IE Circular No. 77-05, Liquid Entrapment in Valve Bonnets
CR77005
MAR 24 1977
MEMORANDUM FOR: J. P. O'Reilly, Director, Region I
N. C. Moseley, Director, Region II
J. G. Keppler, Director, Region III
E. M. Howard, Director, Region IV
R. H. Engelken, Director, Region V
FROM: Dudley Thompson, Acting Director, DFO, IE
SUBJECT: IE CIRCULAR NO. 77-05, LIQUID ENTRAPMENT IN VALVE
BONNETS
The subject document is transmitted for issuance by close of business five
days after date of this letter. The Circular should be issued to all holders
of Construction Permits or Operating Licenses for Power Reactors. Also
enclosed is a draft copy of the transmittal letter.
Dudley Thompson, Acting Director
Division of Field Operations
Office of Inspection and Enforcement
Enclosures:
1. Circular 77-05
2. Draft transmittal letter
.
(Transmittal Letter for IE Circular 77-05 - Liquid Entrapment in Valve
Bonnets)
To all applicants for, or holders of, Construction Permits or Operating
Licenses for Power Reactors:
The enclosed Circular is being distributed for information, in the belief
that the subject matter is of sufficient safety significance to warrant
specific attention. A specific reply is not requested.
Regional Director
Enclosure:
IE Circular 77-05
"Liquid Entrapment
in Valve Bonnets"
.
IE Circular 77-05
Date: MAR 24 1977
LIQUID ENTRAPMENT IN VALVE BONNETS
Description of Circumstances:
Gate valves of the type known variously as "split-disc," "flexible-disc,"
"double-disc," etc., have the ability to seal against both seats at the same
time. Under certain circumstances, when the valve is closed, fluid may be
entrapped in the bonnet cavity, and if the system is then heated up, an
uncontrollable rise in pressure in the bonnet cavity can result. The
reported effects of such pressure rise range from inability to open the
valve, to structural failures of internal parts of the valve or failure of
the bonnet. Consequences range from loss of function of the valve to fluid
escape and injury to personnel or damage to equipment in the vicinity.
Detailed information is provided in the enclosure to this Circular.
Discussion:
The most common cause of fluid entrapment is the orientation of the valve.
Valves in pipelines where the pipe is horizontal, or nearly so, and where
the valve stem is oriented horizontal or below the horizontal, result in the
bonnet cavity constituting a drain pocket, where process fluid or condensate
can collect while the valve is open. If the valve is then closed the
drainage is trapped. Valves are often installed in such positions for
reasons of space or operator convenience. Other pipe and valve orientations
can, under credible circumstances, entrap fluid. An example is filling a
section of steam line for hydrostatic test, draining the line without
opening that particular valve, and then heating up the line with steam. A
variety of actions have been proposed to alleviate the situation, including
internal pressure relief passages, external pressure relief paths, and
specially controlled procedures.
You may wish to alert your engineering, operating and maintenance staff to
the existence and characteristics of the subject of this circular, and to
consider the potential of your facility (s) for an occurrence of the type
described. Depending on circumstances,
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- 2 - IE Circular 77-05
Date: MAR 24 1977
any of a variety of corrective actions may be appropriate. Most of these
are, however, susceptible to human error, and, to the extent feasible, we
suggest that valves be installed to minimize the potential for entrapment of
fluid.
Enclosure:
Ltr., dtd 2/24/76, P. H. Awtrey,
Walworth Co., to J. H. Tillou,
NRC, w/encl.
.
February 24, 1977
United States Nuclear Regulatory Commission
Region IV
611 Ryan Plaza Drive
Arlington, Texas 76012
Attention: Mr. J. H. Tillou, Chief
Licensee Contractor and
Vendor Inspection Program
Subject: Potential Overpressurization Problem in Valves
Gentlemen:
Confirming our conversation of January 30, 1976, this is to
advise you of the possibility of an overpressurization that can happen in
gate valves having flexible wedges or having discs with equivalent
flexibility. Our particular concern is with Pressure Seal steel gate valves
having flexible wedges and being installed with the stems horizontal or
below horizontal.
