Fast, Accurate, Reproducible, and Quantitative
US Corrosion Services is one of the most experienced rising step load testing labs in the country. RSL is the incremental step loading method that became the basis for ASTM F1624, and is now the accelerated method referenced in ASTM F519, ASTM F1940, and ASTM F2660. We run all four in our Houston laboratory on multiple frames, and we build the RSL test equipment ourselves, so we understand the method down to the load cell.
RSL is the fastest reproducible test we know of for hydrogen embrittlement, stress corrosion cracking, and sour service cracking. Instead of a pass/fail answer after 200 hours, you get a quantitative threshold in one to two business days. RSL provides the fastest reproducible test for all kinds of environmental cracking, including stress corrosion cracking, hydrogen embrittlement, and sour stress corrosion.
What is Rising Step Load testing?
Rising step load testing applies load to a notched or precracked specimen in a series of steps, holding at each step long enough for hydrogen to diffuse to the notch and start a crack if the material is susceptible. The test runs under displacement control, which is what makes it work. When a crack initiates during a hold, the specimen gets more compliant and the measured load drops while the displacement stays fixed. That load drop is the signal. The last step completed without a drop defines the threshold stress, reported as a percentage of the notch fracture strength measured on an identical specimen in air.
The step sizes and hold times are set by the hardness of the material, since hydrogen diffusion and crack initiation take longer in higher strength steels. A softer alloy might use larger steps with one hour holds, while a 55 HRC tool steel or 300M landing gear steel gets smaller steps and longer holds. Either way the whole test typically finishes inside two days, and the result is a number you can compare lot to lot, coating to coating, or alloy to alloy.
Why is RSL better than sustained load testing?
The traditional approach, sustained load testing, hangs a specimen at 75 percent of notch fracture strength for 200 hours and reports whether it broke. That is fine for confirming a plating process is not badly out of control, but it tells you nothing about margin. A lot that survives 200 hours at 75 percent might have a real threshold of 78 percent or 98 percent, and you would never know the difference. RSL tells you which one you have.
The practical advantages are speed (days instead of weeks), a quantitative threshold instead of a binary result, excellent reproducibility between specimens and between labs, and the ability to rank materials and coatings against each other. When a plating shop has a bake cycle problem, RSL shows it as a shift in threshold before parts start failing in the field. When a new coating is being qualified, RSL shows exactly how much cracking resistance it costs or gains. We have found that once a client sees RSL data next to their old sustained load results, they rarely go back.
How does Rising Step Load testing work?
Rising step load tests involve gradually increasing the applied load on samples to evaluate their performance and capacity. This testing methodology helps identify bottlenecks, stress points, and performance limits, allowing for proactive optimization and ensuring that the system can handle growing demands effectively. Here’s a list of the most common tests:
ASTM F1624 rising step load tests
ASTM F1624 is the core standard for incremental step load testing and the one most of our RSL work runs under. It covers notched round and square specimens loaded in tension or four point bending, in air or in an environment, with or without applied potential. F1624 is the method that generates a true threshold value, and it is the engine underneath the other three standards on this page. We run F1624 for internal hydrogen embrittlement from plating and processing, for environmental hydrogen embrittlement from corrosion or cathodic protection, and for stress corrosion cracking in chlorides, seawater, and sour fluids. With a precracked specimen the same approach gives a threshold stress intensity, which makes F1624 a fast route to K_IEAC or K_ISCC values that would otherwise take months. We also build and sell F1624 test frames preprogrammed with the standard step profiles, and we can customize a profile for unusual hardness ranges or nonferrous alloys.
ASTM F519 Embrittlement testing
ASTM F519 is the workhorse specification for evaluating plating and coating processes and service environments for hydrogen embrittlement. It defines the familiar specimen types (Type 1a notched rounds, 1e notched square bars, 2a C-rings, and the rest) and the sustained load pass/fail test. F519 also allows the accelerated F1624 approach as an alternative, and that is how we run most F519 work. We can complete F519 testing in one to two business days instead of 200 hours, which lets plating shops release lots faster and lets engineers make decisions on real data. We stock the common specimen types and can test your actual parts alongside them.
ASTM F1940 process control testing for plated fasteners
ASTM F1940 is the process verification standard for plated and coated fasteners. Standardized notched specimens are run through your actual production line, cleaning, plating, and baking included, and then tested by rising step load. If the specimens hold above the required percentage of notch fracture strength through the full step profile, your process is demonstrated to be under control for that lot or that qualification period. F1940 is the answer when a customer specification, a Nadcap audit, or an automotive or aerospace quality plan asks for evidence that your zinc, zinc-nickel, cadmium, or other plating process is not embrittling high strength fasteners. We run F1940 on a routine schedule for plating shops and fastener manufacturers, and we can turn a lot around fast enough that it does not hold up shipping. If a lot fails, we can also tell you why, which is a lot more useful than a red stamp.
