NAPF WHITE PAPER
THE APPARENT CONFLICT BETWEEN AWWA C606 “GROOVED AND SHOULDERED JOINTS” AND GROOVED COUPLING MANUFACTURERS PUBLISHED GROOVED JOINT PIPE SPECIFICATIONS
May 22, 2017
AWWA C606 was originally published on January 28, 1978, and has been revised periodically. The Standard is the seminal reference for consulting engineers who specify grooved joint piping systems. NAPF is a producer member of the AWWA C606 Committee which reviews and revises this document.
When originally published the document reflected current industry practice and was, therefore, the roadmap to accurate fabrication of grooved ductile iron piping. However, NAPF producer members should be aware that no standard should be regarded as a specification. Members should also be aware that standards describe “the minimum requirements and do not contain all of the engineering and administrative information contained in the specifications”. Members should additionally be aware that engineers’ specifications also contain general admonitions to consult manufacturers’ specifications for compatibility.
Here lies the apparent conflict.
Although manufacturers of grooved couplings make reference to AWWA C606 in their published literature, their literature also contains additional and sometimes more restrictive data which have evolved over time. When these differences are displayed contractors and engineers may conclude that these could be the cause of assembly problems or even failures that could result in significant liability for fabricators. Consequently, although pipe fabricators may be diligently following the provisions, dimensions and tolerances set forth in AWWA C606, and be third-party certified to that standard, manufacturers’ guidelines may conflict.
Here are the differences:
1) The nominal “A” dimension for ductile iron pressure pipe flexible radius grooves is defined identically by AWWA C606 and manufacturers’ literature.
However, the manufacturing tolerances are not the same.
AWWA C606 defines the tolerance at +0.016”/-0.047”, while manufacturers’ literature displays +0.000”/-0.020”. Any dimension inside the C606 reference but outside the manufacturers’ data may place the fabricator “out of spec.” as far as the coupling manufacturer, engineer and contractor are concerned. This situation for flexible grooves [rigid radius grooves have been the norm in our industry] has become apparent due to the increase in flexible groove use primarily in Western states where seismic issues have recently served to require flexible joints.
Note: Rigid radius “A” dimensions and tolerances are identical in both AWWA C606 and manufacturers’ published information.
2) Coupling manufacturers define the minimum and maximum tolerances for outside ductile iron pipe diameters suitable for fabrication for both rigid and flexible grooves in 3” and 4” pipe diameters differently than does AWWA C606 and AWWA C151 “Ductile Iron Pipe, Centrifugally Cast”.
For 3” diameter pipe, AWWA C151 permits a tolerance of +/- 0.060. Coupling manufacturers permit a tolerance of only +/- 0.045.
For 4” diameter pipe, AWWA C151 permits a tolerance of +/- 0.060, one manufacturer permits a tolerance of +/- 0.045.
Therefore, even if fabricators produce 3” and 4” pipe grooves to the manufacturers’ groove dimensions and tolerances, there’s a chance for them to be identified as “out of spec.” on the O.D.
Coupling manufacturer O.D. tolerances for all other diameters are identical to those in AWWA C606 and AWWA C151.
3) One coupling manufacturer publishes a note that “Ovality, or out of roundness, must lie within specified tolerances” although there is no reference to what the specified tolerances are. If this is a subjective reference, fabricators might be “out of spec.”
Another coupling manufacturer has this citation: “Pipe out of roundness – difference between maximum O.D. and minimum O.D. measured at 90 degrees must not exceed total O.D. tolerance listed.”
Neither of these requirements is present in AWWA C606 or AWWA C151 and it is, therefore, doubtful that ovality, while it may be noticed, is being measured to fall within practical limits during the fabrication process.
4) One coupling manufacturer requires “the coating thickness applied to the gasket seating surface [A dimension] and within the groove on the pipe exterior should not exceed 0.010”…”. While this seems purely informational, if this dimension has not been considered in the O.D. calculations, the fabricator may be deemed “out of spec.”
Further, if you were not the finish coater of the pipe, you could be drawn into conflicts resulting from an “out of spec.” finished product if you neglected to inform the downstream finishers of that requirement and/or provided a product with O.D.s unable to meet the dimensions for the required thickness of the coating specifications.
5) One coupling manufacturer provides this Note: “This product shall be manufactured by [our Company] or to [our Company’s] specifications. All products to be installed in accordance with current [Company] installation/assembly instructions. [Our Company] reserves the right to change product specifications, designs and standard equipment without notice and without incurring obligations.”
