Flange leakage Calculation acc to Blick method

[DavidL]

Hi,
I wonder if anyone have an old paper for made by Robert G Blick "Bending Moments and Leakage at Flanged Joints"?
I got two formulas presented below but I need the background to get a better understanding similiar as peng presented:

[link Point to another website Only the registered members can access] Checking for leakage
M<G*Ab*Sb/4-p*pi*G²/2*(G/8+b*m)

Checking for gasket crushing:
M<p*pi*G³/16+pi*G²*y*n/2-G*Ab*Sb/4
Ab=Bolt area
Sb=Allowable bolt stress
G=Gasket min diameter
y=Gasket seating stress
m=gasket factor
n=Gasket width
p=design pressure
b=effective gasket width

Regards
D

[tony_black]

I have that article - just give me a day or two to dig it up.

[tony_black]

Find link below for the 3 part series "Bending Moments and Leakage at Flanged Joints"

[link Point to another website Only the registered members can access]

[mariog]

Thanks for sharing your ideas.
Tony_Black, special thanks for sharing Blick articles. I’ve used one of Blick formulas for quite long time having no idea it is Blick work but "rediscovering" it myself!

I would like to add my thoughts on the subject.

First- a simplification- it is very useful to follow ASME approach where forces appear to be "global" but in fact this is just a convention. Let me explain the case of a moment M applied on a circular plate. The reaction on G diameter is 4M/G/(PI*G)*cos (theta) where theta is a polar-angular variable. On theta=0 the peak reaction is 4M/G/(PI*G), on opposite side we say it is -4M/G/(PI*G).
We can apply this local distributed forces (depending on theta) on a "infinitesimal slice" of circular plate and after writing the equilibrium conditions we can say the forces (that must be in equilibrium with M) appears as maximum -4M/G on tensile loaded part and 4M/G on compressed part (signs depends on reference system). So such forces can be written conventionally as "global" while they are local and dependent on theta defined direction- this is the ASME convention.

According to this convention, gasket load on "tensile" loaded part of flange –as circular plate- is:
HG = W -p*PI/4*G^2 -4*M/G-F, where W is Bolts Load and F,M are the external loads, under the assumption that gasket is carrying-on the external loads.

Both Blick method and Kellogg (EQP) method are counting in this way the gasket reaction.
In my opinion none of them counts the stress in flange, rather they are dedicated to count leakage danger.
This opinion may be in contradiction with the common opinion and I try to argue on this subject.

Taylor Forge and ASME VIII are methods counting flange stress and "J" index is a last hour improvement. The only problem would be the way in which we are counting "J" index under pressure and external loads.


A. Kellogg EQP method counts the gasket reaction in terms of equivalent pressure.
For tensile force this "transform" procedure is easy: a tensile F force has the same effect on gasket as a pressure:
P1=F/(PI/4*G^2)=4*F/(PI* G^2).
For a bending moment, the peak effect on gasket is a force of 4M/G magnitude and that force has the same effect on gasket reaction as a pressure:
P2=(4M/G)/(PI/4*G^2)=16*M/(PI* G^3).

So the total pressure is done by:
HG= W - Pt *PI/4*G^2
and the result is
Pt= operating pressure+ 4*F/(PI* G^2)+ 16*M/(PI* G^3), under the assumption the external F and M act on gasket, while bolts are not participating

The condition for "non leakage" is to maintain this gasket reaction "big enough".
Kellogg fellows have considered this condition as "gasket load big enough means over the gasket load in rating pressure", i.e
W - Pt *PI/4*G^2 > W – P_rating*PI/4*G^2

So Pt< P_rating.

I guess the simplicity of this condition explains the success of this approach, while the method is very conservative. In rating pressure status, the gasket can be considerable tight, not near the leakage! Rating pressure is not a real "leakage" limit for gasket; instead it is a conservative one.


B. Blick method follows the same approach but the gasket "leakage" condition is more realistic.
For the case the tensile force F is missing, the gasket reaction is
HG = W -p*PI/4*G^2 -4*M/G
and is considered greater than
2*b*PI*G*m*p
(which is the condition to have at least "mp" stress on gasket, the same as considered by Taylor Forge- ASME VIII)

This condition leads to:
M < G/4*W -PI/16* p*G^3 -PI/2*b* G^2*m*p
or
M < G/4*Sop*Ab-PI/2* p*G^2*(G/8+m*b)
with Sop "operating" bolt stress.

