Ductile Iron Pipe

NAPF 500-03 Surface Preparation Standard for Ductile Iron Pipe and Fittings In Exposed Locations Receiving Special External Coatings and/or Special Internal Linings

Steel versus Ductile Iron Surfaces
 Inherent manufacturing differences between ductile iron pipe and carbon steel necessitate differences in surface preparation requirements. Examples of some of these differences are as follows:
Rolled steel in “mill condition” will normally require (1) blast removal of mill scale, rust or other surface contaminates, and (2) the establishment of an anchor pattern to the normally smooth surface of steel through abrasive blasting. Generally, ductile iron pipe will not require the same degree of blast to achieve equivalent surface cleanliness. Also, ductile iron pipe has a higher anchor profile as cast than can be achieved with steel by abrasive blasting.
The chemistry and metallurgy of ductile iron pipe and fittings versus that of carbon steel result in a surface that has a different texture and color from that of steel. Additionally, the texture and color of ductile iron pipe and fittings also may vary due to the differences in manufacturing processes.
Ductile iron pipe manufactured using the deLavaud centrifugally cast process with dry spray on peen pattern metal molds will have an annealing oxide on the exterior surface. This annealing oxide is different than mill scales typically found on steel surfaces. It is significantly more tenacious, adherent and more difficult to remove by abrasive blasting than mill scale on steel surfaces. Testing by pipe manufacturers, the Ductile Iron Pipe Research Association (DIPRA) and established coating manufacturers have determined that tightly adherent annealing oxide on ductile iron pipe acts as a very corrosion resistant protective layer on the surface of the ductile iron.
For these reasons, narrative visual descriptions and/or visual standards prepared for steel surfaces are not applicable for ductile iron surfaces (i.e.: terns such as white metal abrasive blast and near white metal abrasive blast do not apply). To illustrate, SSPC standards describe the visual appearance changes to steel as abrasive blasting is applied. The surface changes from a dull black/gray (SP 7) to gray (SP 6) to near white (SP 10) to bright white (SP 5). However, ductile iron pipe changes from the “as cast” medium gray to a bluish gray color when abrasive blasting (not recommended by these standards) eventually may produce an uneven black to a mottled dull gray/white surface color. However this activity frequently results in damage to some ductile iron surfaces.
Footnote: Test results are proprietary and available from the ductile iron pipe manufacturers.
Unlike steel surfaces, it is possible to “overblast” the external surface of ductile iron pipe. High nozzle velocities and/or excessive blast times can cause “blistering” and “slivering” of some external deLavaud pipe surfaces resulting in a surface which is unsuitable for coating with any material. This overblasting normally occurs when attempts are made to remove the tenacious, tightly adherent annealing oxide from the external surface of deLavaud dry spray pipe with a peen pattern surface. Damage to the pipe surface due to overblasting normally does not occur on internal surfaces.

National Association of Pipe Fabricators, Edmond, OK, 2006, http://www.napf.com

DIPRA Corrosion Control/Features

Linings Available for Ductile Iron Pipe & Fittings

¹ Maximum service temperatures listed are intended as general guidelines which may vary depending on service conditions and lining formulation. Consult pipe manufacturer for specific recommendations.
² ASTM C150 Type V sulfate resisting cement is recommended for seawater applications and some reclaimed water applications. Consult pipe manufacturer for specific reclaimed water recommendations.
³ Consult pipe manufacturer for specific service use and material details.
⁴ Recommended lining thicknesses may vary depending on service conditions, epoxy formulation, diameter, and other variables. Consult fitting manufacturer for specific recommendations.

Ductile Iron Pipe Research Association, https://www.dipra.org/ductile-iron-pipe-resources/technical-publications

Service Descriptions

Alternate Sludge
Chilled Water Return
Chilled Water Supply
Cooling Water Return
Cooling Water Supply
Dewatering
Digested Sludge
Domestic Cold Water
Drain
Grit
Groundwater
Heated Sludge
Hot Flushing Water
Hot Water Return
Hot Water Supply
Mixed Liquor
Non-Sanitary Drain
Potable Water
Primary Effluent
Primary Influent
Primary Scum
Primary Sludge
Return Activated Sludge
Reuse Water
Roof Drain
Sample
Sanitary Waste
Secondary Scum
Sludge
Storm Drain
Sump Pump Discharge
Thickened Primary Sludge
Thickened Sludge
Unthickened Primary Sludge
Vent
Waste Activated Sludge