Pipe Threads, Dopes & Sealants

Tony Conner

I've been flipping through some catalogues on various dopes, Loctite products, etc. Here's what I've noticed.

Most Loctite products are rated to 300*F max. I've known that for a long time, which is why I don't use much Loctite stuff - a lot of my work is considerably over 300*F. This makes it unsuitable for steam over about 50 PSIG. (Most of you guys won't care about that, anyway.) A LOT of the various products, by a range of manufacturers, is only rated to 2" pipe, max. Some other stuff is rated to 4" max. I'm starting to think that many recently discussed problems are due, at least in part, to dopes and sealants that are only rated to for a maximum pipe size of 2" being used on larger diameter pipe.

Here's some pipe thread info from an old Crane catalogue. It's "No. 41", but I don't see a date in it. I'm guessing WWII era. Along with a lot of other info, it has a table that includes the "Normal Engagement By Hand Between Male & Female Threads". This is how far the fitting should screw on, by hand. Here's the bit from 1/2" through 4":

1/2" - 0.320"

3/4" - 0.339"

1" - 0.400"

1-1/4" - 0.420"

1-1/2" - 0.420"

2" - 0.436"

2-1/2" - 0.682"

3" - 0.766

3-1/2" - 0.821"

4" - 0.844

It goes on to talk about "Leaky Joints".

"Leaky joints can usually be traced to either faulty threading or an improper lubricant. Frequently the trouble lies in the thread on the pipe which may have been cut by dull or improperly adjusted threading tools resulting in wavy, shaved, rough or chewed threads.

Wavy threads are noticeable to the eye and touch, due to circumferential waves or longitudinal flats of slightly helical form rather than the desired true circular form. Shaved threads appear to have been threaded with two dies, one not matching the other, giving a double thread appearance at the start of the thread. Rough or chewed threads are noticeably rough and torn.

Should the threads have any of these defects it is possible that leaky joints might result."

Mark Eatherton1

So....

there's more to threads than meets the eye eh...

My pappy (Rest his soul) used to tell me that back in the good ol' days the only thing they used on their threads was a lubricant made of goose grease and beef tallow. Said it was more a lubricant than a sealant.

I guess times they are a changing. Instead of knowing how to read the threads and make corrections, the suppliers come out with new "products" to help us close the gap of knowledge. Or lack of knowledge depending upon you point of view...

Great post Tony, Merry Christmas to you and yours.

ME

Tony Conner

Here's One...

...from "Machinery's Shop Receipts And Formulas" (1910).

"As a substitute for, or in the absence of red lead, use varnish on air or steam pipe joints. It will dry very hard and last for a long time."

Given all of the threaded joint problems people are struggling with, it might be worth a try. How much worse can it be? And you can get varnish almost anywhere.

Best of the season to you and your family!

bob young

union gasoline plumbers made their own compounds with a varnish base.

Mark Eatherton1

Have you ever...

had occasion to try and unscrew pipe that was done that way? Remember my dad telling me of a compound used on gasoline lines called glycerin letharge. You'd collapse the pipe before you spun the pipe...

Guess they never thought about having to unscrew their work!

ME

bob young

litharge & glycerin---man i haven't even thought of that stuff for years. it would seize the joint like a weld. remember it was reddish in color.

Tony Conner

There Are...

... several old "receipts" as they were called, for pipe dope. Most included red or white lead, and/or litharge, along with various other ingredients. I had to look up what "litharge" is. "Lead monoxide, lead oxide, semi-vitrious oxide of lead, yellow lead oxide". Another easy one is shellac for air or gas lines. (Note that this may no longer be "code compliant" for fuel service.) The author claims it dries fast, and is brittle, so it's easy to disassemble, if required. I haven't tried varnish or shellac, so if anyone ever does, I'd be interested to know how they make out.

bovide

remember

remember "expando". this was a powder you mixed w/water to make a paste dope. the worst in the world - "leak lock"
this is the infamous blue dope that gets hard and brittle enough to cause a leak with vibration. after several years I went back to the old standby grey hercules "pro dope" for most applications - the smell brings me back to my younger years.

Tony Conner

You Can...

...still get Xpando. Not very maintenance friendly for a couple of reasons. The first, of course, is that it's pretty much impossible to get anything apart, and the second is, that it needs 24 hours to cure. We do a lot of maintenance on process steam equipment, and they usually want it back in service about 15 minutes ago.

bob young

how about alumack from the sixties. schmear contained asbestos particles --no lampwick needed on brass pipe . used on sprinkler lines too a lot cleaner than permatex.

