NCPWB Bulletin - Risk of Brittle Fracture of Carbon Steel Piping During Hydrostatic Testing

[DeuceyBusiness]

Have any of you read this bulletin from NCPWB (see link below)? Any opinions on this?
Link

I checked a handful of ASTM A53B & A106B mill test reports and about half did not comply with the manganese to carbon ratio of 5+. Also, I didn't see "grain size" anywhere on the MTR's.

Also curious if anybody knows how they calculated the hydrostatic test pressures on page #3.

14" standard weight, per ASME B31.9.
P = 2SE(T-A)/D
P = 2*14600psi*(0.375"-0)/14"
P = 782psi

0.2 * 782psi = 156psi. the chart in the bulletin shows 163psi.


Thanks

 

[racookpe1978]

But what temperatures did they address their new bulletin against?
Will it really matter in most cases?

 

[TGS4]

Chuck Becht, past Chair of B31.3 also addressed this in a recent blog post. As you can see from the temperatures listed in Chuck's post, material that was exempt from toughness testing down to -29°C, may not have adequate toughness all the way up to 15°C - getting towards typical hydrotest conditions.

 

[DeuceyBusiness]

In carbon steel HVAC piping, 150 PSI is the typical hydrostatic test pressure. Smaller sizes aren't a problem, but when you get to 14" and up the max test pressures get below 150PSI.

 

[MickMc]

In my experience (B31.3) we calculate the minimum wall thickness required based on a design pressure/temp supplied by Process and then refer to appropriate table and calculation from B31.3 therefore IMHO table is not relevant and our test pressure would then be 1.5 x DP.

My assumption is that mill test at usually much higher pressure is no problem as it should be at room temperature therefore it follows that in construction failures the ambient temperatures must be low. I looked at Chuck Becht link which he quotes temperatures under 60F for both test and operating and wonder if anyone can elaborate on the 60F/15 DegC which I guess maybe comes from ASME BPVC over and above min and also why both test and operating as these will be different pressures. Our standards actually stipulate min 17 DegC for hydrotest but we are in Middle East and have no problems maintaining.

I will be raising this to be addressed our contractors especially in regard to possible changes to curves in B31.3 but would welcome any further background information.

 

[rconner]

[As to "how they calculated" could they for whatever reason be using something like a little smaller median diameter for "D" (like a nominal OD 14 inch-.375"?) as opposed to a nominal D you've calc'd (if so I think result would be at least very close to your chart ref)?]

 

[weldstan]

Recently I saw a number of heats of 106 from non US suppliers with Mn at 0.4%. This pipe was to be used in power generation service at temp up to 750 F. I would be more concerned with this materials high temp strength.

With the potentially greater stress induced under a B31.3 hydro test than under a B31.1 test, more concern should be given with regard to test temperature. It is noted that typical Mn:C ratios for the past 50 years for A-53 and A-106 have been between about 3:1 to 5:1.