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150lb Flange Pressure Capability

150lb Flange Pressure Capability

150lb Flange Pressure Capability

Can't find data showing pressure capability of Class 150 steel weldneck flange. Not concerned about pressure vs. temp, but, rather pressure vs. bolt torque.  

I want to use 150lb flanges in an application where system pressure MAY reach 500 psig, normal operating range will be less than 100 psig.  Gasket choice will sustain the pressure.  Question is, can I torque the flanges to handle this pressure?

RE: 150lb Flange Pressure Capability

There is indeed lots of data showing ANSI 150 flange limitation of 285psig at <100degF.

I am trying to justify using 30+ ea 150# flanges already installed in a pipeline rather than remove them.  Will use gaskets capable of pressure needs.  Can I torque bolts enough and rely on the flange to seal at 500 psig?  

RE: 150lb Flange Pressure Capability

As Big Inch pointed out, according to ANSI at the pressure of your system, you will need to replace the flanges and all other components in the system to Class 300.

Unless you have a pressure relief valve that will protect the system should it exceed 285 psi, you should not use the Class 150's.  Liabiltiy will more than offset the cost of replacement - your system will be out of code.

Greg Lamberson
Consultant - Upstream Energy
Website: www.oil-gas-consulting.com

RE: 150lb Flange Pressure Capability

Class #150 flanges are rated for 285 psig <100 degF and are hydro tested at 1.5 times the allowable working pressure 427 psig.  So will these ASME B16.5 flanges leak at 500 psig?  It depends on:

the pipe size (some flange bolting is weaker than others depending on pipe size).   I believe that 6” class #150 flanges have the smallest margin for bolting.  

the mfg safety margin for materials and machining.  Modern metallurgy is more precise than in the past and manufacturing tolerances in most developed nations are better than the past.  If the flanges are new they may have a smaller safety margin than older flanges.

the quality of the manufacturer’s flanges.  It only takes the weakest flange of the lot to create a leak.

So are you feeling lucky?  It would be considered reckless behavior to use ASME B16.5 flanges for a 500 psig design.  If there is ever litigation regarding loss of life, property, etc.  You will be on the loosing side of the litigation and subject to punitive damages (if your in the USA) from the reckless behavior having a 500 psig pipe design using class #150 flanges.

So if you are lucky, the flanges won’t leak provided there is no moment from pipe expansion creating unbalanced forces on the flange and the line size is such that you have one of the flange sizes that have the more robust bolting configuration.

RE: 150lb Flange Pressure Capability

Even worse, you may get listed for unprofessional behavior in the
Professional Ethics in engineering Forum

RE: 150lb Flange Pressure Capability

As was stated above, there are safety factors that "could" prevent failure of a 150 ANSI flange at 500 psi, but if if fails, you personally will be liable and I would bet that this thread would show up in a legal proceeding for Gross Negligence.  If anyone is ever hurt because of undersized flanges on this system there is a really good chance that you will have met the standards for gross negligence and personally go to jail.  

What you are trying to do is very ill advised and you really should stop.


RE: 150lb Flange Pressure Capability

Thanks to all for "setting me straight".

FYI, I specified 300# flanges on my P&ID, reviewed it with the piping contractor, and pointed out conserns on several occasions.  Never the less, after a field inspection we found 150's installed in all the piping hung to date (~40% of an 850ft run flanged every 20ft).  They were stopped immediatately.  

I have been asking for documentation showing criteria by which we can make the 150's work.  Gasket choice helps considerably, but, nothing in the literature showing the flange can handle it.  

Thanks again, consider this a querry only and the solution to replace all flanges with 300class implemented.

RE: 150lb Flange Pressure Capability

There is no document that can be legally produced that will allow this.  Get it changed!  Safety factors have a purpose for being there and your reason (as well as all the above) arn't any one of them.

BigInchworm-born in the trenches.

RE: 150lb Flange Pressure Capability

"I specified 300# flanges on my P&ID, reviewed it with the piping contractor, and pointed out concerns on several occasions.  Never the less, after a field inspection we found 150's installed in all the piping hung to date"

Stop being a nice guy
The contractor made a mistake and wants you to help him save time and cost as not having to cut and reweld the flanges.
If the contractor isn't owning up to his mistake make sure he is not any future bid lists

RE: 150lb Flange Pressure Capability

War Story (sort of)

For me, these situations can (and should) be job busters.  Not that long ago I left the comfort of a 14 year run with a fairly major oil refiner to lead the engineering and inspection groups at another refinery.  What I didn't learn during the interview process but did after less than a month on the job was that the facility had a very lax view on "code" compliance and PSM issues.  Over 60 pressure vessels and heat exchangers had been flagged as having questionable ratings relative to their service conditions.  These flags were raised during PHA/HAZOPs almost 15-years prior and were still unresolved.  That was just the start of things I discovered.

