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Interpretation Response #22-0067


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

Interpretation Response Details

Response Publish Date: 04-20-2023
Company Name: Kidde Aerospace and Defense    Individual Name: Mark Fazzio
Location state: NC    Country: US

View the Interpretation Document


Response text:

April 20, 2023

Mark Fazzio
Chief Engineer
Kidde Aerospace and Defense
4200 Airport Dr.
Wilson, NC  27896

Reference No. 22-0067

Dear Mr. Fazzio:

This letter is in response to your June 22, 2022, email requesting clarification of the Hazardous Materials Regulations (HMR; 49 CFR Parts 171-180) applicable to service and test pressure requirements for DOT-4D, DOT-4DA, and DOT-4DS pressure vessel specifications. Specifically, you provide a scenario of a DOT-4D pressure vessel made from 4130 steel with a service pressure of 500 psi.

Based on the scenario provided we have paraphrased and answered your questions as follows:

Q1. You ask whether the HMR allows for the actual test pressure to exceed two times the service pressure, as prescribed for a DOT-4D (see § 178.53(e)), DOT-4DA (see § 178.58(f)), and DOT-4DS (see § 178.47(f)), respectively.

A1. The answer is yes. However, the actual test pressure must not exceed 110% of the minimum test pressure, with an allowance of +1%, per CGA C-1 Pamphlet (2016), Section 5.2.1. During the hydrostatic test, each specification requires a minimum test pressure of at least two (2) times the service pressure. It is discouraged to have the actual test pressure exceed the guidance provided in the CGA C-1 Pamphlet as it may cause an unsafe condition.

Q2. You ask whether the HMR allows for the wall stress calculation to be based on two times the service pressure, including in cases where the test pressure exceeds two times service pressure.

A2. The answer is yes. Wall stress calculations must be based on the minimum test pressure—which is defined as two (2) times the service pressure. This applies for DOT-4D, DOT-4DA, and DOT-4DS specifications.

Q3. You ask whether the wall stress calculated at a test pressure which is greater than two times the service pressure may exceed the stress threshold, per §§ 178.47(f), 178.53(e), or 178.58(f), provided that the calculated stress at two times service pressure does not exceed the stated limits.

A3. Wall stress must be calculated using a test pressure of two (2) times the service pressure for the DOT-4D, DOT-4DA, and DOT-4DS specifications.

Q4. Prior to performing the hydrostatic test, you ask whether the test can be performed at 90% of actual test pressure, including cases where the test pressure exceeds two times the service pressure.

A4. The answer is yes. For both the DOT-4DA and DOT-4DS specifications, the test can be performed at 90% of the minimum test pressure which is defined as two (2) times the service pressure.

For the DOT-4D specification, the test can be performed at 90% of the minimum test pressure which is two (2) times the service pressure (see § 178.53(h)(3)(ii)). For the lot test in § 178.53(h)(1)(iii), the test can be performed at 90% of the test pressure equal to three (3) times the service pressure (which exceeds two (2) times service pressure). However, if opting to use the latter performance standard, the remainder of the lot must be tested using a proof pressure method. Section 5.7 of the CGA C-1 Pamphlet provides further guidance on performing the 90% system check.

Q5. You ask whether the test pressure may be marked in addition to the markings required in § 178.35.

A5. The answer is yes. As specified in § 178.35(f)(6), other markings are authorized, provided they are made in low stress areas, other than the side wall, and are not of a size and depth that will create harmful stress concentrations. Such marks may not conflict with any DOT required markings. However, a test pressure marking that reflects a pressure higher than the minimum test pressure of two (2) times service pressure is discouraged as it may create confusion and an unsafe condition—especially when the cylinder is due for requalification in accordance with § 180.209.

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

Sincerely,

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

178.35, 178.35(f)(6), 178.47(f), 178.53(e), 178.58(f), 178.53(h)(3)(ii), 178.53(h)(1)(iii),180.209


Regulation Sections

Section Subject
§ 180.209 Requirements for requalification of specification cylinders