For decades, the ductile iron pipe industry has operated under a wall thickness classification system known as the K-class system. Under this framework, pipes were designated K9, K10, K11, and so forth, with higher K values indicating thicker walls and greater pressure-bearing capacity. The K9 grade became the de facto industry standard-the default specification for most water supply projects. This system, however, has a fundamental limitation: it ties wall thickness to a classification index rather than directly to the operating pressure requirements of the pipeline network.
The release of the new national standard GB/T 13295-2026 marks a decisive shift away from this legacy system. The K-class system has been formally retired, and the C-class (pressure class) system has taken its place. This transition is not merely a nomenclature change; it represents a fundamental reorientation of how pipes are specified, manufactured, and procured .
Under the C-class system, pipes are classified by their allowable working pressure: C25, C30, C40, corresponding to working pressures of 2.5 MPa, 3.0 MPa, and 4.0 MPa, respectively. For water utilities and engineering contractors, the question is not "what is the wall thickness?" but rather "what pressure can this pipe withstand?" This is a more rational engineering approach that aligns product specification with actual system requirements .
The practical implications are substantial. For small-diameter pipes (DN80–300), the recommended pressure class is C40; for medium diameters (DN300–600), C30; and for large diameters (DN700–3000), C25. Compared to traditional K9 pipes, C-class pipes offer thinner walls where pressure requirements permit-particularly in the small to medium diameter range-resulting in significant material savings and reduced costs. One industry expert noted that DN500 K9 pipes have a nominal wall thickness of 9.0 mm, while C30 pipes of the same diameter require only 7.5 mm-a 1.5 mm reduction that translates directly into lower material consumption and lighter weight .
The new standard also expands the C-class scope to DN3000 and introduces the C20 minimum wall thickness grade, further optimizing material usage for lower-pressure applications. Crucially, the standard eliminates the vague provision that allowed wall thickness compliance to be proven "by weight control" and establishes a mandatory 100% wall thickness inspection regime. This hard constraint will accelerate industry-wide technological upgrades in wall thickness control and enhance the quality safety of underground pipeline networks across China .
For manufacturers, this transition is both a challenge and an opportunity. Those who can precisely control wall thickness to meet C-class specifications while maintaining structural integrity and pressure performance will gain a competitive edge. Those who cannot will find themselves left behind in an industry that is increasingly prioritizing resource efficiency, lightweighting, and cost-effectiveness over the "heavier is better" mentality of the past.