Mass. Gen. Laws ch. 146, § 87

The provisions of sections eighty-one to eighty-six, inclusive, relative to the examining and licensing of pipefitters shall not apply to pipefitting performed by a person regularly in the employ of an industrial plant, firm corporation, college, gas company, electric company engaged in the generation, sale, transmission or distribution of electricity, or a utility steam distribution system as may be required on the premises and property of such industrial plant, firm corporation, hospital, school, college, gas company, electric company or utility steam distribution system, nor shall such provisions apply to such pipefitting performed by an engineer or fireman, licensed under section forty-six, in a place where he is regularly employed.