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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #23-0054

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: Union Tank Car Company

Individual Name: Jon Schultz

Location State: IL Country: US

View the Interpretation Document

Response text:

September 21, 2023

Jon Schultz
Director of Fleet Engineering
Union Tank Car Company
175 W. Jackson Blvd.
Suite 2100
Chicago, IL  60604

Reference No. 23-0054

Dear Mr. Schultz:

This letter is in response to your June 22, 2023, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to the requirements in Part 179 for tank car jackets and jacket flashing. In your email, you describe several methods that you believe could potentially be used to manufacture and repair flashed openings in tank car jackets:

  1. Fillet weld of faying jacket sheets;
  2. Intermittent fillet weld of faying jacket sheets (known as a skip weld) and sealant caulking;
  3. Non-welded joint consisting of faying jacket sheets with fasteners and gasket or sealant caulk to form a shedding barrier to prevent ingress of weather past the jacket opening; or
  4. Non-welded slip joint consisting of faying jacket sheets that overlap that allow for expansion and contraction of faying surfaces.

Specifically, you ask whether the methods identified here are appropriate to meet the requirements for tank car jackets in §§ 179.100-4(a) or 179.200-4(a).

The answer is that a tank car jacket is in compliance with §§ 179.100-4(a) or 179.200-4(a) if it is metal, not less than 11 gauge thick, and flashed around all openings so as to be weather-tight. Note that tank car jacket patches must have 100% welding around the jacket sheet edges and the jacket patch repair must be in compliance with the original tank car design approval. We further emphasize that tank car jacket patches may not be secured without 100% welding around the jacket patch. For example, the skip weld and caulk method described in option #2 above would not be an acceptable method, unless otherwise authorized by a DOT Special Permit.

I hope this information is helpful. Please contact us if we can be of further assistance.


Dirk Der Kinderen
Chief, Standards Development Branch
Standards and Rulemaking Division

179.100-4(a), 179.200-4(a)

Regulation Sections

Section Subject
179.100-4 Insulation
179.200-4 Insulation