API 650 Tanks

[juanq]

Our upstream folks are building 3 storage tanks API 650 about 58K bbls, A36 steel. Each one has a 48" x 48" clean our door. This entire shell sheet with opening assembly comes to the jobsite already with PWHT. The design drawings show a full size fillet weld between the repad and shell.
The repad and shell are 13 mm thick. However the actual fillet weld size in some places is only about 6 mm not the required 13mm.

What would you recommend? Can we add weld metal to this repad w/o pwht and stay within code? The contractors say no but that does not sound right to me. We are only talking 9/16" thick A36 material where we will be welding.

thanks

 

[prex]

In my opinion the answer depends on why originally PWHT was specified: can you clarify this point? prex

http://www.xcalcs.com

Online tools for structural design

 

[Tankman650]

A36??? You must be in a warm climate since A36 has such brittle fracture problems. I have only seen A36 used in south Fla.

The PWHT of the clean out door is required by API650. You can weld on the assembly but you must do the PWHT again. Contact the fabricator and confirm that the door meets API650 as built. If not, they should take the door back and complete the weld and re-PWHT.

 

[PVRV]

1. Size of Fillet Weld (RF-PAD to SHELL)

Refer to API-650, table 3-7; to outline the required fillet size.

2. Brittle fracture

API 650, clause 2.2.9 & Figure 2-1 address MDMT and impact testing requirements. I see where Tankman650 is coming from, and I believe A36 should not be used for shell, annular, roof and bottom plates. In addition A678 should not be used at all.



3. Thermal Stress Relief

Tankman650, is correct; it is a mandotory requirement as per API 650, clause 3.7.4 It is ironic, 6mm fillet weld size satisfies API-650 but not the client and weld "addition" may violate API-650 if PWHT is not preformed.

General:

a) Does additional weld re-inforcement (no excavation)
constitue a repair?

b) Does API-650 mention at all, sequence to be followed
for repair of a stress relieved assembly.

c) I am reluctant to refer to ASME Sect. VIII, Div.1; UCS-
56 (f); for starters in view of the thickness in
question 13mm

d) Would pre-heat be satisfactory?

juanq, I wouldnt conduct further heat treatment; but whom ever places the API-stamp should have the final say in this.
Sorry I wish I could provide more solid justification.

Cheers

 

[PVRV]

I apologise,

The COD, RF-Pad fillet size has to be equal to the RF pad thickness with a maximum of 40mm.