Theory, History, and Results on Sealants for Subsea Service

Abstract

ABSTRACT A discussion of the theories of repair sealants on ball valves and testing which has been done on various sealants to determine the basic characteristics of the sealants. Preliminary penetration, chemical, and flow testing results are presented along with a discussion of field problems. INTRODUCTION The use and application of sealants to ball valves, both on land and offshore is critical to the long term work ability and reliability of many of the valves. In spite of this critical need, little formal testing has been done, documented, and distributed to the industry on this subject. This paper reflects a first step on behalf of several companies to develop technology in this area which will support standardized guidelines for the specification and use of these products. DEFINATIONS Bridging: The ability of a sealant material to span across and seal a gap in a sealing interface. Grease Worker : A standardized tool to stir grease or sealant at a prescribed speed and by a prescribed method (See ASTM D217-60T). Penetration number : Depth in tenths of a millimeter that a standard cone penetrates the sample of grease or sealant under prescribed conditions of weight, time, and temperature. Penetrometer : A device used to measure the penetration of a standard cone in the grease or sealant under standard conditions. Sealant : A grease-like mixture which is intended to bridge over small gaps in sealing interfaces (i.e. between the ball and seat of a ball valve) and cause effective sealing to occur. Sealing interface : Any surface along which one part is sealed against another. Most specifically in this discussion, the contact area between the ball and seat of a ball valve. Unworked : A sample of grease or lubricant which has been subjected to only the minimum handling in transferring it from the sample can to the test apparatus. Working : Subjecting the lubricant or sealant to any form of agitation or shearing action. EXAMPLE OF A FAILED FIELD APPLICATION Figure no. 1 shows the seat ring pulled in a 24" ANSI 600 ball valve which had been operated at 500-600 p.s.i. on dry gas in the Far East. The pipeline was 800 kilometers long, with 350 kilometers being offshore and 450 kilometers being on shore. In this particular project, a total of approximately 300 valves from 12" thru 30" were used. As can be seen on the figure, the sealant material is so caked and hard that it has completely bridged the seat ring. It was literally supporting the seat ring off of the ball in the valve. The leakage past this seat would be so prolific that an observer would have questioned if the valve was even closed. In the particular case of the photograph in figure no. 1, the line could not be closed off to allow the insertion of a pig in the Pig Trap. Figure no. 2 shows what the seat ring looked like after it was removed and cleaned. Immediately inside the dark band is a small face groove to allow distribution of the sealant around the face of the seat. Small holes are drilled in the interface groove to intersect a second small outer groove which communicates with the external sealant injection fittings.