[ID] => 10622
[post_author] => 34
[post_date] => 2019-02-18 09:26:01
[post_date_gmt] => 2019-02-18 09:26:01
[post_content] => The US National Transportation Safety Board (NTSB) has issued five recommendations as a result of its investigation into a chlorine release incident involving a rail tank car at the Axiall Corp Natrium plant in New Martinsville, West Virginia in August 2016. The leak happened shortly after a tank car had been loaded with 178,400 lb (80,920 kg) liquefied compressed chlorine; the tank sustained a 42-inch (107-cm) crack in its shell, releasing the entire load over the course of 2.5 hours. A large vapour cloud migrated south along the Ohio River valley, resulting in inhalation injuries.
The tank in question was a DOT-105 tank car, manufactured in 1979 by ACF Industries. NTSB notes that the Federal Railroad Administration (FRA) had warned in 2006 that these stub sill tanks were prone to defects, including cracks in several places, that had caused a number of hazardous materials releases in the past. The tank involved in the incident had undergone a five-year internal inspection in January 2016, which had identified corrosion pitting across the bottom of the tank shell; repairs had been made at that time. The August 2016 release occurred following the first loading after the repair.
NTSB says the shell failure in the New Martinsville incident was consistent with crack propagation from a pre-existing, undetected crack, together with stresses induced by uncontrolled post-weld heat treating, shell buckling and low-temperature loading. Its report of its investigation focuses on a number of specific safety issues.
- The general requirements for pressure tank cars in the Association of American Railroads’ (AAR) Manual of Standards and Recommended Practices says that DOT-105 tank cars built after 1 January 1989 must have heads and shell constructed of normalised steel plate; however, AAR estimated that there were about 942 non-normalised steel tank cars in use as of mid-2018, of which nearly 700 were being used to transport chlorine.
- Industry guidance for the inspection and repair of ACF-200 stub sill attachments and cradle pad wells is only applicable to non-pressurised tank cars. There is a need, NTSB says, for similar guidance to be available for pressure tank cars.
- The tank car shop records show that, after extensive corrosion repairs to the interior of the tank shell, multiple attempts were made to stress relieve the repaired surfaces. However, NTSB investigators found evidence of a significantly overheated region and uncontrolled heat treatment.
- Axiall Corp based its tank car inspection scheme on the federally required maximum 10-year interval, which NTSB says is too infrequent. Failure to examine widely recognised, damage-prone weld terminations after the January 2016 repairs, while the tank was in a facility capable of conducting such inspections, was a missed opportunity.
WHAT TO DO NOW
As a result of its investigation, NTSB has made five recommendations. It has asked the Pipeline and Hazardous Materials Safety Administration (PHMSA) to:
- Promulgate a standard for pressure tank cars in toxic inhalation hazard (TIH) service that includes enhanced fracture toughness requirements for tank heads and shells
- Prohibit the use of tank cars constructed of non-normalised steel for the transport of TIH materials
- Issue maintenance guidance to owners of DOT-105 pressure tank cars in TIH use, highlighting their risk factors and establishing structural integrity inspection frequency.
NTSB also recommends that AAR revises its Manual of Standards and Recommended Practices (M-1002) to ensure that local post-weld heat treatment processes are monitored to avoid damage.
NTSB recommends that American Railcar Industries develop inspection and maintenance procedures to address cracks in cradle pad weld attachments on pressure tank cars equipped with ACF-200 stub sill underframes.
The full text of the investigation report can be found on the NTSB website.
[post_title] => Rail: Pressure points
[post_status] => publish
[comment_status] => open
[ping_status] => open
[post_name] => rail-pressure-points
[post_modified] => 2019-03-07 12:03:32
[post_modified_gmt] => 2019-03-07 12:03:32
[post_parent] => 0
[guid] => https://www.hcblive.com/?p=10622
[menu_order] => 0
[post_type] => post
[comment_count] => 0
[filter] => raw
NTSB has identified problems with the existing standards for pressure tank cars in TIH service following a release of chlorine in West Virginia in 2016