An independent federal agency investigating chemical accidents to protect workers, the public, and the environment.

Text Size AA

Preventive Maintenance

A lack of and poor preventive maintenance programs has been a recurring root cause in CSB investigations. The CSB has identified in many of its investigations, instances wherein a robust preventive maintenance program would have identified compromised equipment which led to the incident. Given the number of incidents that the CSB has investigated that have resulted as a result of delayed maintenance, the CSB identified “Preventive Maintenance” as a Driver of Critical Chemical Safety Change.

Preventive Maintenance Investigations
Investigations 15
Recommendations 45
Open Recommendations 13
Closed Recommendations 32

The CSB has found the following root causes have contributed to several of its previous investigations:

  • Inadequate mechanical integrity programs;
  • Delayed or deferred preventive maintenance; and
  • Ageing infrastructure of equipment at chemical facilities.

The CSB has investigated 15 incidents with resulting recommendations to address gaps in facility, corporate, regulatory programs and industry standards aimed to ensure:

  • Damage mechanisms are prompted identified and prevented;
  • Equipment upgrades and replacement is not delayed; and
  • Equipment is not made to last beyond its integrity operating window.

Several of the investigations identified have occurred at refineries including the Tesoro Refinery Fatal Explosion and Fire in Anacortes, Washington, in 2010, and the Chevron Refinery Fire in Richmond, California, in 2012.

Tesoro Refinery Fatal Explosion and Fire

The heat exchanger that failed during a maintenance operation at the Tesoro refinery in Anacortes, was nearly forty years old at the time of the incident. The CSB found that the immediate cause was long-term, undetected High Temperature Hydrogen Attack (HTHA) of steel equipment, which led to the pressure vessel rupture. Tesoro used an inspection strategy that relied on design operating conditions rather than verifying actual operating parameters, and the CSB determined that inspections for this type of damage are unreliable, as the microscopic cracks can be localized and difficult to identify. Although high-chromium steels are highly resistant to this type of damage mechanism, this steel was not used by Tesoro.


Tesoro, like others in the industry, used published data from API, called the Nelson Curves, to predict the susceptibility of the heat Tesoroexplosionexchangers to HTHA damage.  The CSB found these curves unreliable because they use historical experience data concerning HTHA that may not sufficiently reflect actual operating conditions. The CSB found that recommended practices of the API do not require users to verify actual operating conditions in establishing operation limits of the equipment or to confirm that the materials of construction selection will prevent the damage. The CSB found eight additional data points where failure had occurred below the Nelson curve.

Although API has updated its standard that addresses HTHA, API RP 941: Steels for Hydrogen Service at Elevated Temperatures and Pressures in Petroleum Refineries and Petrochemical Plants, to incorporate some of these data points, it has yet to incorporate data from the Tesoro incident. The CSB recommended that API prohibit the use of carbon steel in processes that operate above 400 degrees Fahrenheit and greater than 50 psia hydrogen partial pressure; a level in which HTHA will not occur.

CSB Safety Alert: Preventing High Temperature Hydrogen Attack (HTHA)

As a result of these noted deficiencies, the Board voted on July 13, 2016, to designate the Recommendation 2010-08-I-WA-R10 with the status of Closed – Unacceptable Action.  The CSB’s “Status Change Summary” provides additional detail on the board’s rationale. In the absence of industry guidance that incorporates findings from the Tesoro Anacortes failure, the CSB is issuing a safety alert to provide additional direction for industry.

The Safety Alert provides the following guidance for industry:

1. Identify all carbon steel equipment in hydrogen service that has the potential to harm workers or communities due to catastrophic failure;

2. Verify actual operating conditions (hydrogen partial pressure and temperature) for the identified carbon steel equipment;

3. Replace carbon steel process equipment that operates above 400 °F and greater than 50 psia hydrogen partial pressure; and

4. Use inherently safer materials, such as steels with higher chromium and molybdenum content. 

Chevron Refinery Fire

Chevron U.S.A. Inc. Refinery in Richmond, California, experienced a catastrophic pipe failure in the #4 Crude Unit. The incident occurred from the piping referred to as the “4-sidecut” stream, which was a carbon steel pipe with low silicon concentrations. The pipe ruptured, releasing flammable, hydrocarbon process fluid which partially vaporized into a large vapor cloud. Testing determined that the pipe failed due to thinning caused by sulfidation corrosion, a common damage mechanism in refineries.  Inspection of sufidation corrosion for carbon steel components containing low silicon concentrations is challenging. Rather than switching to an alloy with higher chromium content for high temperature areas susceptible to sulfidation corrosion, Chevron management denied recommendations to replace the 4-sidecut line. The data on which they based this decision was gained primarily from high silicon pipe-fitting components, which did not reflect the corrosion rates of the lower-silicon components of the 4-sidecut piping.


CSB made several recommendations to API to address mechanical integrity issues identified in the investigation including:

  • Establishing minimum requirements for preventing catastrophic rupture of low-silicon carbon steel piping;
  • Requiring users to establish and implement a program to identify carbon steel piping circuits that are susceptible to sulfidation corrosion and may contain low-silicon components; and
  • Requiring users to develop a process fluid leak response protocol specific to their own facility that must be followed when a process fluid leak is discovered.

Currently, API has not made the recommended changes to the various standards identified.

Related Investigationsview_of_three_phosgene_hoses_






Last Updated October 13, 2016

© All rights reserved