VR Scaffolding Fittings Guide
Markings and what they mean, Scaffold Couplers for Tube and Fitting Scaffolds conform to BS EN74-1:2005 with Putlogs or Singles conforming to BS 1139-2.2:2009. The Couplers respective specification can be identified by the markings which are either embossed onto or impressed into the drop forged or pressed fitting.
The markings state the relevant standard, the manufacturer's trade mark, the year and usually the month of manufacture with either L or M which denotes the quality control method used along with the critical load bearing Class A or B.
Scaffold designers or Design Guides state the Class of Coupler required with structural properties for Class A having a design load of 6.1kN or Class B, with greater Slip and strength, having a design load of 9.1kN.
Couplers shall have an original prototype testing certificate with ongoing sample or batch testing, usually carried out at an approved test house with Slip and Failure Load testing.
A drop forged Double Coupler conforming to BS EN74-1 Class B shall have a minimum Slip Load of 15kN and a minimum Failure Load of 30kN. The Class A Coupler shall have a minimum Slip Load of 10kN and a minimum Failure Load of 20kN.
A drop forged Swivel Coupler to BS EN74-1: class A shall have a minimum Slip Load of 10kN and a minimum Failure Load of 14kN.
All tested Couplers have a tightening torque of 50Nm as stated in their respective British standards.
As a brief key point guide the new EN74-1:2005 has the following changes from the old standard BS 1139 Section 2.1:1991 - BS EN74:1988 .....
• Class A & B Double Couplers are now tested also for ROTATION stiffness and moment, PULL APART FORCE, CRUCIFORM bending stiffness on steel tube, CRICIFORM bending stiffness on aluminium tube, CRUCIFORM bending ultimate moment and finally tube INDENTATION. The specified values remain the same.
• Class A & B Swivel Couplers now have the INDENTATION test added but the old test required a Failure Load of 17kN applicable only for Class A, the new test required Class A Failure Load of 14kN and Class B 20kN.
Couplers are usually zinc plated for corrosion protection but still need to be properly maintained by ensuring the nut and bolt freely engage with light oiling required when necessary. There are various lubrication and rust preventatives available to use.
Examination of Couplers before use is imperative as is the need to correctly tighten up all fittings but ensuring that overtightening does not occur as excessive overtightening may damage the nut, bolt, washer or seating face.
When using torque guns extreme caution must be taken in setting and maintaining the correct tightening torque used on fittings. Excess tightening may damage the Bolt, Nut or washer. Under tightening may allow the fitting to slip on the tube.
It is recommended by VR that the torque guns are used for undoing fittings only.
The latest guidance must be followed by the respective bodies such as the NASC / Scaffolding Association which produce guidance information.
The respective standards for extensively used Fittings are as follows:
Drop forged Double Coupler (Right Angle Coupler) ........ BS EN74-1:2005 Class B
Drop forged Swivel Coupler ........ BS EN74-1:2005 Class A
Drop forged Single Coupler (Putlog Coupler) ........ BS 1139 - 2.2:2009
Pressed Double Coupler (Right Angle Coupler) ........ BS EN74-1:2005 Class A
Pressed Swivel Coupler ........ BS EN74-1:2005 Class A
Pressed Single Coupler (Putlog Coupler) ........ BS 1139 - 2.2:2009
Pressed Sleeves ........ BS EN74-1:2005 Class B
Girder Coupler ........ AS 1576.2:2009
Drop forged Swivel Girder Coupler ........ AS 1576.2:2009
Fittings shall have sample batch quantities taken with Slip and failure testing carried out at an independent Test House.