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About API Spec 17D SS and SV Flanges
API Spec 17D, 1st. Edition dated October 30, 1992 marked the introduction of an API “Specification for Subsea Wellhead and Christmas Tree Equipment.”
This Specification introduced a set of dimensions for 5M Flanges in nominal sizes 2-1/16” through 11” based on API Spec 6A, 6B Flanges, but with BX ring grooves designated in the Specification as API Type 17SS Flanges. The Specification also introduced Swivel Flanges designed to join with these new flanges, designated as API Type 17 SV Flanges, and introduced 10M Swivel Flange configurations that join directly to API Spec 6A, 6BX Flanges in sizes 1-13/16” through 13-5/8”, also designated 17 SV.
API Spec 17D accepts, through direct reference, all API Spec 6A, 6BX Flanges in all sizes through 15M Working Pressure. API Spec 17D also accepts all API Spec 16A Clamp Hub connections and Clamps in all sizes through 15M Working Pressure.
API Spec 17D requires all Flanges, Swivel Flanges, and Clamp Hubs used for Subsea applications to have their ring grooves either manufactured from or inlayed with Corrosion Resistant Material.
NOTE: API Spec 17D requires manufacturers to make 10M Working Pressure Swivel Flanges (Hubs and Rings) from 75K Material specified in API Spec 6A. These Swivel Flanges join to API Spec 6A, 6BX 10M Flanges made from 60K Material.
API Spec 17D describes Ring Gaskets special for Subsea make-up, identified as API Type SBX and SRX pressure energized Ring Gaskets. These Ring Gaskets have identical dimensions to those Ring Gaskets identified in API Spec 6A except they all have specially located drilled holes that allow the escape of any fluids (water) trapped behind the Ring Gasket as a result of Subsea connection make-up. API Spec 17D specifies only Ring Gaskets made from Corrosion Resistant Material for all Subsea connections.
API Spec 17D references API Spec 6A for PSL Levels and specifies that all Material and finished equipment meet the minimum requirements for PSL 2, 3, or 3G, as specified by the buyer of the equipment.
NOTE: The inclusion of Swivel Flanges intends to solve the problem of misaligning bolt holes in otherwise parallel flanges by allowing rotation of the Swivel Flange to bring the bolt holes into common alignment. API Spec 16A Clamp Hub connections, included in API Spec 17D by reference, also solve the problem of bolt hole alignment by totally eliminating the joining connection bolt circle. Clamp Hubs, joined by clamps, have the freedom to rotate 360° in any increment before the tightening of the Clamp to seal the connection. The Swivel Flanges in API Spec 17D have Hubs with designs similar to or identical with API Spec 16A Clamp Hubs. When Swivel Flange Hubs have identical dimensions with Clamp Hubs, and sufficient neck length exists to push the Swivel Flange Ring back away from its Hub with sufficient room to fit a Clamp, then a Clamp will secure this seemingly unorthodox connection. This Clamp connection possibility should work with the connections shown in the Table below.
WOODCO USA does not offer this information as a recommendation, but knowledge of this may assist Operators in decision making should they have a problem or emergency.
CAUTION: API Spec 17D specifically states, “All Flanges used on Subsea completions equipment shall be of the ring joint type designed for face-to-face make-up. The connection make-up force and external loads shall react primarily on the raised face of the flange. Therefore, at least one of the Flanges in a connection shall have a raised face.” API Spec 17D specifies an optional raised face on 17D Type SS Blind Flanges. WOODCO USA recommends that manufacturers always make API 17D SS Blind Flanges with raised faces.
API Spec 17D makes no mention of Studded Flange connections as specified in API Spec 6A, but does not prohibit them. The implication of acceptance of API Spec 6A connections, and the fact that API Spec 6A permits the omission of raised faces on studded face 6BX Flanges will surely result in operators attempting to install a 17D SS Blind Flange without a raised face onto a 17D SS Studded Flange, also without a raised face. Without using technical terms, any kind of damage to, or coating on, the face of either of the joining full face flange connectors with BX ring grooves will prevent the face to face contact intended and explained in API Spec 17D.
API Spec 17D requires closure bolting tension of 67% to 70% of the yield strength of the bolts (L7 / B7); torque tables included in API Spec 17D provide torque values intended to achieve this tension.
CAUTION: API Spec 17D requires flange connection bolt tightness (tension stress in the bolt) equal to 67% to 70% of the specified minimum yield strength of L7/B7 bolts. When using some lubricants and/or anti-corrosion coatings on bolts, tightening bolts consistent with the torque tables shown in API Spec 17D may in fact produce tension closer to the actual yield strength of the bolts. Operators should use an alternate method to measure tension in the bolts to confirm the applicability of this table.
The characteristic design of API 17D Swivel Flanges virtually requires their attachment to bodies by welding. All Swivel Flange illustrations in API Spec 17D show full bores, with no specified wall thickness at the end, or any weld preparation. Weld Neck Flanges shown in API Spec 17D have only restricted bores matching Line Pipe sizes.
WOODCO USA offers full bore Weld Necks for all 5M Working Pressure SS and SV Flanges, and 10M Working Pressure SV Flanges included in API Spec 17D. To view dimensions of API Spec 17D SS and SV flanges, go to the Flange Slide Rule Program on this Web Site.
CAUTION: Operators should seek competent engineering advice, use Qualified Welding Procedures, and employ Qualified Welders when attaching any API Flanges made from 60K or 75K Material specified in API Spec 6A.
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