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device to be installed between the source of external pressure and the vessel rather than directly on the

vessel?

Reply 1: Yes

Question 2: May intervening stop valves be installed between the relief device of Question 1 and the

pressure vessel?

Reply 2: In accordance with the provisions of UG-135(e)(2) and UA-354(b), such stop valves are

permitted subject to the acceptance by the legal jurisdiction as stated in UA-350.

Question 3: If a vessel has a source of overpressure internal to itself and was protected against that

source by a suitable set and sized relief device installed directly on the vessel, could the vessel be

protected against an external source of overpressure by another relief device installed as in Questions 1

and 2?

Reply 3: Yes, subject to the qualifying conditions regarding the stop valves given in Reply 2.

Question 4: If a manufacturer furnished to a user an assembly consisting of pressure vessels, piping,

stop valves, and instruments to perform a specific function such as removing moisture from a gas, who is

responsible for furnishing the relief devices under Questions 1, 2, and 3?

Reply 4: This is a contractual matter that probably cannot be resolved by reference to Code rules.

To assist in resolution of this question additional rules which may have some bearing are as follows:

(a) U-2(a) which defines certain responsibilities of the user or his designated agent.

(b) Footnote 2 to U-2(a) which appears to define designated agent so as to apply the

manufacturer of the assembly in Question 4.

(c) Footnote 31 to UG-125(a) which states, "Safety devices need not be provided by the vessel

manufacturer, but overpressure protection shall be provided prior to placing the vessel in service."

In the absence of any specific contractual reference to relief devices, it is our opinion

that the rules would intend, under the provisions of Footnote 2 of U-2(a), that the manufacturer of theassembly would be responsible to furnish the relief device installed directly on the vessel under Question

3. Beyond this opinion, it is not believed that the Code rules can assist in this contractual matter.

Interpretation: VIII-77-90

Subject: Section VIII, Division 1; Size and Volume Limits, U-1

Date Issued: September 30, 1977

File: BC76-615

Question 1: U-1(j) of Section VIII, Division 1 defines the volume and pressure limits for vessels

which may be marked with a "UM" symbol. U-1(j)(2) defines 1-1/2 cu ft in volume and 600 psi design

pressure as one of these limits. How is the 1-1/2 cu ft volume determined for the shell side of a shell andtube heat exchanger?

Reply 1: Where the tube side is an independent pressure chamber as described in UG-19(a), the

volume of the shell side of a shell and tube heat exchanger is the total shell volume minus the volume

taken up by the tube side.

Where the shell can be thoroughly vented, filled, and drained, measuring a suitable liquid

drained from a filled shell is a method frequently used to prove the volume of an independent chamber.