Those issues had always been put on the back burner to accomoade expansion/debottlenecking projects, clean fuel efforts, or whatever else was needed to support production.  It was the first time in my career I lost sleep over such issues and in the end I resigned.  My parting comment was something along the lines of, "The only difference between willful negligence and criminal negligence is that nobody has gotten hurt."

Sorry for the rant.

RE: 150lb Flange Pressure Capability

I think - with respect to 285 psi and up to 100 Deg F rating 150 class is acceptable as per 16.5 if flange material selected is group 1.1 of ASME 16.5. Therefore selection of pressure tewmperature rating is based on selection of material, temperature and pressure. For example if material of group 3.2 is selected than at 100DegF for rating 300 maximum pressure is 360psi.

RE: 150lb Flange Pressure Capability

Install pressure controls and a relief valve that prevents the pressure from exceeding the maximum for Class 150 and avoid replacing the flanges.

RE: 150lb Flange Pressure Capability

Perhaps the difference could be that you are in piping and I am in instruments?

RE: 150lb Flange Pressure Capability

Quote (JLSeagull):

Perhaps the difference could be that you are in piping and I am in instruments?

Probably. Then again, this ain't an instrumentation forum...

I'd favor the flange upgrade simply 'cause its simple. Instruments and valves will fail much more often than properly spec'ed and installed flanges. Its a question of robustness.


RE: 150lb Flange Pressure Capability

Responding to the initial questions, various standards do not permit increasing the bolt torque to accommodate the Class 150 flanges for pressures exceeding the tables in B15.5.  The question applies to bolt torque for Class 150 steel flanges while avoiding other piping system issues.  The point is that you cannot expose Class 150 steel flanges at 500 psig without causing a hazard and violating a few mandatory codes and standards within the USA.

Most serious responses apply to ratings published in codes and standards – generally with safety being a significant consideration.  The flanges are covered by ASME B16.5.  The response of 285 psig up to 100 degree F is accurate for the more liberal material groups.  One of several piping standards may also apply.  As the pressures place the system outside the plumbing standards, the applicable ASME piping design standards in the B31 series cover steam, fuel gas, process, transportation, refrigeration, etc.  The piping engineers are more familiar with these standards than me.  An appendix in some B31 standards applies to allowable stresses for bolting materials.

Some of these systems may include pressure vessels or heat exchanges.  These too are specialty branches within the mechanical realm and bring additional codes and standards into play.  The ASME Boiler and Pressure Vessel Code would apply in such cases.  Within the United States, OSHA regulations make compliance with the applicable codes mandatory.

Now we can go back to the fact that a typical piping system includes devices that limit the pressure.  Pressure safety relief valves, often required, are regarded as a last resort.  Other devices such as pressure control valves normally limit the pressure to the system.  The PSV opens when the regulatory controls fail to maintain the pressure within the limits.  Although some systems may not require pressure controls, most do.  If you already have a PSV to limit the pressure assure that it is sized and set to comply with the maximum pressure for the system.  In this case, 285 psig might be the correct setting.

RE: 150lb Flange Pressure Capability

The fact that the piping contractor failed to incorporate Class 300 flanges is a different issue.  Reject the installation.  We all make mistakes.  Sometimes they are costly.  I understand that business includes relationships.  However, you cannot just decide that everything will be OK.  Reject every Class 150 flange.  Advise the person controlling the contract payments to reject all invoices until the flanges are changed and the piping tested or whatever the contract requires.

RE: 150lb Flange Pressure Capability

For USA pipeline design, Code of Federal Regulations, Title 49, part 192 & 195 are more than a design code... they're the law. blues

BigInchworm-born in the trenches.

RE: 150lb Flange Pressure Capability

The contractor is bound to ask if there is a way around this situation, it is obviously of great financial importance to him.  He would be stupid not to ask.  But it is your duty as a professional to tell him the work is unacceptable and not in conformance with the contract documents.  He'll get over it!

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