ADVISORY – check LP tank for leakage on older Interstates

[InterBlog]

If your Interstate is several years old, and without question if it is a T1N-based Interstate (model year prior to 2008), I strongly advise that you physically check the condition of your LP tank. Either do it yourself if you have the skills, or hire a professional. Get underneath your chassis and examine it closely. Get a squirt bottle of soapy water and spray every connection, looking for bubbles. Evaluate any corrosion that may be present - is it light and surficial, or does it look like it might have started to become structural?

Our tank proved to be so badly corroded that it was leaking propane. This is an 8-year-old tank on a lightly-used Interstate (29,000 miles). I discovered it almost by accident, as I was puttering around doing odd jobs and inspections while helping my husband with the initial portions of our DIY solar panel installation. While searching under the chassis for penetrations large enough for rodents to squeeze through, I heard a funny noise, which proved to be propane escaping.

Our Interstate is still in the shop for the tank replacement, so I don’t have a complete story to tell yet, but here is a photo of one side of the original tank for openers. Parts of the tank are a challenge to both examine and photograph because they are up against the chassis, plus they are obscured by a rock shield. The obscured parts were actually worse looking than this side that has the tank plate. But notice the extent of corrosion at the connection, and also notice that there is bubbling of the metal *underneath* the coating (surface paint). If you just look at the coating itself, it might be misleading. The worst of our rust is actually beneath the coating in places.

Again I will mention as I have in other threads... we paid for a full “professional” evaluation of our Interstate prior to purchase just over a year ago. This is yet another expensive repair item that the so-called inspector failed to call out. Spending that money on inspection was actually worse than flushing it down the toilet, because it gave me a lingering false sense of security, which is part of the reason why I am still discovering serious issues a year after purchase.

[RVBSeeker]

Glad you guys are ok and that you caught it in time. As much as I really like the Interstate, I'm so hesitant to move forward with a purchase because it, like 98% of the RVs are propane based.

[Lily&Me]

Yikes! That looks pretty bad.

My guys at Peterbilt put mine up and look everything over thoroughly at least twice a year, and have reported no problems with the propane tank. I will be sure to ask them about this, specifically, tho, next time I am in.

I have had rust pop up here and there, as would be expected for a Sprinter chassis that is 10 years old, so it is probably just a matter of time before the propane tank needs to be replaced.


Maggie

[Lily&Me]

Originally Posted by RVBSeeker

Glad you guys are ok and that you caught it in time. As much as I really like the Interstate, I'm so hesitant to move forward with a purchase because it, like 98% of the RVs are propane based.

I used to be afraid of propane, but am not any longer.

170,000+ miles on mine, and couldn't love it more.


Maggie

[InterBlog]

I'm not afraid of propane and I don't really see any reason to be afraid of it, as long as the system integrity is maintained. But a leaking tank is a game-changer, and of a type that is beyond the DIY level of response.

I was initially expecting to have the thing back in my possession today but they ran into problems, as is often the case. The issue with the Interstate is that so much is crammed into a small space that any given intervention touches off a very expensive domino effect. In order to get at the mount for the LP tank, they had to remove the fresh water tank inside the vehicle. Furthermore, Airstream *welded* the LP tank onto the chassis, so they had to break the welds at the bolts. Apparently it was not just a matter of grinding off some spot welds - they said they had to melt it off. I asked if that kind of thing (welding on a tank) was common and was told that some manufacturers do it but certainly not all. My new one will NOT be welded on, thank you.

I haven't worked with this outfit before, some local people, family-owned RV center in business almost 50 years. They seem reasonable, even encouraging me to have the tank refurb'd instead of replaced to save me a few bucks. The problem was that the tank has to go through the same dismount procedure regardless of whether it is being repaired or replaced. And it costs so much in labor to dismount and re-mount that, to my way of thinking, it's penny-wise-pound-foolish to re-install a rotten-a$$ tank. So what if I could squeeze a few more years out of it if refurb'd? I'd rather put on a new one and avoid future labor charges. The tank I chose is $517 plus tax (my choice is a future story in itself as the tank Airstream originally installed is not made any longer). I expect the labor to be much more than that.

[Kevin245]

You were wise to replace the pressure vessel (commonly referred to as a tank) rather than attempt to repair it. This is an ASME vessel as indicated by the stamped "U" that can be seen in the top left corner of the data plate. The data plate is equivalent to a birth certificate for pressure vessels. The data plate is paired with a design document called a “U-1” form that lists out vessel design parameters such as dimensions, capacity, national board number, material specifications, weld joint efficiency, and other information that goes along with the numbers displayed on the plate.

