RTJ flange use 12

[samuelo00]

Hi,

Can someone tell me when it's recommended the use of RTJ flange?

I have seen in many projects that for high pressures (i.e. over 600# or 900#) it is always used RTJ in process gas applications. Now I'm facing one in which RF is applied until 1500#, which is surprising for me.

I have read ASME B16.5 and dimensions are given for RF and RTJ for all classes, so I assueme that the use of whichever is possible.

I haven't found any other code or norm.

Any information is appreciated.

Regards
Samuel

 

[BigInch]

Its operator's preference.

For 1500# I'd go with the RTJ myself.

http://virtualpipeline.spaces.msn.com

"What gets us into trouble is not what we don't know, its what we know for sure" - Mark Twain

 

[Giuss]

Today the majority of the industry have gone away from RTJ flanges in favor of RF flanges.
It used to be common for refiners to specify RTJ’s for elevated pressure services. Sometimes this philosophy was also applied to elevated temperature services and/or hydrogen services over a certain partial pressure. Various combinations were also used, i.e. hydrogen service requiring Class 1500 or greater flanges. The benefit of RTJ’s is that the gasket is confined in a groove and has two sealing surfaces. It also tends to be self-actuating (i.e., the sealing pressure, at least on one side, tends to increase with increased service pressure).
Over time, most refiners modified their criteria, reducing the instances in which RTJ flanges were required. For example, it might initially have applied to all Class 900 and greater flanges, then to Class 900 flanges over 12 inch, Class 1500 over 6 inch and then to Class 2500.
current philosophy is to call for raised face flanges with spiral wound gaskets for all services. We have done this for more than 20 years without any problems. Prior to making this change, we had used raised face flanges for all Class 1500 and lower services for many years, also without issues. Recently some refiners have preferred to use Kammprofile gaskets instead of spiral wound.
The change to all raised face flanges was made after observing them perform without incident in Class 2500 service. Many refiners had recommended this change (based upon their experiences) prior to our making it.
Another reason for the change is the potential for crack formation at the intersection of the sides and bottom of the groove in RTJ flanges. These cracks can propagate into the base metal. They can be prevented by properly contouring the groove intersections, but avoiding the “problem” geometry all together was preferred.
Ring type joint grooves may also accumulate dirt, moisture, etc when the flange is open, i.e., they are more difficult to keep clean. A small amount of damage (including corrosion) on the narrow sealing surface(s) may lead to a leak. Also, as the use of RTJ’s declined, warehousing (and finding) the proper gasket(s) became a more important concern. Another factor is that the grooves and gasket must align properly in order to assemble the flange and obtain a seal. They must stay aligned throughout the operating cycle. The latter point becomes an issue when mating flanges are made of different materials and not providing different hardness materials for flange and ring and also thermal expansion is a concern. The first point is an issue at the initial assembly but can be more of a concern at reassembly after service.
Furthermore in those cases where dissimilar joint materials are in contact and where the piping is 10” nominal size or larger the use of RTJ Flanges is strongly not reccomended. In fact, due to the different nature of the two materials, ring joint flanges would experience local stresses due to differential expansion that potentially could lead to ring groove cracking. There are known cases of ring joint flange failures that have led to loss of reactor containment.

 

[jte]

Giuss' comments are on target. I've seen the trend go further - not only not specifying RTJ's for new construction, but actively and systematically converting from RTJ to RF on existing equipment with CL-1500 and lower flanges. The groove cracking potential is a large driver. As stated, spiral wound or GMGC (kammprofile type) gaskets are usually used with the RF. The 2010 edition of ASME PCC-2 Repair of Pressure Equipment and Piping will likely include a few paragraphs on dealing with the conversion in Article 3.5. One way to convert without doing physical work on the flange pair is to use a "conversion gasket" such at one available from Flexitallic:

http://www.flexitallic.com/pro_semi_cgrj.html

jt

 

[gr2vessels]

My two penny,
I tend to disagree with the above firm stand on sending the RTJ's into the oblivion;- they have been rather heavily replaced by the compact flanges (refer "Norsok" flanges)due to their high efficiency, cost effectiveness and ease of use. There is no more any RF flanges in the gas and oil off-shore applications, almost exclusively the compact RTJ's have taken up (some are less than half size of B16.5 / B16.47 flanges) the vacated space. Time is flying...we walk..
cheers,
gr2vessels

 

[moltenmetal]

gr2vessels: a star for you. I'd never seen these flanges before. How widely are they used? How available are they? And at what minimum size do they start making sense relative to the RFs?

 

[jte]

gr2-

Agreed, my perspective is primarily on downstream oil business issues, and the replacements/conversions I've seen are in refineries. Haven't seen one of the "Norsok" flanges in a refinery yet.

But my perspective is widening - I'm doing more and more upstream work...

jt

 

[Giuss]

Also my perspective is on downstream and petrochemicals businesses, where no Licensor/Company yet specifies 'Norsok' Flanges.

Giuss

 

[gr2vessels]

Gents,
The Norsok standard L-005 has been developed on the basis of those available flanges, developed first by "Vector International" (

http://www.vectorint.com),

then a few other follow-up companies. A whole new industry has been created on the back of these flanges, expanding into compact clamps, etc...The most rotten experience I have had with these flanges, when the Victor rep sank flush a compact flange inside the corresponding (equivalent rating) ASME B16.5 flange...Major players in the sub-sea exploration and oil/gas extraction, like Reliance in the Indian ocean, have replaced almost every B16.47 flange with the equivalent Norsok compact flange. I believe this is a relatively new dawn...
Cheers,
gr2vessels

 

[maddocks]

In our extensive acid gas injection work, we've had the most luck with RTJ flanges. Granted, seat cleanliness is critical as is proper bolting technique and torque levels. RTJ can be difficult to work with inside a package where you are unable to "spring" the piping apart to get the valves out. Recent testing last year on a series of RTJ vs RF flange sets proved this again - RTJ provided a consistently better seal. Yes, RTJ can be difficult but it's my connection of choice in high pressure sour applications.

 

[PAN]

Please check this related thread.

RTJ VS RF FLANGES IN 900# SERVICE
thread378-96151

 

[azigue]

Some ather products could be use on RTJ flanges with good results and avoiding cracks and over stress within flanges:

http://www.garlock.eu.com/pdfs/Kataloge_GB/Gasketing_GB/OMICRON_GB_JAN-2000.PDF

http://www.pikotek.com/

 

[gerhardl]

Even if most of you out there seems to be oil, gas and process connected:

For hydroelectric powerplants turbine inlet valves, with flanges at PN25 (25bar) or higher classes (water), (sometimes also for lower classes larger dimensions), flanges are commonly described with o-ring groves one side, and flat face counterflanges.

 

[europipe]

Gerhard, do you know the EN (or DIN) standard of these flanges with o-rings?
Much obliged,
greetings