Engineer 411 Q&A

Q: Our flanged pipe was supplied with a black asphaltic coating and not the primer coating specified in the contract documents. What can be done to correct the situation prior to applying the additional finish coatings?

A: NAPF has published the seminal reference on this subject – NAPF 500-03 “Surface Preparation for Ductile Iron Pipe and Fittings In Exposed Locations Receiving Special External Coatings and/or Special Internal Linings”. The Foreword of this standard contains the following note: “NAPF does not recommend the application of special coatings over asphaltic pipe coatings due to their incompatibility of most such coatings and asphalt. Asphaltic coatings are difficult to remove from centrifugally cast ductile iron pipe surfaces. Therefore, uncoated pipe is recommended when special coatings are required, unless otherwise recommended by the coating manufacturer.”
The porous nature of ductile iron pipe surfaces makes it almost impossible to remove asphalt completely. Over blasting creates problems even more significant. To be totally compliant the pipe should be re-fabricated with new, uncoated pipe and primed per engineers specifications.

Q: During the installation of our 4” diameter piping, the alignment from center became offset from center by 4 degrees. I am told that a beveled filler flange will correct the alignment. What are the dimensions of the beveled filler flange that I need to order?
A: The solution involves some basic geometry, trigonometry and a conversion table. But it’s easy.
Geometry Formula: tan. of x degrees = A/B

Trigonometry Table: tan. of Angle A (see attachment)
1 Degree = .0175
2 Degrees = .0349
3 Degrees = .0542
4 Degrees = .0699
5 Degrees = .0875
6 Degrees = .1051
Computation: tan. of Angle X Degrees = A/B
(tan. Angle A) chart appx. = A/B (Known Value)
(tan. Angle A) .0699 = A/9 (4” Flange OD)
.0699 / 1 = A/9
.0699 x 9 = .6291
A = .6291

Due to fabrication requirements, it is impractical to make a beveled filler flange .6291” at one end and zero at the other end. Consequently, one end must add the minimum machine stock length required to hold the piece while it is machined (usually .375”). Therefore, the minimum dimension for a filler flange maintaining the same degree of bevel would be .375 X 1.0041 or to convert to fractions for ordering; 3/8” X 1”.

Q: Our firm prefers to specify ductile iron flanged pipe for our water treatment plant projects. To be consistent, our piping systems generally specify operating pressures of 350 psi. However, the customary Class 125 flanges used on ductile iron pipe are rated for only 250 psi. We can specify Class 250 flanges, but the cost is prohibitive and the availability of other Class 250 ductile iron products [particularly fittings] is severely limited. We can specify 300# steel pipe and flanges and achieve our rating requirements, but we prefer ductile iron. What can you suggest?

A: In the first place, the 250 psi limitation for Class 125 flanges is a function of the flange material employed. Remember that ANSI B16.1 Class 125 flange performance was initially written around gray cast iron flanges which possess a lower tensile strength. However ductile iron flanges do not share that limitation even though they may be governed by the same ASTM standard designation.
The second limitation to joint performance greater than 250 psi is flat gaskets, since they were designed around the dimensions and pressure carrying characteristics of the original gray iron flanges.
The third limitation to rating flanged pipe higher than 250 psi is the threaded joint between the pipe and flange. This rating is determined by the fabricator of the flanged ductile iron pipe. The fabricator is free to rate his work higher than the 250 AWWA C115 standard designation.
The ductile iron flanged pipe industry has solved your dilemma through AWWA C115 which states:
“ Sec. 1.1. Scope. Flanged pipe and flanges are rated for a maximum working pressure of 250 psi (1,720 kPa). However, 24-in. (600-mm) and smaller flanged joints with ductile iron flanges may be rated for a maximum working pressure of 350 psi (2,413 kPa), as noted in the footnote of Table 1.”
The footnote states:
“Flanged joints with ductile flanges in the 24-in. and smaller sizes may be rated for 350 psi (2,413 kPa) with the use of special gaskets whose rating is supported by performance testing as described in Sec. 4.5 of ANSI/AWWA C111/A21.11. Check with manufacturer.”
These special gaskets typically employ molded annular rings or serrations to achieve greater performance.
Your revised specification should include three elements; 1) reference to AWWA C115, 2) ductile iron flanges be used and 3) the requirement for 350 psi working pressure. Unless these three elements are contained in the contract documents, you are not assured that all provisions are covered. Just specifying ductile iron flanges and/or “special” gaskets per AWWA C111 is not complete.
Armed with this specific information, fabricators will then be able to quote projects appropriately and you’ll get what you want.

