United States Nuclear Regulatory Commission - Protecting People and the Environment

IE Circular No. 77-05, Liquid Entrapment in Valve Bonnets


                                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 


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

1.   Circular 77-05
2.   Draft transmittal letter

(Transmittal Letter for IE Circular 77-05 - Liquid Entrapment in Valve 

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 

IE Circular 77-05
  "Liquid Entrapment
  in Valve Bonnets" 

                                                       IE Circular 77-05 
                                                       Date: MAR 24 1977 


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. 


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, 

                                   - 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 

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 


               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 

               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 



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 

Subject:       BUSHIPS 9480.72 
               Ser 648A5-308 
               18 June 1964 


     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 


                                                               12 FEB 1976 

Walworth Company
P.O. Box 1103 Huff Avenue
Greensburg, Pennsylvania 15601 

Attention Mr. P. H. Awtrey 
          Chief Engineer 


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 


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 

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 

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. 

                                                       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. 

SNDL L1             NAVSHIPYDS               J. J. Stillwell
     L40            NAVREPFAC                By direction
     L19            NAVSHIPREPFAC
     L3             SUBSHIPS
     L2             INDMANS & ASTINDMANS
     E2             INSMATS
     24             TYCOMS
     M53            SPCC
     F26            ALL INSURVS
     29             (less 29S, 29E, USS ENTERPRISE CVA (N)65 & USS 
                    BAINBRIDGE DLGN25)

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, 
                              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 


     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 

     It should be noted that these examples do not take operator error into 

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

     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 

     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 

     The hole should be drilled per the following sketch: 

                                   -3-                   Enclosure (1)     

18 June 1964 

     A plate should be attached in a conspicuous location reading "THIS 

     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: 


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

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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