4" low psi air piping requirements 1

[steveo916]

here is my problem.
i work at a manufacturing plant that is installing a 60psi air line inside using 4" sch 40 steel pipe. all fittings are butt weld type. i was at one time a certified pipe welder but i am not involve in this job. they are using employees that have zero experance in in welding pipe. there is no root pass, instead they but the pipes up with no gap and tig weld the whole thing out. the welds are tearable. they where trying to stick weld them but it looks like they gave up because none of them could weld anything but flat position and even then they where rough. i have mentioned it to managment but no one understands the risks they are taking. is there any osha/B31.3 codes i can use to convince them?

 

[Ron]

Steve..you are right to bring this up. What they are doing is dangerous.

Assuming your piping is tied to a commercial air compressor, which is a certified pressure vessel, the piping and fittings then become an extension of that pressure vessel and at the least come under the International Mechanical Code, which requires all such welds to be done by certified welders in accordance with nationally recognized standards, which would be the ASME Boiler and Pressure Vessel Code for pressure vessels.

 

[zdas04]

Ron,
The BPVC does not cover piping up to or away from a pressure vessel. The piping codes address this piping. I would expect it to come under ASME B31.9 (Building Services Piping) instead of B31.3 (which is focused on high-concentration piping like you would find in a refinery, paper/pulp mill, or cryo plant).

I've seen people say "it's only 60 psig, what's the risk?" 4-inch S40 Grade B piping is rated at 1400 psig (at 100F), so the pipe is overkill for the service. On the other hand improper weld techniques create a whole world of possibilities for both mechanical failure and accelerated corrosion. A brittle failure in a 60 psig line gets really exciting really quickly.

While it doesn't explicitly apply here, API 1104 has a wealth of information on effective processes for welding piping, you might get a copy of it and show management how it should be done.

David

 

[LUDPEKA1]

One of my questions would be. Is this truly a 60 psig system? If they are this careless with the construction, how much thought put into the process design? Is the system properly protected from over pressure? What is the compressor’s maximum psig output and what happens when this poorly constructed piping sees that pressure and not “just” 60 psig?

 

[Ron]

David,
Thanks for the clarification. The mechanical code reference states that the piping is to be considered as an adjunct to the pressure vessel. I haven't dealt with BPVC in over 20 years...back in my ASNT Level III days, so wasn't positive, but was depending on the wording of the code.

Ron

 

[zdas04]

The only time that piping is in the BPVC is when it is on the skid and the fabricator elected to include it. They don't have to and most don't. The code clearly "owns" any penetrating nozzles, but after that there is a lot of wiggle room.

"Adjunct piping" is generally limited to on-skid piping required for control functions, rarely is this piping 4-inch and any piping installed post code-shop is definately not owned by the vessel.

David

 

[BrianCNTFM]

Steve maybe you need to demonstrate what they are playing with stick a cork in the end of the pipe give it a blast and let them see how far it goes and potential damage it could do.

In the UK this would likely fall under Pressure Regulations and the onous would be on the owner to ensure safe design maintenance etc. They would likely end up in court and be sentenced

Brian C

 

[steveo916]

thanks for the replys
the low pressure compessor they are using is a 1000hp two stage turbin compressor and there are large storage tanks in the system so there is lots of supply. the place runs 24-7 and the location of this new piping is in the production area so employees will be around it around the clock. in california

 

[racookpe1978]

That size pressurized tanks (!!!) plus that size pipe gives you a HUGE potential energy danger.

If you can't get the "designer" of this system to listen get to safety/OSHA/insurance as a cover-your-tail position.

This system is deadly - even at low temperature.

 

[racookpe1978]

Tell your boss the alternative to hiring real welders is a very, very large insurance premium and many very, very expensive lawyers. (But remind him not to tell the insurance company exactly why you need that large insurance policy. Go ahead and tell the lawyers though - that way they can tell you to hire even more lawyers before the accident happens.)

 

[jmiles]

Hi Steve,

Just a thought here, by the way i ttoaly agree with what everyone ahs said, but you said the compressor is a 2 stage 1000 HP, i mean damn thats alot of horse power, given there are two stages your probably looking at going from atmosphere to id guess up to 720 PSIG, (assume you can get a 7 fold increase in each stage) so my guess is that this compressor could be putting out pressures requiring ANSI 300# piping, that is fairly significant.

