Pit Gauges - History & Development
Author: Mark Palynchuk, General Manager, Western Instruments Inc.
Background
A means of Pit Depth Measurement has been a requirement of Corrosion Inspectors for many years. Inspectors, being a creative lot, have adapted and developed many different tools for the measurement of Corrosion. The most successful of these tools was a Lever Type Pit Gauge used by Mr. William R. Thorpe, a former Chevron Inspector in the Tulsa area. Mr. Thorpe had company craftsmen fashion a variety of configurations during his tenure there. As a retirement present, his coworkers presented him with a new copy of his latest configuration. The Thorpe Pipe Pit Gauge and the W. R. Thorpe Company were born.
Years of Evolution
Unfortunately Mr. Thorpe passed on soon after his retirement, but his Pit Gauge lived on, through an Accounting Firm. Any further development ceased, but this incredibly simple product became an industry standard for 40 years. As a result of Corrosion Inspectors complaining about the limitations of The Thorpe, the development of our Bridging Pit Gauge™ resulted.
As the operational envelopes of Pressure Equipment (Boilers, Vessels, Piping, and Pipelines) and Structures were pushed, so were their Corrosion Allowances, however today we see an unparalleled safety record. Unfortunately tools were slow to evolve, simply due to cost, but as the cost of equipment (and failures) increased, so did the perceived need (and cost) of equipment to measure Corrosion, increased.
Inspectors were constantly required to perform more accurate measurements of Pit Depth, however their tools were inadequate. Other tools were "adapted" for Pit Measurement, such as Machinist's Depth Gauges, but when high performance is required, adaptation simply isn't good enough. While the Dial Indicators (and Micrometer Barrels) used in Depth Gauges were an improvement in accuracy, they were cumbersome to use in the reality of field inspection. Furthermore, dial indicators were expensive and any modification to them was cost prohibitive.
With the advent of Automatic Machining, and Computer Aided Designs, manufacturers of Dial Indicators were more readily able to perform short runs, with very specific modifications. This lead to the development of Dial Indicator Pit Gauges, while still expensive, these tools provided more accurate measurements, at a cost.
*Photo of Dial Indicator Pit Gauge
With wolrdwide competition, we see the cost of these 'task specific' Dial Indicators coming down. Furthermore, with an aging infrastructure the demand for corrosion measurement and monitoring has increased substantially. Over the last 20 years we have seen the industry evolve, with companies speciallizing in Corrosion Measurement and Monitoring. Specialized manufacturers have evolved, such as ourselves, manufacturing industry specific tools. As business 101 has taught us, when there is a demand, a supply will soon follow. Today we see Digital Indicators, and specialized fixtures, with their increased cost, being offered and used.
Basic Requirements Still Exist
Manufacturers often lose sight of basic requirements and only address the advancements of their technology. Today we see the use of Highly Specialized Computer Controlled CMM's (Coordinate Measuring Machines) mapping entire areas of Weight-Loss Corrosion, today's utimate Pit Gauge costing over $50,000. While these specialized and advanced tools fulfill a niche in industry, they require a skilled technician to operate, a specialist to interpret, and skilled maintenance and repair personnel.
Development comes full circle
The Corrosion Measurement Industry, the Reference Specification Employed, and Regulatory Jurisdictions, are as diverse as the cultures of the countries they exist in. This is further complicated by the Imperial and Metric Measurement systems. Simple Lever Type Pit Gauges have not evolved to meet the industry's requirements. As an example, a Gauge does not exist with both Metric and Imperial Scales, something inspectors have had to deal with by conversions. A development program was undertaken to test and identify the benefits and shortcomings, of Lever Type Pit Gauges, correct them, and manufacture them economically.
The result of this program is a simple to use Lever Type Pit Gauge, with a Metric and Two Imperial Scales, a unique Pointer that aids the inspector to eliminate alignment errors, and a Patent Application.
This same Gauge has applications for Weld Inspection, with such capability as measuring; Undercut Depth, Weld Crown Height, a Porosity Comparator, with Metric and Imperial rules.
Tri-Gauge® Supplement
The Tri-Gauge® is today's most versatile Lever Pit Gauge, with its Metric and dual Imperial Scales. Additionally, the Tri-Gauge® serves as a basic Weld Inspection Gauge for; Undercut Depth; Weld Crown Height; a Porosity Comparator; with Metric and Imperial Rules. The Tri-Gauge® is fitted with a Patented Pointer Offset Correction for improved accuracy and repeatability. Lever Pit Gauges are intended to Evaluate Corrosion, and not as an absolute measuring tool. The Tri-Gauge® is supplied with a Pocket Protector type Case and Instructions.