Dave Faust

Why does pipe dope work?

I understand that conventional screwed fittings force a tapered male thread into a straight female thread. So is dope a lubricant, a sealer, or what? Does the size of the pipe matter? (I know, this can sound like a prudish question). Would soap work or does the joint need the dope after in is assembled? How does Tefflon Tape fit in. I've heard that tape combined with dope is preferable, but no reason as to why. How about just forcing the peices together with longer pipewrenches? I find that many mechanics are reluctant to say much on this topic.

Mike T., Swampeast MO

As I understand pipe dope it is both a lubricant and a sealer. BUT dopes are either of the setting or non-setting variety. Rector Seal is a type that sets; Oatey w/teflon is non-setting.

The lubrication helps you get the tapered pipe into the fitting further with less effort and, I guess, less chance of damaging the threads. The non-setting varieties usually seem to have teflon added--I think it makes a very good, inert "fill-the-gap" for small deviations in the threads. Like anything else, threads have tolerances so they're rarely a perfect fit. I also believe that the tolerances get bigger as the pipes increase in size and threads per inch decrease.

Teflon tape alone seems to work great for brass/copper up to ¾" or so. I like to use teflon tape and non-hardening dope for copper/brass larger than ¾".

For iron/steel, non-hardening, teflon containing dope alone seems to work great up to 2" or so. I don't work with larger iron/steel often, but my small amount of experience has taught me to use setting dope.

Tony Conner

The Thread...

...in fittings will taper to match the threads cut in nipples or pipe. Normal NPT threads will have a spiral clearance where the crests and roots of the mating threads don't quite meet. A sealant is necessary to fill this spiral leak path. This can either be a dope, or teflon tape. Dope/tape will also provide the necessary lubrication to allow the joint to be made-up properly. Read the literature for the various kinds of dopes. There are usually application limits on types of service, temperature, pipe size, etc. Lots of dopes are limited to pipe 2" and under. Others are limited to 4" and under. I'm not aware of any limit on tape.

I think that one of the biggest things you can do to achieve leak-tight screwed piping joints is to cut the threads properly. All threads cut should be clean and sharp - no torn threads, etc. The adjustable die heads used in equipment like Ridgid 300's and 535's can be set all over the place. Cut a test thread the same length as a factory nipple thread of the same pipe size, and see if you get 3 to 4 turns, hand tight. Keep adjusting and testing (usually takes at least a couple of times) this until the dies are set correctly. As often as not, the final setting doesn't quite match the mark on the scale of the die head. The correct setting will minimize the spiral clearance. After that, you don't have to check every thread you cut, unless the dies get adjusted to another pipe size. The drop head dies should be set up when they're replaced. The instructions are on the back of the card they come in. We wire brush the threads we field cut to remove any little chips. (This is just a quick "once over" - it doesn't take more than a few seconds.) Another poster on an earlier string wire brushes the internal threads on fittings, and factory nipples. We don't normally do that, unless they got some rust or dirt in the threads. It's not the wrong thing to do, however. We use the heavy orange teflon tape alone, for pretty much everything. (We don't do fuel work - mostly industrial steam/condensate and compressed air.) It lubricates, and plugs the spiral clearance. (Teflon tape is not permitted for some services, in some jurisdictions, so you have to check.) We apply the tape in the same direction the fitting will screw on, and use the edge of the tape spool to chase the threads, pushing the tape into the root of the thread. Tighten the fitting with the right sized wrench (you shouldn't have to kill yourself), and you should have a leak-free joint that can be adjusted slightly to square the pipe up. Don't tighten the fitting on so fast that a lot of heat is generated by friction.

There is another type of thread - "NPTF". (Well, there are several other types, actually. The NPT are far and away the most common.). Everything is the same, except that the threads are more precise, eliminating the spiral clearance/leak path. The only place I've ever even read about this kind of thread (I've never actually seen one, that I know of) is in a book on industrial hydraulics. Even if you buy the dies, you'd still have to source the matching fittings, to eliminate the spiral leak path. (Hydraulic supply house, maybe? $$$$$?) Even though a sealant isn't required for this kind of thread, a lubricant is. It's very difficult to tell NPTF from NPT threads just by looking at them, so NPTF must be labelled as such.

tom_11

Sealant

what sealant would you use for a 2 inch black pipe for the oil fill pipe. #2 fuel oil . thank you tom

Big Ed

We use to call .....

