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Maximum allowable working pressure rating of pipe fittings 2

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ncstate86a

ncstate86a

Mechanical
Jul 15, 2005
23
I would appreciate any help you guys can give me on this issue.

We are currently investigating the installing a 16" nps 0.500" wall pipe to carry 1200F air at 450 psig. Due to the manufacturing dimensional tolerances of SA312 Type 316, the maximum allowable working pressure calculated per B31.1 is below the design pressure of 450 psig. Instead we have decided to use SA358 Type 316 Class 1. SA358 maintains much tighter manufacturing tolerances as it is made from plate rolled and electric fusion welded (class 1 requires 100% radiograph). Due to the tighter tolerances, the maximum allowable pressure at 1200F is 471 psig.

My question is this: How can I ensure that the fittings I buy (elbows, tees, conc reducers)will meet the pressure/temp requirements? SA403 WP-S/WP-WX is what we normally use with SA312. How can I be sure it will meet the higher pressure allowables of SA358. According to B16.9, the manufacturer calculates the pressure ratings...is this something that the fitting manufacturer provides?
 
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Define your requirements on the inquiry for each fitting. Require the bidder to complete a form verifying that they accommodate the design conditions in their pricing. Require documentation certifying conformance with your requirements. Tag to differentiate from standard fittings. Inspect the material and documentation before releasing for shipment. ...
 
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The fitting manufacturer should have the pressure rating. If they provide this with the purchase is not guaranteed. Be sure to ask for the information. It may be a little trickier to get if you are buying from a vendor and not manufacturer directly. However, you should be able to have the vendor get the information or look up the manufacturer yourself and ask them about specific form/material/size. As JLSeagull said, if this is a safety issue, you NEED to have everything controlled and documented. I would imagine anything at 1200F and 450psi would be a safety issue if it failed.

-- MechEng2005
 
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If you look at 102.2.2 there is guidance for calculating the ratings of fittings listed as standard components in table 126.1. If it is a fitting that comes from one of the B16 standards I find it is tough to get someone to commit to a rating unless they are performing the design.

Regards,
EJL
 
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Just a thought. You don't have much margin for a relief scenario. Maybe you already thought about that. Maybe not.

Anyway.

Regards
StoneCold
 
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Stonecold, I agree but the ASME Codes already have safety margins built into the allowable stress values for Code approved materials. Also, at this temp, pressure and diameter, I am presented with few choices other than innconnel, hastelloy and other exotic alloys that are economically impractical. I trying to ensure that I stay with in the boundaries of the Code. Thanks for the input.
 
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ASME B16.9 Para 2.1 Basis of Ratings "...as for straight seamless pipe of equivalent material....".
 
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4Pipes,

I appreciate your input and is the exact phrase you noted from B16.9 that has ne stumped. When you have two 16" NPS 0.500" wall pipes whose maximum allowable pressures differ by 50 psig simply due to the manufacturing tolerances called out in the material specification (SA312 vs SA358), how do I ensure the fitting will meet the piping specification I am using? From the input I am getting, it appears I have to call out the working pressure and temperature in the RFQ, stating the maximum allowable pressure must atleast meet the higher pressures based on SA358(?). Thankyou all for your responses and please feel free to comment further.
 
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ncstate86a,

This is the answer to your original question. If you buy to the standard this is what you will get. The manufacturer does not need to calculate anything. All he needs to do is supply a fitting with the end preps and pressure rating equal to or greater than that of straight pipe. (+ the specified material). This is why you buy to a schedule and not a thickness. The fitting thickness could be much different even though nominally specified 16" Sch 40 (0.5" nominal). If the pipe bursts before the fitting - job done.
 
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