A review on Joint Industry Program (JIP) 33
In 2020 IOGP released JIP 33, a supplementary specification to API 6DSS, subsea pipeline valves. This article by Karan Sotoodeh focuses on the material requirements for the subsea valves as well as factory acceptance testing.
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Article by Karan Sotoodeh
IOGP (International Association of Oil & Gas Producers) has devised the supplement to improve the level and content of the API 6DSS standard and provide an optimum specification for procurement of the subsea industrial valves.
The supplement has implications for materials used in these valves. Various material data sheets (MDS) for materials such as duplex, super duplex, carbon steel, low alloy steel and nickel alloys are provided in JIP33, Annex R. These provide information about the required chemical composition and mechanical strength of the materials, required material qualification tests, qualification of manufacturers and the process of producing the materials, etc.
A sample material data sheet for low alloy steel in ASTM A694 F60 grade, which can be used for the body of the subsea valves, is shown below in Figure 1.
Fig. 1: An example of a Material Data Sheet
The proposed MDSs inside JIP33 are not limited to the materials for the valve parts. Alternatively, two MDSs are given in JIP33 for applying hard facing alloys such as Stellite or tungsten carbide on the valvesâ€™ internals. The intention of hard facing on the valve internals is to reduce erosion and galling. Galling is defined as metal-to-metal friction between two metalling surfaces which causes wear. Galling could happen between the ball and seats of a ball valve due to opening and closing. Thus, both the ball and seats surfaces or contact surfaces should be hard-faced with tungsten carbide. Figure 2 illustrates galling between two metallic surfaces.
Galling can also occur between bolts and nuts, as well as stem bearings and the stem. A stem bearing is a component which is installed around the stem of the valve to prevent sideways movement. JIP33 is focussed explicitly on galling prevention for bearings.
The common approach in the valve industry is to apply a lining of Teflon to the internal surface of the bearings to prevent the galling with the stem.
Corrosion and erosion risk
The material selection should consider the corrosion risk as well as erosion. The emphasis of both API 6DSS and JIP33 is to add corrosion allowance to compensate metal loss due to carbon dioxide in the hydrocarbon service for non-corrosion resistant alloys (CRA) such as carbon steel. Exotic or CRA materials like duplex and super duplex are not corroded by carbon dioxide so do not require any corrosion allowance.
The proposed impact test by JIP33 is also given in Annex R of the document. Impact testing may be performed on the materials to make sure that they are compatible with the minimum temperature design values. As an example, low-temperature carbon steels (LTCSs) are typically used and designed for a minimum design temperature of -46Â°C, so they are required to be impact tested at -46Â°C.
The additional requirement for soft or non-metallic materials as per JIP33 is to qualify these materials as per Norsok M-710. This standard provides a series of tests for qualification of soft materials typically used for the sealing of valves in different areas such as stem, body and seats, etc. in the offshore industry.
Rapid gas compression
The other important consideration required as per JIP33 is to consider a corrosion-resistant alloy for the spring part of an energized seal like a lip seal. The gas could ingress the soft seals and make them fail through a phenomenon called â€˜rapid gas compressionâ€™ (RGC). This failure mechanism of soft seals could be riskier in high-pressure class gas services, such as pressure nominal 100 bar equal to American Society of Mechanical Engineering (ASME) pressure class 600. However, JIP 33 requires the consideration of RGC for all the seals inside valves exposed to the gas service. The proper sealing properties to prevent RGC is called â€˜anti-explosive decompressionâ€™ (AED).
Forging the preferred choice
Forging is the preferred choice of material manufacturing for subsea valves regarding the high quality associated with this manufacturing process. However, both API 6DSS and JIP 33 allow usage of casting according to API 20A addressing carbon steel, alloy steel, stainless steel, and nickel-based alloy casting for use in the petroleum and natural gas industries.
Carbon equivalent is an important parameter for carbon and low alloy steels which depends on different chemical percentages such as carbon, chromium, molybdenum, etc. High-carbon equivalent of more than 0.43 percent should be prevented according to both API 6DSS and JIP33, since it could reduce the weldability of the carbon and low alloy steel materials.
Subsea valve components in contact with seawater are protected against corrosion by cathodic protection as well as coating. Cathodic protection connects the valve to a sacrificial anode (e.g. aluminium, magnesium or zinc) which loses electrons easily and will therefore corrode in favour of the valve components. Figure 3 illustrates the cathodic protection mechanism for subsea pipeline protection which acts as a cathode. Components in specific materials such as duplex and super duplex, which are subject to cathodic protection, are at the risk of hydrogen induced stress cracking corrosion (HISC). Therefore, the guideline provided in DNV-RP-F112 should be applied to duplex and super duplex materials subject to cathodic protection to prevent HISC.
Fig. 3: Subsea pipe subject to cathodic protection. (Courtesy: Wordpress)
However, both API 6DSS and JIP 33 include only 22Cr duplex for the HISC analysis according to DNV guideline. It should be noted that some hard nickel alloys such as Inconel 718 and 725 could be subject to HISC so probably HISC-analysis is required for hard nickel alloys as well as duplex and super duplex.
The following considerations are requested to be done by JIP33 before valve assembly: check all valve components before assembly to ensure that they are free from rust, damage, sharp edges, etc.; not to re-use non-metallic seals after disassembly of the valve and to remove and replace the seals; to allow lubricants with a certain viscosity for assembling the valve components (these lubricants should be removed after assembly and prior to the test of the valves).
As for testing, this procedure is essential to maintain safety and reliability and to ensure that the valve can provide the required functionality without any need for maintenance over the design life.
JIP 33 provides a sequence for all the tests which should be performed as a part of a factory acceptance test (FAT). Different types of tests, including pressure tests, function tests, drift test, electrical continuity measurement, etc. are listed in this sequence.
Shell-test for primary sealing
A table that lists the sequence of the tests will contain different information such as applicable standard section number for the test implementation, type of test medium (gas or water or air), minimum duration of the tests and application of the test. Pressure tests are those which are applied to the body and seats of the valve to evaluate sealability of the valves. A drift test is performed to check that the bore or internal diameter of the valve has a specific diameter.
An important point added to JIP33 is that the primary sealing, including the stem seal and body and bonnet or body pieces seals, should be tested during the shell test. If during the shell test, the test fluid passes the primary seals and exits the relevant test port, then the primary seals do not function properly. The function test is performed to measure the required torque or force for opening and closing of the valves as well as speed of operation. JIP 33 has requested to apply the function test while the valve is empty as well as under full differential pressure. The test medium in the second case should be water with a corrosion inhibitor.
In general, various aspects of the subsea valves such as selection and type, material, welding, testing, quality control, marking are optimized by JIP33. This article lists some of the main changes and additions proposed by JIP33 over API 6DSS as regards materials and testing to improve the quality and reliability of subsea valves.