Monday, September 8, 2014

NO hit in Safety Factor in federal regs for LF-ERW pipe!

I'm trying to decypher the federal formula for Class, MAOP, PIR, HCA, etc.
These federal regs are really convoluted.

Here's one thing I've found so far--
...specifically, Lap, ERW, and EFW welds,
there is NO HIT in the Safety Factor
under federal regulations for any of these

To explain:

Barlow's Formula is used to determine MAOP: 
MAOP=2*S*T * 1/(D*SF)

Federal MAOP formula is a variant of Barlow's formula:
MAOP=2*S*T * (1/D) * F * E * T

F=Design Factor 
E=Longitudinal Joint Factor
T=Temperature derating Factor

Notice that 1/(F*E*T) = Safety Factor (SF) in Barlow's Formula.
So if F*E*T = 0.1 in the Federal Formula,
this is equivalent to a Safety Factor of 10 in Barlow's formula.

So wherever either F, E, or T=1, this is like a SF=1, meaning, no safety factor.

49 CFR 192.111 - Design factor ( F ) for steel pipe

This is solely a function of Class:
  • Class 1=0.72  (SF=1.39)   Rural
  • Class 2=0.6  (SF=1.7)
  • Class 3=0.5  (SF=2)
  • Class 4=0.4   (SF=2.5)   Cities

49 CFR 192.113 - Longitudinal joint factor ( E ) for steel pipe.

Range is from E=1 (SF=1, no safety factor)
to E=0.6 (SF=1.67)

NOTE that ERW, and EFW are specifically mentioned in the regs,
however they have an E=1 (no safety factor!!)

49 CFR 192.115 - Temperature derating factor ( T ) for steel pipe.

Range from T=1.0 for 250'F (no safety factor)
to T=0.867 for 450'F (SF=1.15)

So if we calculate the cumulative
F(min) * E(min) * T(min) = 0.4 * 0.6 * 0.867 = 0.20808, SF=4.8
F(max) * E(max) * T(max) = 0.72 * 1 * 1 = 0.72, SF=1.39

This does not take into account pipelines rated under Alternate MAOP.

More soon...


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