Welding Inspections for Silo

[dawn836]

Hi all
i have got Silo which will be made from steel plates rolled and welded toghter this silo will operate as follows:-
it's Silo for pressure hot air from the bottom and liquid soap from sprinklers on the sides and the liquid burned to get dry powder soap & the vapor go from the top to another step of manufacturing.

So what weldings inspections should i made for the wedling between steel Plates.

Thanks in Advance

 

[metengr]

Are you referring to construction of the silo in the field or in the shop or both?

Unless you are familiar with welding detail or material fabrication, I would suggest hiring a Certified Welding Inspector (CWI).

A CWI can provide technical input as to proper selection of welding procedures and qualification of welders. They can also recommend nondestructive testing (NDT) to be performed in the shop or in the field, and monitor hold points (perform visual inspections) to assure a quality job.
As with most contracts, cost is important. However, the cost of hiring a competent CWI is minimal in comparison to a poor fabrication job.

 

[henri2]

To get a better feel for the project permit me to pose a few questions.

1. What materials will be used for fabrication?

2. What will the silo hold...liquid, grain? This may help determine NDT methods which will supplement the VT (visual inspection).

3. What type of welds will be used for joining?

4. Briefly describe support struture for silo?

Metengr recommends a CWI and I agree the inspector should have that as a minimum. I prefer one who has in addition to CWI, ICC structural steel/welding as this provides evidence he/she can comprehend blueprints is familiar with AWS D1.1 and AISC provisions.

For NDT make sure the individual is Level II qualified in the method you specifiy.

If you are specifying carbon steel, then refer to AWS D1.1 table 6.1 for visual inspection requirements. In fact D1.1 Chapter 6 deals with inspection. For the structural supporting frame IBC Table 1704.3 might provide some ideas...this table also includes inspection of items which are to be welded.

When you are developing the inspection program for the welding, it's helpful to break it down in three phases..i.e inspection tasks before, during, and after welding.

If the welding will be done in a shop, consider stipulating that the fabricator be accredited. AISC has a reputable program...and AISC accredited fabricators have QC divisions.

 

[henri2]

One question I should have asked, did you use ASME for he silo design? If so you'll have to check out their inspection requirements.

 

[dawn836]

Well Thanks all for quick replys
For Metenger:-
i am asking only about what tests should be made for inspection in shop and filed as well, just name of tests and how many points to be checked.

For henri2:-
-the silo will be made from steel plates of yield strenght 3.6 t/cm2
-from my desprtion in first post the silo will hold liquid and vapur pressure.
-welding will be but weld.

well the problem is that i do not have the AWS code.
just i want good idea about the tests and inspection

 

[henri2]

Visual Inspection/Visual testing (VT)

As I pointed out, there are three phases to consider in developing a visual inspection and testing program/checklist; what happens before welding, during welding, and after welding.

In some of the phases, the inspector will have to use tools to measure for instance: fit-up dimensions (root opening, root face, groove angle) and fusion type discontinuities like porosity to determine if they are in compliance with specifications.

Visual observation that the welding procedure specification (WPS) is adhered to is an essential component of visual inspection/visual testing. In fact before any welding proceeds, the welding inspector must verify that there is a WPS and welding personnel are qualified to use the WPS in production welding. By the way is the joint you are using in the design prequalified? If not it will have to be qualified by testing.

AWS D1.1 Chapter 6 covers INSPECTION, outlines responsibilities of verification (QA) and contractor's (QC) inspector as well as those of the contractor. It then delves into acceptance criteria for VT and NDT, followed by procedures for primarily RT and UT.

AWS D1.1 chapter 6 does not spell out a detailed checklist and set of procedures for visual inspection but it does provide acceptance criteria for welds. AWS has other publications that deal with this. For instance, Figure 10.1 of the AWS WIT is an example of a welding inspection checklist and covers what is to be done by the inspector before welding, during welding, and after welding. I recommend getting a copy of it.

After welding the inspector has to check the weld. D1.1 has a table dealing with this. Discontinuity Category and Inspection Criteria items enumerated in AWS Table 6.1 Visual Inspection (VT) Acceptance Criteria are as follows: 1. Crack prohibition, 2. Weld/Base-Metal Fusion, 3. Crater Cross Section, 4. Weld Profiles (refers to fig 5.4), Time of Inspection, 6. Undersized welds, 7. Undercut, and 8. Porosity.

Item 4 in the preceding paragraph directs us to Figure 5.4 Acceptable and Unacceptable Weld Profiles. Figure 5.4 deals with fillet welds and groove welds. The butt welds (groove welds in butt joints) will have to be checked with appropriate tools to make sure reinforcement is not excessive, there is no underfill, no excessive undercut, and no overlap.

Regarding frequency of visual inspection, if I were you I'd specify continuous VT from start to finish.

NDT

This can get very expensive but is imperative in order to supplement VT. Therefore, I recommend that you to talk to an NDT expert prior to specifying required tests and frequency of testing.

Methods to consider include: RT (x-ray testing...very expensive), UT (ultrasonic testing), LT (leak test), PT, and MT.

Dye penetrant testing (PT) and MT (magnetic particle testing) are relatively inexpensive but have limitations.

IMO in addition to performing NDT when fabrication is complete, there should be hold points during the fabrication process for NDT to be carried out.

To the best of my knowledge D1.1 does not recommend an NDT frequency of testing but ASME Section VIII does.