API-Funded Bolt Research Advances Offshore Safety

Chase Winter
Posted March 8, 2022

New API-backed research on the fatigue life of bolts used in underwater natural gas and oil infrastructure – including critical blowout prevention equipment – is a key advancement in continued efforts to protect workers and the environment from potential problems associated with bolting fatigue in subsea structures.

Research from the multi-year industry project and guidelines developed by subject matter experts will help designers at natural gas and oil equipment manufacturing companies and operators by providing data for future bolting designs.

Anchal Liddar, senior vice president for API’s Global Industry Services division:

“These guidelines are critically important to the safety of our industry’s offshore infrastructure, which translates into protections for employees and the marine environment. This proactiveness reflects the industry’s commitment to providing energy that Americans use every day as safely and responsibly as possible.”

In August 2014, the federal Bureau of Safety and Environmental Enforcement (BSEE) published an evaluation of connectors and bolts in response to an incident a few years prior that prompted a global recall of bolted connections used on a typical subsea blowout preventer. As part of that report, the U.S. regulator called for industry to conduct more studies and address deficiencies in bolting in subsea environments for offshore rigs, as well as develop new and updated industry standards.

That’s what API did, collaborating with the world-renown DNV classification group in Norway to conduct full-scale fatigue laboratory testing of low alloy steel bolting in air and simulated seabed conditions. Specifically, low alloy steel bolts conforming to API 20E-BSL3 were tested in air and saltwater under cathodic protection conditions -- a technique used to control the corrosion of metal -- with water temperature, pH levels and other variables simulating a subsea environment. While cathodic protection is used in the industry to protect materials from corrosion, it has the negative effect of causing hydrogen embrittlement which was investigated in the study. The guidance developed by the research is reflected in API 21TR2, Fatigue Design Guidelines and Test Data for Low Alloy Steel Bolts, 1^st edition.

“Through this research, we are giving designers actual data and tools that they can use to assess the bolting fatigue life more accurately in order to reduce the risk of failures,” said Arshad Bajvani, a senior materials engineer at OneSubsea, a Schlumberger company, and one of the lead researchers for API’s research. “The structural integrity of connector bolts is pivotal for worker safety and the protection of the environment.”

API has developed other standards and revised existing ones related to bolting in response to BSEE’s report, including:

• API 20E, Alloy and Carbon Steel Bolting for Use in the Petroleum and Natural Gas Industries
• API 20F, Corrosion-resistant Bolting for Use in the Petroleum and Natural Gas Industries
• API 21TR1, Materials Selection for Bolting