Many quotations of Blick formula replace Sop with Sb.
The truth is that Sop (I’ve maintained the original notation from article!) is the central point of the problem, not only here, but in every serious method -including FEA, where the user must provide a bolt initial stress, or -alternatively- the initial bolt load. Maybe a value near 1.5Sb is more realistic as stress after bolt-up, but also realistic is to think we may have a variation for an individual bolt load, let's say of plus or minus 25% for one bolt load by manual bolt-up procedure, so finally for a single bolt it would be as 0.75*1.5Sb, let’s say Sb!

I would appreciate Blick method as realistic; however it may be still conservative because the gasket is counted as reacting under loads while the bolt load remains the same.

The formula explains qualitatively why we haven't leakage for most of practical cases; it is likely that we have in practice Sop more than Sb (remember ASME evaluation Sop=45000/sqrt(dia_bolt) in psi) and an experienced worker shall apply an uniform gasket tightening....

C. ASME VIII Div1 is the Taylor-Forge method. ASME VIII Div2 is also Taylor-Forge method modified by Koves. Both of them are specifically written for flange design case and are intended to count stress in flange.
Codes take into consideration two limit states: seating- bolt-up status and "design pressure status" and consider two minimum gasket load HG1 and HG2 for each case. Scope is to evaluate the flange stress in these cases.

When using Code for flange checking, the common perception is that for every pressure the gasket reaction is 2*b*PI*G*m*p. In other words, the Code requirement to have at least 2*b*PI*G*m*p_design -as gasket reaction for p_design- it is currently interpreted as valid for every pressure as 2*b*PI*G*m*p.
If the last were true, in p=0 case HG would be zero, while the actual gasket load for p=0 is that done by bolt-up procedure!
So I would consider that the real meaning of 2*b*PI*G*m*p is that the minimum required gasket load under pressure criteria can be taken as pressure proportional, since the minimum stress on gasket must be at least "mp" to have no leakage.

Probably the best description of this problem has been done by Blick himself, on the first page of Part I: "It should be noted that despite the fact that the code goes to great lengths to avoid defining the gasket load, the implication is there"

So my personal remark is an warning about applying Code for checking flange purpose by using a gasket load which is not in equilibrium with the rest of forces; if you think "this is the Code and I don't care about what it is" you should remember no Code can ask you to consider something out of basics. And one basic aspect is the gasket load is decreasing with pressure (p) and external loads (M and F) for most of practical applications and this is the main reason for which the leakage appears!
One possibility to interpret correctly the Code for flange checking case is to consider a gasket load expression.
It may be considered as HG = W -p*PI/4*G^2 -4*M/G-F, with the same W in bolt-up and under loads; it can be proved that loads and reactions are now in mechanical equilibrium.
This is in fact Blick's approach.
However one can keep in mind that this is "worse gasket scenario", while the actual bolts-gasket behavior can be caught with more accurate methods as EN or FEA.

Best regards.

[aarcela]

please reload it Thanks, the file doesn´t exist in "ifile.it".

[Bublimaddy]

please reload the article it is not available now!

Such classics we cannot get anywhere.

[mbc.engg]

Tony_Black thanks. You are Always ready to support...

[srikanthkumar]

Thanks Tony. Great info.

[DavidL]

Thanks a lot Tony_Black!
Really interesting reading, the formulas seems to be derived from basically two asumptions on page 119 (4 in Tony's pdf) the fG,min=m*p (I can buy this) but the second based on crushing < 2*y why is it two times y which Blick refers to as gasket yield stress?

D

[tony_black]

My instinctive first reaction would be he is considering 'y' as the "yield" strength, and, as is usually the case with metals/steels, the compressive strength is more than the tensile strength, and he figured 2x more, which seems appropriate for gasket metals.

[alp.altinok]

thank you Mr. Black

[Paldex]

hi all
can anyone upload the API674 API Standard , Its required urgent.,

Thnks