The ability to audit joints such as flanges with gaskets is important for critical applications where leakage or rupturing of the connection can have disastrous, costly or environmental implications. Auditing is a preventative quality measure and is a required part of an ISO or other quality management system.
Auditing large bolts is very difficult. Use of a proper auditing tool can make life easy for an auditor.
Torque is an inexact science with a lot of differing variables. Resolving or isolating these variables is the key to improve torque errors and fastening procedure. This is done with data. Auditing provides data to help make improvements to quality.
The Mountz Bolt Auditing System for large bolted applications consists of a HSD torque multiplier with embedded strain gauges to measure torque as well as an angle encoder to measure angle. The multiplier is connected to the TorqueMate® PTT-2000 torque tester designed specifically for torque and angle analysis and data collection. The PTT-2000 Bolt Audit Model is capable of both torque and angle measurement and has the ability to store up to 5000 readings. In addition the system includes PC based Windows software to configure the PTT for torque measurement tests. The stored data can be downloaded to a PC for use with quality control software or for analysis in Excel. A barcode scanner can be used with the system to enhance its function. The system provides two main modes for Auditing; the first is an ” Enhanced First Movement” mode the second is a Torque vs. Angle Audit mode. These modes provide different information depending on the application requirements.
Technically speaking, the angle can be setup for either 360 or 720 pulses per revolution for use with various encoders. It is designed for use with quadrature angle signals so it can resolve either 0.25 degrees, if used with 360 pulses per revolution, or 0.125 if used with used with 720 pulses per revolution. In addition it can be set for “Normal” encoding where Trail follows Lead or with “Reverse” encoding where Lead follows Trail.
Audit Mode 1 for Enhanced First Movement
The torque multiplier is equipped with a reaction foot that provides for fixturing. This allows for a detection of a small angle movement programmed into the meter. When the fastener moves, the angle encoder detects this movement and the torque value is reported on the meter. This method will show the amount of torque achieve at first movement. The result can be compared to the actual desired torque. A series of fastenings can be recorded and all data is stored on the meter. This method allows an Auditor to validate that a joint is properly tightened. The information gathered in this test is very valuable. This test validates the residual torque.
Assume an application calls for 1000 N.m and an auditor finds that the joint moved at 500 N.m, an analysis surrounding why this occurred should ensue. It could be human error, improper fastening method, improper tools, incorrect parts or components, or joint relaxation to name a few variables. Finding the root cause to solve the problem can eliminate failures, improve safety and reduce cost.
Audit Mode 2 for Determining the Angular Movement
The object of this feature is to determine the amount of angular movement required to move from an initial torque value to an expected torque value. Further, this can be done without having to loosen the fastener. The audit device is programmed with a minimum torque value and an expected torque value. Beginning at the minimum value, the audit device starts to count angle. Once the expected torque is obtained, the device “locks” on angle degrees required to move from minimum torque to desired torque. This auditing information is very valuable because it allows an auditor to validate joint relaxation in degrees. It also allows joint designers and quality control to experiment with different amounts of torque and angle as a means to set proper fastening procedure.
The goal of auditing is to improve process results. To do this it is necessary to gather information for evaluation and analysis. An audit that fails to provide relevant information to improve the fastening process is worthless. Sometimes achieving proper torque requires practical experimentation. In order to experiment data is required. Depending on the audit strategy or information desired different techniques should be considered.
Using a quality bolt auditing system makes a safer world through accuracy and precision. Measuring torque is essential for companies to ensure their product’s quality, safety and reliability isn’t compromised. The failure of a three-dollar bolt that isn’t properly tightened can lead to catastrophic or latent failures. Bolts that are insufficiently fastened can vibrate loose and excessive torque can strip threaded fasteners.
For more information about the methods for checking and auditing pipe flanges, pressurized connections and other critical fastened joints, download this White Paper.