I havent typically seen 2 stage compressors to put out somethign as low as 60 PSI, a screw/turbine compressor should be able to get to 60 PSI easily in one stage. (But dont quote me on that im not a compressor specialist)

Point is i think that the 60 PSIG is VERY low, they likely will have this running higher.

Given the poor construction practice i would not be surprised if someone was looking at this system and pointing to one outlet int he air ehader thats been choked back and saying see tis only 60 PSI here, its low pressure, and totalyl neglecting the high pressure portions.

 

[ornerynorsk]

People with no welding experience have no business putting up air piping. 4 inch line will have a helluva lotta energy, even at "only" 60 psi. Management needs to be barked at loudly on this one.

 

[zdas04]

jmiles,
What kind of 1,000 hp recip compressor are you getting 7 ratios per stage? I start getting really nervous at 4.0 and won't set a compressor that requires more than 4.5 ratios/stage.

At 5,200 ft elevation, going from 12 psia to 72 psia is 6 compression ratios or 2.45 CR/stage which isn't horrible. Even closer to sea level, going from 14 to 74 psia is 5.3 ratios or 2.3 CR/stage. On the other hand, trying to do it in a single-stage recip is a pretty big risk of breaking something.

David

 

[jmiles]

David,

please correct me if im wrong here, as i said im nowhere near a compressor expert, but he did say ti was a turbine compressor, which i am assuming is the same as a screw, and ive seen lots of smaller screws that get 6-7 CR's per stage, while its possible they are getting alot less, i was thinking with 1000 HP to burn there is a potential for them to get alot more than 60 PSIG, maybe 720 is a bit much thats about 7 CR's per stage, but even 5 CR's will get you to around 360 PSIG, and 4 CR's per stage will have you at 225 PSIG, even that is almost 3 times what the system is supposed to have.

And finally you are right, recips usually do have a lower compression ratio than screws ive seen, im just saying i have seen, bought and used some scres that were getting 7 CR's in a single stage. its a big what if game without knowing more details.

Either way though 1000 HP gives alot of potential for high pressure.

 

[zdas04]

Sorry, it has been a week or so since I read the earlier posts, I was thinking the compressor was a recip.

When people say "turbine compressor" it almost always means a dynamic machine (like a centrifigul or axial) driven by a gas turbine. The only "turbine compressor" that I know of is the back-end of a gas turbine and that has a bunch of stages, but there could easily be such a beast that I'm not aware of. I don't know of a PD machine (like a recip or a screw) that mates with the rotational velocity of a gas turbine without a serious reduction gear.

Dynamic machines tend to work pretty well between 1.5 and 2.5 ratios per stage. So 0 psig to 60 psig is a good 2 stage application for a dynamic machine. Stall usually happens pretty close to 2.5 CR/stage.

A thousand hp gives you the ability to reach high pressures in a properly configured machine, it also lets you get a big volume at an intermediate pressure. For example, 2-stage recip could move 4.5 MMCF/d from 0 psig to 250 psig. The same driver (with a different recip) could move 8.7 MMCF/d from 0 to 60 psig.

For design conditions I use 10 ratios across a flooded screw as nominal. I've run them up to 20 ratios without problems. Most screws on the market are inappropriate for two stage operations because of their very low maximum suction pressure and low maximum discharge pressure.

David

 

[jmiles]

Thanks for the info David, that clears up alot for me, though im not kicking myself for not realizing wha was meant by turbine before, i guess i was too fixated on the rotational anture of the movement and forgot all about the much higher velocity of that rotation. Which of course is the key difference that makes my post kinda irrelevant, your right it likely wont get much higher than 60 PSIG.

John

 

[MJCronin]

Steve...

The piping system welding is probably in violation of the local building codes which reference the ASME piping codes.

They have probably violated the local codes and possibly the law.

Consider that, if the piping system fails and someone gets badly hurt, a snarling, blood-sucking attorney may make some real money....

-MJC

 

[LUDPEKA1]

"...Consider that, if the piping system fails and someone gets badly hurt, a snarling, blood-sucking attorney may make some real money."

And in this case, rightly so.