30 year old 1/2" thick Steel Piping Header - Will it last? 1

[jimdean]

We are currently working on rehabilitation of a wastewater pumping station by placing 30 years olds pumps and other upgrades. Existing 24" steel piping header, also 30 years old, has a current wall thickness of over 1/2". The wastewater is typical residential wastewater at 60 degrees with a maximum operating pressure of 40 psi and velocity of 6 ft/sec. We would prefer to leave the header and not replace it due to operation shutdown concerns and overall additional costs but not sure if it would last another 20-30 years if not replaced. We do not have any original pipe design or pipe information. Were older steel piping interior coated? We are not sure if the original steel header had any interior lining or just bare steel. Anyone familiar with this or have any recommendation or information on this issue - THANKS!!

 

[metengr]

I would expect that the CS header was not lined in this application, and if you have a consistent wall thickness at 1/2" (as verified by ultrasonic thickness testing at various locations, there was probably little general corrosion.

If you need to confirm adequacy of current wall thickness, use the general hoop stress formula to determine the minimum wall thickness needed to sustain internal pressure. The remaining wall thickness above the minimum required to sustain bursting serves to avoid bucking and collapse from weight and extraneous pipe forces.

 

[rconner]

It seems near incredulous to me that a water/wastewater header with steel pipe was installed on or about 1976 with no lining whatsoever (do you by any chance have any way to drain and are there any hatches, blind flanges, air releases spools etc. that could be quickly removed in a short dowen period to sneak a peek at the interior conditions?); however/regardless, if you have confirmed a consistent steel thickness of 1/2" now in this 24" steel piping after 30 years of service, I'm not sure (even if this is bare piping) that I can come up with a persuasive reason you would not be able to get a few more good years out of same in your rather low pressure/40 psi service!
I believe it has however been some common to line water and domestic wastewater pipes that flow full (and non-acid-producing etc.), for internal corrosion protection and maintenance of flow properties, with cement mortar. It is my understanding this can even be done to steel and other piping in place, e.g. in accordance with ANSI/AWWA standard C602,CEMENT–MORTAR LINING OF WATER PIPELINES IN PLACE— 4 IN. (100 mm) AND LARGER, although I am not sure how practical such operations might be for your operational/waste water header configuration/situation. If you are interested in this you might do a search for experienced in-situ lining contractors in your area, that might help with further evaluation/remediation of any problems.

 

[jimdean]

Thank you for your replies!

 

[unclesyd]

Is the pipe Carbon Steel, as a lot of piping in this service is either cast iron or ductile iron?

There is a possibility that this pipe could be concrete lined.

 

[metengr]

Good point by unclesyd, the header could indeed be ductile iron or even cast iron, for this vintage. One quick check is to inspect for the type of pipe joints (if accessible). Carbon steel piping would probably be butt welded. If you confirm cast or ductile iron piping, there would be no lining and you would need no lining.

 

[jimdean]

Steel header has butt welds and assumed carbon steel. Thanks for your replies.

 

[ApC2Kp]

jimdean,
The 1/2 inch wall thickness would seem to be capable of many more years of service, maybe for more years than either you or me. The steel pipe has better endurance with a minimum flow - more corrosion occurs in dead pockets like drain legs or closed bypasses, so be sure to check those. Another common coating on water service pipe would have been asphalt or coal tar epoxy.