Overpressurization is covered in the following paragraphs
from ANSI B31.1-1973, "Power Piping" and ANSI B16.5-1973, "Steel Pipe
Flanges, Flanged Valves, and Fittings":
ANSI B31.1-1973, Page 26, Paragraph 107.1C
Where liquid trapped in a closed
valve can be heated, an uncontrollable
rise in pressure can result. (An example
might be a flexible wedge gate valve,
installed with the stem horizontal,
having heat from war-up of the pipeline
applied to liquid from the testing,
cleaning, or condensed fluid, such liquid
being entrapped in the bonnet section of
the closed valve.) Where such a condition
is possible, the OWner shall provide
means in design, installation, and/or
operation to assure that the pressure in
the valve shall not exceed that allowed
by the Code for the attained temperature.
Any resulting penetration of the pressure
wall of the valve shall meet the
requirements of this Code and of drains
in ANSI B16.5
.
United States Nuclear
Regulatory Commission February 24, 1976
- 2 -
ANSI B16.5 - 1973, Page 2, Paragraph 2.2.3:
Fluid Thermal Expansion.
Certain double seated valve designs
are capable of sealing
simultaneously against pressure
differential from the bonnet section
to the adjacent pipe in both
directions. In such valves, a
circumstance in which the bonnet
section is filled with liquid and
subjected to an increase in
temperature can result in build up
of pressure in the bonnet section.
Where such a condition is possible,
it is the responsibility of the
purchaser to provide or require to
be provided means in design,
installation, and/or operation to
assure that the pressure in the
valve shall not exceed that allowed
by this standard for the attained
temperature.
For discussions and recommendations concerning this subject
in the aforementioned valves, please refer to attached Exhibits A, B, and C.
We shall be available for discussion relating to this or
shall try to supply further data if desired.
Yours very truly,
P. H. Awtrey
Chief Engineer
PHA:mc
Attachments
P.S. Concerning the Exhibit A (BUSHIPS Instruction 9480.72 with its
Enclosure 1), attached copies of letters of February 2 and 12 give
permission to release this information.
.
February 2, 1976
Naval Ships Engineering Center
Center Building
Price Georges Center
Hyattsville, Maryland 20732
Attention: Mr. J. F. Conway, Section Head
Valves, Piping Components, and Structural Analysis Sect Code
6153E
Subject: BUSHIPS 9480.72
Ser 648A5-308
18 June 1964
Gentlemen:
Confirming our telephone conversation of today permission is requested
for Walworth Company to submit a copy of the subject letter, along with its
Enclosure 1, to the United States Nuclear Regulatory Commission for use by
it in dealing with a possible problem in overpressurization of valves.
I have discussed with the Nuclear Regulatory Commission the possibility
of overpressurization, especially as applied to steel gate valves having
flexible wedges and mounted with the stem horizontal or below horizontal,
and would like to use the subject document as background material.
If you have any material that could likewise be used on this subject, I
would appreciate receiving a copy and permission to submit it to the Nuclear
Regulatory Commission
Your very truly,
P. H. Awtrey
Chief Engineer
PHA:mc
.
12 FEB 1976
Walworth Company
P.O. Box 1103 Huff Avenue
Greensburg, Pennsylvania 15601
Attention Mr. P. H. Awtrey
Chief Engineer
Gentlemen:
Enclosure (1) is forwarded in response to your letter of 2 February 1976.
Please be advised that the Naval Ship Engineering Center has no objection to
enclosure (1) being used in any articles or conversations pertaining to the
subject in questions.
As a matter of information, the pertinent contents of enclosure (1) now, and
have for some years, formed an integral part of the overall steam system
design requirements for Ships of the United States Navy.
Sincerely yours,
J. F. CONWAY
Head, Valves, Piping Components and
Naval Ship Engineering Center
Encl: (1) BUSHIPS INST 9480.72
Ser 648A5-30 of 18 June 1964
.
DEPARTMENT OF THE NAVY
BUREAU OF SHIPS
WASHINGTON, D.C.
