Flanged Valve - Mating Bore 2

[McDermott1711]

Hi everyone,
In most of project I was involved in, flanged valves were purchased based on the rating and size of the mating flanges. I mean nothing is said with regard to the schedule of the pipe. I know that internal bore is important when purchasing welding end valves, but I haven't deal with specifying of internal bore when purchasing flanged valves. ASME B16.34 correlates flange thickness (say internal diameter) to the ASME B16.5, which in turn has mixed dimension for internal diameter (depending on the size and rating). For, say 600#, 24", internal bore shall be specified by purchaser.
My question:
Is it possible to have different bore diameter at the mating flanges (for 24", 6000#). If so, what's maximum allowable difference?
Thanks in advance.

 

[gerhardl]

'Internal bore' of a ball-valve is normally used for the actual opening in the ball itself. For a reuced bore ball-valve, where the opening in the ball is less than the nominal inner piping diameter, the entering opening of the valve flange will match the full opening of a sheduled standard opening of the counter flange on the pipeline, eg. both at full pipeline diameter. From the ball-valve flange there is normally a cone reduction to the ball opening at a reduced bore bsll-valve.

I do however, from your description, belive that you are actually talking about the allowable difference between the entering hole through the valve's flange compared to the bore of the standardized bore of the pipeline's counter flange.

I do not believe anything is noted down in regulations here as long as the flanges matches (strength of flanges and the general construction of pipeline and valve), but others might correct me here.

If we are talking about ball-valves we have also to consider possible pigging and allowed differences according to pig-type, if there is an abrupt change of diameter from pipeline flange to valve flange.

Else, for all types of valves, we will have to consider increased hydraulic loss, possible cavitation, and actual capacity of the valve for the different pressure and flow data. For some types of (smaller) valves other than ball-valves, flow capacity might vary from valvetype to valvetype, not directly proportional to piping diameter. This is often the case for regulation valves.

There are, for some (larger) types of regulation valves (for instance german 'ringkolben' (needle) valves) from 150 mm up to 1000mm) cases where a valve of lesser diameter is used to give the correct regulation for a larger pipeline. The valve is often then mounted to the upstream pipeline with an abrupt diameter change (most often 1 to 2 valve diameters smaller than the pipeline diameter) given by a flat reducing flange. This will (depending of flow amount) give a better linear flow through the valve than a longer cone reducing tube for many cases.

Concluding on your question: for normal cases 'small' differences might be negliable whereas 'larger' differences might be more complicated, but as said: all depending on flow parameters.

(Others may have things to add or correct.)

 

[Manichum]

I am not aware of ``schedules`` playing any part in flanged valves.
Only related Butt end valves.

For tolerances on an ID refer to ASME B16.5

 

[McDermott1711]

Thanks gerhardl and Manichum for your reply.
It seems having different bore sizes at the junction of a full bore, flanged ball valve and its mating weld neck flange is not unlikely. So, what is The allowable difference in this regard? Doesn't this step cause excessive noise in the plant (supposed fluid is natural gas)? And, what about the gasket? Can the vortex damage the gasket?

 

[LittleInch]

Matching internal bore of the valve to the pipe is only really needed for pipeline "through bore" valves where passage of pigs is possible / required. Anywhere else there is no significant impact to a minor mis-match of internal bores.

Gerhardls post says it better than me and I agree with him.

The difference is a few mm so I would not expect any noise or any other effect. The gasket is completely hidden from the flow path so has no impact. Even where the bores match there is a gap between the internal flange faces on ASME flanges all over the place and you don't hear anything.

I assume by the way you meant class 600, not 6000...

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

 

[McDermott1711]

Yes, LittleInch, it's my mistype and 600# is correct. So, if for that 24" valve the step was 20 mm, is it ok or some action should be done.

 

[LittleInch]

If the line isn't to be pigged then I would ignore it, but a step of 20mm sounds rather big. mismatch of bore of 20mm is ok.

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