This is a commonly produced vessel (hence the catalog number) fabricated under a standard design which means that a manufacturer’s certificate is on file. To legally repair this vessel a shop, or repair contractor would need to carry an “R” stamp, which indicates they are a qualified ASME repair shop, and they need the certificate information to facilitate a repair design. This is where it gets tricky, as many ASME shops won’t work on a mass produced vessel because the cost benefit typically does not outweigh the risk. Mass produced units such as this one typically aren’t over designed which makes them lighter and cost effective. Manufacturers typically use the thinnest material that will meet the design standard and allow some wiggle room for vessel shell and head thinning due to wear, scour, corrosion, etc. This is commonly referred to as the Corrosion Allowance (CA) and the CA is a function of the Maximum Allowable Working Pressure (MAWP) at a given temperature, welded joint efficiency, base material properties, etc. When I run T-min calculations on this type of vessel the cost of repair (if a repair is even possible) often exceeds the cost of a new unit.

If the leak was from an area other than a fitting then I would think you were truly riding on borrowed time as there appears to be a lot of exfoliated corrosion just under the paint.

Good catch!!

[73shark]

Originally Posted by InterBlog

My new one will NOT be welded on, thank you.

Recommend using good quality st-st hardware for mounting the new tank.

The old tank appears to have spent a lot of time in the Rust Belt.

[InterBlog]

Originally Posted by 73shark

Recommend using good quality st-st hardware for mounting the new tank.

The old tank appears to have spent a lot of time in the Rust Belt.

I've gotten some off-Forum questions asking me if I know the history of this Interstate, because this situation doesn't seem right - was it kept near the ocean? Was it kept on salt roads? Did something extraordinary happen to it? Inquiring minds want to know. So do I. Before I posted this thread, I researched other tank issues on this Forum, including the trailer section. I did find a few corrosion examples, including one recent motorhome thread which sounds suspiciously like my situation, but those tanks were greater than 20 years old, not 8 years old.

I have all the previous owner's paperwork on maintenance and even the initial purchase. He was a first-stage retiree who lived in the Midwest, appeared to keep the vehicle in the Midwest, and apparently didn't do much in the way of demanding driving (hence the low mileage, about 3,500 miles per year on average). Google suggests he either owned or co-owned a small automobile dealership prior to retirement, which explains his meticulous recordkeeping and maintenance of the Interstate in pristine condition - he was looking ahead to resale value.

[InterBlog]

Here's a description of the replacement process, including a YouTube of the original leaking tank.

THE INTERSTATE BLOG: REPLACING A LEAKING LP TANK ON AN AIRSTREAM INTERSTATE

[InterBlog]

Postscript to this...

I have a mariner friend who looked at our tank pics and suspects that something had been done wrong in initial construction or assembly.

There are different metals (steel and brass) in potential contact, wires running to the tank, electricity running through the Interstate (with unexplained parasitic draws). I must admit that when the shop handed me the tank and its rock plate, the first thought through my head was, "Wow, that looks sacrificial". But my head was unable to trace out a specific scenario in which it might essentially be functioning as the sacrificial anode in the system. My mariner friend says that the wrong small lapse in quality control, such as neglecting to use dielectric grease on the fittings, could cause serious problems.

Two other owners of 2007 Interstates emailed me reporting nowhere near our degree of corrosion, and one of those rigs has almost always been kept in proximity to the ocean with its salty air. So this issue is apparently not endemic to the model year. Something different appears to have transpired with ours. Any engineers care to comment on that angle?

[73shark]

Since most of the corrosion in the picture appears to be isolated to the welds, I'd say poor preparation prior to painting contributed to the problem.

[J. Morgan]

Maybe it is just me, but in my view of the video it looks like the leak is between the threaded in nipple and the welded in bung.

If this is the case, I think I would have replaced the leaking nipple and called it a day.

From what I see, that tank was nowhere near to rusting through for the next twenty years.

In any case, imo of course, whether the leak is on a threaded connection or not, it does not look to be corrosion related to me.

As always, I reserve the right to be wrong, and pics and videos have their limitations, and things may look much different live in person.




Brevi tempore!

[InterBlog]

Originally Posted by 73shark

Since most of the corrosion in the picture appears to be isolated to the welds, I'd say poor preparation prior to painting contributed to the problem.

I thought of that; in fact, I specifically took a look at whether it might be wholly or partly attributable to the volatile organic compound (VOC) emissions limitations that have been imposed on manufacturers in recent years. If they are forced to degrade their coatings and are unable to find a comparably-performing product for the application at hand, then of course end users such as myself would expect to see more problems down the road, problems that would appear abnormal or unprecedented relative to earlier experience with the same or similar products. Excerpt on the relevant industrial sector affected by some of the restrictions:

40 CFR 63.3881: "Miscellaneous metal parts and products include, but are not limited to, metal components of the following types of products as well as the products themselves: motor vehicle parts and accessories, bicycles and sporting goods, recreational vehicles, ..."

Actually your comment prompted me to go back into my email and take a closer look at the other T1N Interstate owner's tank, as he was kind enough to send me photos of it. His Interstate is the same model year as mine, but his LP tank is plated a year younger - I didn't notice that at first. And his coating is a slightly different color. It may have been a different coating formulation, indeed. Hmmm...