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Question:

Why is 4130 material the commonly stocked flange material for 10,000 psi 6BX Weld Neck flanges, and what else can the flanges be made out of and still be Monogram stamped as complying with API 6A? What other materials have been specified in WOODCO USA’s experience?

API Licensed Manufacturers usually use 4130 for all of their 6BX connectors; especially weld neck connectors (flanges and hubs).

API Spec 6A specifies steel chemistry limits, and mechanical property minimums for Bodies, Bonnets, End and Outlet Connections, and Loose Connectors (Adapter Flanges, Blind Flanges and Weld Neck Flanges). For sour service circumstances, API requires that all steels used also meet NACE MR0175 requirements for chemistry and maximum hardness. 4130, properly heat treated, satisfies all of these requirements

Steels other than 4130 that manufacturers may use, include 4140, 8630, and 410 “Stainless Steel.” All of these materials prove more difficult than 4130 to weld, they almost can’t be welded satisfactorily in the field. Of the commonly available low alloy steels, 4130 has the best weldability.

For weld neck flanges of 10,000 psi WP, API specifies 60K minimum yield (and allows substitution of 75K minimum yield). Manufacturers usually use 4130 in a normalized, quenched and tempered condition, to make these flanges. 4130 easily achieves these properties, as well as other requirements for low temperature, sour service, etc.

For weld neck flanges of 15,000 psi WP API specifies 75K minimum yield, and manufacturers use 4130, qualified to 75K minimum yield, for this as well.

WOODCO USA does not recommend attempting to weld 4130, or any of these other low alloy steels, outside of a controlled shop or factory environment.

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