API 6A- QTC Size 1

[Vinay Pawar]

Hi,
In API 6A specfication, what is the criteria to decide the QTC size of Studded Cross/Tee product?

 

[jmec87]

The criteria is in API 6A 21st Edition section 6.4. However, it is quite complicated. It depends on the following:

1. If material is heat-treated in a continuous or batch furnace
- if continuous, a prolongation or sacrificial production part (not a separately-forged QTC) must be used and only production parts having an identical size and shape are qualified

2. If the product is made from a casting or a forging
- if a casting (regardless of PSL), the equivalent round (ER) of the QTC must be equal to or greater than the dimensions of the part it qualified

3. PSL (forgings) and, for PSL 3, required yield strength and part's weight during heat treatment
- if PSL 1 or 2 (forging), the ER of the QTC is not required to exceed 2.5", so a 2.5" diameter QTC would meet the requirements for any size studded tee or cross
- if PSL 3, unless the required yield strength is 75K or greater and the part's weight during heat treat is greater than 454 kg (1000 lb), the ER of the QTC is not required to exceed 5", so a 5" diameter QTC or a 4" x 4" square cross section QTC would meet the requirements for any size studded tee or cross
- if PSL 3 and both the required yield strength is 75K or greater and the part's weight during heat treat is greater than 454 kg (1000 lb), the ER of the QTC is not required to exceed 10", so a 10" diameter QTC or a 8" x 8" square cross section QTC would meet the requirements for any size studded tee or cross
- if PSL 4, a prolongation or production part is required

4. Your interpretation of the requirement in 6.4.2.2 that "The ER of a studded type part shall be determined by using a thickness, T, equal to that of the thickest flange of that part. An ER determination for these parts shall be in accordance with the methods for complex-shaped parts." and your interpretation of the requirements for complex-shaped parts in Figure 4 b.
- this route is complicated and the requirements are unclear
- skipping this point and instead using the "not required to exceed" dimensions from point 3 above is a simple solution that will result in a QTC size guaranteed to meet 6A, but this QTC size might be larger than you could justify if you used this point

 

[Vinay Pawar]

Thanks.
I agree with your suggestion to follow point#3 as described by you.
Tee/Cross is pressure containing part and is in contact with wellbore fluid.So its very difficult to conveincefor API auditor.
IS there any interpreation on this topic by API commitee?

Thanks for your guidance.

 

[jmec87]

The current official API 6A interpretations are available from

http://mycommittees.api.org/standards/techinterp/epequip/Shared Documents/6a.pdf

Interpretation 6A-2014-06 regarding the 20th Edition of API 6A could be helpful. Except for renumbering the sections and the new requirements for PSL4 and (PSL3 + 75K + 1000 lb), the QTC size requirements are essentially unchanged in the 21st Edition compared to the 20th Edition.

Background: I am trying to verify an interpretation of API 6A specification requirements for QTC size mentioned in the paragraph 5.7.2.3. Paragraph 5.7.2.3 specifies: "The ER of the QTC shall be equal to or greater than the dimensions of the part it qualifies, except as follows: a) for PSL 2: 1) forging: size not required to exceed 63 mm (2.5") ER....", the interpretation used in the industry is that the size of the QTC of forged bar products does not have to be larger than 2.5" diameter ER regardless of diameter of the forged bar stock.

Example of the above scenario: a 20" diameter forged bar stock can be qualified by a 2" square QTC for PSL 2 and a 4" square QTC for PSL 3-4 as long as they are heat treated together and they are from the same mill heat.

Question: Is it a correct interpretation? Pls. advise if it is or if it is not. If it is not then pls. explain why not.

Response: No, however, the sizes are correct for batch type heat treatment, not for continuous furnace heat treatment.

 

[Vinay Pawar]

Thank jmec87 for detailed explaination.

This means that,
Example, for PSL3 Tee of size 12"x12"x12", it is accpeteable to have QTC OD 5" or 4" SQ.for batch type furnace.
Whereas For continuous for furnace, the QTC should be OD 10" or 10" SQ.Minimum.

Please advice.

 

[jmec87]

This means that,
Example, for PSL3 Tee of size 12"x12"x12", it is accpeteable to have QTC OD 5" or 4" SQ.for batch type furnace.
Whereas For continuous for furnace, the QTC should be OD 10" or 10" SQ.Minimum.

Maybe and no.
- For the batch furnace, a 5" OD or 4" x 4" square QTC is acceptable, provided at least one of the following is true:
[ul][li]The part weight during heat treat is less than 1000 lbs (if individual 12" x 12" x 12" cubes are being heat treated, this should be true; if a long 12" x 12" square bar is being heat treated, this won't be true)[/li]
[li]The required minimum yield strength is less than 75K. Note that if this is an API 6A flanged/studded cross, then per Table 7, the minimum required yield strength is less than 75K for all flanges rated 10,000 psi or less. [/li][/ul]
- For the continuous furnace, point 1 from my first response applies, so a prolongation (with the same cross-section as the part during heat treat) or a full-size sacrificial part must be used for the QTC. A 10" x 10" does not meet the requirements for the continuous furnace.

 

[Vinay Pawar]

Thanks jmec87 for clarification.