43

Question:

During assembly of a 5,000 psi Choke Manifold we had a problem with one connection, the studs of a DSA extended too far through the flange of a valve and when we fully tightened the bolts with a hammer wrench, we could not remove the wrench from the last stud we tightened. The ends of the studs became so close to the Valve body that insufficient room remained to remove the box end wrench. The studs appeared longer than necessary. We disassembled the problem connection and shortened the studs about 1/4" and this solved the problem. Can you please explain how this problem can occur if all our equipment meets API Spec requirements?

Answer:

You mentioned that  you purchased a 5,000 psi manifold. API 5,000 psi flanges seal with either R or RX ring gaskets. RX gaskets require slightly longer bolts/studs than R gaskets, as RX gaskets increase the stand-off between flanges a little more than 1/4 of an inch. You probably had tap end studs in your DSA that would accommodate RX ring gaskets and you probably assembled your manifold with R ring gaskets. Many manufactures ship studded equipment with tap end studs long enough to accommodate RX gaskets, should operators choose to use them. A problem rarely occurs, but operators may avoid one entirely by discussing with the manufacturer which ring gasket they intend to assemble equipment with, and request tap end studs of the appropriate length.

For through bolts on open face flanges, operators can usually avoid problems caused by close dimensions behind flanges by shifting the excess length of the connecting bolt to the side of the connection with the most space.

To determine the stand-off of flanges using R and RX gaskets, Click Here.

For the AWHEM Specification for lengths of bolts and tap end studs that fit API Spec 6A flanged and studded connections, see TR9501 Specification For Stud Bolts And Tap End Studs.

For a Catalog for Bolts, Nuts, Ring Gaskets and Wrenches, Click Here.

Information above, and in other parts of this Web Site, may help persons who really seek to know. If you have a question, and you think WOODCO USA may have the capacity to answer it, please use our link and give us a chance to help.

WOODCO USA provides Web Site Tools for identification, estimating, and reference only. Do not use this information for manufacturing or inspection. Users of these tools should not use them as a substitute for professional engineering advice.  Anyone making use of the information presented does so at his own risk and assumes any and all liability resulting from such use.