RTJ VS RF FLANGES IN 900# SERVICE 1

[CSGWB]

Can anyone tell me why RTJ flanges are often used over RF Flanges in certain services (eg natural gas) over 900# rating. Is this due to the additional risk of gasket failure in this higher pressure service or are there other factors, for example corrosion with sour gas, which influence the decision away from Spiral Wound gaskets?

Any assistance is appreciated.

 

[hacksaw]

RTJ are still in use but as I recall are been "phased" out. they are not easy to work with. as you expect flange alignment and bolting up is a critical matter.

believe that gaskets have improved and RF solutions are preferred.

 

[grampi1]

Our company (large inegrated oil) still specifies RTJ and often starts at 600lb for better integrity against gasket blowout/leaks. Not saying its right, but this is still a common practice.

While some companies can do a good job with RF, there are many shoddy assembly contractors and if they screw up, its a pretty big deal in hydrocarbon service, particularly at high pressures.

Unless you really know what your doing, might be best to stick with RTJ.

 

[PAN]

grampi1,

Do you reuse RTJ gasket after opening the flanges? We carry out visual inspection the surface of ring joint and reuse if possible. Please comment.

 

[unclesyd]

I don't think RTJ's are being phased out even with the improvement in gasket, namely the spiral wound variety with inner rings. There is also increasing use of different flange types such as the compact flanges like Greylock and especially the Taper-lok.

Our piping specifications still call out RTJs’ on any steam above 300 psig and if there is 100°F superheat at 300 psig a RTJ is called out.
We have a very large distribution network of hot and vaporized heating medium operating at 70 psig @ 700°F with all flanges being RTJs’. Each system/unit is dismantled on regular interval and roughly 200 RTJs’ are broken on each overhaul. We don’t reuse any of the bull rings.
Some of the flanges are 50 years old and been broken 30-40 times and still function. The system operates from vacuum to 30 psig. All rings in this system are Armco Iron (soft iron). We don't use torque wrenches on RTJs'

Over the years I have personally ran several tests on the reuse of bull rings. The results with over 1000 recycled rings there were no leaks. The normal leak rate for new bull rings is probably 1::1000. The first batch (300) of used bull rings were collected, inspected to remove the obviously damaged ones and then cleaned and polished in a vibratory cleaner for 4 hrs. and installed after a quick inspection. The second batch (300) was recycled the same way except that only about 25% of the original time in the vibratory cleaner. The last batch (200) was only carefully inspected and reused.

I don’t know whether it is still true but the Navy did reuse bull tings on their high pressure hydraulic systems. They had lined boxes to hold the rings and treated them with extreme care. At the time I became aware of this I was with an inspector from another company that also uses RTJs’ and after the fact I asked him if they reused the bull rings and his answer was no.

 

[LSThill]

Other Piping Classification Specification have RJ FLANGE:

Class 1500 operating above 500?F and all higher pressure classes shall have raised face or ring joint flanges, Graylocs, or other pressure assisted, metallic connectors.

 

[grampi1]

Re-use of RTJ rings.

One should be very careful, and again understand what is going on, before reusing. For ANSI class RTJ, compression bolting load may or may not result in plastic deformation of the gasket. Plastic deformation will make re-use very problematic. API 6A wellhead BX PEG's may never be re-used for this reason, e.g. the design requires plastic deformation.

If the RTG gasket has not been plasatically deformed, re-use can be considered. But how will you know if the gasket has dimensionally changed unless it is measured?

 

[unclesyd]

grampi1,
Whole hardly agree with you on the reuse of RTJ rings if damaged or there is any question of being able to maintain a tight joint.
In other words "When in Doubt Throw it Out".
This was essentially what I accomplished in my tests. I have found that an oval ring if handled and installed correctly undergoes very little deformation. The thing that helped us was that our flanges were essentially on centers and parallel and the mechanics knew how and would install the rings correctly.
A little anecdote to RTJ gasket installation was the ironclad rule if you installed a ring in a flange ALL bolts were to be installed and tightened before you left the flange even if you had to pee in your pants.

I should have qualified my statements a little further.
All these recycled bull rings were Oval and the largest was R-23 and all were Armco Iron. These bull rings were all used on a Therminol (Vaporized) heating system operating at a maximum of 70 psig and 700°F mostly 30 psig. All this system is in an occupied building and has to be as close to leak free as possible, both from the allowables and people factor.

They are still using new rings on overhauls as the push to reuse rings has changed due to reduction in annual usage of bull rings in this area being cut by 60%-70%. I never attempted to reuse anything larger than R-23 or any type ring in steam service.