17-4 pH bụ ihe na-agafe agafe na-efe efe na-enweghị ike na-enweghị ike na siri ike yana iguzogide nguzogide. 17-4 py nwere ezigbo nhazi agwa ma nwee ike ịgha mkpụrụ obi iji gwọọ ọnọdụ okpomọkụ. 17-5 PH bụ ihe ndị a na-eme n'ọtụtụ ebe na Aerospace, Chemical, Petrochemical, nhazi nri, akwụkwọ na mkpokọta ọla ọrụ na-akwụ ụgwọ ọrụ.