(ASK) QTC and ER in API 6A 21st Edition

[Rizkyffq]

Hello all,

May someone help me to explain in very simple definition, what is the different between QTC (Qualification Test Coupon) and ER (Equivalent Round).

I already read API 6A 21st Edition section 6.4 , but i still didn't get how to distinguish definition both of them.

Maybe to make it simple, i give an example if we want to produce Choke Valve 2", then which one of Choke Valve parts need to be QTC and ER ?

 

[jmec87]

Hello Rizkyffq,

The ER is an estimate of the size of round bar with similar heat treating characteristics to the heat treated product. ER is a dimension in inches or millimeters; it is not a physical part.

The QTC is the physical part that gets tested to qualify the heat treated parts. The QTC must meet the ER size requirements.

For the choke valve example, you must test at least one QTC per heat. The QTC size must be such that has an ER equal to or greater than the parts, subject to the limitations and rules in API 6A 24th Edition 6.4. These rules are complicated for some cases, but can also be easily met for other cases. For example, if the choke body is a forging for PSL1 or PSL2 and batch heat treatment is performed (not continuous), either a 2.5" (or larger) round bar, a 2" x 2" (or larger) square bar, or a sacrificial forging body could be used as the QTC.