An alteration means you intend to modify a boiler or pressure vessel from the original design. To protect the public, most states require the original manufacturer of these items to have an S stamp, U stamp, or H stamp. Changing these designs in the field also requires an R stamp. If you have a Boiler or Pressure Vessel bearing an S Stamp, H Stamp, or U stamp and have work performed by a contractor without an R stamp, you could be in violation of the law and you could void the stamp on your vessel. R stamp companies use certified and tested welders following stringent welding procedures and are required to have a quality control program in place. Companies without an R stamp may not follow these rules. If you are unsure, call and ask us, your insurance provider, or your local Authority Having Jurisdiction. We would be happy to talk about your equipment and help you find a solution.