Dear all,

I couldn’t find the definition of the 2 abbreviations in the BS EN 1591-1.

They are “hD ” in section G.3.4.1 (formula G .1) of Annex G and “m” in section G.3.4.4(formula G .17) of Annex G.

Please help to indicate where they are or clarify them.

Thank you very much.

I never used that informative Annex G of EN 1591-1. It has no correspondent in EN 13445-3.

I can give you just some speculations on the subject, not a documented engineering answer.

1. In the beginning of Annex G there are some explanations. Some gaskets have an outer spacer-ring in the form of a solid metal annulus (or similar 'rigid' material) which is located between the outer periphery of the sealing element of the gasket and the bolts. Spiral-wound gaskets often have an outer spacer-ring of this type.

The bolt load applied at assembly may be sufficiently high to seat the flange faces on the outer spacer ring of the gasket. In this case the flange faces, being (slightly) inclined, make initial contact with the outer periphery of the spacer ring.

In my understanding F_B(0*) is a "limit" force calculated on this bases (and as you can see, I prefer to use "_" instead of subscript).
The relation (G.1) "seems" to be a geometrical condition. By one hand there is the effect of flanges rotation at distance (h_G-h_D) and the (elastic) stiffness of the gasket. By the other hand at the outer edge of spacer there is a change during "bolt it up till spacer ring contact", as difference between e_G(0,0) i.e. the initial thickness of gasket and e_SR (spacer thickness).
So, if my interpretation is correct, h_D must define the outer periphery of the spacer ring.
I would imagine it is an arm defining the outer edge of spacer ring, considered in the same way as h_SR is defined (i.e. measured from the outer edge of spacer to F_B). In fact we may consider that the contact between spacer and flanges is just the beginning of the existence of F_SR, so -as definition- h_D would be similar to h_SR.
Again, this is just my speculation! What about your opinion?

2. About m- just another speculation. "m" is "crying" it is the "gasket compression factor" as it is (still) referred in EN 13445-3 Appendix G, which claims it is based on EN 1591-1. Reading G.9 of EN 13445-3 you can find out some details and values for "m". However, it is clear also that "EN" prefers to work with the "minimum" stress on gasket rather than with minimum "m*p" stress on gasket and that’s why EN 1591-1 tries to eliminate references to "m". In fact EN 1591-2:2008 is focused on this approach, giving you directly "minimum required compressive stress" Q_min[L], Q_Smin[L]
Returning to EN 1591-1 G 3.4.4 "Maximum internal fluid pressure" for me it appears that there EN was "forced" to consider an "m" as a part of non-dimensional parameter, because it was difficult to further complicate that subclause (the alternative would be to force a complicate equation working with Qmin/p instead of "m", but here EN preferred to maintain a "simple" relation). However the price is now a strange "m" appears there!

If you don't want to have this mix (as "m" imported from 13445-3)you may consider there is a note that says " This subclause [G.3.4.4] may be avoided. The next subclauses contain the same information in a more general way, but it does not clearly show the visible effect of the upper limit". Hmm, "clearly"....funny, isn’t it?

My best regards.

Hi Mariog,

Thanks for your reply.

Your speculation is quite logical.

Just follow the clue your provided. I get the defination "h_D".

h_D is the radial distance from bolt circle to circle on which HD acts;(EN 13445-3 Annex D)(and I hope it is right, hah)

Regarding the "m", I think it is gasket factor, as it is used to calcualte the pressure P_max.

By the way, do you have any clue for η_SR(I)in (G.23) of EN 1591?

thanks.

Hi learner,

I guess I succeeded to confuse you by referring to EN 13445-3.
EN 13445-3 has also clause 11. The requirements provided in that clause are based on the well established Taylor Forge rules. For that part it is clear what h_D is.

I made a reference to EN 13445-3 annex G which provides a "modern alternative". That annex G of EN 13445-3 (and only that part) is based on EN 1591-1:2001, Flanges and their joints - Design rules for gasketed circular flange connections.
That is why when discussing on EN 1591-1 you can have some clues in EN 13445-3 annex G but not in the other sections of EN 13445-3.

Unfortunately, you are immersed in a special case of EN 1591-1 which is not covered in EN 13445-3 annex G.
See EN 13445-3 annex G, G.4.1 "Conditions of applicability" , G.4.1.1 "Geometry" where they said:
The following configurations are excluded from the scope of the method:
[...]
— flange joints having metal to metal contact between the flanges or between the flanges and a spacer ring fitted either inside or outside the gasket or inside or outside the bolts. An example is a spiral wound gasket on a high pressure application.

That is why I can only speculate about h_D in this case. We haven't any clue on h_D in EN 13445-3 annex G and they forgot to explain the meaning of h_D inside EN 1591-1.

I made a reference on "m" from EN 13445-3 annex G because I think in both EN 1591-1 and EN 13445-3 annex G, "m" is the gasket compression factor and you can find table with values in EN 13445-3 annex G. I cannot prove it is true my assumption.
One more thing....while "m" is clearly explained in EN 13445-3 annex G, in EN 1591-1 they made great efforts to avoid using of any "m". Inside EN 1591-1 the only place where "m" appears is subclause G.3.4.4.
But - at least- here the things are more "clear" because EN 1591-1 said the subclause [G.3.4.4] may be avoided, and the unexplained "m" appears only in that section.

Now it is a little more clear the matter?

As I said, I never used that informative Annex G of EN 1591-1. Now I understand why it has no correspondent in EN 13445-3- because that Annex G belong to EN 1591-1 seems to be beyond the engineering common sense… It is not sound engineering presenting incomplete information about notation used and I don't understand this approach under European Norm!

You are right, in G.3.4.5 "Forces in subsequent conditions", they present the fluid pressure force F_Q(I*) - that ends the spacer contact- as:
F_Q(I*) = F_SR(0) / η_SR(I) (G.23)
but there is no explanation on η_SR(I).

Probably there is a way to recover the meaning of η_SR(I) if the information in EN 1591-1 Annex G is enough to reconstruct step-by-step the flanges rotations and flexibility parameters related to each status of this nonlinear evolution (due to contact or non-contact with the spacer). It may be interesting for someone who has enough time for it, but is not my case.
In addition, I consider that what really is missing in EN 1591-1 Annex G is they don’t consider any additional (external) load in method- now I understand better why... but now the utility of this special part of EN 1591-1 appears as questionable for a lot of practical applications.

My best regards.