mating valve with the pipe of different class

[JuliusC]

I have a question about the valve and pipe connection, I went through the threads here i couldn;t find an answer.

I want to know if it is possible to mate the valve with the pipeline of different class?? Suppose, flange of the pipe is class 150 and we want to use the valve of class 300 due to the press & temp rating of the valve. Is there any some kind of connector availabe or any othe possible way that enables the valve to connect to the differnt class pipe??

Sorry, I am unfamilier with the valve and pipe system, I would greatly appreciate if I can get some answers on my question.

 

[LittleInch]

Ok, being fairly basic here -

Pipe is designed to a design pressure not a "class". This design pressure is variable and allows different thickness of pipe to be used for different design pressures and reduces steel and cost to a minimum. Whilst some companies decide to set the design pressure to the same as the Flange rating / class, this is inefficient and Design pressure of the pipe / system can vary widely.

Valves and fittings / flanges on the other hand are provided in discrete pressure ratings to limit the number of designs. Hence in the ASME system this is class 150, 300, 600 etc.

When designing a piping system the pressure rating of the valve / flange needs to be at least equal to or above that of the pipe / system.

Hence you can install a class 300 valve with class 300 flanges onto a pipe only designed to the class 150 design pressure OR LESS. You are NOT able to directly connect a valve of one class to flanges of another class - the bolt numbers, size and BCD are all different and it won't work - Don't do it.

Is it a good idea? - NO, because 1) the next person down the line will only look at the valve and could easily assume that the pipe is fir for the same design pressure and 2) it costs a lot more for no benefit.

The excuse "we don't have a class 150 valve / flange / X" is simply lazy and inefficient execution and can lead to incorrect operation at a high pressure and consequential rupture and damage.

hope this helps your understanding


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[gerhardl]

The European view is a bit different, but of course depending of what the end-user allows. The comments below are considering not only petrochemical valves, but also water, steam and chemicals. The practise will vary from branch to branch.

For some valve classes and diameters and flange-norms a valve of higher 'class' (allowed working pressure) than the pipeline will have flanges that directly fit the normal flanges (one flange-class lower) on the pipe.

To my knowledge there is no rules stating that this is not allowed, but the whole systems working pressure is of course determined by the allowed pressure for the weakest component, in this case the pipeline.

QA and documentation and marking of components and pipeline is acknowledged to give correct use of a piping system.

Some smaller valves are even normally produced to cover two or three pipeline cases, and flanges for theese sizes and classes have the same EU norm.

If this is not the case and larger valves with higer classes and more solid flanges have to be used for lower class pipelines I have seen flange borings beeing adjusted to fit lower class flanges. In this case mostly done without qualifying tests (experience shows flanges, OK or 'visually' only small changes). There is of course a question mark with this procedure, but sometimes a special valve is not found or easily procured at the lower, correct class.

There is else always the opportunity to produce adapting flanges with pin-screws mounted on both sides to fit different flanges each side, or use mounting pieces or spool-pieces with flanges adapted to the counterflanges on pipeline and valves.

However, to use a single valve of lower class in a higher class pipeline is not to recommend and should be avoideed. Here I agree with LittleInch. On the other hand for a whole pipeline system to use valves and counterflanges of a lower class is not uncommon, but the systems class is then again given by the valve-class.

 

[LittleInch]

gerhardl,

I accept that there might be a few cases where flanges of one class or pressure rating will match a different one, but my point is that this is quite rare and in any event is not a good thing to do as it can easily confuse people who simply look at the valve and incorrectly assume that the whole system is then "rated" to that pressure or class rating.

The confusion caused by using valves and flanges of a different rating (higher or lower) than the rest of the system has led in the past to a number of incidents and, IMHO, should be avoided. Boring out flange holes or using adaptor plates makes the situation worse and should only be used to connect similar rating, but different code items together, e.g. PN rated to ASME rated systems.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[themad1]

Is a no-no to put in a pipeline a component whith flanges having different pressure rating than those of the system in which it is assembled. Even if the rating of component is greater than the line.

If this where allowed so we could use only 3 pressure ratings (300-900-2500) and than flange adapters! It does not make sense.

This can risult in dangerous misunderstandings

Changing of pressure rating is allowed downstream of pressure regulating valves only in my experience as piping designer.

 

[LittleInch]

themad1,

It is generally a no no to put into a system flanges and equipment rated for a lower design pressure than the system as this then reduces the design pressure to that level.

Most pipeline systems contain flanges and equipment rated to the next highest pressure rating from the pipeline, e.g. class 300 flanges/valves for a pipeline with design pressure of 35 barg and class 600 flanges / valves for a pipeline with design pressure 70 barg. You don't normally see class 900 flanges / valves on a pipeline designed for 70 barg.

I'm afraid I don't understand your point in line 2 and as noted above, you would not be restricted.

I agree with your last para.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.