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Geometric Dimensioning & Tolerancing In Oil & Gas Components

In addition to reduced inspection time, the acquisition of a portable CMM saw a company in the oil and gas industry gaining a new competency. Contributed by Faro 

Founded in July 1997, Rohag is a manufacturer of components and parts for the oil and gas industry. The company is headquartered in Singapore and the team works with customers to develop quality products made to specifications, delivered at competitive prices and in a timely manner.

As the company supplies components such as wellheads, seal rings, and couplings, the main process involved in production is metal machining, specifically with milling and turning with various CNC machine tools and equipment that they possesses.

By Hand

In every project, the team typically conducts inspection on the first article, during production, as well as on each final product before it leaves the facility.

In the earlier days, the production team used to rely purely on hand tools such as internal pitch diameter bore gauges, dimensional inspection gauges, and micrometres to conduct inspections and quality control checks on its products.

While there were no major issues with these methods, they were still intrigued when a customer recommended them a portable coordinate measuring machine called the FaroArm to them back in 2007.

Saving Time

Equipped with several articulating joints, the portable CMM is able to determine and record the location of a probe in 3D space, and report the results through software. In January 2008, the company acquired its first eight-foot version.

One of the first few advantages that the company noticed was the time saved on inspection. Lee Kong Peng, managing director at Rohag recalled that an inspection job that used to take around five hours to complete would only require three hours.

Besides the time-savings using the portable CMM, the company began to address larger components that the older tools could not handle, as it was able to measure parts of varied sizes (up to 1,250 mm) while still providing accuracies of up to 0.025 mm.

The portability offered simplified the inspection job for the team. Instead of having to transport parts to a measurement room, the portable CMM could be deployed right on the shop floor, where production takes place. That way, the team saved on the time and effort that would have been spent moving components around. The team also minimised production downtime since quality checks could be done right on the machines as well.

New Competency

In addition, the company gained the new competency of geometric dimensioning and tolerancing (GD&T) on the components. A system that communicates engineering tolerances, GD&T clearly states the nominal geometry of a given part and its allowable variation.

Mr Lee said that prior to using the portable CMM, they could not acquire the measurements necessary to perform GD&T analysis on their components. Since then, they have learnt how to make full use of the device to obtain such measurements.

The company has since added several newer units of the portable CMM to its collection of tools. At present, the company owns a total of six units in varying lengths and models, utilising them daily for at least six to eight hours, with three people sharing a unit at any one time. Business expansion may require further additions, and the company may explore devices with non-contact scanning capabilities in the near future.

What Is GD&T?

Geometric dimensioning and tolerancing, often referred to as GD&T, is a symbolic language used on engineering drawings and models to define the allowable deviation of feature geometry, according to Sigmetrix.

The language of GD&T consists of dimensions, tolerances, symbols, definitions, rules, and conventions that can be used to precisely communicate the functional requirements for the location, orientation, size, and form of each feature of the design model.

Thus, GD&T is an exact language that enables designers to “say what they mean” with regard to their design models. Production can then use the language to understand the design intent and inspection looks to the language to determine set up requirements.

There are several standards available worldwide. Common ones are the ISO standard, and the Y14.5-2009 standard.


The portable CMM is able to determine and record the location of a probe in 3D space.

Portability offers simplified inspection jobs for a team.

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