We have 3 D.O.T. Design Certifying Engineers including two Mechanical Engineers on staff. We offer a full range of engineering services including designing, calculations and manufacturing drawings. We use ASME Code software to perform pressure vessel calculations and AutoCAD software to produce manufacturing drawings.

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At Worley Welding Works, Inc., we understand the frustration that a customer can have regarding the DOT rules, regulations, and other requirements that come into play regarding the construction of new DOT Specification cargo tanks.  The information below is presented in an effort to properly orient our customers to these requirements.  Additionally, this will simplify the process, reduce frustrations, and ensure that the requirements are more easily understood.

There are three (3) basic stages in the process of producing a certified cargo tank motor vehicle, as listed below.  The following is particularly true for all cargo tanks including twin tanks and pup-trailers, where the cargo tank is removable:


Involves designing and drawing the tanks, and issuing a Design Certification Letter signed by a DOT Design Certifying Engineer, as per 49 CFR § 178.345-15(b)(1).  Per the requirements, this step must be completed  before construction is started.  Completion of the design will also ensure that an accurate bid can be made.

The cost for performing these services may be charged to the customer in one of several ways:

  1. Separately (this usually occurs if the customer has not committed to an order or only wants a firm bid).
  2. Integrated into the unit cost (for a unit that is the first of its particular design and for which there may or may not be future orders of the same unit).
  3. Integrated into the unit cost as equal fractions for a multi-unit order.

NOTE:  The estimated design costs are as follows:  for twin tanks $500 to $1,000; for pup-trailers or transports $1,000 to $2,500.


Involves first bidding, then production of the cargo tanks and/or cargo tank motor vehicles.  If the unit is a cargo tank only (removable), then it is to have a nameplate only attached (per § 178.345-14(b)), and then proceed to Stage Three for mounting.   If the unit is a cargo tank motor vehicle (registered motor vehicle) then it will additionally have a Cargo Tank Motor Vehicle (CTMV) Specification plate attached (per § 178.345-14(c)).


Involves installing the removable cargo tank on a motor vehicle and attaching the CTMV Specification plate (per § 178.345-14©).
This service must be performed by a shop who is registered with DOT to install cargo tanks on motor vehicles (per § 107.502(b)) and who is also registered as a final-stage manufacturer of a motor vehicle (per 49 CFR §§566, 567 and 568).  This may be accomplished by an appropriately registered manufacturer, which may not necessarily be the original cargo tank manufacturer.

DOT's intention in regulating the mounting of cargo tanks is to ensure that the mounting is safe, complete and meets the applicable regulations, including calculated supports and anchoring, accident damage protection, piping and hoses, placarding, markings and certifications, etc.

Call for estimated costs for complete DOT-412 cargo tanks such as:

  • Twin tanks set (unmounted)
  • Mounting twin tanks to customer vehicle
  • Pup-trailer
  • Transport

NOTE:  Sales tax and F.E.T. are charged as applicable.

As of today, we have designed over 50 different DOT-412 cargo tanks, including twin tanks, pup-trailers and transports which may be used for reference in design in order to get through Stage One quickly and go on to Stage Two.  This way, the original design costs can be minimized where possible.