General Term Introduction Of Steel Pipes

Date:2012/4/2

①Delivery state

Delivery state means the state of the final plastic deformation or final heat treatment of delivered product. Generally, the products delivered without heat treatment are called hot-rolled or cold-drawn (rolled) state; the products delivered with heat treatment are called heat treatment state, or they can be called as normalizing, quenching and tempering, solution, annealing states. Delivery state should be indicated in the contract when ordering.

②Delivering according to actual weight or theoretical weight
Actual weight — the product is delivered according to the measured weight (on the scales);
Theoretical weight — when delivering, the weight of product is calculated according to the nominal size of steel material. The calculation formula is as follows (if the products are delivered according to theoretical weight, it should be indicated in the contract)
Calculation formula for the theoretical weight (the density of steel is 7.85 kg/dm3) per meter of steel tube:
      W=0.02466(D-S)S
      In the formula:
      W——theoretical weight per meter of steel tube,kg/m;
      D——nominal external diameter of steel tube,mm;
      S——nominal thickness of wall of steel tube,mm。
③Guarantee conditions
Under the provisions in current standard, testing the products and ensuring to comply with the provisions of standard is known as the guarantee conditions. Guarantee conditions can also be divided into:
A、Basic guarantee conditions (also known as necessary conditions). No matter whether they are specified in the contract by the customer, you should inspect this item according to the provisions in standard, and ensure that the test results meet the provisions in standard. For example, chemical compositions, mechanical properties, dimensional deviation, surface quality, damage detection, water pressure test or technological experiments such as pressing flat and tube end expansion are all necessary conditions.
B、Agreement guarantees conditions: in addition to basic guarantee conditions, there are still "according to the requirements of buyer, the conditions should be negotiated by both sides, and the conditions should be indicated in contract" or "if the buyer requires ..., it should be indicated in the contract"; some customers have stricter requirements on basic guarantee standard conditions (such as compositions, mechanical properties, dimensional deviation, etc.) or increase the testing items (such as ellpticity, uneven wall thickness, etc.). Above provisions and requirements should be negotiated by the both sides of supplier and buyer, an Availability Technology Agreement should be signed, and the requirements should be indicated in the contract. Therefore, these conditions are also called agreement guarantee conditions. In general, the prices of the products with agreement guarantee conditions should be increased.

④"Batch" in the “batch standard” means an inspection unit, ie. inspection batch. The batch divided by the delivery unit is called "delivery batch". If the batch amount of delivery is large, a delivery batch may include several inspection batches; if the batch amount of delivery is small, an inspection batch may include several delivery batched. The compositions of "batch" are usually regulated as follows (see related standards):
A、Each batch should be composed of the steel tubes of the same model (steel grade), the same boiler (tank) number or the same mother boiler number heaters, the same specifications and the same heat treatment system (boiler number).
B、As to the quality carbon steel pipe and fluid tube, the batch can be composed of the same model, the same specification and the same heat treatment system (boiler number) of different boilers (tanks).
C、Each batch of welded steel tubes should be composed of the same model (steel grade) and the same specification.

⑤Quality steel and senior quality steel
In the GB/T699-1999 and GB/T3077-1999 standards, the steel whose model accompanied with "A" is senior quality steel, on the contrary, the steel is general quality steel. Senior quality steel is in advance of quality steel on the following aspects partially or wholly:
A、Reduce the range of composition content;
B、Reduce the content of harmful elements (such as sulfur, phosphorus and copper);
C、Assure higher cleanliness (the content of non-metal inclusions should be small);
D、Assure higher mechanical properties and technological properties.

⑥Longitudinal direction and transverse direction
In the standard, the longitudinal direction is parallel with the processing direction (ie. along the processing direction); transverse direction is vertical with the processing direction (processing direction is the axial direction of steel tube).
During the impact test, the fracture of longitudinal specimen should be vertical with processing direction, thus it is called transverse fracture; the fracture of transverse specimen should be parallel with processing direction, thus it is called longitudinal fracture.