PWHT on Cast Vessel 1

[Spoonful]

Dear Members,

For a vessel made of cast, thickest part of the wall over 50mm, dose PWHT requirements as for welded vessel also applicable?

Are there any special consideration for PWHT a casting?

Regards

Spoonful.

 

[0707]

For the thickness involved I guess PWHT is required. What is the cast material?

 

[jwhit]

What is construction code and what cast material? Also, what type of welding was done and do you have a qualified procedure? For that thickness, more than likely PWHT per the applicable code will be required, except for certain stainless steels and nickel alloys. Keep in mind that there are dozens of cast alloys, so it is necessary to define the alloy or at the least a generic type.

 

[weldstan]

IF you're going to weld on it, and the thickness of the weld or base metal at the weld is such that PWHT is manfdated by the applicable Construction Code, yes.

 

[Spoonful]

Thanks for all the helpful reply, it is cast carbon steel. no welding involved at all. entirely cast. Design code AS1210, but I would also be interested in what ASME VIII Div 1 say about this.

What I wasn't too sure about is if cast vessel should be subject to same PWHT requirement as for welded vessel (for the same material of course).

As the term Post WELD heat treatment, and there is no weld in cast. Also my understanding that the benefit of PWHT is to relief of residue stress by heat from welding. if for cast, there is no welding, so no heat, so no residue stress, so what is the benefit of PWHT on cast?

Thanks

 

[jwhit]

Your vessel should be in the normalized and tempered condition. Since there has been no welding performed the Sec. VIII PWHT is not required. If, later on after the casting is out of your hands, welding is performed, PWHT becomes the responsibility of the organization that is doing the fabricating. In the future, if a similar vessel is welded by your organization, the Section VIII rules would apply to you. Hope this isn't too confusing.

 

[metengr]

First, the construction code AS1210 would apply to this vessel, not ASME B&PV Code. Second, the materials specification for this casting would dictate thermal treatment of the casting, if no welding is performed, major or minor. Third, stress relief treatment can be performed on a casting to relieve stresses, as a separate fabrication step above and beyond code requirements.

For any in-service repairs, the code of construction would be AS and the requirements for weld repair would most likely originate from this code as well.

 

[Spoonful]

Metengr/jwhit,

Thanks for the reply, from you reply, I can summary that PWHT is not a code requirement for entirely cast vessel?(if no weld). As some times there are some minor welding repairs（which is normal for large size casting) from the raw cast, how is this case considered?

Also for AS1210 case, I think PWHT may be be still required, to meet low temperature requirement? correct? unless the casting material is impact tested.

Doesn't ASME BPVC VIII Div 1 cover vessel made by case? then under with ASME code is this covered?

Thanks.

 

[metengr]

Spoonful
I don't have a copy of AS 1210 (pressure vessel code). Major and minor weld repairs are typically characterized by area and depth of weld repair. You cannot cherry pick rules/requirements between various international codes.

If this vessel was originally designed and fabricated to AS 1210, the code rules must be followed regarding repairs. ASME Section VIII, div 1 does cover rules for pressure vessel design and construction but they are not interchangeable with AS 1210.

 

[Spoonful]

Hi Metengr,

Some parts of AS1210 dose allow use rule requirement from ASME.

Regarding weld repairs, it is normally just on surface, and not so deep, so to you interpretation, if no deeper that PWHT requirment depth, them no PWHT needed?

 

[metengr]

Spoonful
Here is some information from ASME Section VIII, Div 1 for carbon steel and repairs during fabrication in UCS-56

(f) Weld repairs to P‐No. 1 Group Nos. 1, 2, and 3 materials
and to P‐No. 3 Group Nos. 1, 2, and 3 materials and to
the weld metals used to join these materials may be made
after the final PWHT but prior to the final hydrostatic test,
without additional PWHT, provided that PWHT is not
required as a service requirement in accordance with
UW-2(a), except for the exemptions in Tables UCS-56-1
through UCS-56-11, or as a service requirement in accordance
with UCS-68. The welded repairs shall meet the requirements
of (1) through (6) below. These requirements
do not apply when the welded repairs are minor restorations
of the material surface, such as those required after
removal of construction fixtures, and provided that the
surface is not exposed to the vessel contents.


(1) The Manufacturer shall give prior notification of
the repair to the user or to his designated agent and shall
not proceed until acceptance has been obtained. Such repairs
shall be recorded on the Data Report.
(2) The total repair depth shall not exceed 11/2 in.
(38 mm) for P‐No. 1 Group Nos. 1, 2, and 3 materials
and 5/8 in. (16 mm) for P‐No. 3 Group Nos. 1, 2, and 3 materials.
The total depth of a weld repair shall be taken as
the sum of the depths for repairs made from both sides
of a weld at a given location.
(3) After removal of the defect, the groove shall be examined,
using either the magnetic particle or the liquid penetrant
examination methods, in accordance with
Mandatory Appendix 6 for MT and Mandatory
Appendix 8 for PT.
(4) In addition to the requirements of Section IX for
qualification of Welding Procedure Specifications for
groove welds, the following requirements shall apply:
(-a) The weld metal shall be deposited by the manual
shielded metal arc process using low hydrogen electrodes.
The electrodes shall be properly conditioned in
accordance with Section II, Part C, SFA-5.1, Annex A,
A6.11; and SFA-5.5, Annex A, A6.12. The maximum bead
width shall be four times the electrode core diameter.
(-b) For P‐No. 1 Group Nos. 1, 2, and 3 materials,
the repair area shall be preheated and maintained at a
minimum temperature of 200°F (95°C) during welding.
(-c) For P‐No. 3 Group Nos. 1, 2, and 3 materials,
the repair weld method shall be limited to the half bead
weld repair and weld temper bead reinforcement technique.
The repair area shall be preheated and maintained
at a minimum temperature of 350°F (175°C) during welding.
The maximum interpass temperature shall be 450°F
(230°C). The initial layer of weld metal shall be deposited
over the entire area using 1/8 in. (3 mm) maximum diameter
electrodes. Approximately one‐half the thickness
of this layer shall be removed by grinding before depositing
subsequent layers. The subsequent weld layers shall
be deposited using 5/32 in. (4 mm) maximum diameter
electrodes in such a manner as to assure tempering of
the prior weld beads and their heat affected zones. A final
temper bead weld shall be applied to a level above the surface
being repaired without contacting the base material
but close enough to the edge of the underlying weld bead
to assure tempering of the base material heat affected
zone. After completing all welding, the repair area shall
be maintained at a temperature of 400°F to 500°F
(205°C to 260°C) for a minimum period of 4 hr. The final
temper bead reinforcement layer shall be removed substantially
flush with the surface of the base material.
(5) After the finished repair weld has reached ambient
temperature, it shall be inspected using the same nondestructive
examination that was used in (3) above,
except that for P‐No. 3, Group No. 3 materials, the examination
shall be made after the material has been at ambient
temperature for a minimum period of 48 hr to
determine the presence of possible delayed cracking of
the weld. If the examination is by the magnetic particle
method, only the alternating current yoke type is acceptable.
In addition, welded repairs greater than 3/8 in.
(10 mm) deep in materials and in welds that are required
to be radiographed by the rules of this Division, shall be
radiographically examined to the requirements of UW-51.
(6) The vessel shall be hydrostatically tested after
making the welded repair.