BUSHIPS 9480.72
Ser 648A5-303
18 June 1964
BUSHIPS INSTRUCTION 9490.72
From: Chief, Bureau of Ships
To: Distribution List
Subj: Surface ship steam system valves, operation of prior to warmup
Encl: (1) Requirements and Procedures for Modifying Steam System
Flexible Gate Valves as Necessary
1. Purpose. To promulgate instructions concerning the operation of valves
prior to the admission of steam to the system.
2. Scope. This instruction applies to all valves in surface ship steam
systems of non-nuclear construction. It does not apply to nuclear
construction for which separate requirements have been developed. Further,
although specifically directed at protecting flexible wedge gate valves from
overpressurization, this instruction applies to all steam system valves due
to the desirability of removing water form all components of steam systems
prior to warmup.
3. Background. The purpose and primary reason for using flexible wedge
gate valves in steam systems is to prevent binding when the valve is in the
closed position. In high pressure-temperature steam systems, pip line
expansion produces stresses and strains at valve end connections which tend
to slightly distort the valve bodies. If the valve wedge is solid, and, in
effect, clamp the valve shut. this problem is over come with flexible
wedges, which are best described as two circular plates attached to each
other by an integral hub in the center. With this design, the wedge will
flex as the valve seats press against it, thus avoiding the clamping effect.
Because of this very desirable characteristic, the Navy, as well as
industry, uses flexible wedge gate valves in all cases where piping system
expansion is a significant factor.
4. Discussion. The necessity of draining steam systems prior to putting
steam on the line is mentioned in several documents, including the BUSHIPS
Manual. Unfortunately, it is not adequately covered in these documents and
there have been instances where the preparatory action of drainage prior to
steam admission has been overlooked. As a result, several isolated instances
of serious damage to flexible wedge gate valves have occurred. It is
characteristic of flexible wedge gate valves that if water enters the body
neck as a result of system hydrostatic tests, or by other means, while the
valve is closed, it will be trapped, regardless of the valve position,
unless the valve is wither opened or the water is removed via a body neck
drain. Briefly, this is due to the fact that with the valve in the closed
position
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BUSHIPS INST 9480.72
18 June 1964
and a differential pressure across the wedge, the upstream side of the wedge
will move away from its seat, permitting water to enter the neck cavity. As
the body neck and line pressures equalize, or the pressure is rapidly taken
off the line, the upstream side of the wedge moves back against its seat,
sealing off the body neck and trapping any water which may have entered.
If the water remains in the body neck, as it will if the valve is not
cycled or drained, and steam is put on the line, a situation closely allied
to a boiler without a relief valve exists. The steam having a higher
pressure than the water in the neck, will prevent water from flowing into
the line even though the upstream face moves away from the seat. At the
pressure equalizes, the cycle whereby the water initially became trapped, is
repeated, only this time the water has been headed by the incoming steam.
The steam, however, continues to heat the water due to its close
proximity and higher temperature, causing the water to expand. If the
initial quantity of trapped water was large enough, the initial temperature
differential between steam and water great enough, and the heating cycle
continues uninterrupted, the end result is predictable. The water pressure
will build up, due to the water's expansion being restricted, until either
the body neck ruptures, the bonnet lifts off, or the seat rings collapse.
It should be noted that his phenomena has been proven by calculations
and controlled tests, during which a pressure was generated in the body neck
equal to ten times that which existed in the line. As far as actual
installations are concerned, there are only two know cases where this
overpressurization has resulted in damage on non-nuclear surface ships and
both occurrences would have been avoided had proper warmup procedures been
employed.
5. Action
a. Warmup Procedures. The following steps should be incorporated into
all operating procedures covering warmup of steam systems, if they already
do not form a part of same, prior to the admission of steam:
(1) Cycle all valves to ascertain that they are operational and
leave them in the open position for at least one minute to permit drainage
of the body into the line.
(2) Open all drains on the valve bodies and in the line.
(3) LIne up the system for warmup in accordance with existing
operating procedures. All valve body drains should be left open to permit
drainage throughout the warmup period. Other drains should be positioned for
existing instructions.
