Sche 40, ERW pipe quality

[wldhair]

I have read several postings that question the quality of carbon steel pipe today versus that 15 or so years ago. I suspect the only source for carbon pipe material today is from recycled steel from mini mills rather than raw steel from blast furnaces. Recycled steel from mini mills was originally provided for bar, rod and tube but in the late 80's the recycled steel began to be used for steel pipe. I am sure the steel specification stayed the same, but did something change in the integrity of the pipe that we are not aware of. The time frame is consistent with our problems.

Our concern is we seem to be getting carbon steel pipe with more interior and exterior mill scale than 15 years ago. On flushing a new HVAC piping installation we were shocked to capture several pounds of iron oxide from the system.

In a several installations where the piping is 12-15 years old, we are finding the exterior of insulated chilled water piping pitted to the level of multiple leaks occurring. The leaks occur principally in 1-1/4" lines but there is everything from 3/4" to 8" pipe installed in the systems. In searching for an explanation we have honed in on a form of concentration cell corrosion as the possible culprit but we are still not sure. In one specific installation leak incidents are isolated but 16 of these leaks over the last 12 years is unacceptable.

Have any of you experienced similar conditions.

 

[metengr]

I disagree that the steel today is potentially inferior because of increased use of steel scrap for melting. Steel melting practices over the last decade have vastly improved resulting in tighter chemcial composition ranges and higher quality.

I do believe that mills need to have direction as to the end use of the product so that some level of surface cleanliness is specified. Steel mills are no different than any other business in cutting costs, so that the end user of their product line must be savvy on what they specify for delivery.

 

[GregLamberson]

I agree with Metengr. Your comment about receiving several pounds of mill scale after flushing is not uncommon at all and is dependent upon the length of the pipe run or pipeline. It is not uncommon at all, and in fact is the norm to receive considerable mill scale after flushing.

As to the leaks encountered, there could be a vcariety of reasons including substandard installation practices. Is the pipe internally coated, externally coated and what type of CP system is being used?

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[wldhair]

Relative to the coatings question: The only coating would have been the exterior paint to prevent rust from short time storage. Internally there was no coating. I remind you this is an economically driven HVAC installation in a commercial office building.

The worst pitting that we have encountered is an area approximately 3/8" wide X 3/4" long. The obvious is that moisture is involved and all of the pitting occurs along the bottom of the pipe. What is very suspicious is the nature of the pitting. For the specific area described above the pitting consists of at least 6 small craters penetrating into the pipe. The area of pitting is not rusty brown but almost a sandblasted white. Adjacent to the pitting are rust deposits that can be scraped off with no damage to the pipe surface. Again the installation is HVAC chilled water, insulated with 1-1/2" fiberglass insulation with foil and paper vapor barrier. We know the vapor barrier is not perfect. Economically driven, we will never see a "perfect" vapor barrier insulation system for HVAC.

I appreciate the confirmation about the large amount of iron oxide (mill scale) that is expected from flushing a system. Even though it is in an HVAC installation, we have decided to step up the degree of flushing our systems by capturing the debris from the system until the system flushes clean. Prior to this procedure the system was filled with a detergent flushing solution, circulated for several days, flushed and refilled for operation. It is our intent to extend the life of valves and pump seals and prevent scaling of heat exchangers.

 

[MikeHalloran]

I'm wondering if maybe a small scrap of foil was in contact with the pipe in that 'sandblasted white' area.



Mike Halloran
Pembroke Pines, FL, USA

 

[unclesyd]

I have to agree with metengr's post about the current pipe stock being somewhat better. Granted if if you shop around you can get some sorry pipe.
25 yrs ago we had to have a cleaning/pickling setup to where we processed every stick of pipe used on site.

If the piping has been in service, even for a short time what you are seeing could be a corrosion product. As far as the outside pitting goes this is just condensate from the moist air surround the pipe. The condensate can be quite corrosive especially if you see green slime in the area.
I would look to your system as the source of the Iron. Which is probably bugs

We have miles of chilled water piping in our manufacturing area and external corrosion is a problem if we don't maintain the integrity of the insulation and pipe coating.

We have our chilled water pipe coated with bitumen, coaltar epoxy or a zinc rich coating with the insulation product being Cork, Expanded CalSil with sodium silicate coating, or FoamGlas. All this insulation is warped and coated with a Foster product to prevent moist air infiltration.

 

[BigInch]

Are you sure there is no electrolitic action taking place? Measured any potential votages lately?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[wldhair]

The "sandblasted white" color has nothing to do with the foil. The foil is quilted and on the exterior vapor barrier. Believe me. Go out and look at freshly sandblasted metal where the grains of the metal can be seen and you have a white to gray color. That is it.

One of you mentioned "bugs". I have heard of bugs eating crude oil in the ground but I have never heard of bugs eating or attacking metal. The appearance of the craters is as if a small bumble bee bored a piece of wood trying to make a home.

We have not detected voltage for the process of electrolysis. What drew us to the concentration cell corrosion was the similarity of the ion exchange process between H20 and Fe. With the ionization process various forms of Fe are transported and oxygen and hydrogen released furthering the corrosion process. We have found that if the pipe is soaked, we observe surficial rust. If there appears to be a small bubble of moisture, we find this pitting process.

 

[metengr]

The reference to "bugs" mentioned by unclesyd is microbiologically influenced corrosion (MIC) and can result in pit tunnels or caves on the exposed surface. These are various types of bacteria that thrive under various environments.