You also need to follow the OSHA Regultaion 1926.550(a)(1) & 1926.550(a)(16)
Here is a link to an Osha Standard Interpetration on crane repairs
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=21677 Here a portion of that document:
Paragraph 1926.550(a)(16) addresses the requirement for manufacturers' approval before any modifications or additions can be made which would affect the safe operation of the crane. The section goes on to address what must be done when the capacity is changed. The intent of this paragraph is to assure any modification or addition that would change the capacity of the crane be reviewed by the manufacturer to make sure the change does not adversely affect other crane functions or components and cause an unsafe condition. By their very nature major repairs to crane components create the potential for adversely affecting capacity or safe operation, and for that reason such repairs should be reviewed and approved by the manufacturer to make sure that the crane's capacity and safe operation are not affected. Alternatively, this could be done by seeking the certification of a registered professional engineer that a repair has restored the crane component to its original configuration and strength so that the capacity and operation of the crane is unaffected by the repair. A crane user who has had major repairs carried out but has not taken appropriate steps to ensure that capacity or safe operation has not been adversely affected could be cited.
Best to avoid doing any welding on a boom unless approved by the manufacturer.
Richard Beldyk PhD, PE
www.6sproductivtycom.com