New WW & F Boilers or ASME Code Riveted Construction

M Austin · **Joined:** Sat Feb 05, 2005 1:05 am **Posts:** 488

Paul Boschan wrote:

M Austin wrote:

As this is presented, from 1914 to 2014 a riveted boiler could be built and certified as ASME Code compliant with a factor of safety of 4. As of 2015, if for what ever reason I should want to build a riveted Santa Fe 2900 boiler and put a Code Stamp on it, originally designed with a factor of safety of 4 for 300 psi, now the the factor of safety by Code is required to be 5 and the boiler maximum allowed pressure would only be 240 psi. Is this a correct read of the new Code rules?

The design condition of 300psi remains the same, just the allowable stress of the material changes. This may mean that thicker material is necessary to accommodate the calculated minimum required thickness of the plate plus the corrosion allowance. A boiler built with 55,000psi tensile strength firebox plate will have an allowable stress of 13,750psi with a factor of safety of 4 and the same boiler built with SA-516-70 (70,000psi tensile strength) will have an allowable stress of 14,000psi with a factor of safety of 5. This assumes the design temperature is below 650° F.

To rephrase the question, what occurred in 2014 that led the ASME to increase the mandatory minimum factory of safety requirement by 25% to 5.0 only for new riveted construction?

Paul Boschan wrote:

So for the same reason the factor of safety in Part PL is 4 to be in line with the FRA requirement, the factor of safety in Part PR is 5 to be in line with the NBIC.

If this is the only justification for the blanket 5.0 factor of safety, since when did the ASME NEW construction CODE care about future repairs or local jurisdictional compliance? Today, if you want to buy a Cleaver-Brooks package boiler for use in Ohio, you have to tell that to C-B before ordering the boiler. Taking responsibility away from the design engineer by adding a 25% penalty can and will lead to serious boiler condemnations and deratings in the distant future without subsequent increase in inherent safety.
For example, the UP 844 second barrel course is 1" thick plate, 70,000 psi tensile strength with a FS of 4.3. Thus an NBIC compliant/certified riveted repair would seriously degrade the boiler psi to unusable. This is over and above the concept that a new exact duplicate ASME riveted boiler would suffer decreased MAWP or for 300 psi, weigh greater than the frame could support.
The fundamental question is, "What was broken in the boiler engineering world?"

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Robby Peartree · **Joined:** Wed Aug 25, 2004 11:16 am **Posts:** 767

Could you explain how a locomotive boiler could not be in part subject to temperatures above 650 F?
Robby Peartree

Overmod · **Joined:** Thu May 24, 2012 1:37 pm **Posts:** 2492

The pressure parts (at least those in contact with water and saturated steam) aren't at 650 F until the boiler pressure is above 2000psi.

Robby Peartree · **Joined:** Wed Aug 25, 2004 11:16 am **Posts:** 767

So we do not have heat sources above 650 or themal gradients in boilers?

Robby Peartree