RF verses RTJ 2

[chasserman]

Hello,

I need to write a decision paper for the selection of RF flanges in lieu of RTJ for 900# oil systems. The project is based in IRAQ where the labour force is low skilled and generally heavy handed with piping systems. The selection of RF will greatly assist systems completion during leak testing and should reduce the amount of leaks due to poor quality installation of gaskets by the workforce which will be difficult to control on plants of this size, $2.5B or greater.

Can anyone offer me some technical support for this selection ?

Thanks

Chasserman
Basra Iraq

 

[BigInch]

I think you just wrote it.

Independent events are seldomly independent.

 

[LittleInch]

Chasserman.

First off, IMHO you are trying to solve your immediate problem at the risk of long term integrity and safety issues. #900 oil systems are not to be trifled with. If anything in this system goes wrong you can end up with an inferno.

I'm sorry but I just can't see why rf will be better than rtj in completing your service. If your workforce is low skilled then you need to employ more inspectors, not change a fundamental design requirement.

The reason that rtj is preferred over rf at these sorts of pressure class is that the sealing force is more concentrated and more importantly in the event of joint failure, the gasket does not fail and only leaks (rtj) vs failing completely (rf) and resulting in a very high velocity jet which can cause serious injury , jet fies and higher leakage.

Like my strapline suggests there is a good reason why virtually every one else does it this way so I think you're going to found it difficult to come up with convincing reasons to do it another way.

Trying to justify a design change by saying that your workforce is not up to the job is, IMHO, not the way to go and at the end of the day that's all I can offer I'm afraid.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[tothepoint]

You are going to end up with many leaking RTJ gaskets if they're installed with low skilled labor. You had better have assembly training for these fitters and a defined assembly procedure and target torque value if you stay with RJ flanges. You didn't mention temperature or pressure, but I would favor conventional spiral wound gaskets and RF class 900 flanges if temp is not >950F.

 

[bigreddog]

tothepoint is right. Good ol SPWD gaskets when over torqued will tend to "curl" and you can see that just by looking at it after bolt-up. If that's the case, throw it out and get a new one.... cheap. RTJ on the other hand will not give you much indication and like the previous post, you will end up with a lot of leaky joints. Also, with the low skilled labour that you speak of, I'm sure that after bolting everything up for hydro, they will get the hang of it (using spiral wound gaskets that is).

 

[Krausen]

RF are the preferred flange types, regardless of pressure class, as an engineer & from most operations points of view nowadays. Liquids has gone completely RF for years.

RTJs can have issues:

1. Keeping clean - the grooves can accumulate dirt, moisture, etc when the flange is open. A small amount of damage (including corrosion) on the narrow sealing surface(s) may lead to a leak.
2. Finding the appropriate RTJ gasket(s) can be problematic nowadays.
3. RTJs require more skilled labor to fit. Grooves and gasket must align properly to obtain the rated seal pressure. They must stay aligned throughout the operating cycle.
4. Dissimilar metals - Thermal expansion is a major concern if mating dissimilar metal RTJ flanges. Local stresses due to differential expansion can potentially lead to ring groove cracking and catastrophic failure.

 

[TWP]

Dear sir,

I'm designing piping systems for 30+ years and did also design all kinds of vessels for the Oil&Gas business. I would always go for spiral wound gaskets (unless customers dictate the use of RTJ's). SPW's from reputable SPW manufacturers are very reliable and have been used up to 350 bar (up to 200 Celsius). Pipe sizes range from NPS 1/2 - NPS 36. Materials from simple plain C steels up to the exotics. Never had problems with SPW,s. SPW with centring ring AND inner ring (!).

Although RTJ gaskets are robust, alignment is very critical. I only would recommend OCTAGONAL type RTJ's if you are forced to use RTJ's. OVAL types require detailed mechanical analysis; otherwise they will not seal for long.

Mechanics must be certified and you must have a flange management system or a detailed torque/ bolting up procedure.
All applications need to be mechanically designed prior to installation. Design on basis of ASME design codes recommended for ASME based flanges. This applies to all used types of gaskets.