φ1000×t15

5 minutes

57 minutes

φ600×t16

5 minutes

61 minutes

φ600×t10

5 minutes

24 minutes

Level of difficulty in joining operation

No requirement for expert skill

Requirement for expert skill (skill test, qualification)

Quality control method

Control of fastening depth of bolt for
pushing and fixing key by the use of depth gauge

RT inspection • UT inspection • PT inspection • Visual inspection

3 to 5 minutes

Time required for joining pipe of φ1000 mm × t12 mm
RT: 88 minutes (entire welding line); UT: 35 minutes (entire
welding line); PT: 22 minutes (entire welding line)
About 30 minutes additionally required until lowering of
welding heat

Site BTime required for quality control*Welding: Operating time by two welders; Laqnican Joint: Operating time by one worker

Load-carrying Capacity and Corrosion Resistance of Laqnican Joint■ Load-carrying Capacity of Steel Pipes with Laqnican Joint

3000

Laqnican Joint

Underground simulated test condition

Steel Pipe

Test solution
Test temperature
Test duration

Yield load

2500
2000

Steel pipe with Laqnican Joint

1500

Steel pipe with no joint

Contact section

Jack

1000
500
0

Tar•Eposeal(epoxy resin-type treatment agent)

Different metals contact specimen

Maximum load

0

20

40

60

80

100

Bending test for pipe with φ1000, t=16

120

140

160

Deflection (mm)The tensile, compression, bending and shear strengths and deformation capacity of steel pipes with Laqnican Joint are equal or superior tothose of steel pipes with no joints.

Plate thickness loss (mm)Load (kN): Total of both jacks

3500■ Corrosion Resistance of Steel Pipes with Laqnican Joint

1000Ω•cm
40˚C（104˚F）
1,000-hour

Average value of single pipe corrosion test
Laqnican Joint side of different metal contact specimen
Steel pipe side of different metal contact specimen
0.11
0.09

No peculiar corrosion due to the contact ofdifferent metals is observed in the contact section.

0.07
0.05
0.03

Contact section

Laqnican Joint

Steel Pipe

0.01
-0.01
-130 -110 -90

-70

-50

-30

-10

10

30

50

70

90

110

130

Measurement position (mm)*Laqnican Joint possess the corrosion resistance equal to that of steel pipe.

5

Examples of Piling Methods Employing Laqnican Joint
Pile driving Method

Vibro-hammer Method

Composit pile Method of
Steel pipe pile and soil cement

Rotation pressing-in
pile Method

Screwed pile Method

Press-in Method

Center Bored pile Method

6

Hydraulic rotation
Center Bored pile Method

Application Examples of Laqnican Joint
Application to temporary
working platform column

Application to port construction*Example using a pile driving barge

Application to railway construction*Example of application to platform columns

Application to highway construction*Example of night time construction during railway tracks closing

Application to steel pipe sheet pile foundation* Cutoff performance of Laqnican Joints can be improvedby the use of cutoff materials.

*Example of construction under the condition in which
an overhead clearance is restricted.

7

Various Optional Functions of Laqnican Joint
Construction instruments (example: protection of pin joints)

Rotation-Suppression key for preventing from loosening*Number of rotation-suppression keys changes depending on
piling methods and construction machinery.

Nut for preventing from loosening*Example of application in Gantetsu piling method (soil cement method)

Stop ring*Applied to prevent from loosening ofrotation-suppression key*Applied to prevent from loosening ofbolt for pushing and fixing keys

Removal Procedures for Laqnican Joint

1 Condition before removal

2 Removal of bolt for pushing and fixing key

4 Pulling load-transfer key to box side

8

Attachment of hexagonal socket

Attachment of hexagonal socket
3 headcap bolt to load-transfer key

5 Completion of removal*(Note) Confirm that the load-transfer key is housed at the box side*(Note) There is a case in which Laqnican Joint cannot be removed
depending on construction conditions.

Evaluation Reports（Public Works Research Center）
Certification organization: Public Works Research Center
Certification date: January 11, 2002（Renewal: January
11, 2022）
Certification No.: No. 0115
Name of technology: Laqnican Joint Mechanical Joints for
Steel Pipe Piles and Steel Pipe Sheet Piles
Dimensional range: Pipe outside diameter=φ400〜φ1600
mm; Pipe wall thickness= t9~t30 mm
Applicable pile Method: Vibro-Hammer Method, Pile driving
Method, Bored precast pile Method（Center Bored pile
Method, Composit pile Method of Steel pipe pile and soil
cementt, etc）, Screwed pile Method, Press-in Method

Evaluation Reports (Coastal Development Institute of Technology)
Evaluation organization: Coastal Development Institute ofTechnology
Evaluation date: April 28, 2004（Renewal: March 31, 2019）
Evaluation No.: No. 08002
Name of technology: Laqnican Joint Mechanical Joints for
Steel Pipe Piles and Steel Pipe Sheet Piles
Dimensional range: Pipe outside diameter=φ400~φ1600
mm; Pipe wall thickness=t9~t30 mm
Applicable pile Method: Vibro-Hammer Method, Pile driving
Method, Bored precast pile Method (Center Bored pile
Method, Composit pile Method of Steel pipe pile and soil
cement, etc), Screwed pile Method, Press-in Method

Evaluation organization: Coastal Development Institute ofTechnology
Evaluation date: November 29, 2012（Partial renewal:
March 31, 2021）
Evaluation No.: No. 20001
Name of technology: Laqnican Joint（Step Type）
Mechanical Joints for Steel Pipe Piles and Steel Pipe
Sheet Piles
Dimensional range: Pipe outside diameter=φ400~φ1500
mm; Pipe wall thickness= t9~t25 mm（SKK490）
Applicable pile Method: Vibro-Hammer Method, Pile
driving Method, Bored precast pile Method（Center
Bored pile Method, Composit pile Method of Steel pipe
pile and soil cement, etc）, Screwed pile Method,
Press-in Method9Laqnican Joint Website

1-3, Kyobashi 2-Chome, Chuo-ku, Tokyo, 104-8307 Japan
Steel Pipe Business Unit
+81-3-3245-3259
Head Office: 1-1-1, Hama, Amagasaki, Hyogo 661-8567, Japan+81-6-6470-5008

ver.3 SIG 2023.6