Stress in Pipe due to Shear Lug/Plate 1

[StressGuy]

Alright, I'm working my way through a design and I'm struggling a bit with this last step. I have a horizontal line that is restrained using a hold down strap (vibration strap) and I am attaching a rolled plate to the top 180° of the line. It basically looks like half of a full encirclement reinforcement pad. The plate is to act as a bumper against the clamp as an emergency stop in the event of a line break. I've designed the strap, bolting, shear plate, and weld for the load due to the pressure thrust of the line.

However, I'm having trouble making the final step of the effect of the weld line itself on the stress in the pipe. The plate is welded to the line on three sides - the two longitudinal sides, and one of the 180° sides. The other 180° side is up against the strap. This configuration was chosen to keep the force on the pipe as close to a pure shear as possible and minimize bending. Most of the references and techniques I'm familiar with are concerned with the effect of bending due to the moment arm of an attachment like a shoe or dummy leg. The shear aspect seems to generally be neglected as not contributing greatly to the stress. However, in this case, the shear is really the only contributor to the stress.

I'm going to take another run through my Roark Stress and Strain to see if I've just missed the application somewhere. If anyone has any other references, I'd appreciate it.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.

 

[MJCronin]

Ed,

Find someone with Nuclear Plant piping design experience and see if they have an old Bechtel or Stone & Webster pipe lug guideline. These companies developed an integrated guideline for evaluation of pipe lugs and the combination of stresses on the pipe wall.

The Piping fabrication Institute (PFI) published a guidleine on lugs and allowable weld shear versus temperature (

http://www.pfi-institute.org)

see publication ES-26

Additionally, ASME wrote two code cases some 15 years ago that addresses the problem you are interested with. You should contact a Mr. John Breen (a frequent eng-tips contributor)who is very familiar with these code cases and thier application.....

Hope that this helps


MJC

 

[abeltio]

depending on the size of the piping, would the zick´s method give an approximate result of any value?

 

[MJCronin]

abeltio,

Nope,

The LP Zick methodology is used where there is a saddle support on a thin-walled horizontal cylinder. The highest developed stresses are commonly found at the "horns" of the saddle. Since the problem described by "STRESSGUY" is on a piping system, the Zick method is inappropriate....

The 1950's era Zick paper is still in use because it contains empirical curves which were developed at considerable time and expense.

See these links for more info:

http://www.computereng.com/products/zss.htm

revobiz.dyndns.org/group/seaint/2002a/msg00741.html


Good Luck

MJC

 

[piping1971]

Ed,
Right now I am working on a nuclear project in Taiwan and
we analyzed all rectangular or circular attachments on piping and here are the Nuclear Code Cases(ASME SEC III Div. 1) that we used.

N-122-2 Procedure for Evaluation of the Design of Rectangular Cross Section Attachmnents on Class 1 piping

N-318-5 Procedure for Evaluation of the Design of Rectangular Cross Section Attachmnents on Class 2 & 3 piping

N-391-2 Procedure for Evaluation of the Design of Hollow Circular Cross Section Attachmnents on Class 1 piping

N-392-3 Procedure for Evaluation of the Design of Hollow Circular Cross Section Attachmnents on Class 2 & 3 piping

These code cases are already in a program by GE,so the only thing that we do is just specify the lug sizes and input the
load on the lugs and the program will combine the stress due to lugs.

Regards,
Ellie

 

[StressGuy]

I'll definitely check those out. Thanks! Edward L. Klein
Pipe Stress Engineer
Houston, Texas

All opinions expressed here are my own and not my company's.