Establish pressure ratings .MSS-SP-44, B16.5

[nipra03]

both MSS-sp-44 and B16.5 state:
"Rat ings for welding neck flanges covered by this
Standard are based upon their hubs at the welding end
having thickness at least equal to that calculated for pipe
having 276 MPa (40,000 psi) specified minimum yield
strength.1"

It is not clear which piping code rules should be used for calculating the pipe wall thickness ?
Appreciate any help here.

A contractor has installed SA350 LF2 flange welded to a 16" grade X56 pipe with wall thickness 12.7 mm. The flange hub thickness at the weld end is also 12.7mm thus violating rule 5.3.2 of MSS-SP-44.
Design pressure/temp. 1440 psig @38 C.
The calculations for pipe wall were performed using a design factor 0f 0.6 in lieu of 0.8.(design code Z662)
I'm wondering if this can be used to get around the problem - hence my question above.

 

[BigInch]

Your quote of the specs isn't totally relevant, as that would not prohibit the same or higher ratings, from being attained by thinner walls of higher strength steel. All that says is that the ratings were obtained using flanges of that thickness and yield strength material. I also believe that the ratings are based on design factors other than 0.6 and 0.8.

The ASME B31.8 design factor for tie-ins and piping component assemblies must be appropriate for your area classification and must never be greater than 0.60, so you CANNOT not use 0.8 for a B31.8 tie-in, nor could it be used in a regulated gas pipeline system in the USA. If the 0.8 design factor of your Canadian Z662 code is allowed to be applied to tie-ins and fabricated assemblies in Canada, I suppose your flange would be OK, as long as your design code is Z662.

 

[LittleInch]

I beg to differ. My normal version of this is that once your pipe exceeds the basis of the calculation (basically SMYS of 40K), then your flange material needs to match the pipe material in terms of yield stress precisely because of this reason. From what I see of A350, the SMYS is 36Kpsi

IMHO, your contractor has incorrectly welded this flange (35K SMYS) onto that pipe (52K SMYS) and needs to cut it off and replace it with a A694 F52 flange material then matched to your pipe wall thickness.

I have seen forgings (bends mainly) made from lower grade material than the pipe where they enlarged the OD and then made up the difference with weld metal.

Stop trying to "get round the problem" and just replace the flange. whatever factor you use for the pipe applies to the flange. Anything else leaves you open to litigation and costs well beyond the cost of cutting off a flange and buying the one you should have used in the first place

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigInch]

LI, I don't see it as that complicated.

The DF = 0.6 case
FLANGE PIPE
df 0.6 0.6
P PSIG 1440 1440
D IN 16 16
SMYS 36000 56000
Required Wall thicknesses
wt in 0.53 0.34 in
wt mm [highlight #EF2929]13.55[/highlight] 8.71 mm

Flange wall of 12.7mm is insufficient in the above design factor DF case 0.6, so the maximum pressure would have to be reduced to 1350 psig

For a design using DF 0.8
FLANGE PIPE
df 0.8 0.8
P PSIG 1440 1440
D IN 16 16
smys 36000 56000
wt in 0.40 0.26
wt mm 10.16 6.53

A 12.7mm flange wall thickness is sufficient, as only 10.2mm is required. It works if A662 allows 0.8 DF for connections.

Some say that there can be a possibility of some difficulty welding Grade B to X56, so I might place a X42, or X52 pipe transition between the two, if I was worried about welding material compatibility.

So, what is the A662 DF for connections?

 

[LittleInch]

But why is the pipe 12.7mm instead of 8.7? Corrosion allowance maybe? in which case the 0.8 factor won't work either.

My main point is that it is simply bad practice to use different strength materials at the same wall thickness and then somehow magically think they can have the same design pressure.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BigInch]

Since the 56000 yield is a bit strange these days, I might guess that it was originally built were somewhere in the X42-X52 era, wanted to match X42 wt which would have been 0.500" (12.7mm), but were delivered X56 yield pipe. Then they said, "Ya that'll work."

Or they just used the first bigger thing they found in the warehouse.

Not sure, but I suspect that A662 has a 0.6 DF for connections. Whenever I look something up in that code I find the basics aren't all that different than other codes. That's the key item to check here.

 

[LittleInch]

Dunno, we seem to have lost the OP enroute though....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[KevinNZ]

The WN end of the flange has to has to have the same minimum thickness as if it was a piece of pipe with the same material. It can be thinner than the pipe it is attached to (taper the pipe to match), but your load/stress calculations need to allow for the short thinner WN thickness.