Y coefficient B31.3

Can anyone tell me the origin of the Y coefficient (table 304.1.1, B31.3). Any references?

Thanks in advance

Hello Mr. Massabie,

The "Y" coefficient is just to address the increased ductility of piping materials as the temperature increases (and we only use it in our "hoop stress" based pipe wall thickness calculation). It has been with us for a long time (pre 1955) but I think you would have to go back to some of the very early ASME collected papers publications to see how it was developed. I don't have anything in the way of a reference here at the office. I shall have a look around.

Regards, John.

Well, thanks if you find something just let me know.

Thanks again

John is right…
Please refer to the ASME Paper No. 52-A-151, “A Wall Thickness Formula for High-pressure High-temperature Piping”, 1952, W.R.Burrows, R.Michel, and A.W.Rankin

This paper was contributed by the Power Division for presentation at the Anunual Meeting, Nov.30~Oct.05, 1952 of the ASME.

The Y factor actually comes from the Boardman equation which provides an empirical correlation w.r.t the complex Lame equation .

According to Lame eqn. the hoop stress is a function of radius. This intuitively indicates that the hoop stress eqn. based on ID will be less conservative for the Inner Radius and more conservative for the outer radius.

To get a physical understanding of the Y factor, it is best that you write the expression for wall thickness using the ID formula. Then non dimensionalize it ( factors like sigma/P, D/T etc will come where sigma is the stress, P is the pressure, D is the diameter and T is the thickness).

You should get an expression of the form :
sigma/P= (D/2T)-1, where D is the outer diameter.T is the wall thickness.Now sigma increases ( for a constant P, D and T) as the factor 1 drops down further ie. if we subtract a value less than one, we get the value of sigma which is more conservative. Suppose we subtract a factor of 0.4 we get a more conservative value of sigma.

This is how the factor Y can be explained. More precisely if we base the hoop stress on some intermediate Diamemer instead of ID, we approach what is known as Boardman's eqn.

At high temp. stress tend to equalize across the thickness.So Y increases.

Regards

In Indian Boiler Regulation 350, piping thickness calculation under internal pressure considers 0.5 in place of Y in eq 3a of 304.1.2 of ASME B 31.3 for all types of ferritic,austenitic steels & other ductile metals.

Is IBR-350 formula based on any older thickness calculation formula than ASME thickness calculation chosen among many such formulae available ?

I have a query regarding ASME allowable stress in creep range: when creep & rupture based allowables are for 100,000 hrs, how do we design a power/process plant for 30/40 years (2.5E5 -3.5E5 hrs) continuous operation ?

If we do not meet hoop stress allowables at design temperature in creep range, does it mean that it will remain safe for, say first 5 years of construction, considering higher allowable Sh ?

regards,

sam

Sam,

I cannot tell about the exact origin of the Indian Boiler Regulation IBR-350 Formula, but can throw a light on the probable sources.

The current code ( American Codes) formulas area result of work done by
Bailey-Nadai,Barlows, Boardman , Lame etc.Based on what you have mentioned it seems that they are probably based on Barlow's and Boardman's approaches.

For your second question, I would like to mention the use of Larson Miller parameter. It is not possible to give a full description of the Larson Miller Parameter as it is quite a lengthy one. I would advise that you go to google or yahoo and type "Larson-Miller Parameter" in search. You will get ample information on this subject.

Regards

As mentioned, table 304.1.1 in B31.3 lists some values for this Y coefficient. Are these values implemented in ceasars material database? I have not come across any user input alternative yet.

Regards,

Jon Arne Habostad

In C2, Y defaults to 0.4 throughout.

As I was looking for the origin of the Y coefficient in the wall thickness calculation in the equations used in B31.3 and B31.1., I came across this post, and I found the link below covering it very well.

http://dalili.us/origin-of-y-coefficient-in-wall-thickness-calculation/