RESISTANCE VALVE

SEALS

OF SEALING TO THE

GREASES

ACTION

FOR

GATE

OF AGGRESSIVE

MEDIA

Kh. and

T. Kakhramanov, T. A. l~minbeili

R.

S.

Safarov,

UDC 622.276.51:621.89.001.5

A very widespread and relatively reliable means of hermetizing gate valve seals for gusher apparatus is the u s e of a m e t a l - m e t a l seal and a sealing g r e a s e . At p r e s e n t sealing g r e a s e LZ-162, developed by the Shaumyan Leningrad experimental petroleum oil plant (ONMZ) together with the AzINmash, is used as the sealing g r e a s e for seals of straight-through gate valves of well-mouth equipment. In the AzINmash investigations have been made of the chemical r e s i s t a n c e and hermetizing ability of sealing g r e a s e s in gas media containing a g g r e s s i v e components (H2S and CO2). To determine the effect of hydrogen sulfide, the g r e a s e s were placed in hermetic v e s s e l s filled with condensate {a 3% NaC1 solution, acidified with CH3COOH to pH 3.5-4.0}. The condensate was saturated daily with hydrogen sulfide through a tube brought up to a hole in the cap, to a content of 1700-3000 m g / l i t e r . The p e r cent H2S in the condensate was determined by an iodometric method. In connection with that fact acid t r e a t m e n t of wells is effected through the wellhead equipment during the time of operation by using a mixture of methanol and hydrochloric acid, which come into contact with the sealing g r e a s e , we also investigated the chemical r e s i s t a n c e of the g r e a s e s in these m e d i a . We investigated the s e r i a l l y produced g r e a s e s LZ-162 and ~Sh-176, and experimental s p e c i mens of the g r e a s e s LZ-15 and LZ-19, developed by the Shaumyan LONMZ. The g r e a s e s were tested for 10 days in a medium containing H2S in a mixture of 25% HC1 and 10% methanol, for a day in k e r o s e n e , and also under industrial conditions in the action of natural gas at the Orenburg gas-condensate field. The t e s t s showed that LZ-162 g r e a s e {Fig. 1) after keeping in a hydrogen sulfide containing medium floats up, changes color and consistency, formation of granules is obs e r v e d plus partial solution, and oily spots appear on the s u r f a c e of the condensate. After keeping in the mixture of HC1 and methanol, floating is o b s e r v e d , and change in color and consistency; and after keeping in k e r o s e n e , swelling and c r a c k formation; thereupon the kerosene remains t r a n s p a r e n t .

Fig. 1. LZ-162 g r e a s e : a) after action of medium containing H2S; b) in state as supplied; c) a f t e r a c tion of natural gas. Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 4, pp. 29-30, April, 1979.

306

0009-2355/79/1504-0306 $07.50

9 1979 Plenum Publishing Corporation

12

I

Working Water medium Fig. 2 Fig. 3 Fig. 2. l~Sh-176 g r e a s e : a) in s t a t e as supplied; b) a f t e r action of natural g a s . Fig. 3. Constructional s c h e m e of flat s e a l model: 1) upper flange; 2) piston to squeeze plates; 3) u p p e r contact plate; 4) supply valve; 5) equalizing piston; 6) lower contact plate; 7) lower flange; 8) hydraulic p r e s s u r e feed line; 9) working medium feed line; 10, 12) m a n o m e t e r s ; 11) bolt. T e s t s of t~Sh-176 g r e a s e (Fig. 2) in a m e d i u m containing hydrogen sulfide showed that a f t e r keeping in this m e d i u m , it is softened, a turbidity is o b s e r v e d in the condensate, a p r e c i p i t a t e a p p e a r s , its c o l o r c h a n ges (darkens), and oily spots a p p e a r on the s u r f a c e of the condensate. After keeping in the H C l - m e t h a n o l m i x t u r e , drying out is o b s e r v e d plus a change in consistency; black p a r t i c l e s a p p e a r on the s u r f a c e of the m i x t u r e ; a f t e r keeping in k e r o s e n e t h e r e is p a r t i a l d e c o m p o s i t i o n , the k e r o s e n e b e c o m e s turbid, and a black precipitate appears. Investigation of the c h e m i c a l r e s i s t a n c e of the e x p e r i m e n t a l g r e a s e s L Z - 1 9 and LZ-15 in a medium con-

