Forensic Engineering Investigation and Analysis of Crack Formation in Acetal Resin Nuts Used for Water Supply Lines




Acetal resin nut, plastic nut, threaded nut, stress concentrations, creep rupture, scanning electron microscopy, SEM, liquid dye penetrant, fracture morphology


Non-destructive and destructive techniques were used to document and model crack formation in acetal resin nuts used for household toilet water supply lines. The morphologies of creep rupture and overload failure were documented using optical microscopy and scanning electron microscopy (SEM). The forensic investigation stemmed from litigation between a homeowner, plumbing contractor, and parts supplier related to a failure at a single residence. Fortuitously, 447 fittings in service for approximately two years under similar conditions were available for examination. In many properly installed fittings, cracks had initiated at the notch created by the sharp thread root radius, as predicted by engineering mechanics and finite element analysis. This study found that the cracks had propagated via plastic creep.


Anderson P, McCormick DF. Parties for Steven Rensel v. Fluidmaster, Inc., 8:14-cv-00648. CourtListener. 2014 Apr 14 [accessed 2020 Oct 21].

Integrated Database. Docket for Trabakoolas v. Watts Water Technologies, Inc., 3:12-cv-01172. CourtListener. 2012 Mar 8 [accessed 2020 Oct 21].

Jones JW. Forensic Engineering Analysis of Toilet Connector Failures in a Class-Action Lawsuit. Journal of the National Academy of Forensic Engineers. 2015 Jan 1 [accessed 2020 Oct 21].

Timpanaroa A, Scherzer R, Keifer OP, Eason PD. Case Studies in Engineering Failure Analysis; Analysis of acetal toilet fill valve supply line nut failure. Jacksonville, FL: Elsevier Ltd; 2017.

Shigley JE, Budynas RG, Mischke CR. Mechanical engineering design. Boston, ny: McGraw-Hill Higher Education; 2004.

General Electric Company. GE Plastics. Processing. GE Engineering Thermoplastics Injection Molding Processing Guide. Guide. Injection Molding. PDF Free Download. 1999 Jan 1 [accessed 2020 Oct 21].

DuPont Delrin. acetal resin PRODUCT AND PROPERTY GUIDE. PDF Free Download. 2006 [accessed 2020 Oct 21].

Masters JE, Gilbertson LN. Fractography of modern engineering materials. 1993 Jan 1 [accessed 2020 Oct 21].

Fractography of Modern Engineering Materials. Composites and Metals. Copyright by American Society for Testing and Materials 1987, STP 948.

ASTM E1417/E1417M-16 Standard Practice for Liquid Penetrant Testing.




How to Cite

George, Edward, Donald Fournier, Paul Eason, and Charles King. 2022. “Forensic Engineering Investigation and Analysis of Crack Formation in Acetal Resin Nuts Used for Water Supply Lines”. Journal of the National Academy of Forensic Engineers 38 (2).