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The RTJ flange: An introduction for oil and gas engineers

Posted by Simon Pownall on Aug 25, 2015 11:05:00 AM


    

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Knowing the basics of all flanges, connections and pipelines you work with can make it easier to maintain the quality and efficiency of the product. Despite being especially developed for the petroleum and petrochemical industry, the RTJ flange (ring type joint) still runs into the same problems as any other flange would.

To guide you through the best practice maintenance, here’s our introduction for oil and gas engineers on RTJ flanges.

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RTJ flange characteristics

The effect of being used first in the petrochemicals industry means the flanges offer a superb metal-to-metal seal under high pressures and high temperatures too. The flanges typical characteristics include matching groove cuts on the face, and when the bolts are tightened, the gaskets compress into each other providing a strong and robust connection – which is also very easy to assemble and dis-assemble.

RTJ flange designs

There are two different types of RTJ flange designs, oval and octagonal cross sections. Despite both types having identical pitch diameters, octagonal cross sections are more widely used due to their higher sealing efficiency with pressures up to 10,000 PSI.

There are other ranges of RTJ flanges that have been adapted to cope with both a higher pressure (up to 15,000 PSI) and a lower pressure (up to 5,000 PSI). These are called RX and BX styles respectively.

The standardised designs of these sometimes includes a pressure passage hole which is created to equalise the pressure on the sealing faces. Sometimes, the internal pressure of flanges and gaskets means no hole is required as the seal pressure balance is maintained internally in the pipeline already.

Industry standards and tolerances

A great way to understand a flange in more detail requires engineers to understand the industry standards on designs giving information on strengths, weaknesses and tolerances of each flange and gasket.

For RTJs, engineers should refer to the following industry standards which can be viewed in detail by clicking on the links below:

Alongside the standards, it is recommended to view and use the Texas Flange rule for RTJ flanges. The online tool and PDF version, both outline the depth, width, pitch diameter, angle and radius at bottom statistics for all RTJ set-ups.

Avoiding corrosion

Despite a tight seal, the contents of the pipeline usually handled by RTJs means corrosion and damage to the gasket comes through poor maintenance. Simply keeping flanges clean is the simplest solution to avoid corrosion.

At no point should tools or wire brushes be used to clean RTJs. For a more in-depth look at stress corrosion cracking on RTJs, take a look at our RTJ petrochemical blog here.

Time to repair

Knowing how long repairs to RTJs takes gives you the insight you require to charge or budget for in your pipeline projects. The Estimator’s Piping Man-Hour Manual gives a good insight into how long it takes to repair an RTJ if the face has experience oxidation.

The manual suggests the following man hours are required depending upon the flange size in inches:

  •          3” – 0.6 hours
  •          4” – 0.9 hours
  •          6” – 1.0 hours
  •          8” – 1.3 hours
  •          10” – 1.6 hours
  •          12” – 1.9 hours

For additional operations such as x-rays and pre-heating coupling welds, naturally this would take more hours on top of the benchmarks above.

Required maintenance tools

For RTJs, Mirage’s internally mounted flange facing machines are ideal for your applications. Featuring a lightweight construction, continuous groove facing feeds, swivel tool post for grooves and quick set independent bases, the machines can operate at a high quality in demanding conditions. 

 

 

Photo Credit: Wermac

 

Topics: flanges

   

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