To prevent…..
Minimum Data required to start supporting:
Pipe Span :
Typically piping is supported at regular intervals on steel supports embedded in concrete foundation or directly on steel structure. The distance between supports is the span.
Basis for calculation of Maximum support span:
There are three main factors which affects the support span.
ii. Supporting of non critical lines:
iii. Supporting of Insulated Pipes:
iv. Supporting of Non- Insulated Pipes:
Directly rested except following
v. Vertical pipes:
Basically codes do not take account of local stresses in pipe support not like pressure containment parts. It is because normally the structural members are analyzed using beam type elements. The constant stress is special and the buckling shall be another design consideration to take care.
For example, ASME B31.3 requires stresses for pipe supporting elements in the following:
321.1.3 Stresses for Pipe Supporting Elements.
Allowable stresses for materials used for pipe supporting elements, except springs, shall be in accordance with para. 302.3.1. Longitudinal weld joint factors, Ej, however, need not be applied to the allowable stresses for welded piping components which are to be used for pipe supporting elements.
302.3.1 General. The allowable stresses defined in paras. 302.3.1(a), (b), and (c) shall be used in design calculations unless modified by other provisions of this Code.
...
(b) Shear and Bearing. Allowable stresses in shear shall be 0.80 times the basic allowable stress in tension tabulated in Table A-1 or A-2. Allowable stress in bearing shall be 1.60 times that value.
The detailed analyses using FEM performed to categorize clamp induce piping loads as primary, secondary and peak in nature, and the due considerations shall be paid to allowable stresses in accordance with the corresponding failure modes regarding pressure components and supporting devices. If bolts and nut are modeled with threads, the maximum stress is easily beyond yield at first thread when fastened. But this phenomena is allowed if the integrity is guaranteed as a whole.
In addition, the experimental performance check validates the integrity as well.
Please consult hanger manufactures what they think about the best practice for their support design in standing point of safety and cost.
Related information
WRC Bulletin No 353 - Position Paper on Nuclear Plant Pipe Supports
Pipe hanger manufactures
http://www.thomasnet.com/products/pipe-hangers-36890200-1.html
http://www.amfibi.com/us/7085-pipe_hangers_manufacturers
http://dir.indiamart.com/impcat/pipe-hangers.html
http://www.alibaba.com/showroom/pipe-hanger.html
MSS SP-58 Pipe Hangers and Supports - Materials, Design, Manufacture, Selection, Application, and Installation (ANSI-approved American National Standard)
MSS SP-69 Pipe e Hangers and Supports – Selection and Application (ANSI-approved American National Standard)
MSS SP-77 Guidelines for Pipe Support Contractual Relationships and Responsibilities of the Pipe Hanger Contractor with the Purchaser's Engineer or the Pipe Fabricator and/or Erector
MSS SP-89 Pipe Hangers and Supports - Fabrication and Installation Practices
MSS SP-90 Guidelines on Terminology for Pipe Hangers and Supports
MSS SP-127 Bracing for Piping Systems Seismic-Wind-Dynamic Design, Selection, Application
Design practice - Bare pipe on beam
Kellogg formula, beam on elastic foundation,
(2/3)S(d+b)(t^2)
Allowable span L (feet) = ----------------------
(0.644)W(R/t)^0.5
S - Hot Basic Allow. Stress (psi)
d - support beam width, inches
b - bearing width, 1.5% of pipe OD, inches
t - corroded wall thickness, plus any repad, inches
W - unit weight of pipe and contents, lb/ft
R - pipe radius, OD/2, inches
This limits the local stress due to bearing to 67% of S(hot)
Peng book, chapter 5.6, where the circumferential membrane stress in pipe is taken as
S=0.643*f*[sqrt(R)]/[t^1.5]. There "f" is the load per unit length of circumference,
f =W*L/(d+b)
So, S=0.643*[W*L/(d+b)]*[(R/t)^0.5]/t
Limiting stress to 67% of S_hot (a safety coefficient of 1.5)
Normally pad should be provided for nominal diameter larger than 10".