.....that dope "Paint" . Never used it but we use to curse it on repairs before we armed or selfs with sawsalls

mp1969

Letharge and glycerin

I remember picking up litharge and glycerin at the drug store, we always used it on the push nipples on sectional boilers it worked extremely well for that application.
X pando was also always used on all our threaded hot water piping. We were not concerned about taking apart threads we only wanted permanent water tight joints. The jobs were commercial and institutional bid and spec jobs so we always had time for set up of the compound.
Today it is not uncommon to get nipples from Mexico, fittings from Indonesia and valves from America all on one order and the tolerances seem sloppier today than ever. If I was still doing large threaeded heating jobs I would definitely use X-pando again (If it was allowed in the specs)On the rare occasion that we had to take apart a joint you could break the seal by hitting around the thread in about thrre places.

MP 1969

[Deleted User]

here is an interesting product-

has anyone tried this, sounds good--copy & pasted the following-
Hernon's line of Dripstop sealants for plumbing, refrigeration and hydraulics are engineered with many advantages over conventional pipe dopes. These materials harden without shrinkage in the joints creating a tough, insoluble, vibration proof seal that will not leak even if threads are damaged.Dripstop sealants are 100% active containing no solvents to evaporate. They do no shred like tape dope and are not subject to cold flow, pressure and temperature phenomena like non-hardening dopes.Grade numbers 920, 940 and 427 (see Thread Locking Section), have been tested and classified by the Underwriters Laboratory's (UL) File Number MH14222.Anaerobic pipe sealants/adhesives are superior to other sealing methods.Increased Profitability: Lower Costs, Less Down Time Reduced Inventories - no pipe dopes, paints needed. Reduced Maintenance - hydraulics and pneumatics don't become fouled with shreds of Teflon tape. Superior Reliability - 10,000 psi - tough integrity. They contain no solvents and do not shrink, stretch, split, rot, distort, wear-out, or relax and joints never loosen under vibration. Pressure cycling does not weaken or loosen the sealant path.Because the sealant path is formed when parts are made - up, that is, threaded together, the plastic shim formed during cure is truly a "custom" seal. Sealant not forced out cures to a helical path in the thread roots to form an exacting match of the surface irregularities. The shim mirrors and fills all the voids, scratches, and thread nicks present in even the best machined straight or pipe threads, Unlike Teflon tape, any non-confined or excess sealant material does not cure and pose the threat presented by shredded tape fouling valves or circuit elements

Tony Conner

If You...

...keep the T-tape back one thread, there will be no problems with it coming off in strings, and fouling things. You can look into the open end of a fitting that's been wrenched on, and not see any tape at all.

What's the maximum temp & pipe size rating of Hernon's products? Loctite has some neat stuff, but most of it runs out of gas at 300*F and/or 2" pipe, which means it's no good for a lot of the work I get into.

[Deleted User]

the temp was

rated at 400 degreesF, but i didn't see a pipe size on the literature.

Dave_14

Sealants

Check out Gasoila, they have a wide variety of products suitable for "hard-to-seal" fluids.

www.gasoila.com

Dave

bob young

gasoilia

what the heck is that stuff made oughta? a one pound can weighs about a hundred pounds. some heavy metal

gtr/tes

compounds

Still wick with Hercules Mega-Lock.

Tony Conner

The Can Says...

... that Megaloc is rated to 400*F. I disagree. I've had nothing but problems with it in 125 PSIG/353*F steam service. You can watch it run out of the joints as the lines heat up, and that nice blue colour "cooks-out" to a pale biege as the lines come up to pressure. My experience with anything that changes colour on a temp increase is that "This just has 'TROUBLE' written all over it..." Our experience in fixing steam leaks on joints where it's been used is two big guys, a 3 foot pipe wrench and a 2-1/2 lb hammer to get 1" nipples out of fittings.

I'm sure Megaloc is great for a lot of applications. High pressure steam isn't one of them, in spite of what the can says.

joe_17

Good subject

I too work on steam up to 250psi.Pipe up to 2inches.I see all different types of dopes and tape.I see tape applied improperly and winding up in reducing valve ,on seats in strainers,and causing havoc.