6) One coupling manufacturer also publishes a minimum wall thickness requirement which is the nominal Class 53 thickness contained in AWWA C606 and AWWA C151. However, this dimension is provided without a minus tolerance provision which is referenced in both the aforementioned standards. This is yet another opportunity for the fabricator to be “out of spec.”
Fabricators should also be aware that wall thickness variations exist between coupling manufacturers in the 18” and larger diameters.
7) Coupling manufacturers also publish tolerances for square cut ends – “maximum allowable tolerance from square cut ends is 0.030” for 3” size, 0.045 for sizes 4” and 6”, 0.060 for sizes 8” through 36”. These are not contained in AWWA C606 or AWWA C151. However, these tolerances should not be of concern for pipe fabricators who cut ductile iron pipe conventionally in flat bed saws, pipe threading machines, lathes or other devices with self-leveling features. Field cut grooved ends are also subject to these tolerances and contractors should be advised accordingly.
It should be noted that the differences enumerated above may not necessarily be causative of assembly problems or failures. Some dimensions and tolerances are more critical than others. However, when such problems occur and these variations come to the attention of contractors and consulting engineers, the usual result is to cast suspicion on the fabricator’s work, since the only dimensions and tolerances that are verifiable [within both AWWA 606 and manufacturer’s literature] are for the pipe and the machined groove.
These inconsistencies and their potential for increased fabricator liability, is being addressed with the coupling manufacturers, both directly, and through the appropriate AWWA committees. However, their resolution will take some time and remedies may not be available through the normal standards revision process [which is not scheduled to occur until 2020]. Keep in mind that a standard is the minimum requirement and manufacturers are free to adopt more stringent requirements. However, it is also true that standards should be representative of industry practice.
In the interim, fabricators are urged to take the following precautionary measures:
1) Be familiarized with all the latest published coupling manufacturer specifications, dimensions, tolerances and installation instructions.
2) As with any joining method, when fabricating grooved pipe, determine the coupling source and use that manufacturer’s information for your protection. In light of changed specifications, fabricators may additionally choose to assess whether they are able to produce conforming product within guidelines other than those enumerated in AWWA C606. Fabricators are not obligated to do work they cannot perform with confidence.
3) When producing flexible grooves for seismic installations, consult the engineer to determine whether sufficient thrust restraint has been provided at affected locations in the piping arrangement.
4) Consider whether high-build, high-performance coatings will compromise the integrity of your work and/or adjust raw pipe selection accordingly, if possible. Fabricators might also issue advisory information for subsequent coating applicators regarding permitted coating thicknesses for grooved pipe.
5) Maintain calibrated gages, employ min./max. charts for comparison, and gage all coupling manufacturers’ published dimensions.
If you use Landis or other go/no-go gages, determine from the coupling manufacturers whether these meet their specifications or only those of AWWA C606.
Utilize bead gages or other specifically directed devices to accurately measure the groove diameter. Simply measuring the pipe O.D. and groove depth does not necessarily yield a groove diameter within either the Standard or coupling manufacturers’ specifications.
6) In order to maintain the nominal wall thickness required by one coupling manufacturer, fabricators may need to consider utilizing thicker pipe classes when bidding grooved pipe projects.
7) If problems or failures occur with grooved projects, investigate the installation yourself to be familiarized with all aspects of the work. Engineering and installation errors should not be ruled out as they account for the vast majority of manufactured product failures.
8) If presented with evidence of “out of spec.” dimensions by others, seek an interpretation from the coupling manufacturer whether any such differences can actually be the cause of the condition experienced. Generally, the diameter of the pipe and the diameter of the groove are the main issues regarding assembly and performance.
In summary, fabricators have always borne a disproportionate share of scrutiny when groove piping system problems occur. The only measurable dimensions and tolerances that exist in both AWWA C606 and manufacturer’s literature are for pipe. Consequently, these are the first to be checked and anything “out of spec.” provides contractors and engineers with evidence of cause or carelessness, regardless of whether the dimensions or tolerances are germane to the issue.
The scope of the differences between Standard and specification has widened over time to potentially place greater liability at the door of pipe fabricators. Consequently, NAPF is working on your behalf to remedy the situation and provide some clarity going forward. This paper is the first step.
While we have sought to be thorough, if any other issue exists with regard to this part of your business, please contact the writer. If any such issues can be incorporated into the standards process or can be addressed in another collaborative manner, we will try to do so. If you would like to be part of a committee to help, please let me know.
Ted Muntz, NAPF Standards Council Chairman