Recalculate MAWP for used pressure vessel 1

[vgs1133]

Hey Guys,

I want to use an older bulk propane tank as an air receiver in an industrial compressed air system. The tank is a horizontal vessel that was built in 1947 and has a volume of 30,000 gallons. I have a NB data sheet for the vessel that indicates it was constructed from ASTM A-212 GR.B steel (Firebox 70.000). The shell material is 15/16 thick and the heads 13/16, or at least it was when built, and that Joint Efficiency was 80%. State codes (GA) require (among other things) thickness testing and new calculations for MAWP be submitted with a "State Special" Change of Use Permit Application (from propane to air). I would like to run the calculations myself to see if the tank will be usable at the pressure I need, before I pay someone thousands to submit the application.

I want to know the minimum material thickness required to get the vessel permitted for 150 PSIG or higher at ambient temperatures. The vessel had a design burst pressure of 1008 PSIG, and a U-69 Code rating of 200 PSIG at 150 degrees F.

All help will be greatly appreciated.

 

[SnTMan]

Well, there's a lot of work to do. I assume the vessel was originally built to ASME Sec VIII, Div. 1. If so:

You need to calculate the various MAWP's of all the vessel components at the proposed design temperature and identify the lowest. You could base your initial calculations on the nominal thicknesses less any corrosion allowance although a full survey will probably be required before you're done. All components includes any openings or other special features, as well as the cylinders and heads.

You should also evaluate each components' Minimum Design Metal Temperature, at your proposed MAWP to guard against the possibility of brittle fracture.

You are going to need as much detail about the vessel materials, weld joint configurations and other design features as you can get. Original shop drawings would be very helpful.

You are going to need a Code book and a fair amount of familiarity with it, including material properties, and some vessel software would be useful, although you can make your own spreadsheets.

You will need to talk to the Authorized Inspector for the jurisdiction where the vessel will be located to find out how you may go about re-rating, as to which Code Edition is applicable, etc.

Having said all that, if it was good for 200 psig at 150 deg. F, it should be good for 200 at ambient, given that no excessive material loss has occurred.

Regards,

Mike

 

[gr2vessels]

vgs1133,

It will be a lot cheaper (and quicker) to send it in Australia, have it assessed and re-tested to your spec and imported back in USA with full AS 1210 approval.

Cheers,

gr2vessels

 

[deanc]

Suggest you see NBIC RB-9000 and Appendix H. You will also need to contact the Local Jurisdiction. It would be a good idea to speak with your insurance carrier.

 

[rzrbk]

As a first pass, the nameplate should have a corrosion allowance stamped on it. As long as the wall thickness loss is under this, you should be OK; although there is usually some additional fat available. In 1947, I believe allowable stresses for materials were constant all the way up to 650degF so 'in general' temperatures under this should not affect the MAWP.

As a basic check, minimum thickness of the shell will be given by (design pressure x Radius in inches)/(Allowable Stress x Joint Efficiency - 0.6 x design pressure). With this old a vessel, rerate calcs will have to be done per pre 2001 code, and I don't have the old allowable stress tables.

If a rerate looks possible, I recommend getting a local vessel shop to do all the calcs, nameplate fabrication, and paperwork required. Cost for this is usually fairly reasonable. New nameplate can usually be installed by your personnel with the AI witnessing.

 

[waskillywabbit]

Built in 1947 and you want to rerate it now in 2006? Am I the only one here who thinks this is a bad idea?

Brian

 

[dtn6770]

My experience (14-yrs) in the petroleum refining industy has involved a LOT of vessel and heat exchanger (S&T and air fin) re-rates of all varieties and vintages with API-510 as the guide (often referring to original code of construction). Don't be intimidated.

Assuming the vessel has been out of service for some time, start with a good thickness survey and possibly a fitness for service study (API RP 579). If the documented corrosion allowance hasn't been consumed, the original rating should still be good. If you're not that lucky and have to have calculations made, they'll probably have to be in accordance with the code of construction.

Finally, a good pressure (hydrostatic) test can go a long way.

 

[robsalv]

...sounds possible in principal. 200psig originally, 150 psig in new service... assuming corrosion losses are acceptable.

Not sure how the weld configs and design will hold up to today's requirements. I'd guess that any conservative stance would also have a bunch of NDE required to test for weld quality and inservice degradation, especially if there's any cycling involved.

Can you determine which component set the MAWP in the first place?? Sometimes this is stated on drawings.


You haven't stated an inside diameter, so none of us can even run a simple cylindrical wall thickness calc.



Hey gr2vessels, where are you in Oz? Interesting suggestion you made there.

Cheers,

Rob [from Melbourne]

 

[JStephen]

Wabbit, I was wondering the same thing. If there is ever a reason to decommission a vessel because it is just too old, that one should be a candidate.

 

[unclesyd]

Why would one want to retire a perfectly good PV because it is 50 years old if it has been inspected and well maintained during it life?

 

[robsalv]

Large sections of my plant are 46yo... I'm with UncleSyd.

Some of the vessels still have original boiler maker / welder chalk marks...

