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vvvipin (Structural) (OP)
26 Sep 01 2:51
My client wants forged collars for 550NB API5L GrB pipes.( A collar is similar to a flange except that there are no bolt holes. The collars are connected by "quick release couplings")The material specified for the collar is A36.Most of the forging vendors do forging with A105. My question is-which is a superior material for this work A105 or A36.?

The pipes are used in a power plant to convey pulverised fuel from the pulveriser to the coal burners. The design temperature is 130 degrees centigrade and pressure is 350kPa.

Any suggestions!!

Regards

V.V.Vipin
Guest (Visitor)
26 Sep 01 8:44
Hello,

ASTM A-36 is a specification for plate material.  This indicates that the "collars" are fabricated (likely by welding) and they are not forged.  The ASTM A-105 material is a forging material.  You might want to look at B31.3, Appendix A to compare allowable stresses (A-105 is stronger).  Also, I think that if you remember the infamous "Chinese Flange Incident" of a decade ago (the National Board has an excellent report available), you will conclude that forged flanges are superior to fabricated flanges in every way.  If the component at issue is not of a "listed" type and material you will want to look at B31.3, paragraph 302.2.3 and especially paragraph 304.7.2 ($$$).

Regards, John.
Guest (Visitor)
26 Sep 01 9:21
Hello,

A few more thoughts.

The design of pulverized coal fuel piping systems is an art as well as a science.  Typically, these systems are highly articulated as most power boilers are "hung" from the top of the structure and the vertical (down) movement of the burners as the boiler goes from cold to hot is significant.  Special in-line pipe couplings (Dresser or Grey-lok) are included in the design to allow for the movement a (and to essentially release a lot of the torsion in the pipe by axial rotation).  

You will notice that these systems are explicitly excluded from the scope of the B31.1 Power Piping Code (see B31.1, paragraph 100.1.3(K)) and reference is made to NFPA Standard 8503.

These systems are complicated as the various pulverizer mills have to supply any of several burners under various operating modes - this leads to a "maze" of piping which all has to be supported.  "Box gang" supports are commonly used to support several "runs" of pipe at one point - some of these include spring hangers.  Most of these systems employ large "constant force" spring hangers located at the "four corners" of the boiler above the burner elevations.  

The pulverized coal is very abrasive, especially at changes in direction.  Over the last 20 (or so) years, there has been a trend to replacing the worn pipe elbows with steel, ceramic lined (internally) elbows which are much heavier that the original (or even the most resent replacement)components.  Unfortunately, sometimes these new components are installed without a proper structural analysis and the result is that the original pipe supports (and the structures that they are attached to) are over stressed.  Usually, the constant force hangers are "bottomed-out" and the special joints located in-line are forced to try to accommodate rotations beyond their design capacity.  The loadings placed on the burners and the mill nozzles under these circumstances are very high.

There is a need to perform comprehensive structural analyses on pulverized coal fuel piping systems whenever changes and or updates are made.

Regards, John.
PAN (Mechanical)
12 Oct 01 23:00
ASTM A36 is in structural quality steel plate. For the case of pressure vessel quality steel plate, ASTM A285 Gr.C should be considered.

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