ASME STP-PT-086-2017 — Effects of High Temperatures and Fit-up of Riveted Joints on Steel Rivets

🔨 ASME STP-PT-086-2017 is a technical study funded by ASME Standards Technology, LLC (ASME ST-LLC), coordinated by the Strasburg Railroad Company and with metallurgical testing performed by Diamond Technical Services, Inc. It addresses a long-standing controversy in boiler construction: how high may a steel rivet be heated for hot driving. The investigation extends beyond temperature alone to include installation quality factors — rivet-hole clearance, plate fit-up, and joint tightness — and their effect on the mechanical properties and microstructure of finished steel rivets. The report is of direct engineering value for quality control of hot-riveted joints in steam boilers, tanks, bridges, and structural steelwork.

1. Background and the Questions Asked 📌

In riveted boiler construction the rivet is heated to a target temperature and, while hot, driven into the hole and formed into a head. A previous privately funded study had evaluated a maximum driving temperature of 1950 °F (about 1065 °C) but looked only at temperature as a single variable. Conflicting information existed on whether heating to 2250 °F (about 1230 °C) for driving is harmful to the final steel rivet properties compared with the 1950 °F practice.

To answer this, the project fixed on the two temperatures above and deliberately introduced three installation “anomalies” beyond recommended standard hot-riveting practice:

• Holes 1/8 in (3.2 mm) oversized: to see whether the extra upsetting needed to fill the larger hole is detrimental to the finished product.
• Holes 1/16 in (1.6 mm) oversized with plates not tightly fit: simulating the situation where plates spring back during driving, cycling the rivet through compression and stretch.
• Holes 1/16 in (1.6 mm) oversized with plates tightly clamped: rivets soaked at 1950 °F and 2250 °F for 10 and 20 minutes before driving, to study prolonged soaking.

2. Test Material and Program 🔧

The test rivets were produced from ASTM A675 carbon steel bar, 7/8 in (22 mm) diameter. Heating was performed by electric resistance heating and a gas-fired furnace, and a pneumatic hammer was used to form the button-head style heads after heating to the designated metal temperature. The three test conditions (temperature × clearance × fit-up) are summarized below.

Every rivet was carefully extracted from its carbon-steel test plate and then subjected to the battery of metallurgical tests listed in Appendix A, including tensile testing (by SGS MSi), hardness testing, macro-etch inspection of the head-to-shank transition, and micrographs of the hot-driven microstructure.

3. Metallurgical Evaluation and Microstructure 🔬

A core chapter compares the microstructure of undriven rivet steel with rivets driven under each process condition. Figure 4-2 shows the hot-driven steel rivets after extraction from the plates; Appendix B provides macro-etched head-to-shank transitions for rivets 1A2, 1B2, 2A1, 2B1, 3A2, 3B2, 3C2; Appendix D presents micrographs of the hot-driven rivet microstructures covering both the 2250 °F (1230 °C) and 1950 °F (1065 °C) driving temperatures.

The tensile and hardness results appear in Tables 4-1, 4-2, and 4-3. Table 4-2 specifically reports the percentage change in tensile properties relative to the undriven rivet steel, quantifying the net effect of the hot-driving process on mechanical properties.

4. Principal Conclusions and Technical Points 🛠️

• ✅ Evidence-based temperature ceiling: by systematically comparing rivets driven at 2250 °F (1230 °C) with those driven at 1950 °F (1065 °C), the project supplied direct test data for setting a maximum hot-driving temperature.
• ✅ Fit-up brought into scope: the study confirms that oversized holes forcing extra upset, loose plates causing repeated compression-tension, and high-temperature long soaks can all alter the finished rivet, and such deviations from recommended practice should be avoided.
• ✅ Properties tied to microstructure: tensile, hardness, and microstructural evidence reinforce one another, giving a complete chain from process deviation → microstructure change → property impact.
• 📋 Complete documentation: Appendix A lists the full metallurgical test program; Appendix B holds the head-to-shank macro-etch images; Appendix C the SGS MSi results; and Appendix D the microstructure micrographs, ready for engineering and inspection use.

5. Engineering Practice Recommendations 🏭

For boiler, bridge, and tank maintenance organizations that still use riveted construction, the report offers actionable guidance:

• 🔍 Temperature control: heat only to the minimum temperature that allows proper upset and head formation; set a process ceiling using the 1950 °F (1065 °C) versus 2250 °F (1230 °C) comparison, and avoid overheating and burning.
• 🔧 Hole-to-rivet match: machine rivet holes close to standard clearance to avoid excessive upset; check hole diameter and plate fit-up before assembly.
• 📊 Soak and drive rhythm: drive rivets promptly after they reach temperature to prevent long soaks (10 to 20 minutes) from degrading the microstructure; standardize pneumatic-hammer operation sequence.
• 📋 Inspection system: for critical joints, adopt the report’s approach — sample tensile, hardness, and macro/micro examination — and build a traceable chain of material certificates, process records, and test results.

6. Frequently Asked Questions ❓