Q: Our pipe fabricator recently informed us that they would not direct tap 2” iron pipe threads in to a 12” piece of flanged pipe. He said that 1 ¼” was the maximum the standard would allow. He suggested that we use a saddle. Since we didn’t have room for a saddle we contacted another fabricator who said he could do it, meet the AWWA standard for this work and certify it accordingly. What gives?

A: Both the curvature and the thickness of the pipe work to limit the size of direct taps that can be accommodated. Class 53 is the standard thickness for flanged ductile iron pipe and diameters in this class larger than 14” can easily accept 2” iron pipe taps. Smaller pipe diameters are a little trickier. The charts in Appendix A of AWWA C151 provide the basic guidelines, but there is a range of “standards” to be achieved depending on variables like tread type, material being joined, and industry preferences. To my knowledge, and due to the variability of materials and installations, there is no AWWA standard for the number of complete threads required to make a leak tight seal. However, I am aware that the accepted standard practice for mechanical and plumbing connections is four complete threads.
The response from the first fabricator was correct on the basis of four threads – 1 ¼” is the maximum for class 53 ductile iron pipe. The second fabricator would have been correct to direct tap 2” IPT on the basis of three threads. The second fabricator may also have been more aware of your dilemma and therefore, without you being aware, employed a heavier pipe class than standard – say Class 56 pipe which would [since the pipe is sufficiently thick] achieve four complete threads. This decision whether to use thicker pipe is usually based on the fabricator’s availability of Class 56 pipe; or cost, since the cost of using a long piece of Class 56 pipe may greatly exceed the cost of just using a saddle on Class 53 pipe.
In any case, you must indicate how many complete threads you require and any other space limitations that are involved. Then your fabricator can present the options.

Q: Our consulting firm requires that all products contacting potable water be certified to the NSF 61 Standard. A fabricator in our area has reported that although his flanged pipe is certified, his competitor is not. When asked, the competitor advised us that his pipe has indeed been NSF certified at the foundry by his supplier. We received certifications from both fabricators. The complainant says they are not the same. The competitor says that the only surface that contacts potable water is not affected by his work. This sounds reasonable. Is it correct?

A: No. NSF certifications are not portable.
Secondary manufacturers (pipe fabricators) of previously certified products are required to certify their own products. This is because additional shipping, storage and manufacturing may expose interior pipe surfaces to potential contamination. Suppose a fabricator is located next to a chemical, pesticide or other industrial producer. The manufacturing process of flanged ductile iron pipe involves cutting with abrasives, threading with cutting oils, welding hazards, blast media and finish painting. All these activities may compromise contact surfaces. In addition, all NSF certifications are site specific. Inspections are conducted, testing completed and certification accorded only to the products of that particular plant site.
The complaining company is correct. In addition, he could have informed you that the by virtue of the fact that the competitor has no site certification to NSF 61, his competitor also does not conform to AWWA C115, the flanged pipe standard, which states as follows:
“4.1.2. Certification. Products intended for contact with potable water shall be certified to the requirements of NSF/ANSI 61. Certification shall be accomplished by a certification organization accredited by the American National Standards Institute (ANSI).”

Bookmark the permalink.

Comments are closed