What a grade actually encodes
Where a design sets a hardness limit for a grade, that limit comes from the buyer's specification, stated in the enquiry — it is not carried by the grade name alone. Grade selection is therefore a load calculation before it is a price negotiation: the designer works out the burst, collapse and tensile cases for each interval of the well and chooses the grade whose published properties cover those cases with the required design factors. The factory's published grade list — J55, K55, N80-1, N80Q, L80-1, P110, then the chromium series L80-3Cr, 9Cr, 13Cr, P110-13Cr and 28Cr — names the grades in full. The same grade names appear in the coupling family: BTC casing couplings are listed in J55, K55, N80, L80 and P110.
J55 and K55: the first two names in the list
J55 is a named catalogue entry for this factory, in the same published grade list as K55; the casing sizes are published separately, and a grade at a given size is confirmed in the quotation. This site publishes no chemistry or property comparison between the two. The correct response to a tender is to quote what the tender names rather than substitute silently. J55 casing pipe is a named entry of the family; the casing family's size list and its STC, LTC and BTC thread forms are published as separate lists, and the combination on a line is confirmed in the quotation.
N80: name the variant
The factory's N80 product data for its named 5 in casing sample states yield strength of 552 to 758 MPa and tensile strength of 689 MPa, achieved in the route described for that sample through 36Mn2V micro-alloyed steel with controlled rolling. Procurement must name the variant — N80-1 or N80Q — because the two differ in heat-treatment route and testing expectation, and a tender that specifies Q is not satisfied by 1 at a lower price.
L80: a separate designation in the list
L80-1 is a separate designation from N80 in the published list, and this site publishes no yield-level comparison between them. It is the grade the design names for the sections it assigns to L80. Where the design sets a hardness limit for the grade, that limit is part of the specification: state it in the enquiry and it is applied to the order — it is not read off the grade name alone. L80-1 is the variant in this factory's list, and L80 is also the base grade of the corrosion-resistant family — L80-13Cr carries the L80 name in a chromium steel, which is why the two conversations belong together. N80 and L80 must not be treated as interchangeable line items to be value-engineered at purchase: they are different promises. The purchase order should follow the designer.
P110: a standard grade in the list
P110 is one of the standard grades in the published list; which sections a design assigns to it is the design's decision. The grade calls for handling discipline — like any threaded product it is unforgiving of thread damage and off-spec make-up, and it is not a sour-service answer by default. In this catalogue P110 is named in the published grade list and appears concretely in the coupling family as a listed 13-3/8 in P110 BTC casing coupling held in stock.
When none of the five is right: the chromium series
The published list also names the chromium designations L80-3Cr, 9Cr, 13Cr, P110-13Cr and 28Cr; L80-13Cr is this factory's dedicated six-entry series. Published service data exists on this site for the 13Cr series; for the other designations no duty is assigned here, and none may be inferred from the 13Cr text. For sour duty proper, if your design names anti-sulphur grades such as 80S, 90S or 110S, raise them in the enquiry; those grades sit outside this factory's first-party published list, so supply is confirmed in the written quotation, grade by grade, rather than assumed from a web page. The rule that survives: grade follows the well — its loads, its fluids, its design factors — and price follows grade.
Grade paperwork: what the enquiry names for each line
State the documentation for each programme section in the enquiry — the mill and inspection documentation for the material supplied, and the marking to be applied to the joints and couplings — against the purchase order line that names the grade and variant, and ask for that scope to be confirmed in the quotation. Where your programme specifies PSL2 or PSL3, state the level on the enquiry line, and ask for the documentation scope for that level to be confirmed in the quotation for the order.
Variant discipline belongs in the same conversation. N80-1 and N80Q are one grade name with two delivery conditions; L80-1 is a variant distinct from N80-1 and N80Q, and any hardness requirement on an L80-1 line comes from the design's specification, not from the grade name; P110-13Cr is not P110 with a coating but a different material family wearing a familiar strength number. None of those distinctions can be read from a photograph of finished pipe; each grade distinction is carried in the grade designation itself — full grade name and variant as named on the order line. A PSL level is not part of the grade designation: where an order carries one, it is named on the order line as its own field. Grade information is safety information; treat every number in it as load-bearing.
Finally, grades age with the well. Specifying cleanly means the full grade, variant, PSL, thread and size on every order line.
Which grade is cheapest per metre?
This site publishes no grade price comparison, and price would be irrelevant if the interval's loads exceeded the grade. Grade economy is real only inside the design envelope: the correct grade for the interval is the goal, and price follows the specification in the quotation.
Can grades be mixed in one order?
They can be: a programme can name different grades for different sections on a single purchase order, each section its own fully specified line. Mixing inside a section is what must never happen.
Request a Quotation
Send your size, grade, thread and quantity. MOQ, packing and lead time are confirmed in the quotation for your exact specification — no generic promise replaces a written quote.