ASME Code - Conditions requiring post weld heat treatment

The Code requires post weld heat treatment of pressure vessels for certain design and service conditions (see Code Pars. UW-40 and UCS-56 for prescribed procedures). Post weld heat treatment requirements (according to materials, thicknesses, service, etc.) include the following:

All carbon-steel weld joints must be post weld heat-treated if their thickness exceeds 11 ⁄4 in or exceeds 11 ⁄2 in if the material has been preheated to a minimum temperature of 200°F during welding [Code Par. UCS-56 and Table UCS-56 Fn. 2 (a)]

Vessels containing lethal substances must be post weld heat treated (Code Par. UW-2)

Carbon- and low-alloy steel vessels must be post weld heat treated when the minimum design metal temperatures are below 50°F, unless exempted from impact tests (Code Par. UCS-68)

Ferritic steel flanges must be given a normalizing or fully annealing heat treatment if the thickness of the flange section exceeds in (Code Par. UA-46)

Unfired steam boilers with a design pressure exceeding 50 psi and fabricated with carbon or low-alloy steels must be post weld heat treated (Code Par. UW-2)

Castings repaired by welding to obtain a 90 or 100 percent casting factor must be post weld heat-treated (Code Par. UG-24)

Carbon- and low-alloy steel plates formed by blows at a forging temperature must be post weld heat-treated (Code Par UCS-79).

Some vessels of integrally clad or applied corrosion-resistance lining material must be post weld heat-treated when the base plate is required to be post weld heat-treated (Code Par. UCL-34)

Some high-alloy chromium steel vessels must be post weld heat treated (Code Pars. UHA-32 and UHA-105 and Table UHA-32)

Some welded repairs on forgings require post weld heat treatment (Code Par. UF-37) (See Table 6.2)

When the thickness of welded joints for vessel parts or pressure vessels constructed with carbon (P-No. 1) steels exceeds 5⁄8 in and for all thicknesses of low-alloy steels (other than P-No. 1 steels) which are subject to direct firing, post weld heat treatment must be performed (Code Par. UW-2)

All carbon- and low-alloy steel seams must be post weld heat-treated if nominal thickness exceeds 11 ⁄4 in or 11 ⁄2 in if preheated to 200°F before welding

ASME Section VIII Division 1 reference - Pars. UCS-56

Some materials must be post weld heat-treated at lower thickness

ASME Section VIII Division 1 reference - Table UCS-56

Vessels containing lethal substances must be post weld Heat Treated

ASME Section VIII Division 1 reference - Pars UW-2

Unfired steam boilers

ASME Section VIII Division 1 reference - Pars. UW-2

Carbon-steel vessels for service at lowered temperature must be post weld heat-treated unless exempted from impact test

ASME Section VIII Division 1 reference - Pars. UCS-66, UCS-67, UCS-68

Welded vessels

ASME Section VIII Division 1 reference - Pars. UW-10, UW-40

Carbon- and low-alloy steel vessels

ASME Section VIII Division 1 reference - Pars. UCS-56, UCS-66, UCS-67, UCS-79, UCS-85

High-alloy steel vessels

ASME Section VIII Division 1 reference - Pars. UHA-32

Cast-iron vessels

ASME Section VIII Division 1 reference - Pars. UCI-3

Clad-plate vessels

ASME Section VIII Division 1 reference - Pars. UCL-34

Bolted flange connections

ASME Section VIII Division 1 reference - Appendix 2

Castings

ASME Section VIII Division 1 reference - Pars. UG-24

Forgings

ASME Section VIII Division 1 reference - Pars. UF-31

When only part of vessel is post weld heat-treated, extent of post weld heat treatment must be stated on Manufacturer’s Data Report Form U-1

ASME Section VIII Division 1 reference - Pars. UG-116

The letters HT must be stamped under the Code symbol when the entire vessel has been post weld heat-treated

ASME Section VIII Division 1 reference - Pars. UG-116

The letters PHT must be stamped under the Code symbol when only part of the vessel has been post weld heat-treated

ASME Section VIII Division 1 reference - Pars. UG-116

Low-temperature vessels

ASME Section VIII Division 1 reference - Pars. ULT-56

Ferritic steel vessels

ASME Section VIII Division 1 reference - Pars. UHT-80, UHT-81

Nonferrous vessels

ASME Section VIII Division 1 reference - Pars. UNF-56

Layered vessels

ASME Section VIII Division 1 reference - Pars. ULW-26

Vessels or parts subject to direct firing, when thickness exceeds5 ⁄8 in

ASME Section VIII Division 1 reference - Pars. UW-2