taining H2S showed that they do not undergo changes, the condensate r e m a i n s t r a n s p a r e n t , and s e p a r a t i o n of an oil is not o b s e r v e d . After keeping in the H C l - m e t h a n o l m i x t u r e , no i m p o r t a n t changes in L Z - 1 5 and L Z 19 g r e a s e s a r e o b s e r v e d . A defect of t h e s e g r e a s e s is solution of s o m e of t h e i r components in k e r o s e n e . Thus, a f t e r keeping the g r e a s e s in k e r o s e n e f o r s e v e r a l d a y s , they w e r e converted into a p r e c i p i t a t e which f o r m s a g r a i n y m i x t u r e on shaking. However, considering that the L Z - 1 5 and L Z - 1 9 g r e a s e s a r e intended f o r operation in a gas well, t h e i r h e r m e t i z i n g p r o p e r t i e s w e r e investigated both as supplied and a l s o a f t e r the action of the hydrogen sulfide containing m e d i u m . T e s t s w e r e conducted on a s p e c i a l a t t a c h m e n t (Fig. 3) which i m i t a t e d the operation of the s e a l of a s t r a i g h t - t h r o u g h gate valve with a sealing g r e a s e . This a t t a c h m e n t consists of an u p p e r and a lower flange, connected to each other by t h r e e bolts. In the cylindrical drilling of the u p p e r flange was placed a piston, which under the action of hydraulic p r e s s u r e supplied through a line, squeezes against plates located between the flanges. The n e c e s s a r y contact load between the plates was c r e a t e d with the aid of liquid p r e s s u r e o v e r the piston. On the contact s u r f a c e of one of the plates (in the p r e s e n t c a s e , the upper plate) t h e r e is an annular d r i l l e d - o u t p l a c e , which was filled with the g r e a s e to be t e s t e d with the aid of a manual f o r c e pump through a pump valve. With the objective of eliminating the effect of m e d i u m p r e s s u r e on the axial downward p r e s s u r e , and a l s o to obtain u n i f o r m distribution of the supplied m e d i u m p r e s s u r e o v e r the contact s u r f a c e an equalizing piston was installed in the cylindrical boring of the contact plates. B e f o r e the t e s t s , we checked the p l a n e - p a r a l l e l i s m and finish of the contact s u r f a c e s of the plates ; and the contact s u r f a c e s w e r e d e g r e a s e d with alcohol and dried. The t e s t s w e r e c a r r i e d out at specific loads on the contact s u r f a c e s of the plates of 76.5; 153; 229.5; 306; 382.2; and 459 k g f / c m 2. The d e h e r m e t i z i n g p r e s s u r e of the s e a l was d e t e r m i n e d with the aid of a m a n o m e t e r installed on the working m e d i u m feed line, and visually. As the c r i t e r i o n f o r evaluating the h e r m e t i z i n g ability of the e x p e r i m e n t a l g r e a s e s we took the h e r m e t i z ing ability of the s e r i a l l y produced L Z - 1 6 2 g r e a s e . T h e r e f o r e , t o g e t h e r with the L Z - 1 5 and L Z - 1 9 g r e a s e s , 307

LZ-162 g r e a s e was a l s o subjected to the t e s t s . The g r e a s e s w e r e t e s t e d both as supplied, and a l s o a f t e r keeping t h e m f o r 10 days in a m e d i u m s a t u r a t e d with H2S to a concentration of 1700-3000 r a g / l i t e r . Investigations of the dependence of the h e r m e t i z i n g ability of the g r e a s e s on specific contact load showed that as supplied the h e r m e t i z i n g p r o p e r t i e s of the L Z - 1 5 and L Z - 1 9 g r e a s e s w e r e 8-10 and 20-25% higher, r e s p e c t i v e l y , than those of the LZ-162 g r e a s e . A f t e r keeping in the hydrogen suifide m e d i u m , the h e r m e t i z ing ability of the L Z - 1 5 g r e a s e was s o m e w h a t i n c r e a s e d , but that of L Z - 1 9 g r e a s e wus r e d u c e d , while r e t a i n ing adequate s e r v i c e a b i l i t y thereupon. It was not p o s s i b l e to study the h e r m e t i z i n g ability of LZ-162 g r e a s e a f t e r keeping in the hydrogen sulfide m e d i u m , due to the c o n s i d e r a b l e change in its s t r u c t u r e and consistency. Thus, on the b a s i s of the studies p e r f o r m e d , the e x p e r i m e n t a l g r e a s e s p e c i m e n s L Z - 1 5 and L Z - 1 9 may be r e c o m m e n d e d f o r u s e in gas and g a s - c o n d e n s a t e fields having a content of hydrogen sulfide in the m e d i u m up to 6% by volume.

308