 

[waskillywabbit]

2006-1947=59

If you guys can't add, how can we trust your opinions?

Brian

 

[robsalv]

Wabbit, that's a rather academic statement you make. The general point is, what does the age matter if the vessel is FFS?

 

[unclesyd]

waskillywabbit,
Please check your math as it may not be quite right.

 

[deanc]

Just because something is old does not make it bad. I know a few people who fall into this class,including myself.

How about a number of 100+ year old steam locomotives that still see daily service?

Think the clue is to understand what you are looking at so one may properly evaluate it. Caution-yes,arbitrary rejection-no.

 

[waskillywabbit]

robsalv - come on and lighten up, note the smiley face in the previous post

I do not see any given statements by the initial poster as to the inspected and maintainted condition of the vessel in question

unclesyd - but I used my calculator and they are always right

deanc - I will rephrase my initial statement

"Built in 1947 and you want to rerate it now in 2006? Proceed with caution."



Brian

 

[unclesyd]

waskillywabbit,
Your calculator could be up to 1/6 of a unit off if the vessels were built in November or December of 1947.

I agree that caution is required for rerating not only older vessels but any vessel that has been in service no matter how long. A clear understanding of vessel's condition is the first order of business.

 

[robsalv]

...nah, pretty light already man...

Still, I felt that the point needed to be made since yourself and JStephen were advocating scrapping the vessel based solely on age... which is no basis at all... unless the vessel is as degraded as it is old...

 

[JStephen]

"Why would one want to retire a perfectly good PV because it is 50 (59) years old if it has been inspected and well maintained during it life?"

I see a parallel between this question and this thread:

http://www.eng-tips.com/viewthread.cfm?qid=169323&page=1

Some quotes from it, and from the link referenced:
"However, many of the old refineries like that former Amoco do not follow current guidelines. Perhaps the fault is largely with the dinosaurs who run many of the old plants bought by BP."

"Have you notice that "most" facilities are operating with very "old" systems!?? ...I've worked on the Alaskan Pipeline and afew oil refineries ...most are very old and desperately needing up-grading! The Alaskan Pipeline was only designed to have a 15 year service life ...been going now for 28 yr.s! Seems the philosophy is to operate system until they catastrophically fail and THEN pick up the pieces!"

"Ms. Merritt pointed to earlier CSB findings that the equipment directly involved in the flammable release on March 23 was of an obsolete design already phased out in most refineries and chemical plants... Don Holmstrom, the CSB supervisory investigator who is heading the inquiry, said that since last October the Board has uncovered additional previous incidents involving the same ISOM unit blowdown drum, which was designed in the 1950’s."

The question asked above: "How about a number of 100+ year old steam locomotives that still see daily service?" You might want to consider if these locomotives have all-original boilers. I find, for example, a website stating that two more of the Texas State Railroad's locomotives had been re-boilered in the last few years. They don't run daily, just one or two out of 5 runs on weekends during most of the year, perhaps daily in summer. As I understand it, the main parts of a locomotive that aren't replaceable are the large castings comprising the cylinders and whatnot- look up the Austin steam locomotive for example. But boilers and tubes are replaced as required. Keep in mind too that these locomotives are in service specifically because they are historic relics- they would all have been retired before I was born in normal business practice.

You might also peruse this link:

http://www.aws.org/itrends/05-02/bulletin.html

I find that the original ASME Boiler Code was published in 1914-1915. Consequently, any boiler or pressure vessel that is now 100 years old wasn't built to the ASME boiler code. Is it safe? I don't know. Would you trust the pressure tank being discussed if it had been built prior to the B&PV code?

Now, as to the general question of whether a piece of equipment should be replaced because of age, if it otherwise appears sound. It seems to me that part of our comfort level with potentially dangerous equipment comes from familiarity with the way things are done. In the case of an old pressure tank, it was built to a version of the code that probably few if any of us are very familiar with. It's probably made from steels that aren't used anymore, welded with welding rods that aren't made anymore, based on a procedure specification that isn't used anymore. The company/shop that made it is likely gone or merged umpteen times, and the welders that welded it are probably dead. How much has the code changed since that tank was built? And why? Have standards of acceptable risk changed since the tank was constructed? Did they radiograph welds back then, or do impact testing on weld specimens? How uniform was steel quality back then (remembering the tests on the Titanic hull plate here!)

I don't think you could come to a point where you could say that 1935 tanks were okay, but 1934 is too old. If this was something like a log cabin where it could quietly rot away and not hurt anything, it would be a lot different. But when you have a potential bomb setting there, it does seem prudent at some point to retire the thing regardless of thickness remaining. And a change of service seems like a good time.

 

[gr2vessels]

Guys,

Just a quick reminder that the engineering is based on facts, measurements and evaluation;- so is this bloke in the top of the thread asking for help. He needs evidence for scraping the vessel or to keep it. Scraping or keeping an investment item based on emotions is the subject of another site, the believers.

From deanc .."Think the clue is to understand what you are looking at so one may properly evaluate it. Caution-yes,arbitrary rejection-no." - that's engineering.

Cheers,

gr2vessels