Buried Rigid vs PVC

[TwoBlocked]

I expect to be involved in running conduit in a trench with gas well piping. When discussing rigid vs PVC, I hear a lot of "Always dun it this-away" comments. But the gas industry isn't THAT old here and there's a lot of different "Always dun it this-aways" with darn near everything. One knowledge person said that if the conduit is run directly with the gas piping, rigid is best. but if the piping is first covered, then PVC is best. Another says to use PVC but tape each joint with "3M tape" to strengthen it. (I'm pretty dubious on this...)

My factory background is rigid, rigid, rigid, but certainly see the advantage of PVC in corrosive environments like brine plants. But underground? Looking for insights from you fine folks, especially those of you that have seen failures occur.

 

[roger]

IMO for underground PVC is the best choice.

 

[Strathead]

IMO for underground PVC is the best choice.

Especially in a state like Florida where contact with the earth is pretty corrosive to iron.

 

[ptonsparky]

PVC.
CableCon if the distance is substantial.

 

[Dennis Alwon]

I agree with the pvc unless the gas company has some regulation that would disallow the install. Btw, you can install pvc coated rmc... $$$$$
50 years ago we installed some rigid outdoors at an IBM plant in Kingston, NY.. My boss had us tar the conduit after we put the pipe together. It must have been an IBM requirement.

 

[Strathead]

I agree with the pvc unless the gas company has some regulation that would disallow the install. Btw, you can install pvc coated rmc... $$$$$
50 years ago we installed some rigid outdoors at an IBM plant in Kingston, NY.. My boss had us tar the conduit after we put the pipe together. It must have been an IBM requirement.

We are usually required to coat our conduit with Bitumastic specifically Carboline, because it is listed for the purpose, in Florida. We have been busted for using roofing mastic.

 

[electrofelon]

I don't know why on earth anyone would run RMC underground, except for specific situations like low burial depth/high likelihood of damage and such.

 

[4-20mA]

Never heard of taping pvc couplings, that's different. We do tape and coat all of our Robroy RC bends and fittings though. But, in time, even carefully taped and painted connections still corrode, especially in a corrosive environment like our plant. Thank goodness I don't have to run the 535 anymore these days ha

Curious as to what comes about.

 

[kwired]

Never heard of taping pvc couplings, that's different. We do tape and coat all of our Robroy RC bends and fittings though. But, in time, even carefully taped and painted connections still corrode, especially in a corrosive environment like our plant. Thank goodness I don't have to run the 535 anymore these days ha

Curious as to what comes about.

Taping if useful at all is for while you are handling it.

Best thing is to avoid couplings and only use bell ends as much as possible. They are strong enough tape won't improve anything. Most anymore have at least twice the socket depth as standard couplings have. Elbows with bell end on one end are available also.

 

[TwoBlocked]

Wow! Lots of great responses. We do plan on using rigid coming up, including the sweep, which I plan to bend. I will keep in mind using the bell ends.

 

[TwoBlocked]

So has anyone experienced an underground PVC conduit breaking? I've seen plenty of above ground ones snap, but never a rigid. And have you experienced a rigid becoming unusable underground?

 

[Fred B]

Only time I've seen an issue with PVC underground has been installation error (usually improper backfill) or secondary to some excavation.
Seen old rigid that was corroded to the point of pin holes around the threaded area and no longer able to pull thru for the corrosion. (more than 50 yrs in ground though)

 

[ptonsparky]

I've seen GRC that was nothing but rust stains in the sand. THWN/THHN was still good.

 

[winnie]

There is always naval brass GRC, but for the cost I'd use PVC and then back fill with dollar bills....

 

[Strathead]

Wow! Lots of great responses. We do plan on using rigid coming up, including the sweep, which I plan to bend. I will keep in mind using the bell ends.

they also make couplings called long line couplings that are deep like the end bells on elbows and conduit sticks.

 

[mtnelect]

I expect to be involved in running conduit in a trench with gas well piping. When discussing rigid vs PVC, I hear a lot of "Always dun it this-away" comments. But the gas industry isn't THAT old here and there's a lot of different "Always dun it this-aways" with darn near everything. One knowledge person said that if the conduit is run directly with the gas piping, rigid is best. but if the piping is first covered, then PVC is best. Another says to use PVC but tape each joint with "3M tape" to strengthen it. (I'm pretty dubious on this...)

My factory background is rigid, rigid, rigid, but certainly see the advantage of PVC in corrosive environments like brine plants. But underground? Looking for insights from you fine folks, especially those of you that have seen failures occur.

Don't forget the yellow or red "Danger Tape" before you back fill.

 

[kwired]

Don't forget the yellow or red "Danger Tape" before you back fill.

So that someone excavating in the future will know what they already hit when they see the tape coming out of the hole

 

[tom baker]

So that someone excavating in the future will know what they already hit when they see the tape coming out of the hole

I have seen that happen

 

[tom baker]

A good solution is PVC conduit encased in one sack concrete mix. Some will add red dye

 

[letgomywago]

A good solution is PVC conduit encased in one sack concrete mix. Some will add red dye

I'm glad concrete covered pvc is allowed for gas stations. I wish it was allowed for more situations