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BUSHIPS INST 9480.72
18 June 1964
(4) Proceed with warmup operation and close valve body drains at
the conclusion of same.
b. Modifications. Valves located with their stems below the horizontal
may require modification in addition to the requirements of section 5.a to
protect them form the possibility of overpressurization. The modifications
and how to perform them as necessary, are given enclosure (1). These
modifications are generally considered to be outside the normal capabilities
of a ship's force. Therefore, they should be performed during a shipyard or
tender availability period.
c. BUSHIPS Manual. The Manual will be revised with regard to steam
system drainage and the subject will considerably amplified.
6. Effective Date. This instruction becomes effective upon receipt.
DISTRIBUTION LIST:
SNDL L1 NAVSHIPYDS J. J. Stillwell
L40 NAVREPFAC By direction
L19 NAVSHIPREPFAC
L3 SUBSHIPS
L2 INDMANS & ASTINDMANS
E2 INSMATS
ONM
24 TYCOMS
M53 SPCC
F26 ALL INSURVS
29 (less 29S, 29E, USS ENTERPRISE CVA (N)65 & USS
BAINBRIDGE DLGN25)
31
32
THIS DIRECTIVE STOCKED AT:
Supply Dept., NAVSTA (Wash Copy to:
NAVYD Annex, Code 514.25 F23 A (Brazil only)
Washington, D. C. 20390 J 56 CO (Attn: Damage Control Schools
Command, Treas. Is. San Fran, Calif
J68 O in C U. S. Naval School. Deep Sea
Divers, U. S. Naval Station,
Washington, D. C. 20390
J56 CO (Attn: U. S. Naval School Shipfitter
(M) & (D), U. S. Naval Schools Command,
Norfolk, Va.
J33 CO (Attn: Shipfitter, M&F Schools Class
A) Service School, Command, NTC SDIEGC,
Calif.
J33 CO Enginemen School Class A, SSC, USNTC,
Great Lakes, Ill.
X-7 BUSHIPS Special List
- 3 -
.
Enclosure (1)
BUSHIPS INST 9480.72
18 June 1964
REQUIREMENTS AND PROCEDURES FOR MODIFYING STEAM
SYSTEM FLEXIBLE GATE VALVES AS NECESSARY
If a gate valve is installed with its stem located below the horizontal
and a drain is not located on the valve neck, there is no means of removing
any water which might be located therein except by cycling the valve. The
wedge or disc entering the neck cavity will displace its volume of water
into the piping system, where it can be drained off. Unfortunately, the
quantity of water removed by this action from the necks of flexible wedge
gate valves may not prevent overpressurization because the wedge only
displaces about 30 percent of the cavity, which is not enough. Additionally,
there is no way of preventing some of the displace water from re-entering
the neck cavity as the wedge is moved to the closed position.
This being the case, modifications may be necessary to all inverted
flex-wedge gate valves in steam systems, if prevention of overpressurization
is to be guaranteed. If these valves already have body neck drains, no
modifications are necessary. The required modifications in turn, are
dependent upon whether a valve is considered as being a "one way" or "two
way" valve.
Briefly, a one way valve is any valve which when closed, will realize a
pressure differential from only one direction under any conditions. Any
valve whose location falls outside of this limitation is, of necessity,
considered a two way valve.
There are valves which are borderline cases and/or can fall into either
category, particularly if an error in line up is made. Therefore, the
following sketches and more detailed description have been included to
clarify what determines whether a particular valve is "one way" or "two
way".
It should be noted that these examples do not take operator error into
account.
.
BUSHIPS 9480.72
June 1964
The "one way" valves in the above sketch, by the aforementioned
inition, are 5, 6, 7, 8, 10.
The "two way" valves in the above sketch, by the aforementioned
inition, ar 3, 4, and 9.
The "borderline" valves, depending upon a particular installation are
nd 2.
Based on the above sketch, the definition of a "one way" valve can
expanded as follows:
a. Any valve located in a system after any cross connections so t
it cannot be pressurized from the direction that is opposite to mal. Refer
to valve numbers 5, 6, 7, 8, 10.
b. The last valve in any system. Refer to valve numbers 5, 8, 10.
c. Any valve located before any cross connection from other tems,
which has a valve located between it and the cross connection, that it can
be isolated if the cross-connect valve is open. For example, ves 1 and 2 can
be isolated if the cross-connect valve 9 is opened, closing valves 3 and 4,
respectively. Since these valves will only ize pressure* from the broiler
side normally and can be isolated from er systems, they can be considered as
"one way" valves.
