High Yield Pipe in B31.3 Facilities
High Yield Pipe in B31.3 Facilities
(OP)
Hello,
I have noticed that many companies do not utilize high yield pipe (e.g. API 5L Grade X42) in their pipe specs for facilities that will conform to B31.3. However, the same companies do utilize high yield pipe in their specs for facilities conforming to B31.8.
Is there a reason that high yield pipe is avoided for B31.3 facilities?
It seems that it would allow using STD instead of XH in certain sizes/pressure classes, which would save a bit of money.
I have noticed that many companies do not utilize high yield pipe (e.g. API 5L Grade X42) in their pipe specs for facilities that will conform to B31.3. However, the same companies do utilize high yield pipe in their specs for facilities conforming to B31.8.
Is there a reason that high yield pipe is avoided for B31.3 facilities?
It seems that it would allow using STD instead of XH in certain sizes/pressure classes, which would save a bit of money.





RE: High Yield Pipe in B31.3 Facilities
B31.3 uses the allowable stress as defined in the code for a given material which is an input into the wall thickness formula. B31.3 allowable stresses are constant because everyone knows that the only place you can use it is in a plant environment and only one safety level is required.
What is the allowable stress given in B31.3 for API 5L X-42???
you must get smarter than the software you're using.
RE: High Yield Pipe in B31.3 Facilities
RE: High Yield Pipe in B31.3 Facilities
RE: High Yield Pipe in B31.3 Facilities
Given normal temperatures, the B31.8 design stress allowables
for X42 are 0.4, 0.5, 0.6, 0.72 or 0.8 x 42ksi, depending on area class factor.
giving, 16,800 psi 21,000 psi 25,200 psi 30,240 psi or 33,600 psi
For API 5L Grade B, and for ASTM A106B, both yield stresses are so allowables are 35ksi x 0.4, 0.5, 0.6, 0.72 or 0.8
giving 14,000 psi 17,500 psi 21,000 psi 25,200 psi, or 28,000 psi
As you can see from a comparison to Weldstan's post, B31.8 is more conservative when inside compressor stations as the area class factor there is 0.4, or 0.5 and the allowable stress calculates to only 14,000 or 17,500 psi for 5L-B and 16,800 psi for X42, or instead of the 20,000 psi allowable stress of B31.3. Elsewhere B31.8 would give lesser wall thicknesses.
you must get smarter than the software you're using.
RE: High Yield Pipe in B31.3 Facilities
So if my math is correct, it appears that B31.3 allows me to use the more economical API 5L X52 with STD wall for that particular size. Strikes me as odd though that I typically see A106 Gr. B with XH wall called out for this case in pipe specs.
One of my coworkers thought that A106B XH may be called out because it is more readily available, but I haven't had any trouble procuring seamless X52 piping on recent compressor stations.
RE: High Yield Pipe in B31.3 Facilities
you must get smarter than the software you're using.
RE: High Yield Pipe in B31.3 Facilities
RE: High Yield Pipe in B31.3 Facilities
As noted very well above, you get very little benefit for increased SMYS and any reduction is close to the small extra cost of higher grade material. Moreover, use of higher SMYS pipe requires use of higher strength fittings, especially flanges and tees which are not commonly available, are higher cost, longer lead time and lead to potential issues of using the wrong flange in the wrong place as one 8" flange looks pretty much like another one of the same size and schedule.
Hence any small saving, unless you have hundreds of metres of only pipe, is normally wiped out b these practical considerations. The construction contractor will not thank you for introducing multiple grades of steel when he may already have multiple type sof steel (C Stl Stl, CRA etc) to contend with.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: High Yield Pipe in B31.3 Facilities
The recent compressor stations were built to 31.8. We occasionally get involved with small gas plant projects though, so I have been reviewing pipe specs for B31.3 facilities lately in preparation for the next one.