ASTM F2660 environmental hydrogen embrittlement testing of coated structural bolts
ASTM F2660 addresses a different problem. F519 and F1940 look at hydrogen introduced during manufacturing. F2660 looks at hydrogen generated in service, when a coated high strength bolt sits in a wet, corrosive environment and the coating itself produces hydrogen through galvanic corrosion. The standard was written to qualify coatings for ASTM F3125 Grade A490 structural bolts, which are strong enough to be embrittled by their own sacrificial coating. The coated specimens are loaded by rising step load while immersed in a salt solution, so the coating generates hydrogen exactly as it would on a bridge or a building. We use F2660 to qualify thermal diffusion galvanizing, zinc flake, zinc-nickel, mechanical zinc, and other coatings on A490 and similar bolts, and we use the same approach to evaluate any high strength fastener that will spend its life outdoors.
What types of samples can be used?
Rising step load testing is applicable to samples of all kinds and sizes. In addition the numerous standard specimen designs provided in ASTM F519, US Corrosion can also tests many other sizes and types of samples. We’ve evaluated everything from 1.25″ long screws to 36′ long bolts!
What can RSL testing be used for?
Failure analysis. When a bolt, spring, or high strength component breaks and the fracture surface shows intergranular features under the SEM, the next question is always whether the material was actually susceptible or whether the load was simply too high. RSL answers that directly. We test exemplar parts from the same lot, or sections of the failed part itself, and compare the threshold to the applied stress. We regularly run RSL as part of hydrogen embrittlement failure analysis and broader metallurgical failure analysis, and our principal engineer has presented RSL data as a court-qualified expert witness.
Consulting and materials selection. RSL lets us compare alloys, heat treatments, hardness levels, and coatings on an equal footing in a few days. If you are choosing between a 40 HRC and a 46 HRC fastener for a cathodically protected structure, or deciding whether a coating change will introduce a cracking risk, we can put numbers on the decision. See our hydrogen embrittlement consulting and materials selection pages for how we approach this.
Research and development. Because the method is quantitative and fast, RSL is an excellent screening tool for new alloys, additively manufactured materials, weld metals, and coatings. We can generate threshold versus hardness curves, evaluate the effect of bake time and temperature, run specimens at controlled cathodic potentials to simulate charging, and determine environmental fracture toughness on precracked specimens. We have supported university, government, and industrial R&D programs and have co-authored AMPP and NACE papers on cracking behavior.
Production quality control. For plating shops, fastener manufacturers, and OEMs, RSL turns hydrogen embrittlement control from a monthly hope into a weekly measurement. We run F1940 and F519 on a recurring basis, track thresholds over time, and flag drift before it becomes a field failure. We also test incoming lots for buyers who want independent verification of what their supplier says.
Litigation and claims. When hydrogen embrittlement is alleged in a product liability or construction matter, RSL provides a robust, well-supported way to establish whether the material was susceptible under the conditions in question. Our litigation support and corrosion expert witness pages describe how we work with counsel.
What environments can we test in?
Air, deionized water, 3.5 percent sodium chloride, ASTM D1141 artificial seawater, simulated sour fluids per NACE TM0177 solutions, and customer-supplied fluids. Specimens can be tested at open circuit, at an applied cathodic potential to simulate cathodic protection or galvanic coupling, or after hydrogen precharging. We can also run AMPP TM21546 for hydrogen stress cracking in welds using the same frames.
What types of samples can be tested?
Almost anything that can be gripped or bent. In addition to the standard F519 specimen types, we test actual production fasteners, springs, machined coupons cut from plate or bar, weld cross sections, and sections removed from failed components. We have evaluated everything from 1.25 inch screws to 36 foot long bolts. If your part is unusual, send us a drawing or a photo and we will tell you how we would fixture it.
Can I test per ASTM F519 with a rapid test?
Absolutely. F519 permits the accelerated F1624 approach, and that is how we run it. Most F519 lot testing is complete in one to two business days, which lets you be confident the parts you are making and shipping are safe without holding up production.
What supplements RSL testing?
RSL tells you the threshold. Understanding why the threshold moved usually takes a few more tools, and we have them under one roof. Electron microscopy and EDS for fracture surface analysis and coating evaluation, hardness and tensile testing, fracture toughness, chemical composition analysis, coatings characterization, and metallography are all available on the same work order.
Why US Corrosion Services for RSL testing?
Our principal engineer, Dr. Joshua Jackson, is a PhD metallurgist with degrees from MIT and Colorado School of Mines and a licensed Professional Engineer in Texas. He has run this laboratory since 2007, is active in ASTM committee work on hydrogen embrittlement test methods, and has been qualified as an expert witness on stress corrosion cracking, hydrogen embrittlement, and fractography. We operate under an ISO 9001 aligned quality system, we run multiple RSL frames so large lots do not wait in line, and we build the equipment we test on. Most importantly, we read every curve ourselves. A load drop at step 12 means something different from a load drop at step 4, and we will tell you what it means for your parts.