Valves 1 and 2 therefore are examples of the "border line" es
mentioned above. If valves 3 and/or 4 were not present, then valves and/or 2
must be considered as "two way" valves since it would not be sible to
isolated them if valve 9 were open.
definition of "two way" valves can be expanded as follows:
a. Any valve which will be pressurized* from the boiler side but
closed and the cross-connect valve is open (valve 9), they would be ssurized
for the opposite direction.
b. Any valves in branch connections which lead to a common header
cannot be isolated from the header by closure of a valve between them the
header. Refer to valve numbers 3 and 4. If boiler "B" was secured valves 2
and 4 closed to isolate it, then valve 4 would be pressurized* the boiler
"A" side, or opposite to normal. Reversal of this procedure d then replace
valve 4 with 3.
E: The terms "pressurized", "realize pressure", etcetera, refer to valves
being subjected to a pressure differential when in the closed tion.
Enclosure (1) - 2 -
.
BUSHIPSINST 9480.72
18 June 1964
There is one other example, which follows, and which has been included
to demonstrate the care that must be taken in determining whether a valve is
"one" or "two" way and, further, the care which must be taken in determining
the correct modification.
The case in point is a conventional reducing station, per the following
sketch:
The valves to be considered here 11, 12, and 13.
Valve 11 is a one way valve, when closed, with steam pressure always
coming from the "IN" side.
Valve 12 is a throttle valve, globe or needle type, and is not
involved.
Valve 13 is a one way valve BUT, it is a one way valve in the direction
opposite to normal. If valves 11 and 13 are closed to isolate valve 14, and
12 is opened for operational purposes, then valve 13 will be pressurized
from the downstream side and it must be modified accordingly.
With the above examples as a basis for determining the type of valve,
the modifications to be applied are:
a. One way valve - Drill a hole in the upstream side of the wedge.
b. Two way valve - Install a drain to atmosphere in the valve
neck.
The hole should be drilled per the following sketch:
-3- Enclosure (1)
.
BUSHIPSINST 9280.72
18 June 1964
A plate should be attached in a conspicuous location reading "THIS
VALVE HAS A VENT HOLE IN THE UPSTREAM SIDE OF THE WEDGE. IF WEDGE IS REMOVED
MAKE SURE IT IS REPLACED THE SAME WAY."
This modification for "one way" valves will prevent over pressurization
since the hole provides a constant vent to the upstream piping. The reason
for using this type of modification for these valves is to minimize the
number of drains that must be installed.
For "two way" valves, the drilled disc is unacceptable since it would
provide a constant leakage path through the valve when closed, and steam
pressure is applied to the side opposite the drilled hole. Therefore, "two
way" valves with the stem located below horizontal must be provided with
body neck drains to atmosphere per the following:
NOTES
1. Location of drain hole in the neck should be close to the top of the
neck BUT care should be taken not to drill through the pressure seal region.
Someplace between 1/3 to 1/2 down from the top of the valve (looking at the
valve in the upright position) should avoid the region, but this should be
checked before any drilling. See Note 9.
2. Pre-heating and stress relieving (as necessary) should be in accordance
with MIL-STD-271A.
3. Drain valves per MIL-V-22094.
4. Welding per MIL-STD-278.
5. Drain holes into valve bodies shall be in accordance with MIL-STD-22A.
6. Drain valves and piping shall be 1/4" IPS. Materials same as gate valve
body.
7. When drilling hole, drill far enough off center to avoid wedge guides
inside the valve body.
8. Be careful to avoid valve stem if hole is drilled with the valve
partially assemble.
9. The pressure seal region is in the top of the valve body and is
evidenced by a stainless steel or stellited overlay; hole should be drilled
below this overlay.
Enclosure (1) -4-
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Page Last Reviewed/Updated Tuesday, March 09, 2021