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Understanding ISO 6789 - The New Standard for Hand Torque Tools

08 Mar, 2017 | Return|

The 2017 edition was published at the end of February and is considerably modified from the 2003 edition.  This article is designed to explain the key differences and how the new standard is intended to be used.

During March, four further articles will explain the changes from the perspective of different users of the standard. Questions are welcome. Please follow the link at the end to email us.

What has changed?

The 2003 edition was itself a development of the 1993 edition. The 2003 standard divided requirements into three sections of: design conformance testing; quality conformance testing and recalibration.  The intention was to allow different groups of users to identify the relevant clauses for their needs.

The 2017 edition takes this logic even further and divides the standard into two distinct parts.

Part 1 still provides requirements for design and quality control during manufacture.  It also provides specifications for documenting conformance of hand torque tools.  This documentation is referred to as a declaration of conformance because it is stating that the torque tool conforms to the requirements of the standard.

Part 2 defines the requirements for calibration of torque tools including the establishment of uncertainty budgets and the content of certificates of calibration.

Calibration is defined by ISO as: “a set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring instrument or measuring system ....  and the corresponding values realized by standards.” 

Calibration does not include adjustment or imply conformance, it provides information for the user to assess and act upon.

When does it come into effect?

The standard is now published and can now be used. However, in Europe the Euro Norm or EN version has a 12 month period of overlap where either edition can be used. In the case of this new standard that is important because calibration accreditation bodies will take up to a year to audit all of their laboratories against the new edition of the standard.

Why make it more complex?

The standard is splitting into two parts because it has been recognised that torque tool calibration requirements have moved on since the standard was last published in 2003.

The two new parts can be described as one part which follows closely to the existing standard and one part which provides a consistent framework for calibrating a hand torque tool to the level that exists in accredited calibration laboratories across the world. The titles of the standards help clarify the difference.

EN ISO 6789:2017 Part 1: Requirements and Methods for design conformance testing and quality conformance testing - Minimum requirements for declaration of conformance.

The quality conformance testing performed under Part 1 is the testing performed on a new torque tool during manufacture. The document that manufacturers will now deliver is a "declaration of conformance" rather than a "calibration certificate". This is because the manufacturer is declaring that the tool conforms to the standard.

EN ISO 6789:2017 Part 2: Requirements for calibration and determination of measurement uncertainty

The calibration performed under Part 2 is a traceable calibration including steps to understand the factors for that particular torque tool that might cause the calibration values to vary from calibration to calibration. Any UKAS accredited laboratory in the United Kingdom, or indeed any laboratory accredited to ISO 17025 by an appropriate organisation, will be required to establish the uncertainty by conducting these steps. A model of torque tool that the laboratory has not seen before would take about 60 minutes to calibrate to the new standard.

How does it affect a torque tool user?

The next four articles mentioned earlier will explore the question from the perspective of a manufacturer, a calibration laboratory, an automotive user and an industrial user. For those of you who cannot wait a few weeks, one can summarise the logic as follows:

If a current end user was previously content to buy a new torque tool and put it into service on the basis of the "calibration certificate" supplied with the tool by the manufacturer, then they can continue to do so after the standard changes, even though the new piece of paper is now called a "declaration of conformance".

If the end user's quality control processes currently require a traceable calibration certificate issued by an accredited laboratory then they will already not accept the current manufacturer's piece of paper but will be paying for a calibration in an accredited laboratory.

If the end user is currently happy with the manufacturer's piece of paper for a new tool, then a periodic assessment from their in-house facility or from a sub-contractor should provide an equivalent level of confidence in the performance of the tool. Under the new Part 1 these sub-contractors will be able to continue that work as long as they observe the new changes, (see the article next week) but they will not be able to call it a calibration and will not be able to issue a "calibration certificate". They will be able to issue a "declaration of conformance".

In essence, one of the key changes in the standard is to protect the use of the term "calibration". It will initially be confusing to both end users and service providers, but the International Standards Organisation has clear definitions of words such as "calibration" and we will have to adapt our thinking to conform.

If you have any questions please make contact with us here: ISO6789@norbar.com.

Neill Brodey

Member of ISO Working Group on ISO 6789